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runs fine then stalls out and wont start for a few minutes

hello,

I have a 1980 Porsche 928. This car normally gives me no trouble. However this morning it gave me a bit of an issue. I was driving to school and all of a sudden it bogged down and stalled out. It took a few minutes of cranking it to start it again. when it fired up, it fired up with out wanting to stall. almost like nothing happened. Idle was good and throttle response was good. I proceeded to drive and maybe five minutes later it died again and it did it to me a few more times after that. I got it home and have been trouble shooting it and cant really come up with any ideas. It sees to run fine now but I havent tried driviing it again since. here is a list of all the things Ive donw recently to this car.

1) literally yesterday I just changed out the final drive fluid (It was really nasty)
2) O2 sensor failed on it again so I have it disconnected at the moment.
3) I bought and insatallled headers about 7 months ago. I dont have a complete exhaust system built for it. I built a ghetto one out of some pipe and put on a glass pack for temporariy use
4) installed new injectors and cold start valve about a year ago
5)Installed MSD blaster two ignition coil (because the former owner broke the coil and tried tapping it togehter)
6) new 8MM thick Magnacore racing spark plug wires. (cheaper than original)

so far Ive ruled out the igntion system, and the cold start valve. Ive tetsted the thermo time switch and it seems to test good (at least when its below 84 degrees fahrenheight) and Ive also tested the coil and to see if power was leading to the coil. every thing checks out fine. I was going to check relays next to see if any of them may be bad. Any ways, any pointers in the right direction would be helpful
Old 12-14-2016, 02:30 PM
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Dan I would suggest to call 928 INTL and buy all the used parts you can to restore the engine to original spec. they are having the half price sale on used parts buy a used coil distributor and computer get a new green wire.
Replace the fuel pump fuse and relay,
if the pump is original it might be good to get a used pump and new check valve and new sealing rings
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Old 12-14-2016, 04:03 PM
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Thats where I was headed next. I was doing more trouble shooting and came to the conclusion that according to the specs from the F.S.M. All my sensors, coils, and wiring seem to be ok. I havent checked the green wire from the distributor yet. I forgot about that wire being an issue on these cars. I dont think mine has ever been replaced. The car sat for 21 years before I got ahold of it. Is it possible to build A new green wire? I havent looked at it too close but im sure it is. I was just curious to see if I needed some kind of special crimp or something. I also ask because I just graduated form avionics school and am currently getting my A&P certification. So I know how to build a harness/wire but that is besides the point. Ill have to look into the computers and all that. I am a bit short on cash being a student and all at the moment but I will look into the parts. Anyways enough of my rambling and thanks for the pointers.
Old 12-14-2016, 08:08 PM
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Anything can be kludged to work. I've got a 2TB drive with a broken SATA connector and best solution looks like soldering a cable directly to the board. You really don't want to start down that path with a 928, its not a path to a happy place.

First thing I would suspect are all the non stock parts, especially the coil, but also the wires.
Old 12-15-2016, 01:41 AM
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Dan,
Went through the exact same problem with my 1980 awhile back. Checked everything, replaced the "green wire", ignition switch, added a fuel pressure gauge, and even tried a spare computer, etc.
It turned out to be the injection relay, which would operate OK sometimes, and not others. Have not had any issues since it was replaced. Good luck!!!
Old 12-15-2016, 05:23 AM
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928gene which relay is it that your refering to? I am looking through the FSM and found the AFC fuel injection relay. Is that the one you are refering to?
Old 12-19-2016, 11:53 AM
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Relay

Dan,
That's the one. Sure hope it fixes your problem like it did mine. I guess that after 36 years, any relay can wear out. Again, good luck, and have a great Holiday.
Old 12-20-2016, 05:59 AM
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