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Help! Fuel Pump Issues

Ok...Im stumped, Hoping for some help. Thanks in advance guys
The other night my 87 930 died while driving. Fuel pumps were'nt running with ignition on. Both pump relays and fuse were very hot. Got it home and went through all the diagnostics. Ground out the boost pressure switch and that was it..Pumps ran. changed out the switch and thought everything was great. Well..I drove the car the next day. After a few miles the same thing happened car died, relays hot, same deal. I tried grounding the pressure switch and nothing. Now..Ive jumped speed relay, jumped yellow relay, ground boost switch to no avail. Jumping the FP relays= pumps run and car runs fine. Fuse is fine. My car has a factory alarm. I'm thinking that may have something to do with it. I removed the fresh air blower and gained access to the alarm module behind it. Is there a way to test or eliminate this? Could it be the ignition switch? Any other ideas??
THANKS

Old 10-07-2016, 11:20 AM
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I've attached a link to one of our tech articles that I hope will be useful in diagnosing the issue and hopefully addressing it. If you have any other questions, feel free to post a Comment just below the article and someone will get back to you with more detailed info. Good luck!

Porsche 911 Fuel Pump Replacement | 911 (1965-89) - 930 Turbo (1975-89) | Pelican Parts DIY Maintenance Article


-Dmitry
Old 10-07-2016, 12:43 PM
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Thanks, but the fuel pumps were confirmed to work fine by jumping the FP relays. They are not the problem
Old 10-07-2016, 12:50 PM
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Mighty Meatlocker Turbo
 
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Another thing that can cause a "no run/no fuel pumps" situation like you describe is the "speed relay" (aka - the rev limiter) that is under the driver's seat on later 1980's models - it is the metal encased relay that is farthest to the left.

Another member, JFairman, had a problem like you describe and simply unplugging the connector and cleaning the pins was the fix. You can also pry the metal cover off and look for broken solder connections if cleaning the pins doesn't work. I have never found info on how to actually test that component, though.
Old 10-07-2016, 01:04 PM
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Mighty Meatlocker Turbo
 
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^^^

BUTT, you can bypass it for troubleshooting purposes (see pic - item "B"). By the way, 1986 and 1987 are the same.


Old 10-07-2016, 01:08 PM
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Thanks so much for posting that diagram. I used that one or something similar to to find the overboost switch was the culprit before. I have already done all the checks and bypasses on the bottom though. Still No pumps running with the ignition. Thus the reason Im stumped. Thinking maybe something to do with the alarm system or key switch?????
Old 10-07-2016, 02:25 PM
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Stuff like this makes you want to install a 25 amp DPST switch hidden somewhere in the car to supply 12 volts directly from the battery to both fuel pump relay terminal 87 wires... for when this might happen.
Old 10-07-2016, 07:46 PM
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''Stuff like this makes you want to install a 25 amp DPST switch hidden somewhere in the car to supply 12 volts directly from the battery to both fuel pump relay terminal 87 wires... for when this might happen.''

You know..That sounds like a great Idea! I'd love to do this. Has anyone done this? Would there be any repercussions you think for running the car this way???
Old 10-08-2016, 08:52 AM
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You probably wouldn't want to run your car this way on a permanent basis as it would allow the pumps to run when the engine was shut off. If there is an engine fire this could be real problem. This could be a temporary fix to get home.

Rahl
Old 10-08-2016, 11:08 AM
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Having similar problem

I have a 1981 turbo and have developed a similar problem. I had a bad fuel pump and replaced it and also eliminated the in tank pump with the strainer instead. Replaced fuel filter too and noticed the positive cable was getting very hot which I don't think was happening before. Replaced both battery cables and still gets hot. I have 4 wires that attach to the positive battery terminal and one of them seems to be the culprit. Not sure where to go from here and am taking a break for now. The diagram you got from Rawknees was great and I would love to know where it came from. I have been working with an old blown up copy of the wiring diagram from a Haynes book and have not had much success with understanding it.
Old 10-11-2016, 05:30 AM
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Do the fuel pump relays feel snug in their sockets? I have had similar issues which I now believe stem from weak connectivity between the relay and the socket in my ‘87 turbo. A poor connection would also cause overheating.
Old 10-11-2016, 07:22 AM
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what are you grounding the over boost sw to? ground the wire to the body for testing. leave it grounded.
then jumper 30-87a of yel, rly.
then jumper 1-2 of rev limiter.

I have not verified this but I have heard of another fuse that was only in the 87. I think it feeds the rev limiter, but if you jumper 1-2 that should rule that fuse out.

I split my circuit onto 2 fuse and didi it so it looks factory and you cant tell.
I don't remember which rly but I cut the wire going to pin 30 of one of the FP rly's and ran it back to a spare fuse on the factory fuse block. then I ran a red wire from the same source that feeds the original fuse over to the top of the spare fuse so it would have an adequate sized wire.
figuring out which wire to cut is the hard part.

that FP fuse feeds more that just the FP's. not very smart on porsches part.
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Old 10-11-2016, 08:15 AM
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Mighty Meatlocker Turbo
 
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Quote:
Originally Posted by pearlspapa View Post
The diagram you got from Rawknees was great and I would love to know where it came from. I have been working with an old blown up copy of the wiring diagram from a Haynes book and have not had much success with understanding it.
That diagram was created by another forum member, billjam; he sold his Turbo years ago, though, so seldom posts here now.

Here's a thread he posted in in the past. He's made several of those type drawings and would likely email them to you.

Speed Relay


Last edited by Rawknees'Turbo; 10-11-2016 at 08:27 AM..
Old 10-11-2016, 08:20 AM
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