Two odd lean conditions

I am having two odd lean conditions and I'm not certain they are related.

The first:
after extended engine braking (like approaching a red light thats still far away) once I press the clutch in the idle will drop hard (~500rpm), may even want to stall, AFR pegs lean. I have to blip the throttle a couple times to get it back. You can see in the log that the IDC drops to 0% during decel, the idle switch is on, and once a press the clutch the idle drops like a rock. You can see me blip the throttle a couple times. Apparently I killed the log before the afr returned to 14.7, but the idle did recover. It seems that this only starts to happen after the engine is warm. I didn't want to muddy the picture too much, but the stock o2 gauges are behaving as expected and fuel trims are >10% (I know have those within 2% and the issue persists). I find it interesting that the ISC doesn't try to correct the problem until I start to blip the throttle.
Attachment 9748



The second:
very occasionally on light acceleration I'll get a blip of lean with a loss of power. What I find interesting is that the IDC drops during that time as well, almost like the ECU wanted it to happen...
Attachment 9744


EDIT - Possible 3rd issue, although perhaps its related to the second. Occasionally during cruise the car goes full lean (>18AFR). It will eventually recover on its own. It will also temporarily recover once getting into boost (or perhaps into open-loop). The whole event will last 10 seconds or so, and after coming back out of boost it will likely go back to being lean again.

1) I drove around yesterday with short term fuel trims disabled and I noticed that I wasn't having the lean after engine brake problem. It wasn't a scientific test in the sense that I didn't engine brake for as long, or as hard, as possible. So I dont really understand what portion of code is being used during engine braking, and I don't really understand what tells the injectors to basically turn off even though the AFRMAP output still reads 14.7. That being said I assume that short term fuel trims are not updated during engine braking so my guess is that whatever entry I have in the VE smoothing table for the airflow associate with the cruise condition just before engine braking must be rich so the short term fuel trim starts to lean it out but then once I return to a normal idle (where I've tested pretty thoroughly that the VE smoothing table entry is correct) I am temporarily lean until the short term fuel trim catches up.

2) No progress here except that I can get it to happen pretty regularly under a certain light throttle, slight acceleration, condition. Not that I think this is the problem, but I just ordered some standard tune-up stuff since its been awhile (5+ years / <10k miles).

On 2), weird that your injector duty cycle is dropping as your wb02 is reading leaner. Am I reading that plot correctly?

How’s your fuel pressure looking?

Yea, that's how I read it as well which make's me think the car is doing exactly what the computer is telling it to do... Fuel pressure (at idle) is fine, but I have no way to look/log it while driving.

I decided to redo my tune by adjusting injector latency and size to set fuel trims, and then driving around with short term fuel trims off to set the VE smoothing table. (By the way... this is a really annoying process because I want to get the 200-300 Hz range working better, but that's always the place where I am increasing throttle and so I get some tip-in lean condition that contaminates the measurement).

Anyway, between that, changing my PTU, and uninstalling my Apexi Neo (which was disabled, but still installed) and I have yet to notice either of these conditions. I only have about 40 miles on it though so there's a chance I just got lucky.

Quote:

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Originally Posted by q2418130103p

Yea, that's how I read it as well which make's me think the car is doing exactly what the computer is telling it to do... Fuel pressure (at idle) is fine, but I have no way to look/log it while driving.

I decided to redo my tune by adjusting injector latency and size to set fuel trims, and then driving around with short term fuel trims off to set the VE smoothing table. (By the way... this is a really annoying process because I want to get the 200-300 Hz range working better, but that's always the place where I am increasing throttle and so I get some tip-in lean condition that contaminates the measurement).

Anyway, between that, changing my PTU, and uninstalling my Apexi Neo (which was disabled, but still installed) and I have yet to notice either of these conditions. I only have about 40 miles on it though so there's a chance I just got lucky.

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Fingers crossed!

So its decidedly NOT fixed.

As far as '1' goes (lean condition at idle after engine braking), the problem seems to be a bit masked by a better ability to hold idle. Maybe that's coincidence, maybe that's the PTU, maybe thats a better tune, I don't know. But I do know that the car continues to have this issue of lean idle (>20AFR) after heavy engine braking which resolves itself after 5-10 seconds.

For '2' (occasional lean condition on slight acceleration) I've found that there are certain sections of road, gear, and throttle position that can force it to happen. Which makes me think this issue might have to do with turbo stability (slightly wrong sized turbos). I would expect that issue to result in a rich condition (double metering air or something like that). Maybe I should try a datalog with just airflow, will that get better time resolution in the log?

If fact, '2' seems to have gotten even worse (or maybe its a new problem entirely). Occasionally under light cruise throttle I'll get a near total fuel cut (>20AFR). The gas pedal will basically do nothing, the car will continue to idle, but not great. Obviously, there's no power to speak of. Here's the interesting part though, if I open the throttle enough to get to 0 psi boost i IMMEDIATELY get fuel back... This was VERY repeatable, I was able to do this at least 5 times during the last spell.

I wonder if all three issues stem from some sort of vacuum problem? I decided to get a new diaphragm for my AEM A1000 FPR just in case.

Could the issue possibly have to do with an ECU signal for high/low mode? I am running a hotwire walbro pump. Maybe I could set chrome to never take the pump out of 'high' mode and see what happens, or maybe bypass the fuel pump resistor (although I think I've done this already, I'll have to check).

Your second issue looks like what my stealth was doing with 13Ts. I went through 3 different sized injectors and they all did it.

How I fixed it was with ChromeECU lowering the point where the transition from close to open loop changed. I think you're just getting into a point in the maps Mitsu never expected you to get to, so leaning is sort of an 'error handling'

What are you even running? Inj size? Turbos? Tuning using?

13t, 550cc pte injectors, chromedecu. I don't know a ton about turbo sizing but after looking at some compressor curves and trying to overlay load lines I think that 13t's operate on the hairy edge of stable under low rpm 2-5psi situations... although I guess that doesn't apply here since this situation was solidly in vacuum.

I like where your head is at with your suggestion. It is certainly the case for the 2nd issue that the ecu is commanding the condition to happen since you can see the injector pulse width drop. I'm a bit confused about your suggestion though. Do you think its running open-loop when it should be closed, or closed when it should be open?

If its running closed loop then I don't think any maps are being used. I think it's just the airflow, trim and ve smoothing table. I just checked the log and the afrmap was 14.7 the whole time, the load was ~25, and the tps was ~14%. I'm pretty sure that's all closed loop. I attached a new plot of that log that has that info, as well as the VE (as proof that it's unlikely my VE smoothing table is causing the problem). Just an fyi on that plot, the left axis is air flow, and VE.

Attachment 9760

It's trying to close the loop when it shouldn't be. Looking again, my issue was probably different. My ECU was trying really hard to keep me at 14.7afr at low rpm into boost (like 4-5psi). I think there's an old thread on here somewhere.

Gotta remember your trim only moves so fast and so far, so if you're using the same trim at cruising (which I was), it would be way off when I got into this condition and wouldn't be able to adjust fast enough. IE, pulls fuel at cruise, now causing a lean condition to be more lean.

I'm dealing with pretty ancient information in my head, but Open and closed loops use the same base maps/tables, closed loop is just adjusted by o2 feedback. IIRC in later years certain trims would affect open-loop control as well.

Regardless, you're saying you were in vacuum the whole time. Do a leak down and makes sure your IAC is working.

Trims are just adders to the final fuel calculation. Long term trim is applied even in open loop. So yes, all the maps are used all the time, open or closed loop.

Oh yeah, you guys are totally right, I'm not sure what I was thinking.

Anyway, I replaced the diaphragm in the AFPR as a precaution. That didn't change anything. I didn't check the ISC, nor the fuel pump relay, yet. I did a pressure test as well. I tested both with and without the TB blocked off, both tests seemed fine.

I got a couple more logs, one of which shows the behavior where getting into boost gets me out of the lean condition. At first glance it looks like it might be getting under control right at the point where the car goes open-loop (based on load, rpms and tps). Without having really looked at the log yet this sounds like the short-term fuel trim may have gotten really off. Anyway, I'm going to check a couple other things today and try to analyze those logs before I post them later.

Welp, I made a few changes and I wasn't able to reproduce any of the 3 issues in 100 miles of driving. I'm not saying its fixed, cause that seems to be the thing that breaks it.
Here's what I did this weekend:
- Lowered 'Fuel Pump Relay Trigger Load' so that the fuel pump is always 'high' (mind you... my fuel pump is hot-wired so this signal is really just feeding the relay in the trunk so who knows if that did anything)
- Lowered the throttle position sensor by ~1%. The TPS was adjusted originally according the the manual (using the appropriate feeler gauge), but I noticed that after driving for awhile the TPS would creep up to almost 14% at idle. I decided to drop it to 12%. I don't really think this mattered at all.
- Tightened the BOV. I didn't think it was loose before, but I guess there was some room for adjustment still.

I probably wont get to drive it again until the weekend. Hopefully its either still fine, or I get another log or two.

Open atmosphere BOV?

Yea. I'm actually working on changing it to recirc, hasn't happened yet though.

EDIT - BTW, this is hardly scientific but I loosened the BOV 1/8 turn (so still 2/8 turns tighter than before) and notice that I was getting a couple of the issues again. Not nearly as bad as before, and not repeatable like it was before. The two issue were the 'lean idle after engine braking' and 'random lean cruise until getting into boost'. I haven't noticed the 'occasional lean spike during light acceleration'.

I've had this car since 2005, and when I got it there was already a chinese knock-off open atmosphere BOV in it. Ten years ago I bought a nicer BOV, and an adapter to recirc it. I put the BOV in but was too lazy to install the recirc fitting. So it sat on a shelf for ten years. That is the single biggest mistake I have ever made with this car, and that's really saying something... I switched to recirc this weekend and now I have a completely different car. It's so much easier to drive, the RPMs stay between shifts much better than I could have expected, its so much easier to shift.

I drove it over 100 miles like this. I slightly experienced issue '2' once (lean spikes during very light acceleration), but neither of the other two issues. And honestly, the one I did experience is not a big deal in the slightest although I do think it is still abnormal.

To summarize:
- Switched BOV to recirc, very pleased with the increased drivability (maybe thats the wrong word).
- The issues (at least 1 and 3) seem to be totally gone
- Issue 2 persists, but very rare, and very slight. I will still pursue this and try and get another log.

Case closed, then? Glad this had a good ending.

Yeah, I think so.

Well this at least marks the "end of major combat operations", but I'll probably keep thinking about the remaining issue (the lean spikes during very light acceleration). But at this point its really being nit-picky.