924Board.org

[bureau13]

So I've had these issues for a while. I got frustrated and basically stopped driving it, but now my daughter has her license and is using my daily driver, so....back to the 931 I guess.

It actually drives OK as long as your don't give it too much throttle or let the revs go over 3K-ish. In other words, if you don't try to have any fun, it will get the job done. However, if you give it much throttle at all near that 3K mark, it will cough and buck and backfire to an extremely alarming degree.

I fixed a bunch of vacuum leaks trying to fix this, so that should all be good, and I have that Mittlemotor ignition so I was sure that timing was the issue but I'm doubting that now. So I went to test my CIS system, but have some questions.

Can i do this with the car running? Or do I have to jump the relay and all that? I was trying to avoid that because you need to be a contortionist, that is the worst relay placement ever, and my back already hurts. But I'll do it if I have to.

I did do a quick check, engine cold, and got control pressure of 1.4 bar and and system pressure of 2.7 bar...but when I closed the valve to measure system pressure, the car ran poorly, which I guess makes sense. Anyway, I'm curious if these numbers are in the ballpark or if my test method (car running) is completely invalid. I found a lot of discussions of hooking up the gauges but nothing saying what I should measure. I also don't think these basic tests are likely to find the problem but it's a start at least.
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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)

[bureau13]

OK, I actually was able to find some additional info for the standard 924, not sure that it is all applicable but I suspect the basic tests are, at least.

I went out and reran the test, and this time I got only 1.1 bar control pressure at startup, and then I let it run for a bit and it crept up to that 1.4-ish level after a few minutes. So that seems quite low, right? Warmed-up, I think it should be closer to 3.6? Which if I understand things, would make my car very rich. But it idles pretty well and right about where you'd want it. So I'm not really sure what to make of that.
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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]

Based on how your car behaves and what you see in the test I think you are looking in the right place. Those numbers seem low to me as well

Do you have this?

https://members.rennlist.com/vilhuer/K%20Jetronic%20Workshop%20Manual.pdf
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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]

I do now! Thanks, that's good info I will read through that now.

Somewhere I have the Haynes manual, but I can't find it

I'm trying to rule out the components upstream of the fuel distributor but unfortunately my CIS tester kit doesn't have all the fittings I need to T into the larger fuel supply lines. Not sure what adapters I need, or at least what to call them, in order to find them.

[bureau13]

Just to put a bow on this, I decided not to bother trying to diagnose and fix the CIS system and installed Ciprian's EFI kit instead. No regrets! It runs better now than it ever has since I bought the car.
_________________
-----------------------------------------
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)

[chuck21401]

[bureau13]

So I will say for someone used to working on these cars, its going to be a lot easier. I'm very slow, and I haven't done it enough to remember how to do most things, but Ciprian made himself available whenever I needed help. I was honestly surprised at the level of support.

One thing, the AC compressor tensioning mechanism won't fit with the crank position sensor bracket that's supplied. However, this sounds odd, but I positioned the bracket so the compressor pushing against it can't move it closer to the crank pulley, and then backed the sensor itself out with washers. I didn't really want to evacuate the freon and remove the compressor, because AC is REALLY necessary in South Florida, and I figured a new different bracket could be designed. However, I put the belt on, which was a bit of a pain, but it's tight enough that it works. Unexpected! Someone else found a different solution I think but I don't know details.

I am running 10 psi. I have a wideband O2, currently just for a display, but I would like to hook it up to the ECU. It doesn't really seem to be needed.

Ultimately I think it would be fun to use the ECU for boost control and then run water/meth injection. However, that would require additional tuning and I am not dealing with all of that right now.

The MaxxECU Mini that he supplied is a very cool piece of kit. Their tuning software is excellent.

[morghen]

Crank case vent sudden unclogging and discharge of gunk directly into the intake tract?
Check the inlet tubing from the point where the crank case vent connects onwards toward the TB. If its clean then most likely its the fuel system as you said (tho i dont think it would run with so much crap flowing trough it) but if the inlet hoses are dirty then its the crank case venting that gunk into the engine and maybe its a good idea to get an epurator installed, at least until it clears out.
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Supercharger and EFI kits
https://www.the924.com