Limp mode on track - any thoughts?

[Paul_D]

On Thursday at Brands Hatch my car had a problem in one of the sessions, and I wonder if anyone had experienced similar.

Coming out of a corner, I tried to accelerate and there was no power at all. I slowed down slightly and the car would accelerate back up to 4000rpm and then stop, so it was obviously in some sort of limp mode.

There were absolutely no lights on the dash to indicate that anything was wrong. I cruised back to the pits, and after I'd left the car a while and restarted it the fault was gone. I did two more sessions, and a 120 mile journey home with no problems.

A fellow owner reminded me that the brake light switch can cause problems....BUT, my car was still in Sport mode when I got back to the pits. I thought issues with the brake switch kicked you out of Sport mode? Or is that not always the case?

I've connected a standard OBD reader to the car, and there are no fault codes stored.

Here's a video of it happening:

Any thoughts? 

[Tex]

I had something similar on mine but the red redline lights came on simultaneously at 4,000rpm and wouldn’t let me rev higher.

Fortunately at Silverstone and Ben got  it in straight away to do diagnostics, but nothing came up. He wasn’t sure why and it’s never done it since.

[Paul_D]

@Tex Cheers for that mate. Hopefully mine was just a one off glitch too. I reckon I’ll probably just leave it and see if it does it again. 

[ec]

Could have been a fuel surge. 

[Kristof Thys]

On the analog dash you typically get the 3 red lights at 4k RPM when the car is in limp home mode.  I have no clue what the "AIM dash version" of that looks like; same goes for the CEL.  Only thing I can think of is that the code cleared after restart (so not a persistent code thus not emissions related) - fuel surge is possible, but it would throw a code, albeit maybe not a persistent one; would need to look that up.

Anyway, it is fixed now he 😉 

 

[Toqcars]

@Paul_D can't see what was your fuel level at. Was it less than 50%? If less than 50%, could be the fuel surge. But I guess car would go back to normal after a few seconds of a slow straight drive.

[Paul_D]

It’s a possibility, but I don’t think it was likely to be fuel surge.  The tank was over 50% full, and the track was still a bit damp so I wasn’t cornering particularly hard. 
 

I don’t know if I’ve been lucky, but I’ve run the tank much lower than that before on a dry track and never had a problem with fuel surge. 

[rmaurer]

Was your AIM dash in track mode and recording? If so you will have a data log of a load of ECU parameters you can search through to try and identify the issue. I diagnosed a faulty yaw sensor on my car doing exactly this:

You can see in the graph here my car dropping out of sport mode (blue line) to normal and the ECU Yaw flat lining at -163.8 degrees/sec of rotation (like the car was spinning) when I was travelling in a fairly straight line. 

You can also use the AIM to diagnose brake switch issues by looking at the brake switch output (2 of them) and also the cruise control value which triggers a fault code when the switch is not setup correctly (think it switches to value 3).

Have a look through the graphs and see if you can see any odd values. Accelerator position and revs should allow you to pinpoint roughly the time when this happened as revs will stop increasing despite you pressing the accelerator... Then work back from that time period.

 

 

Edited June 27, 2022 by rmaurer

[Paul_D]

@rmaurer Unfortunately, for the first time since I got it I didn't actually have the dash in track mode for those sessions. 

One of the first things to go through my mind when I got back to the pits was 'damn it, I'm not in track mode so I can't even analyse the data when I get home'

[rmaurer]

Sods law strikes again! 

[DangerousDave]

I've had power cuts that dont limp mode but on the aim it says warm engine or something to that effect, ironically i also get that same message when i hit the redline rpm cut. Car is for sure not cold.... It doesn't do it for the first 20 minute session more so middle of the day after i park to cool down.

[Paul_D]

It's far from conclusive, but first signs after fitting a new chargecooler coolant tank are good. I did several sessions at Cadwell Park yesterday and the car ran perfectly all day. There was no sign of any expelled coolant in the engine bay. 

[Team Lotus]

hello Paul, my car is acting exactly like your car in the video except I was making a left turn. this happened on both track event I attended. Is your car fixed? what is the cause of it? appreciated

 

Wilson 

[Paul_D]

Hi Wilson,

Yep, the cause of my issue at the time did indeed appear to be related to the chargecooler coolant tank. The issue seemed to coincide with coolant being spurted out of the relief valve over the engine bay.

Obviously that doesn't help you if you have a 350, as your must be a different issue. 

Maybe a proper Lotus Diagnostic tool would give you a code that might give a clue?

[Team Lotus]

thanks for letting me know.

If issue is brake light sensor, it would show a CEL + TC light?

[Rolf]

Even a small steering play may result in similar behaviour as the breaklight switch problem.

Drove my 410 on the autobahn on a hot day in summer. During acceleration and overtaking at 100 mph car went into limp mode, quite scary.
Display showed TC fault and CEL, but that disappeared after a  few restarts. 
Drove home 2 hours with no further problems at this day, but problem randomly appeared again.
Exchange of break light switch did not cure the problem.

Final result: Lower U-joint in the steering column was the culprit for steering play and exchanged under warranty.

[MrD]

Not sure whether mine is the same but I had the early limiter coming in early (around 4k rpm) for a brief moment during a spirited drive back in the summer - out of the blue, no lights on the dash.

I was driving on Sport - i switched to TC off and it sorted itself out. I'm not sure whether there was something with the solenoid controlling the exhaust valve - does the limiter kick in early if it "thinks" that the valve is off?

Worth mentioning that I don't have a valved exhaust but I guess the ECU is still trying to control it?

As said, no lights in the dash and it was cured by switching TC modes so I put it down as one of those things.