Cold starting and fuel consumption
Discussion
I needed to get something out the garage last night and while I was down there I was overcome with a sudden urge to take the car out. I had no intention of doing so, it was pitch black outside and somewhat below zero, but I could not physically leave the garage before taking it for a run. So I grabbed the keys and jumped in...
Along with most of the Chims I drove beforehand it seems to take a certain amount of cranking before the engine fires. And when it finally does it smells very rich and doesn't sound quite right to start with, plus the throttle response seems dulled. Any ideas what may be the cause of that (or is it just a 'they all do that Sir' moment)?
Also, although I haven't had the chance to drive it much since the last fill up to check methodically it does - according to the fuel gauge - seem to be using quite a lot of petrol. It's used about 1/3rd of a tank in 60 miles of mixed driving. There has been some town traffic and a few 'enthusiastic' blasts, but overall it's been fairly normal conditions. Do you think this sounds right?
Once its up to temperature the engine pulls well with good oil pressure and no visible smoke etc. and to be fair I am something of an automotive hypochondriac, so it's probably nothing.
Along with most of the Chims I drove beforehand it seems to take a certain amount of cranking before the engine fires. And when it finally does it smells very rich and doesn't sound quite right to start with, plus the throttle response seems dulled. Any ideas what may be the cause of that (or is it just a 'they all do that Sir' moment)?
Also, although I haven't had the chance to drive it much since the last fill up to check methodically it does - according to the fuel gauge - seem to be using quite a lot of petrol. It's used about 1/3rd of a tank in 60 miles of mixed driving. There has been some town traffic and a few 'enthusiastic' blasts, but overall it's been fairly normal conditions. Do you think this sounds right?
Once its up to temperature the engine pulls well with good oil pressure and no visible smoke etc. and to be fair I am something of an automotive hypochondriac, so it's probably nothing.
Chris,
On the fuel front, the gauge moves all over the place, especially as the tank gets lower.
As a general rule most people get about 200 miles per tank, so you are not too far off that.
The throttle response on mine is always a bit slow immediately after starting. Pressing the accelerator results in a slight dip in revs before an increase. This soon dissapears and I have
never noticed it once moving.
Depending on the state of your battery and how cold it is the initial cranking can be slower.
I keep mine on an accumate after a bout of slow cranking and now it turns over fast and starts
quickly.
Can't really comment on the sound of the engine when it starts up.
On the fuel front, the gauge moves all over the place, especially as the tank gets lower.
As a general rule most people get about 200 miles per tank, so you are not too far off that.
The throttle response on mine is always a bit slow immediately after starting. Pressing the accelerator results in a slight dip in revs before an increase. This soon dissapears and I have
never noticed it once moving.
Depending on the state of your battery and how cold it is the initial cranking can be slower.
I keep mine on an accumate after a bout of slow cranking and now it turns over fast and starts
quickly.
Can't really comment on the sound of the engine when it starts up.
The engine will normally sound like its on choke and stink of fuel from stone cold, and this is quite normal as the fuel map puts in too much fuel (designed for Range Rovers in the Arctic!). It should however start to run more normally after about 20-30 seconds as the Lambda probes get hot, and the ECU then corrects the mixture and the change in engine note when this happens is quite marked. If however you dont give the car this idle time, the ECU can have problems making the big fuelling adjustments when you drive the car as everything is changing like AFM, RPM, and TP setting, so it does not have a stable platform to set the initial fuelling level. This can lead to some bad engine manners and economy, so its worth giving the car some idle time to start with.
Cool, sounds like I was indeed being a touch paranoid.
The other thing I've noticed is the gearbox isn't as slick as it might be. It felt okay on a 5 minute test drive, but it's actually quite notchy. It was only a quick run last night though - how long would you expect it to take for the gearbox oil to warm up and is there a noticeable difference?
On an unconnected note, do the aftermarket ECUs smooth out the engine braking when you back off the pedal? It almost kangeroos if you go on and off the gas.
The other thing I've noticed is the gearbox isn't as slick as it might be. It felt okay on a 5 minute test drive, but it's actually quite notchy. It was only a quick run last night though - how long would you expect it to take for the gearbox oil to warm up and is there a noticeable difference?
On an unconnected note, do the aftermarket ECUs smooth out the engine braking when you back off the pedal? It almost kangeroos if you go on and off the gas.
Chris71 said:
On an unconnected note, do the aftermarket ECUs smooth out the engine braking when you back off the pedal? It almost kangeroos if you go on and off the gas.
Before you head off down that road are you actually sure the car is running as it should be in the first place?If you take everything you read on here too seriously you might incorrectly assume these cars won't do anything properly unless tinkered with, the opposite tends to be nearer the truth.
Yes but frequently to fix the mess made by 'tinkerers' of the original stuff then the easiest solution to put it right is likely a newer ECU + wiring + sensors....
For example having seen countless looms & cables rendered useless by performing stab in the dark tests/diagnoses advised on here & elsewhere (not just limited to DIY'ers either) is there any wonder folks want to start again with a clean slate?
For example having seen countless looms & cables rendered useless by performing stab in the dark tests/diagnoses advised on here & elsewhere (not just limited to DIY'ers either) is there any wonder folks want to start again with a clean slate?
Ribol said:
Chris71 said:
On an unconnected note, do the aftermarket ECUs smooth out the engine braking when you back off the pedal? It almost kangeroos if you go on and off the gas.
Before you head off down that road are you actually sure the car is running as it should be in the first place?If you take everything you read on here too seriously you might incorrectly assume these cars won't do anything properly unless tinkered with, the opposite tends to be nearer the truth.
I do take your point though, and it's particularly relevant to this car - I know it's had a basic service recently, but it came with a rather patchy history, so I can't vouch for the state of the plugs, HT leads etc. and I will of course check these before making any rash decisions.
Although I have a reasonable level of basic mechanical competence I did think about getting someone like The TVR Centre to check it over and suggest a 'to do' list. I'm going to be away a lot over the next few months though, so that can probably wait 'till MOT time in March.
Well we all seem to be in agreement that most of our cars have this characteristic.
My car exhibits over fuelling on cold start, but I must say its greatly improved since fitting the Mark Adams chip.
So how about some ideas on a solution guys?
I will start the bidding with this:
If the ECU is putting the car on cold start fueling in response to the resistance within the ECU coolant temp sender, perhaps the resistance could be modified?
In my experience when the coolant temperature reaches only 10 degrees the fuelling comes good, just don't try and drive it before then.
I would need to test an ECU temp sender over its temperature range to map the resistance changes, but surely armed with this data you could add an in-line resistor of the correct value.
This would effectively trick the ECU into thinking the coolant was 10 degrees when in truth it was zero, I have no doubt the car would still start in this condition.
The resistance in the ECU temp sensor would need to return to the standard resistance curve after the false 10 degrees setting or it could initiate other running faults.
Obviously the lambda sensors play a part in the cold start fuelling too.
With the car stone cold it would be worth seeing what effect gently warming the manifolds close to the lambdas with a blow torch would have to the cold start over fuelling issue.
In the same way as I have suggested with the temp sensor the lambda output resistance could be tweaked on cold start to trick the ECU into thinking the car was slightly warmer than it actually is.
Remember our cars don't have this problem in the summer, on a frosty morning if we can make the ECU just think things are a little bit warmer outside the problem will be sorted.
One thing is for sure, my engine definitely doesn't need the massive amount of fuel its currently getting to start it on a cold morning.
Shoot my ideas down in flames by all means, after all I'm just thinking aloud.
But in my defence at least I am attempting to think out a solution.
Anyone got ideas to add?
PS: On the subject of flames, I'm not sure TVRs and blow torches make very comfortable bed fellows
My car exhibits over fuelling on cold start, but I must say its greatly improved since fitting the Mark Adams chip.
So how about some ideas on a solution guys?
I will start the bidding with this:
If the ECU is putting the car on cold start fueling in response to the resistance within the ECU coolant temp sender, perhaps the resistance could be modified?
In my experience when the coolant temperature reaches only 10 degrees the fuelling comes good, just don't try and drive it before then.
I would need to test an ECU temp sender over its temperature range to map the resistance changes, but surely armed with this data you could add an in-line resistor of the correct value.
This would effectively trick the ECU into thinking the coolant was 10 degrees when in truth it was zero, I have no doubt the car would still start in this condition.
The resistance in the ECU temp sensor would need to return to the standard resistance curve after the false 10 degrees setting or it could initiate other running faults.
Obviously the lambda sensors play a part in the cold start fuelling too.
With the car stone cold it would be worth seeing what effect gently warming the manifolds close to the lambdas with a blow torch would have to the cold start over fuelling issue.
In the same way as I have suggested with the temp sensor the lambda output resistance could be tweaked on cold start to trick the ECU into thinking the car was slightly warmer than it actually is.
Remember our cars don't have this problem in the summer, on a frosty morning if we can make the ECU just think things are a little bit warmer outside the problem will be sorted.
One thing is for sure, my engine definitely doesn't need the massive amount of fuel its currently getting to start it on a cold morning.
Shoot my ideas down in flames by all means, after all I'm just thinking aloud.
But in my defence at least I am attempting to think out a solution.
Anyone got ideas to add?
PS: On the subject of flames, I'm not sure TVRs and blow torches make very comfortable bed fellows
When you say not to drive it until it's up to temperature... Does that just upset things until it reaches the right temperature or is there some sort of learning process going on which will offset the fuelling right the way until the ECU is next powered down?
Believe it or not I used to deal with this sort of thing for a living, but I only dealt with diesel engines and the software was a little bit more comprehensive than early '90s Land Rover stuff probably is. I can't remember how many maps we had in the DW10 and 12 (current Ford/PSA 2/2.2-litre diesels) but it was well into the tens of thousands. In contrast, I know many of the early systems are in single figures and were done by a bloke who was still a bit miffed to be deprived of mixture screws and float chambers.
Believe it or not I used to deal with this sort of thing for a living, but I only dealt with diesel engines and the software was a little bit more comprehensive than early '90s Land Rover stuff probably is. I can't remember how many maps we had in the DW10 and 12 (current Ford/PSA 2/2.2-litre diesels) but it was well into the tens of thousands. In contrast, I know many of the early systems are in single figures and were done by a bloke who was still a bit miffed to be deprived of mixture screws and float chambers.
Chris71 said:
The other thing I've noticed is the gearbox isn't as slick as it might be. It felt okay on a 5 minute test drive, but it's actually quite notchy. It was only a quick run last night though - how long would you expect it to take for the gearbox oil to warm up and is there a noticeable difference?
I found the gearbox took some getting used too - when trying to change quickly from second to third I kept missing the gate in the early days which really took the wind out of my sails when accelerating hard.I got used to it after a month or so, but it's no less notchy now TBH. I love how short the throw is though - I'd now hate to drive a car with a long stick!
No I did not say wait until the engine was warm, it just needs the Lambda probes to be hot, from a combination of exhaust gas, and internal 12 v heaters, hence the 20-30 seconds wait time, no more. The ECU constantly trims the mixture when the car is running, and seems to make the overall setting at idle as a starting point. On modern ECU's its referred to long term fuel trim when it sets the overall fueling, and short term fuel trim when it just needs a small tweak to get it right once a base setting has been reached, and the 14CUX pretty much does the same. It does not learn as such, just constantly corrects as conditions change.
As for the Engine braking, it is controlled within the chipping, and it appears that after the car starts to move the stepper motor is opened up to bring the base idle up to around 1500 rpm, so it does not drop too low between gears. I don't yet know exactly when this happens, Ive made a nice test cable and LED to find out, but none of the local TVR's or my car are on the road at present.
You can alter the temp sender reading to the ECU by putting a resistor across it, not in series as this would make the engine look even colder. A value of 10 k would be a good point to start, as it will lift the apparent engine temp much more when the engine is cold, say 0'c by about 10' (5.8k becomes 3.7 k) and has little effect when the engine is hot, due to the very non linear response of the sender. A 10 k resistor across 300 ohms at 80'c can be ignored. A Tornado chip certainly sorts the cold fueling, but is a tad pricey compared to an extra resistor.
As for the Engine braking, it is controlled within the chipping, and it appears that after the car starts to move the stepper motor is opened up to bring the base idle up to around 1500 rpm, so it does not drop too low between gears. I don't yet know exactly when this happens, Ive made a nice test cable and LED to find out, but none of the local TVR's or my car are on the road at present.
You can alter the temp sender reading to the ECU by putting a resistor across it, not in series as this would make the engine look even colder. A value of 10 k would be a good point to start, as it will lift the apparent engine temp much more when the engine is cold, say 0'c by about 10' (5.8k becomes 3.7 k) and has little effect when the engine is hot, due to the very non linear response of the sender. A 10 k resistor across 300 ohms at 80'c can be ignored. A Tornado chip certainly sorts the cold fueling, but is a tad pricey compared to an extra resistor.
Edited by blitzracing on Friday 26th November 17:25
Chris71 said:
When you say not to drive it until it's up to temperature... Does that just upset things until it reaches the right temperature or is there some sort of learning process going on which will offset the fuelling right the way until the ECU is next powered down?
Believe it or not I used to deal with this sort of thing for a living, but I only dealt with diesel engines and the software was a little bit more comprehensive than early '90s Land Rover stuff probably is. I can't remember how many maps we had in the DW10 and 12 (current Ford/PSA 2/2.2-litre diesels) but it was well into the tens of thousands. In contrast, I know many of the early systems are in single figures and were done by a bloke who was still a bit miffed to be deprived of mixture screws and float chambers.
Hi Chris, Believe it or not I used to deal with this sort of thing for a living, but I only dealt with diesel engines and the software was a little bit more comprehensive than early '90s Land Rover stuff probably is. I can't remember how many maps we had in the DW10 and 12 (current Ford/PSA 2/2.2-litre diesels) but it was well into the tens of thousands. In contrast, I know many of the early systems are in single figures and were done by a bloke who was still a bit miffed to be deprived of mixture screws and float chambers.
I only say that because typically you only have to touch the throttle when the car is doing it's over fuelling thing, and the car will stall.
After its stalled you try and start it again!
Very, very difficult and totally flooded.
If you are unfortunate enough to stall from a cold start like this you need to walk away for at least 10 minutes before trying again, or you will just make things worse.
When you come back to try again open the throttle fully and crank, she should start.
The best solution is to never go there in the first place.
That's why I said don't derive it until it warms up a fraction.
What I should have said is don't touch the throttle.
I'm really enjoying all the information from you guys on here. Very informative. The more i read on several topics, the more i gather there are several common problems. This "problem" of over-fuelling when very cold is interesting as i thought the opposite that my cold start mechanism may not have been working properly and as such the mixture was too lean until warmed up. The over-fuelling also explains the exhaust "smoke" and fuel smell from very cold. Basically unburned fuel being dumped. Doesn't help fuel consumption either.
I have made some points on some of my other posts re engine management systems and better efficiency in general. It seems the current Lucas ECU map is a little "crude" and set up for Land Rovers in Arctic conditions as said. Whilst surly the best answer is to get rid of the distributor and have a fully mapped system for both fuel and ignition as the current system cannot do timing as i understand.
Nevertheless, surely the current Lucas ECU can be re programmed better to deal with the cold difficulties and hence better running straight away and indeed fuel economy? If as mentioned an after market ECU can be used with better results then why not remap the Lucas?
Despite the age of the design etc. there is really no reason to put up with this surely when a "proper" management system could sort it all out. The engine should start any time, hot or very cold and idle cleanly STRAIGHT AWAY and drive smoothly straight away. I realise that many will think the current way has "a certain charm" but..................
I have made some points on some of my other posts re engine management systems and better efficiency in general. It seems the current Lucas ECU map is a little "crude" and set up for Land Rovers in Arctic conditions as said. Whilst surly the best answer is to get rid of the distributor and have a fully mapped system for both fuel and ignition as the current system cannot do timing as i understand.
Nevertheless, surely the current Lucas ECU can be re programmed better to deal with the cold difficulties and hence better running straight away and indeed fuel economy? If as mentioned an after market ECU can be used with better results then why not remap the Lucas?
Despite the age of the design etc. there is really no reason to put up with this surely when a "proper" management system could sort it all out. The engine should start any time, hot or very cold and idle cleanly STRAIGHT AWAY and drive smoothly straight away. I realise that many will think the current way has "a certain charm" but..................
spend said:
Why do you all assume its the coolant temp rather than the air temp causing problems? I know which one I'd have more faith in 
and which one affects the fueling calc more intimately?
But this is already taken into account with the AFM output voltage as part of its function, but Ive not done tests against a fixed airflow and various temps to see the effect. This could be an interesting experiment, Ive got an AFM on the bench at the moment, Ill try a hair dryer cold and at full heat and see what the output voltage does. and which one affects the fueling calc more intimately?
captaintact said:
I'm really enjoying all the information from you guys on here. Very informative. The more i read on several topics, the more i gather there are several common problems. This "problem" of over-fuelling when very cold is interesting as i thought the opposite that my cold start mechanism may not have been working properly and as such the mixture was too lean until warmed up. The over-fuelling also explains the exhaust "smoke" and fuel smell from very cold. Basically unburned fuel being dumped. Doesn't help fuel consumption either.
I have made some points on some of my other posts re engine management systems and better efficiency in general. It seems the current Lucas ECU map is a little "crude" and set up for Land Rovers in Arctic conditions as said. Whilst surly the best answer is to get rid of the distributor and have a fully mapped system for both fuel and ignition as the current system cannot do timing as i understand.
Nevertheless, surely the current Lucas ECU can be re programmed better to deal with the cold difficulties and hence better running straight away and indeed fuel economy? If as mentioned an after market ECU can be used with better results then why not remap the Lucas?
Despite the age of the design etc. there is really no reason to put up with this surely when a "proper" management system could sort it all out. The engine should start any time, hot or very cold and idle cleanly STRAIGHT AWAY and drive smoothly straight away. I realise that many will think the current way has "a certain charm" but..................
This is where Mark Adams (Tornado systems) has made his trade (in the past at least), and its perfectly possible. Chips are around £400, so not cheap, but he knows his stuff, and re chipping does improve things in a number of subtle areas, including cold starts. If you search for 14CUX on Ebay you will find the details of his chips. The Lucas 14CUX is actually a Bosch design, and there is a program that can be used to access and reprogram the map called WinOLS, that cost about £1k Im told (for commercial use) and on top of that you need an Eprom emulator that costs about £200. This allows you to change the live map data on the rolling road, before blowing a new chip to make the map permanent.I have made some points on some of my other posts re engine management systems and better efficiency in general. It seems the current Lucas ECU map is a little "crude" and set up for Land Rovers in Arctic conditions as said. Whilst surly the best answer is to get rid of the distributor and have a fully mapped system for both fuel and ignition as the current system cannot do timing as i understand.
Nevertheless, surely the current Lucas ECU can be re programmed better to deal with the cold difficulties and hence better running straight away and indeed fuel economy? If as mentioned an after market ECU can be used with better results then why not remap the Lucas?
Despite the age of the design etc. there is really no reason to put up with this surely when a "proper" management system could sort it all out. The engine should start any time, hot or very cold and idle cleanly STRAIGHT AWAY and drive smoothly straight away. I realise that many will think the current way has "a certain charm" but..................
blitzracing said:
spend said:
Why do you all assume its the coolant temp rather than the air temp causing problems? I know which one I'd have more faith in and which one affects the fueling calc more intimately?
But this is already taken into account with the AFM output voltage as part of its function, but Ive not done tests against a fixed airflow and various temps to see the effect. This could be an interesting experiment, Ive got an AFM on the bench at the moment, Ill try a hair dryer cold and at full heat and see what the output voltage does. and which one affects the fueling calc more intimately?If the AFM was that accurate the lambdas would only be needed for errant injectors / regulators?
OK thats simply down to the terms you use, AFM, air flow meter, might be better termed air mass meter in this case, but after all the available oxygen depends both on air speed and density, and both of these should be taken into account with the cooling affect of the hot wire, and temp sensor along side the hot wire.
...Tank's now down to a quarter (down from full) and reading 130 miles. Assuming the 5-litre uses the same 57-litre tank as the 400s(?) that makes it about 14mpg.
It is fully decatted (which I'm told upsets the fuelling a little), but still sounds excessive for the way its been driven. I certainly haven't been hooning around like a mentalist.
It is fully decatted (which I'm told upsets the fuelling a little), but still sounds excessive for the way its been driven. I certainly haven't been hooning around like a mentalist.
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