New observation related to shunting
Discussion
My car has developed a new problem but one which seems to have mysteriously improved the shunting, thought it may be of use to those trying to resolve the problem:
First thing I noticed was that the fuel economy has been consistenly improved for last 3 months (car is a daily driver). I do the same driving every week near enough and am now getting 200+ miles to a tank whereas I used to get around 180. Coupled with this I noticed that on starting from cold, blipping the throttle in neutral causes the revs to drop but steady increases in throttle will be tolerated. My guess was something had failed in relation to the cold enrichment (maybe one of the temperature sensors), hence the increased mileage per tank also.
The new development I have noticed is on coming to a stop, the idle speed now drops much lower than usual (750 ish) but interestingly, the shunting that used to happen when you lifted right off the throttle has almost completely gone. The car now just gently coasts to a stop in gear, which it has never done - a marked difference. Could this development be due to a failed stepper motor ?
Could failure of a stepper motor or cold enrichment (or both) resolve shunting or is this just a coincedence ? I'd like to investigate but the combination of better fuel economy and no shunting is such an improvement, I don't want to change it.
Cheers, Matt
First thing I noticed was that the fuel economy has been consistenly improved for last 3 months (car is a daily driver). I do the same driving every week near enough and am now getting 200+ miles to a tank whereas I used to get around 180. Coupled with this I noticed that on starting from cold, blipping the throttle in neutral causes the revs to drop but steady increases in throttle will be tolerated. My guess was something had failed in relation to the cold enrichment (maybe one of the temperature sensors), hence the increased mileage per tank also.
The new development I have noticed is on coming to a stop, the idle speed now drops much lower than usual (750 ish) but interestingly, the shunting that used to happen when you lifted right off the throttle has almost completely gone. The car now just gently coasts to a stop in gear, which it has never done - a marked difference. Could this development be due to a failed stepper motor ?
Could failure of a stepper motor or cold enrichment (or both) resolve shunting or is this just a coincedence ? I'd like to investigate but the combination of better fuel economy and no shunting is such an improvement, I don't want to change it.
Cheers, Matt
taylormj4 said:
My car has developed a new problem but one which seems to have mysteriously improved the shunting, thought it may be of use to those trying to resolve the problem:
First thing I noticed was that the fuel economy has been consistenly improved for last 3 months (car is a daily driver). I do the same driving every week near enough and am now getting 200+ miles to a tank whereas I used to get around 180. Coupled with this I noticed that on starting from cold, blipping the throttle in neutral causes the revs to drop but steady increases in throttle will be tolerated. My guess was something had failed in relation to the cold enrichment (maybe one of the temperature sensors), hence the increased mileage per tank also.
The new development I have noticed is on coming to a stop, the idle speed now drops much lower than usual (750 ish) but interestingly, the shunting that used to happen when you lifted right off the throttle has almost completely gone. The car now just gently coasts to a stop in gear, which it has never done - a marked difference. Could this development be due to a failed stepper motor ?
Could failure of a stepper motor or cold enrichment (or both) resolve shunting or is this just a coincedence ? I'd like to investigate but the combination of better fuel economy and no shunting is such an improvement, I don't want to change it.
Cheers, Matt
I've had the same thing with mine, stepper motor doesn't work, which in turn means that the cold start doesn't work either, but the car runs better and no shunting at all, once its warmed up, which doesn't take long, it runs really smooth! not sure on the fuel economy as I dont use it enough to check it.First thing I noticed was that the fuel economy has been consistenly improved for last 3 months (car is a daily driver). I do the same driving every week near enough and am now getting 200+ miles to a tank whereas I used to get around 180. Coupled with this I noticed that on starting from cold, blipping the throttle in neutral causes the revs to drop but steady increases in throttle will be tolerated. My guess was something had failed in relation to the cold enrichment (maybe one of the temperature sensors), hence the increased mileage per tank also.
The new development I have noticed is on coming to a stop, the idle speed now drops much lower than usual (750 ish) but interestingly, the shunting that used to happen when you lifted right off the throttle has almost completely gone. The car now just gently coasts to a stop in gear, which it has never done - a marked difference. Could this development be due to a failed stepper motor ?
Could failure of a stepper motor or cold enrichment (or both) resolve shunting or is this just a coincedence ? I'd like to investigate but the combination of better fuel economy and no shunting is such an improvement, I don't want to change it.
Cheers, Matt
I think too much is said about the stepper motor. Mine if fully functional, yet clean or dirty, it seems to make no difference to how the car drives (i dont suffer from shuinting though).
I do get frustrated when topics get answered 'clean the stepper motor' as if it is the cause to all problems.
I do get frustrated when topics get answered 'clean the stepper motor' as if it is the cause to all problems.
Some interesting observations from taylormj4 that may tie in with my theory.
Personally I think its all down to running lean at the lower end of the rev range where the shunting typically occurs.
Interestingly I solved my shunting problem by fitting an SC Power plenum spacer, bell mouths & plenum base heat insulating gasket.
However after looking at the air fuel ratio on a rolling road I expect what the plenum spacer does is mask the erratic fuelling delivered by the TVR ECU chip.
When the AFR is observed with the TVR chip installed you can see the map delivers a very lean mixture at exactly the same point shunting happens (1800 - 2200 RPM).
I did a second run with the Mark Adams Tornado chip and the AFR is very linear throughout the rev range, as such it delivers a richer mixture at 1800 - 2200 RPM.
I wouldn't mind betting that's how the Mark Adams chip eliminates shunting.
Personally I think its all down to running lean at the lower end of the rev range where the shunting typically occurs.
Interestingly I solved my shunting problem by fitting an SC Power plenum spacer, bell mouths & plenum base heat insulating gasket.
However after looking at the air fuel ratio on a rolling road I expect what the plenum spacer does is mask the erratic fuelling delivered by the TVR ECU chip.
When the AFR is observed with the TVR chip installed you can see the map delivers a very lean mixture at exactly the same point shunting happens (1800 - 2200 RPM).
I did a second run with the Mark Adams Tornado chip and the AFR is very linear throughout the rev range, as such it delivers a richer mixture at 1800 - 2200 RPM.
I wouldn't mind betting that's how the Mark Adams chip eliminates shunting.
Edited by Chimpafrolic on Thursday 4th November 18:05
jsr said:
I think too much is said about the stepper motor. Mine if fully functional, yet clean or dirty, it seems to make no difference to how the car drives (i dont suffer from shuinting though).
I do get frustrated when topics get answered 'clean the stepper motor' as if it is the cause to all problems.
Locked myself out the car, please help, ha clean the stepper motor I do get frustrated when topics get answered 'clean the stepper motor' as if it is the cause to all problems.
Chimpafrolic said:
Some interesting observations from taylormj4 that may tie in with my theory.
Personally I think its all down to running lean at the lower end of the rev range where the shunting typically occurs.
Interestingly I solved my shunting problem by fitting an SC Power plenum spacer, bell mouths & plenum base heat insulating gasket.
However after looking at the air fuel ratio on a rolling road I expect what the plenum spacer does is mask the erratic fuelling delivered by the TVR ECU chip.
When the AFR is observed with the TVR chip installed you can see the map delivers a very lean mixture at exactly the same point shunting happens (1800 - 2200 RPM).
I did a second run with the Mark Adams Tornado chip and the AFR is very linear throughout the rev range, as such it delivers a richer mixture at 1800 - 2200 RPM.
I wouldn't mind betting that's how the Mark Adams chip eliminates shunting.
Only problem with all of that is that the throttle angle on the RR will be nothing like it would be on the road when the shunting occurs. Timing and mixture can do lots to mask it but the cause is almost certainly valve overlap working against the single plenum. Ask anyone that runs a properly big cam but hasn't yet gone to throttle bodies Personally I think its all down to running lean at the lower end of the rev range where the shunting typically occurs.
Interestingly I solved my shunting problem by fitting an SC Power plenum spacer, bell mouths & plenum base heat insulating gasket.
However after looking at the air fuel ratio on a rolling road I expect what the plenum spacer does is mask the erratic fuelling delivered by the TVR ECU chip.
When the AFR is observed with the TVR chip installed you can see the map delivers a very lean mixture at exactly the same point shunting happens (1800 - 2200 RPM).
I did a second run with the Mark Adams Tornado chip and the AFR is very linear throughout the rev range, as such it delivers a richer mixture at 1800 - 2200 RPM.
I wouldn't mind betting that's how the Mark Adams chip eliminates shunting.
SILICONE KID said:
What does linear mean?or does it mean your doing the laundry laterWhy do you have a picture of a rabbits head on your Mark Adams Tornado chip graph,he must be doing some magic
DAZ!Why do you have a picture of a rabbits head on your Mark Adams Tornado chip graph,he must be doing some magicEdited by SILICONE KID on Thursday 4th November 19:11
The word linear comes from the Latin word linearis, which means created by lines.
Think about how a piece of plastic plumbers pipe follows a straight line.
What I am saying is the fuelling on the MA chip follows a straighter line on the graph indicating a more consistent AFR throughout the rev range.
The rabbits head is a new secret economy feature from Mark Adams, the technology behind it is very hutch hutch.
Basically when the revs rise over 5,600rpm the engine runs on carrots.
It works OK but you do get some bunny hops.
Well spotted Daz
lesstatt said:
jsr said:
I think too much is said about the stepper motor. Mine if fully functional, yet clean or dirty, it seems to make no difference to how the car drives (i dont suffer from shuinting though).
I do get frustrated when topics get answered 'clean the stepper motor' as if it is the cause to all problems.
Locked myself out the car, please help, ha clean the stepper motor I do get frustrated when topics get answered 'clean the stepper motor' as if it is the cause to all problems.
Chimpafrolic said:
Some interesting observations from taylormj4 that may tie in with my theory.
Personally I think its all down to running lean at the lower end of the rev range where the shunting typically occurs.
Interestingly I solved my shunting problem by fitting an SC Power plenum spacer, bell mouths & plenum base heat insulating gasket.
However after looking at the air fuel ratio on a rolling road I expect what the plenum spacer does is mask the erratic fuelling delivered by the TVR ECU chip.
When the AFR is observed with the TVR chip installed you can see the map delivers a very lean mixture at exactly the same point shunting happens (1800 - 2200 RPM).
I did a second run with the Mark Adams Tornado chip and the AFR is very linear throughout the rev range, as such it delivers a richer mixture at 1800 - 2200 RPM.
I wouldn't mind betting that's how the Mark Adams chip eliminates shunting.
This ties in very nicely with the fact if you run the non catalyst fuel map it improves things considerably, as you can set the mixture with the CO trim on the side of the AFM. I would suspect the very early part of the curve that the ECU is still running in closed loop and trying to control the mixure, at 14.35:1 and this is where it all falls apart. The AFM is getting a somewhat mixed message from the airflow due to the more erratic / poorer airflow at low rpm on a long duration cam and this leads to incorrect fueling (in particular as the RV8 does not run well at 14.35:1 anyway,) that the ECU tries to correct after the event, and can then lead to over fueling correction. This all takes place fairly slowly (up to around a second on each correction on a 5ltr) so it all becomes unstable and the car shunts. The MA chip would help ovecome this by making the fuel map run richer at this point, and it can be done to a level the ECU simply runs out its corrction range (about +/- 20 % ) so it ends up only running lean for a moment at maximum correction. You can do the same by lifting the AFM output at this shunting exact point.Personally I think its all down to running lean at the lower end of the rev range where the shunting typically occurs.
Interestingly I solved my shunting problem by fitting an SC Power plenum spacer, bell mouths & plenum base heat insulating gasket.
However after looking at the air fuel ratio on a rolling road I expect what the plenum spacer does is mask the erratic fuelling delivered by the TVR ECU chip.
When the AFR is observed with the TVR chip installed you can see the map delivers a very lean mixture at exactly the same point shunting happens (1800 - 2200 RPM).
I did a second run with the Mark Adams Tornado chip and the AFR is very linear throughout the rev range, as such it delivers a richer mixture at 1800 - 2200 RPM.
I wouldn't mind betting that's how the Mark Adams chip eliminates shunting.
Edited by Chimpafrolic on Thursday 4th November 18:05
I think the plenum spacer simply gives a bit more space when some of the exhaust gas gets blown back into the plenum at low speed, so the contamination is not quite so concentrated when the air is draw back down into the combustion chamber, so the burn is better.
As for the stepper and shunting, the stepper control circuit "should" be totally turned off above about 3 mph, so should not cause shunting as the car is travelling much faster when it happens. It could happen if the TVR box of tricks that produces the speed signal went faulty and stopped producing the speed signal, so the stepper would become active with the car still moving.
As for the stepper and shunting, the stepper control circuit "should" be totally turned off above about 3 mph, so should not cause shunting as the car is travelling much faster when it happens. It could happen if the TVR box of tricks that produces the speed signal went faulty and stopped producing the speed signal, so the stepper would become active with the car still moving.
[/quote]
Hiya
If the stepper control is turned off once rolling, does it close off the air bleed valve first, then open it again just before the car comes to a halt ?
Reason I ask is that since disconnecting my stepper due to it frequently giving me a unstable idle the car has been transformed in terms of a smooth strong and long power delivery and cannot understand why this has improved it.
My car a 500 does not run the cat map and do not have any shunting issues at all, being able to tootle around town at 1200 rpm in top, throttle subtle on /off without any issues.
Andy
[/quote]
Hiya
If the stepper control is turned off once rolling, does it close off the air bleed valve first, then open it again just before the car comes to a halt ?
Reason I ask is that since disconnecting my stepper due to it frequently giving me a unstable idle the car has been transformed in terms of a smooth strong and long power delivery and cannot understand why this has improved it.
My car a 500 does not run the cat map and do not have any shunting issues at all, being able to tootle around town at 1200 rpm in top, throttle subtle on /off without any issues.
Andy
No, it just leaves it at its last idle setting. It really should not affect the overall running at all, after all its just another air passage past the throttle plate, and the air its providing is still metered by the AFM, so the amount of fuel required is set accordingly. A bit more air this way is no different to opening the throttle a bit more. If you had an air leak in the stepper feed pipe, or stepper motor itself (it does happen) it will make the fueling incorrect as this air is not metered.
Edited by blitzracing on Friday 5th November 14:19
blitzracing said:
No, it just leaves it at its last idle setting. It really should not affect the overall running at all, after all its just another air passage past the throttle plate, and the air its providing is still metered by the AFM, so the amount of fuel required is set accordingly. A bit more air this way is no different to opening the throttle a bit more. If you had an air leak in the stepper feed pipe, or stepper motor itself (it does happen) it will make the fueling incorrect as this air is not metered.
I don't think that's right. More air through the stepper route would be metered as you say but it is different to opening the throttle a bit more as the throttle position sensor position would be different, no ?Edited by blitzracing on Friday 5th November 14:19
Cheers, Matt
The TPS is not really part of the fuel metering system, it just tells the ECU that you are at idle, over run, full power, or accelerating hard. This basically means its looks at full throttle voltage and shut throttle voltage, and rate of change. I dont think the mid range settings have much effect. The AFM does the donkey work of setting the fuel requirements.
Edited by blitzracing on Tuesday 16th November 18:01
blitzracing said:
The TPS is not really part of the fuel metering system, it just tells the ECU that you are at idle, over run, full power, or accelerating hard. This basically means its looks at full throttle voltage and shut throttle voltage, and rate of change. I dont think the mid range settings have much effect. The AFM does the donkey work of setting the fuel requirements.
Surely the TPS is part of the fuel metering then, i.e. more fuel is needed at 2000rpm with full throttle than at 2000rpm with throttle shut ? So if the stepper did get stuck open and you subsequently used less throttle for cruising/acceleration or whatever, the TPS would think you were using less throttle and meter the fuel accordingly ?Edited by blitzracing on Tuesday 16th November 18:01
Not really, it uses the AFM to work out how much fuel you need, so if you reduce the throttle, the airflow drops accordingly, so does the fuel. The TPS is there to work out if the throttle is shut for an idle or overun situation, above 2/3 turned to go open loop, and at fully open for full power enrichment. The car can run on TPS only if you disconnect the AFM, but they run really badly like this. There is a problem in so much that catalsys fitted cars are constantly being pulled back to 14.35:1 AF (in closed loop- which is most of the time) so whatever you do with sensor inputs, it just goes ahead and fixes the mixture, so a tweak of the stepper / base idle wont make the blindest bit of difference to overall mixture. The ECU has much more control of the mixture in non catalyst mode, and can run between about 12.5:1 and 15:1 depending on the load, and the TPS may have more effect then, like it can lean off the mixture for light crusing. It has been mentioned that the stepper may open up when the car is running to increase the overun idle to prevent wheel lock up, so this may have some effect, but I cant prove this one way or the other at the moment.
blitzracing said:
Not really, it uses the AFM to work out how much fuel you need, so if you reduce the throttle, the airflow drops accordingly, so does the fuel. The TPS is there to work out if the throttle is shut for an idle or overun situation, above 2/3 turned to go open loop, and at fully open for full power enrichment. The car can run on TPS only if you disconnect the AFM, but they run really badly like this. There is a problem in so much that catalsys fitted cars are constantly being pulled back to 14.35:1 AF (in closed loop- which is most of the time) so whatever you do with sensor inputs, it just goes ahead and fixes the mixture, so a tweak of the stepper / base idle wont make the blindest bit of difference to overall mixture. The ECU has much more control of the mixture in non catalyst mode, and can run between about 12.5:1 and 15:1 depending on the load, and the TPS may have more effect then, like it can lean off the mixture for light crusing. It has been mentioned that the stepper may open up when the car is running to increase the overun idle to prevent wheel lock up, so this may have some effect, but I cant prove this one way or the other at the moment.
Interesting and good explanation, thanks Blitz.Going back to the start of this topic. If the cold enrichment is faulty on my car as suspected, wouldn't that cause it to run leaner and cause worse shunting, whereas reduced shunting is what I am experiencing. I can actually roll down to a near stop now without the shunting occuring on many occasions, which has never been the case in 8 years of daily driving - always had to shove the clutch in / shift to neutral.
Cheers, Matt
To be honest you need to look at the lambda cycling patterns with it shunting and without it shunting to get some idea of how the ECU is dealing with the mixture, or we could carry on speculating for ever. On the whole bad shunting is acompanied with slow mixture swings and some overshooting as seen as hanging in the lean part of the cycle, and a car thats running well will cycle much faster in a uniform manner, but its pretty subtle to observe. The problem is the whole system is so dynamic its difficult to make precise readings, and it has been described as trying to put up a level shelf (as the mixture control) with a bubble gauge (lambda feedback), whilst on a boat in a stormy sea(ECU making mixture changes). You are much better off doing shunting tests on the non catalyst fuel map, as at least the mixture platform your are dealing with is constant.
Gassing Station | Chimaera | Top of Page | What's New | My Stuff