Endgame setup- BW s257sxe

Got a tune adjustment back and drove the car just now. LTFT is back in check. It's definitely idling better and didn't stall on me once. It did come close though a few times. Dipping to 500rpm and holding real low for a few seconds. We're getting somewhere at least.

 

Drove the car out to work this morning 26mi with no issues. On my way home it pretty much stalled at every damn traffic light. I can keep it running if I keep giving it throttle pressure in neutral, obviously. No relevant CEL's set or pending that I see. LTFT is in check while cruising, accelerating, and at idle. And I don't see STFT going crazy reacting to anything. I'm sure there's something I'm not seeing. I'll grab a log of exact conditions and post it up. Decel coming to a stop, rpms dropping below 600, and then stalling. Other times it will rev surge for 10sec. before finally settling at set idle.

Sent from tapioca

 

Throttle position and MAFV.
Post a screenshot of it stalling with the above visible in log (text form, not graph form).

 

What is your idle set at?

 

Whats your fpr set to at idle?

I had similar issues on my 6 when pressure was set too low.

Wouldn't hurt to turn it up a few psi and see if it stops acting up

 

When it settles it appears to be 1000-1050

Sent from tapioca

 

It's set right at 40psi pre vacuum. Where tuna wanted it set

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Didn't even have to leave the driveway. It's that bad now. I took a log at cold startup because it was struggling already and another at temp. I only backed out and pulled forward for it to stall. I went ahead and sprayed carb cleaner all over the bay, but found no change in idle.

 

See a couple of things:
Throttle is constantly changing, but only a little (sometimes this is all it takes)
Timing is also changing (normally this is how idle target is managed)
Airflow is changing (could be linked to throttle and/or timing changes but not sure/doesn't really matter)
AFR is changing as well

Idle is all over the place but doesn't look like it's actually dying; it does go below normal 700 idle at some points, but also recovers. So long as you aren't going clutch out when it does that, it won't stall.

So here's the thing. With the MAF dropping below 1v, the ECU is very unhappy. I know this because when you cold start a Genwon, if it's not running by the time it sees 1v MAF, it throws a code. There are a couple ways to fix this, but that doesn't matter for your situation (just an example).

I'm reasonably sure this can be tuned out, as with the AFRs changing and the trims not, some MAFCAL work could potentially correct this. You could also just let it sit and idle for a while and see if it eventually starts running well again, then send THAT idle log to your tuner. Might take upwards of 15 minutes to do though, since it's all over the place. Alternatively, your tuner could create a new map with trim breakpoints specific to your car (ending at high idle, city cruise, highway cruise and city accel peak). I thought this was a thing everyone did already but maybe not? This would likely only make it faster to correct, but not fix the underlying issue.

Might be some room for throttle and other fueling tweaks too. What throttle body are you running right now?

 

Thanks for that breakdown Enk. The car is pretty much undrivable at this point. The at temp log has captured data of it actually stalling I thought. I'm running the stock throttle body

Sent from tapioca

 

You're right; I didn't scroll far enough.

Funny thing after it shuts down, the TPS is changing constantly still; reasonably sure it should be steady. Might be a good idea to swap the TB, maybe back to a CS one?

 

Man, plagued by throttle body problems. Yeah, I still have 2 CS throttle bodies. I'll throw one on and see if things get better or worse. I assume my tuner recently made the adjustment from CS to stock. But I can load the previous rev if need be. I sent both logs to my tuner as well.

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I took the liberty to open up a CS throttle body and make sure everything inside was functioning properly, before reinstalling it again. Definitely voided any warranty, but meh. It's a pretty simple design utilizing plastic gears. Everything appeared brand new, as it should. No teeth missing or bent. This throttle body never caused any CEL, so I assume it's electrically sound.

 

check all of the wiring to the throttle body too, could be your issue and could have been your issue with all the throttle bodies previously

 

I have been reading that most throttle by wire controlled bodies usually need some sort of relearn procedure. Seems pretty simple and silly to be honest.
Drain capacitors in ecm (disconnect battery)
Reconnect.
KOEO and immediately full pedal pressure 3 times.
Bring it up to full temp and introduce loads, such as brake pressure, power steering, and A/C one by one

Sent from tapioca

 

Noticed KOEO throttle position is locked at 5 with varying pedal pressure. TPS shit the bed?
Throttle body reset "procedure" did nothing lol

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Quick little update to my build's unsolved mysteries. After reviewing logs and noticing irregular TPS readings, I swapped out the OEM throttle body for the same CS TB that previously gave me idle surging issues. This completely fixed the rough idle, surging, and most importantly stalling. So that's nice.

However I just realized the surging idle issue I was having previously with the same CS TB was installed with a spacer/reducer for difference in bore between ST manifold and throttle body. Both the manifold and CS TB have o rings. So the lack of the spacer this time is puzzling. If it works, it works. I'm not fckn touching it.

Sent from tapioca

 

It would be valuable to know if that had any part in it though. How long would it take to reinstall?

 

Not long. If I can find the spacer lol
Damond says the spacer is required to prevent possible throttle plate bending. I don't see that happening unless at WOT the plate touches the manifold inlet. As of now I assume the large o ring on the throttle body is sealing against the manifold or else i would see vacuum issues. The smaller o ring on the manifold may have the potential to get sucked in though if its not seating against anything? Regardless, I better put the spacer back on I think

It's also quite possible, the throttle body extension harness may have been my problem the whole time. Just a theory though, as its functioning properly at the moment

 

Another possibility. Maybe you can get a replacement for either part if that's the case?