924Board.org

bureau13 · Joined: 07 Sep 2017 Posts: 480 Location: South Florida

I saw the video...yeah, at no/light load, you're getting very lean with no misses. Interesting...I may have been chasing the wrong stuff all this time. Wouldn't be the first time!

I did set to 9 BTDC initially, and it didn't seem to be loose or anything when I was poking around before but I will definitely go through all of that stuff.

I was actually thinking a misfire would show rich, because of the unburnt fuel, but I keep forgetting its an OXYGEN sensor, so unburnt fuel also has unburnt oxygen. Doh! Good stuff guys, thanks for the assistance. I will report back with what I find when I go through the ignition system. If I can't find anything obvious and it's still timed as it should be I will likely just replace the coil to rule it out, if nothing else. I have some store credit at FCP

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1982 931
1986.5 Silver 928S
2007 Hummer H3 (Daily Driver)

Past lives (I miss them all):
2004 RX-8 (Wrecked)
1993 RX-7 (Sold)
1987 RX-7 Turbo II (Sold)
1985 RX-7 GSL (Stolen)

kondzi · Joined: 02 Jul 2018 Posts: 485 Location: Poland/EU

Doesn't look to me like misfires causing lean reading.
What controller you have? I see Innovate Gauge, what you have LC-1, LC-2?
Had a faulty LC-1 (Innovate support stopped responding to my claims) that was behaving similar as yours, and then dropped to low 8's. Did you calibrate the o2 controller with o2 sensor out in fresh air?
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Konrad
'89 951 US
'88 Mustang 5.0 LX Convertible (factory specs)
'84 911 Carrera 3.2 RoW (factory specs)
'81 931 RoW (TBD)
'81 Ford Capri 2.8i (factory specs)
'79 Ford Capri 2.9 (heavily modded)

bureau13 · Joined: 07 Sep 2017 Posts: 480 Location: South Florida

It's a Zeitronix controller, which uses a Bosch 5-wire wideband sensor. No calibration required. This is definitely NOT a wideband gauge/sensor/controller problem. There are some weird things I have to do to get the gauge to work, but that's a different story. This is a driveability issue, which the wideband has nothing to do with. It's just an observer...I'm not using the narrowband emulation, which is the only means it might have to actually influence things.

chuck21401 · Joined: 20 Feb 2005 Posts: 526 Location: Annapolis, MD

So I noticed some odd readings on my A/F meter before blowing the fuel pump fuse and then finding low voltage to the fuel pump. Have you checked the voltage at the pump?
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1981 Porsche 931 w/S1 engine & g31 transmission. Water-cooled intercooler

bureau13 · Joined: 07 Sep 2017 Posts: 480 Location: South Florida

I was going to do that until I went down the ignition path. Which, I'm happy to report, was correct! I ordered a replacement ignition coil, because that's the one piece of the ignition puzzle that I hadn't touched, and it arrived today. I don't think the old one was original actually, but it certainly wasn't a Bosch. Put the new one in, and it's back to driving like it should. Very pleased

Thanks to everyone who helped me get here!

Fasteddie313 · Joined: 29 Sep 2013 Posts: 2596 Location: MI

Congrats!!!

I was worried about you..
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80 Turbo - Slightly Modified

bureau13 · Joined: 07 Sep 2017 Posts: 480 Location: South Florida

Honestly, me too! I still can't believe it was the coil. That just seems too easy. I could have saved myself a lot of trouble had I tried that first, but in the long run, I'll be better for having fixed all those small vacuum leaks, etc.

Mike9311 · Joined: 14 Dec 2004 Posts: 1678 Location: Chicago-ish

bureau13 · Joined: 07 Sep 2017 Posts: 480 Location: South Florida

Smoking would have helped diagnose it! I drove it tonight, ran perfectly. To be honest, it's never really run right until I removed the weird homebrew ignition setup and replaced it with the Mittelmotor, but I barely got to enjoy it when the coil went.
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-----------------------------------------
1982 931
1986.5 Silver 928S
2007 Hummer H3 (Daily Driver)

Past lives (I miss them all):
2004 RX-8 (Wrecked)
1993 RX-7 (Sold)
1987 RX-7 Turbo II (Sold)
1985 RX-7 GSL (Stolen)

Mike9311 · Joined: 14 Dec 2004 Posts: 1678 Location: Chicago-ish

I wonder if you are the only one in the US with the Mittelmotor ignition?
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1980 931 since 1989
1981 Ideola 931 Club Sport
1982 931 Entwicklungsfahrzeug
1979 924 NA ohne 650 mit 471
1982 931 Red Resurrection - 951 IC
1982 931 parts car / resurrection?
1980 924 NA (R&D lightweight)
1982 931 wana-be GTR race car

bureau13 · Joined: 07 Sep 2017 Posts: 480 Location: South Florida

That's an interesting question. I never see them discussed here, even in Porsche clubs most people just get a blank look on their face.

I have seen some US-centered discussions of the 123ignition gear, mainly as a retrofit for muscle cars I think.

kondzi · Joined: 02 Jul 2018 Posts: 485 Location: Poland/EU

bureau13 · Joined: 07 Sep 2017 Posts: 480 Location: South Florida

OK, someone explain this to me: The problem is back

At first it was pretty subtle...just a slight stumble around 2500-3K. I tweaked my ignition map to take some advance, no real change. It seems subsequent drives during the day get worse, although the car isn't really hot.

Earlier today I took it for a drive to try to characterize it a bit better, and it was really not bad. A bit of a stumble with light throttle around 2500-3K. If I gave it a bit more throttle it would stumble initially (AFR would go to maybe low 15s...possibly just misfire related as it seemed before) then richen up as the WUR saw boost (I'm guessing this is why) and everything would be fine.

An hour or two later, I went to drive, and it's bad like before. The slight stumble is a fairly violent bucking.

I don't get it. When I replaced the coil it seemed fine. It certainly wasn't doing this. And when I had problems the first time around, it was fine, then the slight stumble appeared, and then it got bad. Same exact thing. But why did replacing the coil "fix" it for a a bit? It's a Bosch coil, btw. I didn't get some off-brand crappy one.

I also have a hard time believing it's an ignition map issue. I've been doing the math to see what sort of advance numbers I'm getting under the conditions its happening, and I've pulled a bunch of timing out to see if it would make a difference, but it didn't.

This is doubly annoying because my other car is also having weird problems as well. I'm getting it from both ends

_________________
-----------------------------------------
1982 931
1986.5 Silver 928S
2007 Hummer H3 (Daily Driver)

Past lives (I miss them all):
2004 RX-8 (Wrecked)
1993 RX-7 (Sold)
1987 RX-7 Turbo II (Sold)
1985 RX-7 GSL (Stolen)

Carrera RSR · Joined: 08 Jan 2010 Posts: 2309 Location: Somerset, UK

Take it to a dyno assuming they have K Jet knowledge and let them work it out. Then you can try and replicate it on the rollers under any load, speed, rpm and measure fuel pressures, boost and timing all at the same time.......they will either find the fault or it will be tuned so no further issues.
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1980 931 - forged pistons, Piper cam, K27/26 3257 6.10 hybrid turbo, 951 FMIC, custom intake, Mittelmotor dizzy & cam pulley, H&S exhaust, GAZ Gold, Fuch'ed, Quaife
Now www.924board.org/viewtopic.php?t=34690
Then www.924board.org/viewtopic.php?t=31252

peterld · Posted: Sat Sep 26, 2020 10:14 pm Post subject:

+ 1 above.
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80/81 932/8 ROW