OVER FUELLING ON COLD START
Discussion
Hi all.
I realise this subject has been dealt with in the past and apologies for posting about it again!
On starting from stone cold, my car appears to "miss" for thirty seconds or more and will not rev cleanly. After this initial period the car is absolutely fine and the symptoms only reoccur after an overnight wait.
As stated in a previous post, all of the ignition components are new, I have just fitted a new, genuine stepper and an FAE coolant temp sensor. Don't ever fit one of the "Lucas" CTS parts as they are rubbish!
I am at a bit of a loss as to the next step. Go back to an old Weber or Su and I'd be fine but even an ancient injection system like the Lucas one has me baffled.
Is there a fuel temp ECU connected on these cars? the Steve Heath book suggests they are unused on the TVR.
Any thoughts would be appreciated.
Regards Chris.
I realise this subject has been dealt with in the past and apologies for posting about it again!
On starting from stone cold, my car appears to "miss" for thirty seconds or more and will not rev cleanly. After this initial period the car is absolutely fine and the symptoms only reoccur after an overnight wait.
As stated in a previous post, all of the ignition components are new, I have just fitted a new, genuine stepper and an FAE coolant temp sensor. Don't ever fit one of the "Lucas" CTS parts as they are rubbish!
I am at a bit of a loss as to the next step. Go back to an old Weber or Su and I'd be fine but even an ancient injection system like the Lucas one has me baffled.
Is there a fuel temp ECU connected on these cars? the Steve Heath book suggests they are unused on the TVR.
Any thoughts would be appreciated.
Regards Chris.
I could be wrong but I think 'over fuelling' can be partly caused by the ECU's double injector rate used during initial or cold start, where the injector banks are fired alternately as normal but for every spark pulse. After a few seconds the injector firing rate reverts to every other spark pulse. This choke feature was introduced in 14CUX to replace the dedicated cold start injector used in previous systems.
Some 14CUX aftermarket tunes also include a feature where the engine is briefly cranked without firing at start up for oil circulation purposes.
You could check that your spark plugs and battery are in good order.
Some 14CUX aftermarket tunes also include a feature where the engine is briefly cranked without firing at start up for oil circulation purposes.
You could check that your spark plugs and battery are in good order.
I did a lot of thread searching on this issue myself. The general consensus was to live with it. If I push the throttle on mine within about 30s of starting it, it will stall. Then it is hard to start (it starts easily from cold without touching the throttle).
It is a bit lumpy for the first minute or so of driving too but is then fine. Apart from hearing 'TADTS,' annoyingly, my friend's 500 isn't like this. Drives fine straight away, but his had a recent engine rebuild which may be an advantage. No build up of carbon inside?
It is a bit lumpy for the first minute or so of driving too but is then fine. Apart from hearing 'TADTS,' annoyingly, my friend's 500 isn't like this. Drives fine straight away, but his had a recent engine rebuild which may be an advantage. No build up of carbon inside?
Mine (400 Serpentine) has done exactly what you have described sine I have had it which is approaching 13 years.
It was a daily driver for the first 10 and up until two years ago (when I redid the chassis) was serviced at the recommended schedule by various garages. I now do all the servicing myself.
None of the garages have ever found anything wrong with the engine or ECU which would put this behaviour down to a fault.
I have also checked components and had it plugged into the laptop and found no faults.
The only thing I have not done is to get the injectors tested but as it easily passes the MOT for emissions, even when not fully hot, and drives nicely and as economically as can be expected (300+ miles to a tank on a long run) I don't think that there can be much wrong with them.
I have now resigned to the fact that this is what mine and from reading and talking to other owners, other cars do, which I realise is probably not what you want to hear.
I find that it is worse the colder the day is the worse it is so it is probably the 'choke' being a bit over zealous as has been mentioned.
It was a daily driver for the first 10 and up until two years ago (when I redid the chassis) was serviced at the recommended schedule by various garages. I now do all the servicing myself.
None of the garages have ever found anything wrong with the engine or ECU which would put this behaviour down to a fault.
I have also checked components and had it plugged into the laptop and found no faults.
The only thing I have not done is to get the injectors tested but as it easily passes the MOT for emissions, even when not fully hot, and drives nicely and as economically as can be expected (300+ miles to a tank on a long run) I don't think that there can be much wrong with them.
I have now resigned to the fact that this is what mine and from reading and talking to other owners, other cars do, which I realise is probably not what you want to hear.
I find that it is worse the colder the day is the worse it is so it is probably the 'choke' being a bit over zealous as has been mentioned.
Do you get two wet lines behind the car if you leave it idling?
I did yesterday, then spent the rest of the morning finding and curing the misfire with V8 Developments help.
Turned out I had a dead plug extender and was running on 7.
It ran pretty well ok at speed, you only really noticed the misfire at low speed or accelerating from 30 in 4th.
I do get what you describe on a damp morning, but it clears as the moisture evaporates.
I did yesterday, then spent the rest of the morning finding and curing the misfire with V8 Developments help.
Turned out I had a dead plug extender and was running on 7.
It ran pretty well ok at speed, you only really noticed the misfire at low speed or accelerating from 30 in 4th.
I do get what you describe on a damp morning, but it clears as the moisture evaporates.
What ever the amount of fuel is thrown in by the ECU, the mixture should start to trim it itself pretty quickly as the lambda probes heat up- but there has been some discussion on this. Ive always thought the mixture would start to trim within about 20 second (the probe heat up time) but Ive now seen several examples where the trim is not applied at all until the engine is give a blip on the throttle, and suddenly they start to cycle, and the mixture then leans out. As you have RoverGauge it would be worth watching the short term trim from cold, and see when it starts to move, with or without a throttle blip.
Mine does exactly the same with a brand new engine. Made the mistake of thinking I let itnroll off my drive so I could put out the bins while warmed up. Of course it stalled in the middle of the road leading to a day of trying to get it started as it flooded in my haste to get it out of the way.
Glad I'm not the only one
Glad I'm not the only one
frubes said:
Mine does exactly the same with a brand new engine. Made the mistake of thinking I let itnroll off my drive so I could put out the bins while warmed up. Of course it stalled in the middle of the road leading to a day of trying to get it started as it flooded in my haste to get it out of the way.
FrubesThe next time it stalls pop the inertia switch and then crank it to clear the excess fuel, it may briefly fire up and die. Please let me know what happens as I have an idea but no promises.
frubes said:
Glad I'm not the only one
Dave,Sounds like its time I start experimenting with the temperature adjustment fueling tables to see if we can help these chaps.
Cheers, Steve Sprint.
blitzracing said:
What ever the amount of fuel is thrown in by the ECU, the mixture should start to trim it itself pretty quickly as the lambda probes heat up- but there has been some discussion on this. Ive always thought the mixture would start to trim within about 20 second (the probe heat up time) but Ive now seen several examples where the trim is not applied at all until the engine is give a blip on the throttle, and suddenly they start to cycle, and the mixture then leans out. As you have RoverGauge it would be worth watching the short term trim from cold, and see when it starts to move, with or without a throttle blip.
As Above Lumpy until you can get a blip then all is well (about 10-20sec)
Hi and thanks for the replies.
I tried mine again today and no change. The smell of fuel is quite strong and a little worrying, but as before, after about a minute all was fine.
Is the fuel temp sensor connected/fitted on our cars? It seems strange that after all these years so many of us suffer from the same problem. Surely the over fuelling on a cold start must be detrimental to the engine?
I only got my car, a 1997 400, last year and admittedly have only done less than 2000 miles in it. Most of the time it has been in the garage having work done on it! The strange thing is I don't recall any issues like this last year.
Regards Chris
I tried mine again today and no change. The smell of fuel is quite strong and a little worrying, but as before, after about a minute all was fine.
Is the fuel temp sensor connected/fitted on our cars? It seems strange that after all these years so many of us suffer from the same problem. Surely the over fuelling on a cold start must be detrimental to the engine?
I only got my car, a 1997 400, last year and admittedly have only done less than 2000 miles in it. Most of the time it has been in the garage having work done on it! The strange thing is I don't recall any issues like this last year.
Regards Chris
s3c chris said:
Thanks for that Paul.
The coolant sensor has been changed. A genuine TVR one is now fitted but no difference has been made.
The Steve Heath book mentions the fuel sensor but says that is not connected or used on the TVR?
Regards Chris.
Dont know where that myth came from, the ECU very much needs it. You really need some diagnostics plugged into the ECU to check the sensor values or any fault codes, as the MIL light does not work on the TVR.The coolant sensor has been changed. A genuine TVR one is now fitted but no difference has been made.
The Steve Heath book mentions the fuel sensor but says that is not connected or used on the TVR?
Regards Chris.
We have talked about changing the engine temp reading to reduce the cold start fuelling- well Ive tried it now, and 5k ohms across the sensor gives 10'C to 15' C increase in the temp the ECU sees. Mine started just fine like this, and it does not significantly affect the hot engine temp the ECU sees, as the sensor value drops to a few hundred ohms and running temp, so 5k has little affect across it. Ive used a variable resistor, so you can set the cold start value, and it plugs in line with the current connector. Anyone fancy being a Gunnie pig who has the problem?
blitzracing said:
We have talked about changing the engine temp reading to reduce the cold start fuelling- well Ive tried it now, and 5k ohms across the sensor gives 10'C to 15' C increase in the temp the ECU sees. Mine started just fine like this, and it does not significantly affect the hot engine temp the ECU sees, as the sensor value drops to a few hundred ohms and running temp, so 5k has little affect across it. Ive used a variable resistor, so you can set the cold start value, and it plugs in line with the current connector. Anyone fancy being a Gunnie pig who has the problem?
I did a test some years ago when I was still on the 14CUX, all I did was try a stone cold start with the ECU temp sensor in a mug of hot water to fool the ECU into thinking the engine was warm.The car started much better with no over fueling and none of it's normal habit of stalling if you touched the throttle during the first 30 seconds after a fully cold start.
The resister mod was due to be my next step but never happened as I went for the Canems dual fuel engine management system in the end.
My idea was to wire a variable resistor across the temp sensor and back to the dash to act as a kind of electric choke, or more accurately a way of turning down the 14CUx's habit of over fueling on cold start.
It now looks like Blitz has done all this and proved it can help if 14CUX users are suffering the cold start over fueling & stalling syndrome that seems quite common on these cars.
Nice one Blitz
The other thing I'd encourage the OP to do is bin the unsuitable shrouded NGK B7ECS spark plugs, I recommend switching to the projected electrode NGK BPR6ES or better still NGK BPR6EIX iridium plugs.
Despite a few Muppets on this forum insisting I'd destroy my engine by running NGK BPR6EIX iridiums I have conclusively proven over the last few years that these plugs are an excellent upgrade. Immediately after fitting these plugs (still on 14CUX & distributor at the time) I enjoyed a noticeably smoother idle, better cold starting, and a smoother drive at lower RPMs.
Read about the plug switch here in my 2012 post when my pre-gas name was ChimpOfDarkness
http://www.pistonheads.com/gassing/topic.asp?h=1&a...
I'd put money on the OP solving his cold start problem if he both adds the Blitz ECU temp resister mod and fits a set of NGK BPR6ES or BPR6EIX iridium plugs.
Try it, then tell me I'm wrong
The other thing that will help is to bin the cats (especially the big main one), removing the restrictions the cats impose will help the engine breath more efficiently and will have the added benefit of releasing 5-10hp.
Good luck to the OP
Edited by ChimpOnGas on Sunday 29th March 10:41
ChimpOnGas said:
The other thing I'd encourage the OP to do is bin the unsuitable shrouded NGK B7ECS spark plugs, I recommend switching to the projected electrode NGK BPR6ES or better still NGK BPR6EIX iridium plugs.
Despite a few Muppets on this forum insisting I'd destroy my engine by running NGK BPR6EIX iridiums I have conclusively proven over the last few years that these plugs are an excellent upgrade. Immediately after fitting these plugs (still on 14CUX & distributor at the time) I enjoyed a noticeably smoother idle, better cold starting, and a smoother drive at lower RPMs.
Read about the plug switch here in my 2012 post when my pre-gas name was ChimpOfDarkness
http://www.pistonheads.com/gassing/topic.asp?h=1&a...
Did anyone actually insist you'd destroy your engine Dave; I don't recall that? I do recall some offering views on why the 7ECS might still be an appropriate plug on engines in a higher state of tune or being pushed harder. Despite a few Muppets on this forum insisting I'd destroy my engine by running NGK BPR6EIX iridiums I have conclusively proven over the last few years that these plugs are an excellent upgrade. Immediately after fitting these plugs (still on 14CUX & distributor at the time) I enjoyed a noticeably smoother idle, better cold starting, and a smoother drive at lower RPMs.
Read about the plug switch here in my 2012 post when my pre-gas name was ChimpOfDarkness
http://www.pistonheads.com/gassing/topic.asp?h=1&a...
If someone offers a different perspective to yours in real life, do you call them muppets too?
blitzracing said:
We have talked about changing the engine temp reading to reduce the cold start fuelling- well Ive tried it now, and 5k ohms across the sensor gives 10'C to 15' C increase in the temp the ECU sees. Mine started just fine like this, and it does not significantly affect the hot engine temp the ECU sees, as the sensor value drops to a few hundred ohms and running temp, so 5k has little affect across it. Ive used a variable resistor, so you can set the cold start value, and it plugs in line with the current connector. Anyone fancy being a Gunnie pig who has the problem?
When you say 'in line', please can you confirm if it is in parallel or series with the sensor?Gassing Station | Chimaera | Top of Page | What's New | My Stuff