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GT3 tries to stall when revving from cold start


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Hi all, my GT3 starts perfectly from cold and idles at about 1300rpm, all of which is fine but when you depress the accelerator pedal it wants to stall, in fact it sometimes will stall if you try to pull away. The symptom slowly subsides as the car warms up and the runs fine when warm although there is a momentary stutter if you briefly floor the throttle with no load on the engine. To me this Indicates a throttle position sensor issue  but this was replaced recently due to another running fault.  Could it be something to do with set up of he TPS or am I barking up the wrong tree?  The engine management light has not come on at all, hot or cold

Shaun

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The TPS needs to be setup using freescan or espritmon. You need to check this first before even thinking about anything else.

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Only here once

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Have you just got it back from Geoff from some work including the replacement TPS? I'd be having a chat with him myself.

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Similar symptoms to what I had only in that the issue goes away after the car is warmed up. Turned out to be the lambda (O2) sensor, replacement totally fixed it. 

 

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In general, when pressing the throttle causes hesitation or the car to die, it indicates that it's running lean. So either it's not adding the fuel that it should or there's an air leak. I believe air leaks are more likely to cause the issue on cars using AFM rather than MAP though.

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On 04/07/2022 at 17:25, shaunw said:

when you depress the accelerator pedal it wants to stall, in fact it sometimes will stall if you try to pull away. The symptom slowly subsides as the car warms up

Hi Shaun,

This was an issue I was experiencing. Cured completely with a set of new injectors (RC)

Are you still on the originals?

Andy.

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13 hours ago, AndyPG said:

Hi Shaun,

This was an issue I was experiencing. Cured completely with a set of new injectors (RC)

Are you still on the originals?

Andy.

Yes I believe they are. I discovered a couple of weeks ago during a 500 mile round trip to the Peak District that the car also occasionally stalls when warm when slowing or stopping at a junction. I have wondered about the condition of the injectors as although the car has only done 21000 miles, it has been left standing for long periods which often does more harm than good. I spoke to Geoff at Esprit engineering a few days ago and he was very helpful in giving me some basic stuff to check so the plan is to work through that and if I have no joy, take the car to him, and see if they can trace the fault. How did you diagnose the injector problem?

Shaun

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32 minutes ago, shaunw said:

How did you diagnose the injector problem?

Hi Shaun,

When I first bought the car, a few years ago, I pulled the injectors and tested them for flow rate and spray pattern.

After cleaning they tested perfectly with normal spray patterns and identical flow rates.

But the engine always has a slight hiccup when blipping the throttle, especially when cold. Also pulling away at junctions needed careful clutch use due to the resultant slight flat-spot just off idle. My issue was not a severe as yours.

A couple of months ago (2 years later) the engine's idle became rather lumpy. After pulling each injector plug in turn, I decided one wasn't right.

I removed the injectors and tested them again to find one was now down on flow rate by about 8%. I tried cleaning again but couldn't improve it so I bit the bullet and ordered a set of RC's.

Not only is the car back on all four now, the engine runs much smoother and the historic hiccup/flat-spot has completely gone. My original injectors had 80k miles on them.

Obviously, your issue, although very similar to mine, could be down to other things. Your new TPS may even be faulty. I have heard of folk fitting three of them before finding a good one (unusual of course)

Hope you find a nice cheap resolve but definitely worth keeping the injectors in mind.

Regards,

Andy.

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I may be selling my five-0 injectors soon, if you do go down that route, let me know. They have about 5k miles on them. I'm aiming for ~400hp, so will be going with bigger primaries and secondaries.

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Glad you seem to have fixed it but I didn't think the GT3 had a throttle jack? We don't have a valve in the exhaust and the idle is handled by the idle control valve.

 

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2 hours ago, cammmy said:

Glad you seem to have fixed it but I didn't think the GT3 had a throttle jack? We don't have a valve in the exhaust and the idle is handled by the idle control valve.

 

Mmmm, curious. The relay is definitely listed as throttle jack in the handbook. I can't remember exactly what Geoff said but he did think that a bad connection or a faulty relay in the 'rear relay station' could be causing the fault .  The idle Control valve is new but made no difference to the fault.  It could be that today was a fluke and the stalling issue hasn't been cured of course. I'll update the thread when I'm certain one way or another. 

Shaun

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Have you had a look at your charcoal cannister? They open/close under specific circumstances and could potentially cause issues if not behaving as expected. If the problem comes back, you could try capping it to test. From memory it's connected into the timing belt end of the little manifold that's used to get a MAP reading.

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6 hours ago, cammmy said:

Have you had a look at your charcoal cannister? They open/close under specific circumstances and could potentially cause issues if not behaving as expected. If the problem comes back, you could try capping it to test. From memory it's connected into the timing belt end of the little manifold that's used to get a MAP reading.

🤔You could well be on to something there! I'm getting a strong fuel smell that's coming from the breather attached to the charcoal canister ( definitely not from the usual suspects like fuel tanks connecting pipes etc. ) Haven't got round to looking at that in detail yet as it looks like a pig of a job to access the pipes from the canister to the tank but when I first got the car I pressurised the fuel system and used a smoke machine  to check for leaks and the only place I got smoke was from the pipe from the canister that terminates by the roll over valve. Being used to the very basic fuel system of my old Excel I need to learn more about this more 'modern' set up to understand how everything works! So are you saying I can cap the pipe from the Manifold to the canister and completely bypass it? I suppose that wouldn't prevent the fuel smell as the canister would still be connected at the tank end. ( like I say I need to learn how these things work 😄)

Thanks for the Info 

Shaun

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The tank vents through the cannister, which catches the fumes. There's a solenoid on top of the cannister which connects to a pipe that runs to the manifold. Under certain conditions (manifold vacuum and certain RPM range), the solenoid opens. Manifold vacuum pulls air through the charcoal and brings the vapours into the engine to be burned. Under boost, the solenoid is closed but there is also a check valve in the pipe near the manifold to stop boost getting to the cannister. When pulling vapour from the cannister, this will cause the mixture to become more rich. I'm not sure if there is anything specific in the code to pull fuel or whether it just relies on the O2 sensor but If something is not right here, it could be messing with your fueling. You could cap it temporarily to see if it changes the behaviour. It could be that if your solenoid isn't opening, the cannister is saturated and allowing fumes through.

Unfortunately, I don't know enough about the system to say for certain which conditions cause which symptoms other than it sounds like your engine may be stalling because it's going lean.

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Interesting that my GT has the same problem, luckily only when cold but unluckily the engine management occasionally comes on, then goes out with a restart when warm.  In my book the throttle jack is listed as relay B?

I've not had time to look further as yet but fearing what I might find, drives perfect when warm, when I get time to get out, hence my diagnosis of not used enough!

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