Car started to misbehave yesterday misfiring at low revs and light throttle inputs (anything closed loop really). On boost it’s absolutely fine and pulls clean.

Car is running speed density on stand-alone management and has not thrown a CEL. Initial thoughts were lambda, but unplugging this made no difference at all.

I did notice it seemed to drive ok when it was cold but started to misfire and back fire and cruising speeds once it started to get some temp in it. It did seem to take slightly longer than usual to get up to temp too. Possible faulty coolant temp sensor?

Annoyingly I need to do a firmware update on the ECU to run off logs, and need a battery trickle charger to do this which I don’t have currently, so can’t log.

 

Stat or as said CTS.

 

Stat is a new RCM low temp thermostat so unlikely but not impossible, so I’m still leaning towards CTS as it’s one of the few original sensors left on the car.

 

small vac leak somewhere??

 

I’ve had a good look over and can’t see anything. With it being speed density I would be surprised that a small leak would make it hesitate so badly?

I’ve just been out in it again and it’s smooth as butter when stone cold, as soon as it gets to around a quarter of the way up the temp gauge it’s starting to act up. I’m annoyed I can’t log it as I’m sure I’d be able to see that the coolant temp reading is off.

 

Get rid of that stat not good for engine wear a high flow stat if anything.

 

Nothing wrong with the stat and the way it operates, not sure how early you think the stat opens that’s going to increase engine wear. On my engine it’s working perfectly. Logs show coolant temps are well within expected ranges and I have a “low coolant temp” rpm limit failsafe set up on the stand-alone and it’s never once got anywhere close to it, even on a long motorway run. This is a near 600bhp engine, not a standard build.

 

I'll let someone else explain cause I don't type and as you know most engine wear occurs when cold. we run Syvecs in three cars and data logging shows on long runs the engine oil and water temp doesn't get to where it should do and neither does the the oil temp so no evaporation of unwanted fluids occurs.. We also have a low temp rev limit on these vehicles and all other alarms and engine cut on anything serious including fuel pressure etc.

 

Just a quick look at others opinions. Also as said before high flow not low temp.
The truth about thermostats, don?t get caught in the hype! | IW STi Forum

 

I know the ins and outs of thermostats and exactly how they work, I don’t want this thread to go off subject. I use a low temp thermostat as this car is used on track and used hard on the road. I wouldn’t put a low temp thermostat in a daily driver. This car isn’t that.

The problem isn’t the thermostat. The coolant temps hold stable under driving conditions, they don’t fluctuate indicating a bad thermostat. My car is overfuelling as it’s still running cold start when warm I believe. Coupled with 1300cc injectors it’s exacerbating the hesitation under low throttle input and light load conditions. As soon as the car goes open loop it pulls cleanly. I’ve ruled out the lambda, so next clue in poor closed loop
running would be the coolant temp sensor, I’m just looking for confirmation before I go pulling it.

 

Well they're not expensive and 20 mins changes it. Do it when stone cold and don't take cap off and you'll not loose an egg cup of coolant. But seriously try a high flow stat far more efficient. Only a 2p sized hole in a standard stat. What ecu have you and I'll send you a cold start up map to compare. As for the injectors we've 1700cc in one car and they don't cause any problems but of course we haven't any problems. You could always check the resistance of your CTS

 

could borrow You ring charger https://www.ringautomotive.com/en/product/RSC612
there is maintenance mode ,not sure any good for You

 

Year ??? the 2006 over have relay A/F front sensor, if have problem in this relay the car have your symptom.

 

2015< VA ,think car scrapped now

 

Forgot to update this, managed to sort a battery charger and update firmware on the Emtron. Took about twenty seconds to then see my wideband lambda had flat lined. Too much launch control methinks 🙈. All sorted now.