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chaparral2f · Joined: 29 Jan 2011 Posts: 33 Location: southern oregon

The Antichrist has been living under a tarp for quite a while as I have been involved with other projects. A few days ago I uncovered it and low and behold it started. It ran really smoothly for about thirty seconds then started to start missing. the longer it idled, the rougher it ran. I am at a total loss as to why. Here is some background: I've done a valve job,(comp is 150lb +/- .3lb) I cleaned the gas tank, checked the fuel pump. I replaced the fuel filter, the fuel distributor, all the injector lines and the injectors. The vacuum lines have all been smoked and there are no leaks. The battery and the air filter are new, and the auxiliary air valve has been replaced as have the plugs, wires,dist cap and rotor. The advance(Vacuum and centrifigul) have been checked and are in good shape. It has never run correctly ( one more reason it has been tarped down) My wife really likes the car and it has been making me crazy that I can't get it to run. I would apreciate any suggestions anyone might have.
Thanks
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If you're gonna be stupid, you gotta be tough.
1980 Porsche 924
1997 GMC Jimmy (DD)
1984 300zx Tube chassis, Jag suspension, 400hp sbc

fiat22turbo · Joined: 18 Jan 2006 Posts: 4040 Location: Portland, OR

Have you checked the warm up regulator?
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Stefan
1979 924 Carrera GTS (clone-ish)
1988 944 Turbo S (Silver Rose)

chaparral2f · Joined: 29 Jan 2011 Posts: 33 Location: southern oregon

Yes, I have checked it. I just forgot to write it down.

_________________
If you're gonna be stupid, you gotta be tough.
1980 Porsche 924
1997 GMC Jimmy (DD)
1984 300zx Tube chassis, Jag suspension, 400hp sbc

fiat22turbo · Joined: 18 Jan 2006 Posts: 4040 Location: Portland, OR

As it warms up, the AAR will close and it should rely on the air bypassing the throttle plates after going through the fuel distributor.

What is the idle RPM when cold and when it begins to warm up?

The cold start valve should also be shut off after a short period of time and the WUR will be adjusting fuel flow based on temperature. Could the CSV not be working properly?

Have you checked the thermo switches near the rear of the head to ensure they are working?

Do you have a CIS fuel pressure test set?

Do you have access to a oxygen sensor and an A/F meter or data logger? It would be interesting to see what's happening to the A/F ratio when it starts stumbling. Perhaps the plugs are drowning in fuel or you've got a weak coil, or a bad ignition box, etc.

How are the valve tolerances? You may need to check them when cold and when warm (ouch, that just sucks, but it can help)

When it starts stumbling, can you manually manipulate the air plate in the fuel distributor to make it worse or better?

Just shots in the dark, but without being there or perhaps having a video, there is t much more to do than spit-balling at this point. I'm sure we'll get it sorted out eventually though.
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Stefan
1979 924 Carrera GTS (clone-ish)
1988 944 Turbo S (Silver Rose)

Paul · Posted: Fri Jul 05, 2013 5:15 am Post subject:

Check the fuel pump relay or bypass it by removing it and installing a cable between poles 30 and 87.

Double check your valve timing.
_________________
White 87 924S "Ghost"
Silver 98 986 3.6l 320 HP "Frank N Stein"
White 01 986 "Christine"
Polar Silver 02 996TT. "Turbo"
Owned and repaired 924s since 1977
Porsche: It's not driving, it's therapy.

Tiny · Joined: 10 Apr 2006 Posts: 502 Location: London, UK

Hi chaparral2f... a suggestion; Check that the plunger in the fuel distributor is moving smoothly and freely.

I once had similar symptoms and for me it turned out to be an ultra miniscule amount of dirt/gunk trapped between the plunger and bore that had been impeding it's ability to function correctly. Cleaned it up and the problem went away.

I also think fiat22turbo's idea of checking the valve clearances warm and cold is good too. I accidentally mal-adjusted mine way too tight once. Car was fine on startup, (nice and quiet top end..haha...I thought I was onto a winner!) but soonafter ran like a pig. I was so sure the clearances were ok, until I checked the 3rd time.

Hope that helps, don't give up...the good part is just around the corner ; ]
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*****1981 - 924 - Auto - London, UK******

chaparral2f · Joined: 29 Jan 2011 Posts: 33 Location: southern oregon

Tiny, The fuel dist is new, but Ill pull it and check

Paul, the relay is also new. (I've hot wired it so often that I have a jumper wire made up just for it.)

FiatA22turbo, When I got the car the AAR was bad so it was replaced and works. The RPMs are e a little high (1000/1100 cold) and drop to about 900 warm. The cold start valve works, and the thermo time switch has been tested and is good. I have run all the fuel pressure tests before I gave up and covered the car. I will re adjust the valves as soon as I find the time, just to be sure. I don't have an AFM but the O2 sensor has been replaced.
I haven't started on the ignition other than to test the coil, replace the plugs, wires, dist cap and rotor and check centrif and vac advance.

Does anyone have any doubt as to why I named this thing the Antichrist?
_________________
If you're gonna be stupid, you gotta be tough.
1980 Porsche 924
1997 GMC Jimmy (DD)
1984 300zx Tube chassis, Jag suspension, 400hp sbc