Running rich except at idle

[Fejjj951]

89 951.

2.8 Stroker
Mtune/ Rogue DME
INNOVATE Lc-1 wideband

Sitting in the driveway with the car fully warmed up, I am seeing my AFR go from 14.9 at idle and dropping to 11.1 at 3k RPM doing a slow rev.

Cruising in 5th at 75, I am seeing mid 12’s.

Under full boost, low 10’s.

So it is running rich everywhere except idle.

Any help would be greatly appreciated.

[Tom]

Unless you disabled it for some reason, the factory O2 sensor (narrow band) should create a closed feedback loop that keeps the dithering around 14.7 AFR at idle and part throttle. It takes a second to adjust if you rev it up to 3k, but in general it should dither around 14.7 at idle, and when holding it steady at 3k rpm in the drive way. So, I'd start there. If your 02 sensor is working and those are the numbers you are seeing, I'd question the basic maps -- some m-tunes were out of whack unless/until Josh made adjustments.

On the other hand, if the motor was running fine and suddenly started doing this, then I'd suspect something like the maf or FPR, etc. Did it ever run right with normal AFRs?

Also, are you able to log data on the DME? I seem to recall some weirdness around that DME's handling of the idle/part throttle/full load status (though I can't remember if the weirdness was just in the logger or also affected the actual engine management). If the DME is running off the full load maps, it could explain the lack of O2 closed loop, and why it's running so rich when cruising. If you can't log, you can check if it's incorrectly triggering the full load signal at the diagnostic port under the hood. Also, I've seen 2 different KLR's with cracked solder joint that were incorrectly triggering the full load signal.

[Fejjj951]

All good information Tom!

AFR was good across the spectrum until a few days ago.

I revved it very slowly up to 3K and ended up at 11.1.

Also, under full boost I was seeing low 10’s.

I do have the ability to do a log so will dig out my windows 7 laptop for that. I will attempt to upload the log but may need help in doing so.

I am also wondering if I have a bad FPR or leaky injector. What do you think about that?

[Tom]

All good information Tom!

AFR was good across the spectrum until a few days ago.

I revved it very slowly up to 3K and ended up at 11.1.

Also, under full boost I was seeing low 10’s.

I do have the ability to do a log so will dig out my windows 7 laptop for that. I will attempt to upload the log but may need help in doing so.

I am also wondering if I have a bad FPR or leaky injector. What do you think about that?

Ah, ok. I'd check the FPR -- make sure it holds vacuum and that the vacuum hose to it is connected and doesn't smell like gas. I'd also check the full load signal to see if it's stuck in the WOT maps. What was the AFR under full boost before this happened? If way different, it suggests it's something other than the WOT maps. Might also clean the MAF wire for good order's sake, and the m-tune map sensor.

[Fejjj951]

Okay.

Full boost was 11.2-11.4

I did remove the MAF sensor and sprayed it and the connections with MAF cleaner. I did not spray the MAP sensor.

FPR vac line is connected. I will check for fuel.

I am not sure how to check that the FPR holds vacuum.

[cda951]

I agree with Tom that the fuel pressure regulator is a possibility. Not so much because of its ability to hold vacuum or not, but because it can get jammed internally and restrict fuel return flow, which causes fuel pressure to rise. I have seen this numerous times on customer 911 Carrera 3.2s and 944s, which use the same style of Bosch FPR---in most cases the symptom was intermittent, engine would run normally until a sudden load change such as lifting off for an upshift, fuel pressure would go high enough to impede the fuel injectors from opening against rail pressure, and the engine would stall. The engine would immediately restart and run normally until the FPR stuck closed again.

You should start by checking fuel pressure---if the pressure is normal and responds as it should to vacuum, and you still have the rich condition, then look elsewhere. But fuel pressure should always be checked early on in such cases before other possible tuning issues, as it affects any tune across the board.

[Fejjj951]

Thank you for the help guys!

My plan is to have my shop test the FPR and pressure first.

I failed to mention that I had this same situation well over a year ago. I had Covid last July and it messed with my memory which is still not good!

Last year the rich condition suddenly stopped and the car had been running normal since.

I plan on doing a log in the next few days.

[Tom]

Thank you for the help guys!

My plan is to have my shop test the FPR and pressure first.

I failed to mention that I had this same situation well over a year ago. I had Covid last July and it messed with my memory which is still not good!

Last year the rich condition suddenly stopped and the car had been running normal since.

I plan on doing a log in the next few days.

If the FPR is jamming as Cda951 suggests, I suppose that could be intermittent. Cracked solder joints in the KLR (or bad harness connections) could create intermittent issues as well. If the car is consistently running as you described, a good shop should be able to track it down. Things get much harder when the problem only crops up once in a while (and never while tryin to find it....).

[Fejjj951]

I have a known good KLR that I can swap in, so will try that tonight or tomorrow before proceeding with the other testing.

[cda951]

If the FPR is jamming as Cda951 suggests, I suppose that could be intermittent. Cracked solder joints in the KLR (or bad harness connections) could create intermittent issues as well. If the car is consistently running as you described, a good shop should be able to track it down. Things get much harder when the problem only crops up once in a while (and never while tryin to find it....).

Indeed. My own 951 had the same FPR issue some years ago, would initially only happen towards the end of a 20+ minute track session on a hot day, engine would bog down coming out of a turn, people behind said it would belch black smoke out of the tailpipe. Rapidly pumping the throttle pedal would restore normal engine running, which was a major clue (rapid vacuum fluctuations would un-stick the FPR).

Finally the same happened on the street after a long drive on a hot day and I was able to prove the issue using a fuel pressure gauge.

Dealing with very intermittent running issues is a pain, I often deal with such things on customer cars. My usual method with an '80s-vintage Porsche is to connect an inline breakout box between the DME and its connector (can do same with 951 KLR, but not at the same time) and use one of our portable oscilloscopes to monitor any suspected circuits. With experience, the difference between a sensor fault and engine wiring harness issue can be sussed out, and any bell housing ground issues can be seen on the scope waveform.

One of my customers bought one of the Focus 9 updated DME units with OBD function, which is quite cool, but unfortunately the first one he bought was faulty and had to be sent back for warranty repair for an intermittent stalling issue (was using the OBD function to chase down a pre-existing TPS issue), but they stood behind the product and it worked well after that.