Kangaroo Griff
Discussion
.. but under closed loop it's going to target lambda 1 come what may .. if you add 10% to a load site the ecu will trim it back to get blambda 1 ie it'll just take 10% trim out. I've never understood how constant part throttle lambda trimmed fuelling can make teh blindest bit of difference, the whole point is the mixture is trimmed back to lambda 1 no matter what base map you give it.
The only way you'd improve it is if the lucas actually isn't as clever as we've been told it is ...
The only way you'd improve it is if the lucas actually isn't as clever as we've been told it is ...
Carbs aren't all that brilliant, they tend to be work on pressure drop i.e. propertional to air velocity squared, which makes them sensitive to pulsing effects in the intake. This is why you typically have to retune carbs when you change the engine spec.
But if the AFM genuinely measures mass air flow then it should be trivially simple to divide by rpm to get fuel mass requirements, lookup the pulse duration to get that fuel quantity from the injector under those conditions, and generate that pulse. I don't see turbulence/atomisation etc as having any effect on the fuel mass requirements, they might have some impact on the transient fuelling requirements but that's a different matter. Steady state, why isn't an AFM based system always right?
One possible explanation is that the AFM isn't actually measuring mass air flow accurately and suffers from the same pulsing effects that carbs do.
But if the AFM genuinely measures mass air flow then it should be trivially simple to divide by rpm to get fuel mass requirements, lookup the pulse duration to get that fuel quantity from the injector under those conditions, and generate that pulse. I don't see turbulence/atomisation etc as having any effect on the fuel mass requirements, they might have some impact on the transient fuelling requirements but that's a different matter. Steady state, why isn't an AFM based system always right?
One possible explanation is that the AFM isn't actually measuring mass air flow accurately and suffers from the same pulsing effects that carbs do.
If you look at the ideal gas law and how you calculate the correct fuel mass to air mass that goes into the car then you will see that a key part of the equation is the Volumetric Efficiency of the engine.
As the VE increases so should the fuel but this is done by the map in the ECU. I think this is what's going wrong with wixers car. The map is slightly off now that the induction and exhaust have been improved.
Not sure why the standard cars do it unless it is just down to the fact that they are throttled for emmisions compliance.
As the VE increases so should the fuel but this is done by the map in the ECU. I think this is what's going wrong with wixers car. The map is slightly off now that the induction and exhaust have been improved.
Not sure why the standard cars do it unless it is just down to the fact that they are throttled for emmisions compliance.
There is a chance that these symptoms could be caused by more than one problem, or combination of problems.
With my car, it's only occured once, and that was when it was wet. This I think, rules out any permanent arrangement like cam, AFM etc, and suggests that the most likely candidate is a control signal going a bit haywire.
I believe that the ECU works only on the values from one Look-up-table, but these values are modified by the various control signals fed back from the sensors. It is a fact that the 14 CUX changes its fuelling outputs by some kind of "learning" process - I believe that this is intended to take account of sensors with varying tolerances - but there are limitations. I have first hand experience of my ECU learning its way into a diabolical state due to an ignition problem such that when the ignition problem is fixed, the ECU got "stuck" in this diabolical state, and the simple fix was to re-set the ECU to get back to factory settings.
So it might be an idea to re-set your ECU if this is happening to you.
My understanding of the purpose of the Lambda sensor is to get the engine running in stoichiometric condition (ideal combustion where fuel is COMPLETELY burned), thus hydro-carbons are eliminated from the exhaust. But this only occurs at steady throttle and engine load conditions, the mixture is considerably richened when you plant your foot to the boards. I believe that the response time for typical modern Lambda sensors is in the region of half a second, and this period may very well correspond with the frequency of our kangaroo - what I'm getting at here is that maybe the lambda signal starts to oscillate for some unknown reason which then sets up a positive feedback (this means that when a problem starts, the feedback just adds to the problem i.e the kangaroo gets progressively worse very quickly) which then causes the kangaroo. Mine certainly felt like positive feedback behaviour.
With my car, it's only occured once, and that was when it was wet. This I think, rules out any permanent arrangement like cam, AFM etc, and suggests that the most likely candidate is a control signal going a bit haywire.
I believe that the ECU works only on the values from one Look-up-table, but these values are modified by the various control signals fed back from the sensors. It is a fact that the 14 CUX changes its fuelling outputs by some kind of "learning" process - I believe that this is intended to take account of sensors with varying tolerances - but there are limitations. I have first hand experience of my ECU learning its way into a diabolical state due to an ignition problem such that when the ignition problem is fixed, the ECU got "stuck" in this diabolical state, and the simple fix was to re-set the ECU to get back to factory settings.
So it might be an idea to re-set your ECU if this is happening to you.
My understanding of the purpose of the Lambda sensor is to get the engine running in stoichiometric condition (ideal combustion where fuel is COMPLETELY burned), thus hydro-carbons are eliminated from the exhaust. But this only occurs at steady throttle and engine load conditions, the mixture is considerably richened when you plant your foot to the boards. I believe that the response time for typical modern Lambda sensors is in the region of half a second, and this period may very well correspond with the frequency of our kangaroo - what I'm getting at here is that maybe the lambda signal starts to oscillate for some unknown reason which then sets up a positive feedback (this means that when a problem starts, the feedback just adds to the problem i.e the kangaroo gets progressively worse very quickly) which then causes the kangaroo. Mine certainly felt like positive feedback behaviour.
I thought the Kangaroo may have been down to the Lambda feedback ossilating like red_griff_500 suggested but the Lambda Gauge did not confirm this. There was not swing on the gauge indicating a lean-rich-lean ossilation when the Kangaroo happens.
The Lambda gauge suggests that the mixture is lean when it happens. I which case a miss fire is more likly the case. As we can't retard the ignition in these conditions then increasing the fueling for this part of the map has to be the answer.
The Lambda gauge suggests that the mixture is lean when it happens. I which case a miss fire is more likly the case. As we can't retard the ignition in these conditions then increasing the fueling for this part of the map has to be the answer.
The oscillating lambda signal is normal and healthy - when it stops oscillating you know the ECU is no longer successfully controlling the air/fuel ratio based on lambda feedback. This may be because it has dropped out of closed loop mode (due to throttle movement, or the revs exceeding the threshhold, or a serious fault putting it into limp home mode, or the wrong tune resister selecting non-cat mode) or it may be that the map is so wrong that the ECU has hit the 'end stops' on the lambda feedback.
Wow - I've been busy tending my clients for a couple of days, and this has really kicked off!
There are some outstanding contributions here IMHO from GreenV8S, raw-sewedge, Quinny, wixer, red_griff_500 and Grifter. Although this is a mega post I'll try and resolve as many of the issues as I can. Here goes!
Fair questions - Red_Griff has got it right though. The fuel actually burns in the cat with the residual Oxygen in the exhaust gas, and can make the cats white hot.
This happens either if the mixture is too rich, or excessively lean. Note that with a lean mixture, the problem only occurs if it is so lean that it pushes up the hydrocarbon (HC) level in the exhaust. At this level you generally feel it misfiring though.
Of course there are other things that can cause excess fuel to appear at the cat, but we digress.
Yes - TVR only reprogrammed the one tune for the car, so all others are just standard Land Rover. Even the default limp-home tune is standard Land Rover, although I do reprogram this to suit the car in all my own software.
It's a little difficult to do this without it looking to much like a blatant sales plug. However I will say that there are several potential causes, and that each model has it's own particular issues. I'll expand on that in a moment....
In general you are right about this - although sometimes a quick flash appearance of lean mixture to a Lambda probe is actually caused by a misfire or major injector problem. This is of course assuming that there are no air leaks on the exhaust manifold.
Most TVR 5.0 Litre standard motors do run lean on the standard map. Since you are monitoring the Lambda sensors directly, if they are showing lean then it means the error has already exceeded the system's ability to compensate.
With the Lucas 14CUX system, the Lambda sensors are meant to trim the mixture from the values in the map. In the original Land Rover application, most vehicles fall inside a +/-12% correction. When the correction gets up to around +/-18% you can start to feel the sensors fighting with the map. Most 5.0 Litre cars are up in the +16 to +21% range, which is why some of them feel shunty.
Out of interest, most 4.0 Litre cat cars are too rich and are removing a similar amount of fuel. The conflict feels the same to the driver, whether it is lean or rich.
If the mixture specified in the map is inside the Lambda compensation range then you won't see any changes in the exhaust gas, but you will feel it. When I map these cars (whatever the ECU) on a Lambda tune, I always monitor the correction that is being made. This is a software value only, and nearly always requires the ECU's own setup software to make it visible. If you change a value in a Lambda-controlled are of the map, there will generally be no change in the exhaust gas composition. So you need the proper software to do it accurately.
There are various places in the map where it is actually desirable to have the Lambda compensation either adding or subtracting fuel. In fact this is inherent in the way Lambda sensors correct the mixture. It is also influenced by the application for the vehicle, and engine spec, camshaft, etc. However I can't give away everything!
Some hotter camshafts also require a mixture slightly richer than Lambda 1.0 at certain points, and will produce shunting unless freed of Lambda control.
Unfortunately there are loads more causes of shunting, including strange distributor advance curves (too eager to advance). 4.5 Litre cat cars are very prone to shunting too, and in some cases this is related to the use of the 5.0 Litre camshaft. I usually have one or two cars a year (especially 4.5s) that need considerably more effort and persistence to resolve shunting.
In an ideal world of perfect efficient engines, this would be true. However the entire point of mapping is that all engines are far from perfect, and we are effectively mapping varying efficiencies at different combinations of speeds and loads.
Since it is actually the load (proportional to torque output) that determines the fuelling requirement, the airflow meter AFM is the weapon of choice to measure this (where it is possible to use one). Manifold pressure systems (sometimes called speed-density metering) have to estimate the load by including factors such as air temperature. Throttle-angle systems must use Barometric pressure also as a minimum.
MAF metering will compensate for the engine aging process, as torque output drops off with increasing compression loss, valvetrain wear, etc.,. However these aging processes also produce a drop in manifold depression, which appears as an increase in load to a MAP system with a corresponding increase in fuelling, and corresponding increase in wear rates.
Bear in mind that many of my clients see 200K+ miles, and the longest-serving one on my books has over 330K on it (although it has definitely passed it's sell-by date)! I also have twin-turbo motors on cats with over 100K Miles on board that still run perfectly. One of my own test motors has just passed 180K Miles - like the last one in fact. Many of my clients have racked up massive mileages over several years, and yet the motors are running just as accurately as when they were originally set up when re-tested.
Once the car has been properly set up with a good quality system, there is no pressing reason why it should need remapping again if there are no mechanical changes made to it.
This is the reason why all mainstream manufacturers have dumped MAP and gone for MAF in order to meet emissions requirements, which are only satisfied by accuracy. On the road - if a system is properly set up - regardless of the metering method chosen - it should drive just the same. The driver should not be able to tell the metering system from his seat. This is only true if the management system has the required internal software sophistication to enable this.
However it has to be said that MAF is significantly more difficult to map than MAP, and MAP is harder than throttle angle. That's why most people avoid it - most of the aftermarket ECUs cannot support MAF. Don't worry if you've chosen MAP - remember I'm obsessed with accuracy and detail, and that's why people come to see me!
Also the system should behave the same if it is used high up the Alps at -25C, or in a Desert at 48C (as indeed several of my clients can verify). If it cannot, then again it means there is something lacking in the sophistication of the system. In fuelling terms the 14CUX has passed all of these tests.
Finally if your cat car runs better on a non-cat tune, then you have fairly strongly linked a mixture error in the basic map to your symptoms.
>> Edited by Mark Adams on Thursday 15th September 19:25
There are some outstanding contributions here IMHO from GreenV8S, raw-sewedge, Quinny, wixer, red_griff_500 and Grifter. Although this is a mega post I'll try and resolve as many of the issues as I can. Here goes!
wixer said:
...if more fuel did get through the engine, wouldn't it help cool the gases, therefore the cats ??
Fair questions - Red_Griff has got it right though. The fuel actually burns in the cat with the residual Oxygen in the exhaust gas, and can make the cats white hot.
This happens either if the mixture is too rich, or excessively lean. Note that with a lean mixture, the problem only occurs if it is so lean that it pushes up the hydrocarbon (HC) level in the exhaust. At this level you generally feel it misfiring though.
Of course there are other things that can cause excess fuel to appear at the cat, but we digress.
wixer said:
Does this mean TVR only re-programmed one tune on the chip, the cat tune ?? and every other tune on the chip is standard LandRover ??
Yes - TVR only reprogrammed the one tune for the car, so all others are just standard Land Rover. Even the default limp-home tune is standard Land Rover, although I do reprogram this to suit the car in all my own software.
wixer said:
I'd be interested in knowing what your recommendations would be to get rid of the hunting symptoms, as you've only told people on here what NOT to do, as far as tune resistors go. Especially as the problem does seem to be quite wide spread.
It's a little difficult to do this without it looking to much like a blatant sales plug. However I will say that there are several potential causes, and that each model has it's own particular issues. I'll expand on that in a moment....
raw-sewedge said:
Using a home made Lambda gauge which I got working today I notice when the shunting/stumbling occurs the mixture did tend to be lean.
In general you are right about this - although sometimes a quick flash appearance of lean mixture to a Lambda probe is actually caused by a misfire or major injector problem. This is of course assuming that there are no air leaks on the exhaust manifold.
Most TVR 5.0 Litre standard motors do run lean on the standard map. Since you are monitoring the Lambda sensors directly, if they are showing lean then it means the error has already exceeded the system's ability to compensate.
With the Lucas 14CUX system, the Lambda sensors are meant to trim the mixture from the values in the map. In the original Land Rover application, most vehicles fall inside a +/-12% correction. When the correction gets up to around +/-18% you can start to feel the sensors fighting with the map. Most 5.0 Litre cars are up in the +16 to +21% range, which is why some of them feel shunty.
Out of interest, most 4.0 Litre cat cars are too rich and are removing a similar amount of fuel. The conflict feels the same to the driver, whether it is lean or rich.
If the mixture specified in the map is inside the Lambda compensation range then you won't see any changes in the exhaust gas, but you will feel it. When I map these cars (whatever the ECU) on a Lambda tune, I always monitor the correction that is being made. This is a software value only, and nearly always requires the ECU's own setup software to make it visible. If you change a value in a Lambda-controlled are of the map, there will generally be no change in the exhaust gas composition. So you need the proper software to do it accurately.
There are various places in the map where it is actually desirable to have the Lambda compensation either adding or subtracting fuel. In fact this is inherent in the way Lambda sensors correct the mixture. It is also influenced by the application for the vehicle, and engine spec, camshaft, etc. However I can't give away everything!
Some hotter camshafts also require a mixture slightly richer than Lambda 1.0 at certain points, and will produce shunting unless freed of Lambda control.
Unfortunately there are loads more causes of shunting, including strange distributor advance curves (too eager to advance). 4.5 Litre cat cars are very prone to shunting too, and in some cases this is related to the use of the 5.0 Litre camshaft. I usually have one or two cars a year (especially 4.5s) that need considerably more effort and persistence to resolve shunting.
GreenV8S said:
Must confess I've never understood why an AFM based system ever has to be remapped; the AFM measures the mass of air coming in, the ECU adds the corresponding amount of fuel
In an ideal world of perfect efficient engines, this would be true. However the entire point of mapping is that all engines are far from perfect, and we are effectively mapping varying efficiencies at different combinations of speeds and loads.
raw-sewedge said:
...a key part of the equation is the Volumetric Efficiency of the engine...
Since it is actually the load (proportional to torque output) that determines the fuelling requirement, the airflow meter AFM is the weapon of choice to measure this (where it is possible to use one). Manifold pressure systems (sometimes called speed-density metering) have to estimate the load by including factors such as air temperature. Throttle-angle systems must use Barometric pressure also as a minimum.
MAF metering will compensate for the engine aging process, as torque output drops off with increasing compression loss, valvetrain wear, etc.,. However these aging processes also produce a drop in manifold depression, which appears as an increase in load to a MAP system with a corresponding increase in fuelling, and corresponding increase in wear rates.
Bear in mind that many of my clients see 200K+ miles, and the longest-serving one on my books has over 330K on it (although it has definitely passed it's sell-by date)! I also have twin-turbo motors on cats with over 100K Miles on board that still run perfectly. One of my own test motors has just passed 180K Miles - like the last one in fact. Many of my clients have racked up massive mileages over several years, and yet the motors are running just as accurately as when they were originally set up when re-tested.
Once the car has been properly set up with a good quality system, there is no pressing reason why it should need remapping again if there are no mechanical changes made to it.
This is the reason why all mainstream manufacturers have dumped MAP and gone for MAF in order to meet emissions requirements, which are only satisfied by accuracy. On the road - if a system is properly set up - regardless of the metering method chosen - it should drive just the same. The driver should not be able to tell the metering system from his seat. This is only true if the management system has the required internal software sophistication to enable this.
However it has to be said that MAF is significantly more difficult to map than MAP, and MAP is harder than throttle angle. That's why most people avoid it - most of the aftermarket ECUs cannot support MAF. Don't worry if you've chosen MAP - remember I'm obsessed with accuracy and detail, and that's why people come to see me!
Also the system should behave the same if it is used high up the Alps at -25C, or in a Desert at 48C (as indeed several of my clients can verify). If it cannot, then again it means there is something lacking in the sophistication of the system. In fuelling terms the 14CUX has passed all of these tests.
Finally if your cat car runs better on a non-cat tune, then you have fairly strongly linked a mixture error in the basic map to your symptoms.
>> Edited by Mark Adams on Thursday 15th September 19:25
Maybe going out on a limb here, i ran with my old ECU with the original chip today, kangaroo hairier than with ECU 2 with TVR power chip. I will swap back to the new chip ECU in the morning, just to make sure it wasnt my imagination. Before the upgrade i had always ran without vac advance connected, always smooth. I know some say the vac thing is rubbish, but it worked for me for 4 years. Providing i have the all clear, i will be with Mark on Monday at Austec, see what can be done. Thinking about ACT carbon, Jag air flow and posh injectors.
Mark Adams said:
Finally if your cat car runs better on a non-cat tune, then you have fairly strongly linked a mixture error in the basic map to your symptoms.
Mark's reply took some reading but I think the above quote captures it all for me. Trouble is, I'm completely
ed off with spending money on my car at the moment, so I s'pose I'll have to live with the shunting for a little longer.Hi Mark thanks for the post....
I'd still like to know your feelings / experience about the AFM CO trim setting??? from what you've said there was only one map for cat cars produced presumably then the CO trim value was set by the factory to a common value for all cars??..
I thought also that the non cat cars have a different ecu map therefore do they have a different CO trim setting as standard from the factory??
I presume that when you re-map an ecu you measure this value or even reset it to a common value??
My question is leading to what should this be?? Reading the RPI website it says 1.5 non cat and 1.8 cat if I remember correctly. is this still relevant for TVRs?
I've had a play with this on a spare AFM. Mine (a precat 4.0) was 'originally set to 0.03v!!! I reset this to 1.5v as suggested by the RPI info and it ran very very rich .. i've since lowered this back down to 0.5v but it still seems rich.. from my limited experience this changes the AFR throughout the rev range not just idle?? is this true??? if so shouldn't the engines all be running with similar settings still..
I'm trying to understand why, since I replaced my coil, ignition amp, and cleaned injectors solving a hot temp mis fire the shunting has got worse??
Also if as (Quinny suggests)CAM wear can effect shunting could oil viscosity effect this as well, seeing as the engine uses hydraulic lifters, and also coincides with the time the engine has least oil pressure..
thanks for the help
chris
I'd still like to know your feelings / experience about the AFM CO trim setting??? from what you've said there was only one map for cat cars produced presumably then the CO trim value was set by the factory to a common value for all cars??..
I thought also that the non cat cars have a different ecu map therefore do they have a different CO trim setting as standard from the factory??
I presume that when you re-map an ecu you measure this value or even reset it to a common value??
My question is leading to what should this be?? Reading the RPI website it says 1.5 non cat and 1.8 cat if I remember correctly. is this still relevant for TVRs?
I've had a play with this on a spare AFM. Mine (a precat 4.0) was 'originally set to 0.03v!!! I reset this to 1.5v as suggested by the RPI info and it ran very very rich .. i've since lowered this back down to 0.5v but it still seems rich.. from my limited experience this changes the AFR throughout the rev range not just idle?? is this true??? if so shouldn't the engines all be running with similar settings still..
I'm trying to understand why, since I replaced my coil, ignition amp, and cleaned injectors solving a hot temp mis fire the shunting has got worse??
Also if as (Quinny suggests)CAM wear can effect shunting could oil viscosity effect this as well, seeing as the engine uses hydraulic lifters, and also coincides with the time the engine has least oil pressure..
thanks for the help
chris
Hi Chris
All cat cars have the AFM CO trimmer set to 1.8 Volts. On non-cat cars, you would typically expect the correct CO reading between 1.0-1.5 Volts.
The values given on the RPI website are recommended starting points for Tornado or standard chips. I do a lot of work with RPI so I know who produced the figures
When I remap an ECU, I always preset the CO trimmer to an appropriate value (1.5/1.8 Volts) - otherwise it distorts the mapping process.
The CO trim setting does make a difference on cat cars. Although the exhaust composition is controlled by the Oxygen sensors, the setting of the CO trimmer still changes the amount of compensation they have to do. CO trim settings affect the mixture from idle to light cruise.
In the past, it appears that someone has fiddled with your CO trimmer. There must be a reason why it was turned down, but that would usually be covering another issue. Maybe there is an airflow meter or fuel pressure issue, or it might not even have the original chip in it. Have you tried another AFM?
From your profile I see you have an early model 4.0 pre-cat. Normally these run quite well, although later cat 4.0 Litre cars normally run rich. Rich running may well be a factor in your shunting issues.
However it is important to make sure the car really is running rich. If it's stinky, that is the Hydrocarbons in the exhaust which will happen whether it is too rich or too lean. You really need to get it on a gas tester to be sure.
With regard to oil viscosity, I don't think it would really have a major influence on the lifters within the normal range of oil viscosities. Lifters are normally very slow to react - unless you take away their feed altogether or heavily over-rev them.
Please ask if you need more info!
All cat cars have the AFM CO trimmer set to 1.8 Volts. On non-cat cars, you would typically expect the correct CO reading between 1.0-1.5 Volts.
The values given on the RPI website are recommended starting points for Tornado or standard chips. I do a lot of work with RPI so I know who produced the figures
When I remap an ECU, I always preset the CO trimmer to an appropriate value (1.5/1.8 Volts) - otherwise it distorts the mapping process.
The CO trim setting does make a difference on cat cars. Although the exhaust composition is controlled by the Oxygen sensors, the setting of the CO trimmer still changes the amount of compensation they have to do. CO trim settings affect the mixture from idle to light cruise.
In the past, it appears that someone has fiddled with your CO trimmer. There must be a reason why it was turned down, but that would usually be covering another issue. Maybe there is an airflow meter or fuel pressure issue, or it might not even have the original chip in it. Have you tried another AFM?
From your profile I see you have an early model 4.0 pre-cat. Normally these run quite well, although later cat 4.0 Litre cars normally run rich. Rich running may well be a factor in your shunting issues.
However it is important to make sure the car really is running rich. If it's stinky, that is the Hydrocarbons in the exhaust which will happen whether it is too rich or too lean. You really need to get it on a gas tester to be sure.
With regard to oil viscosity, I don't think it would really have a major influence on the lifters within the normal range of oil viscosities. Lifters are normally very slow to react - unless you take away their feed altogether or heavily over-rev them.
Please ask if you need more info!
GreenV8S said:
Carbs aren't all that brilliant.
bloody cheek!
13.5:1 heads, 400bhp, triple paddle twin plate race clutch...and its smooooth as silk...from 7500 down to 1500!
basic CAN work well, not perfect i know but to be quite honest, fuel injection is only in its adolescent stage on these BIG engines. you need BIG TAPS (injectors) to make the big numbers and they are difficult to control at low fuel/rev rates...
At the moment! Mark, Tim and Paul are making MASSIVE improvements all the time! A 300bhp "Monster" was a very rare thing two years ago, but there are now lots about. and driveablity/mid range figures are also improving on almost a daily basis.
I took the safest - max power - root with mine as its for trackday use almost exclusively now, but if i was building from stock again, i'd go OMEX by MA with triple ACT. they're improving all the time and 340+ is becoming the norm on a 500!
Incredible
>> Edited by Guillotine on Saturday 17th September 16:52
Guillotine said:
At the moment! Mark, Tim and Paul are making MASSIVE improvements all the time! A 300bhp "Monster" was a very rare thing two years ago, but there are now lots about. and driveablity/mid range figures are also improving on almost a daily basis.
And a couple of other builders as well
Guillotine said:I'm very close on bhp and waaaaaaaaaaaayyyyyyy over on the old pulling stuff
340+ is becoming the norm on a 500!
Mark Adams said:
All cat cars have the AFM CO trimmer set to 1.8 Volts. On non-cat cars, you would typically expect the correct CO reading between 1.0-1.5 Volts.
Given these values, Chris's 0.03v and my 0.005v would sound way too low! Are we running very very lean at idle/light cruise then? How does the engine run at all? - Or is the CO trim in fact only a very small part of the factors determining fuelling under these circumstances?
Mark Adams said:
When I remap an ECU, I always preset the CO trimmer to an appropriate value (1.5/1.8 Volts) - otherwise it distorts the mapping process.
Someone's fiddled with mine then!! Would turning the trim down be used to mask an overfuelling issue? Why else might someone do it?
Mark Adams said:
However it is important to make sure the car really is running rich. If it's stinky, that is the Hydrocarbons in the exhaust which will happen whether it is too rich or too lean. You really need to get it on a gas tester to be sure.
Is the 'stinky'-ness from hydrocarbons a 'petrol' smell? Could the CO trim be the cause of my occasional light cruise misfire - feels like the engine's missing on 2 or 3 cylinders - and sometimes accompanied by a smell of petrol?
Mark Adams said:
The CO trim setting does make a difference on cat cars. Although the exhaust composition is controlled by the Oxygen sensors, the setting of the CO trimmer still changes the amount of compensation they have to do. CO trim settings affect the mixture from idle to light cruise.
In the past, it appears that someone has fiddled with your CO trimmer. There must be a reason why it was turned down, but that would usually be covering another issue. Maybe there is an airflow meter or fuel pressure issue, or it might not even have the original chip in it. Have you tried another AFM?
However it is important to make sure the car really is running rich. If it's stinky, that is the Hydrocarbons in the exhaust which will happen whether it is too rich or too lean. You really need to get it on a gas tester to be sure.
Nice one Mark...
It seems my car is indeed running lean!!! much to my surprise. I went to the Surrey Rolling Road day on saturday and my car is down on power by 10-20 bhp achieving 203 bhp at the flywheel and 255 ftlb of torque. I think its loosing power throughout the rev range but mainly at and after 4800 rpm.
From the AFR graph Charlie printed out he advised that the car was running lean.. from about 1600rpm it 13.4 sloping off to 12.3 ish at 4600. but then at 4800 rpm it takes a dive to 13.5.. is this really bad??
from what you have said before the shunting could be caused by lean mixture.. does this seem viable from these values of or are the values tested on a rolling road outside of the CO trim effective range?
As you suggested above the co trim could have been used to try to hind another issue and with the results of AFR it seems likely one of the culprits you mentioned either AFM or a fuel pressure issue.. what the best way of testing each of these?
I have tried a different meter in the past and it is still fitted to the car this was so I could alter the co trim from the originals setting of 0.03 v to assess the effects.without damaging the original part. I carried out the Air flow signal tests as defined buy the bible on both meters and have very comparable results.. could it still be duff?? how do I test the fuel pressure regulator or pump? I have recently had the injectors cleaned so I'm ignoring these for now??
Thanks for any advise you can give, initially I was concerned about the shunting. Although it may be connected, whats worrying me more now is the generally low AFR and the jump higher up the rev range?
thanks chris
Let's try a slightly different approach, Griffmates.
My Kangaroo had the following characteristics;
1.-It only occurs on constant, low throttle setting.
2.-It starts with a very small kangaroo, then gets progressively worse over a very short time (2-3 seconds) to a point where it is diabolical.
3.-The Kangaroo oscillates at about half a second frequency (i.e. each power surge occurs about every half a second).
4.-It occurs at any engine speed below 2000rpm.
Please bear with me on this.
The engine power is generated by mechanical parts and fuel/air, and the power is governed by means of a number of control inputs, one of them being your right foot, but many more of them being electronic.
It seems reasonable to suppose that, if our engine power oscillates when our foot is rock steady, then one of the other inputs is oscillating. The big question is - which one(s) (bear with me Quinney, I’ll get to your cam change).
It also seems reasonable to suppose that the frequency at which the errant control oscillates is similar to our Kangaroo oscillation, otherwise, you’d expect it to oscillate at a different frequency. It also seems reasonable to suppose that the errant signal is in some closed loop control system which is the only thing that can explain the behaviour of quickly getting progressively worse (no. 2 above).
If the logic applied here is sound, then we are looking for a control input that oscillates at the frequency of our Kangaroos, and resides in a closed loop control system. If you consider this information along with the excellent point made by TRACKCAR which is that the Lambda feedback attempts to adjust the fuelling to achieve “1” when in constant throttle position (bearing in mind that this is when it works in closed loop control) whatever map you’ve got, then we have a strong suspect. The question is, what can cause it to oscillate? We need to consider the whole system and not just the sensor. For example, it could be that electrical noise gets on the sensor supply wire which then causes the sensor to wobble which in turn causes the fuel adjustment to wobble which then causes the exhaust gases to wobble which then makes the sensor wobble even more because it’s trying to correct for the exhaust gas wobble (this is known as “positive feedback” in a control system – you can think of it as like hitting a kind of resonance with no damping to remove the energy, thus the damn thing just gets worse until it shakes itself to bits).
Quinny, it’s just possible that in changing your cam, your wiring has been disturbed (the lambda wiring does go over the top of the engine I think), and this may have had the effect I described above.
I’m not arrogant enough to assert that what I’ve described IS the cause of all our Kangaroos, but there may be an inkling of an idea that you guys can develop?
My Kangaroo had the following characteristics;
1.-It only occurs on constant, low throttle setting.
2.-It starts with a very small kangaroo, then gets progressively worse over a very short time (2-3 seconds) to a point where it is diabolical.
3.-The Kangaroo oscillates at about half a second frequency (i.e. each power surge occurs about every half a second).
4.-It occurs at any engine speed below 2000rpm.
Please bear with me on this.
The engine power is generated by mechanical parts and fuel/air, and the power is governed by means of a number of control inputs, one of them being your right foot, but many more of them being electronic.
It seems reasonable to suppose that, if our engine power oscillates when our foot is rock steady, then one of the other inputs is oscillating. The big question is - which one(s) (bear with me Quinney, I’ll get to your cam change).
It also seems reasonable to suppose that the frequency at which the errant control oscillates is similar to our Kangaroo oscillation, otherwise, you’d expect it to oscillate at a different frequency. It also seems reasonable to suppose that the errant signal is in some closed loop control system which is the only thing that can explain the behaviour of quickly getting progressively worse (no. 2 above).
If the logic applied here is sound, then we are looking for a control input that oscillates at the frequency of our Kangaroos, and resides in a closed loop control system. If you consider this information along with the excellent point made by TRACKCAR which is that the Lambda feedback attempts to adjust the fuelling to achieve “1” when in constant throttle position (bearing in mind that this is when it works in closed loop control) whatever map you’ve got, then we have a strong suspect. The question is, what can cause it to oscillate? We need to consider the whole system and not just the sensor. For example, it could be that electrical noise gets on the sensor supply wire which then causes the sensor to wobble which in turn causes the fuel adjustment to wobble which then causes the exhaust gases to wobble which then makes the sensor wobble even more because it’s trying to correct for the exhaust gas wobble (this is known as “positive feedback” in a control system – you can think of it as like hitting a kind of resonance with no damping to remove the energy, thus the damn thing just gets worse until it shakes itself to bits).
Quinny, it’s just possible that in changing your cam, your wiring has been disturbed (the lambda wiring does go over the top of the engine I think), and this may have had the effect I described above.
I’m not arrogant enough to assert that what I’ve described IS the cause of all our Kangaroos, but there may be an inkling of an idea that you guys can develop?
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