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Registered User
Join Date: Nov 2010
Location: Mountain Lakes, NJ
Posts: 28
Running Issues- Thinking Ignition or Fuel Pump

Hey Guys!

Been here a while but finally got a car. Havn't got a chance to start a car dedicated thread, but I picked her up back in October.

FS thread here on Pelican-

Porsche 911 1986 Carrera Coupe 3.6 Vario

Been to a couple track events, car is ok and has potential but needs alotta sorting. Not sure if it is an ignition issue or fuel pump (my guesses) but the car now will not start.

Starting at VIR, on track at speed the car would momentarily cut out while on the gas. Thought I was hitting the rev limiter until it happened at lower RPMs. It happened probably 1-2 times a session.

Drove the car back to NJ with no issue. It has happened one other time while on the street (happened to be when I was moving the seat, so one thought is that it could be something electrical under there).

Was out for a drive last weekend, pulled up to a stop sign and the car stalled and would not start. After it sat for a couple minutes it started up and drove a couple hundred yards, stalling again. Got it back to a friends house, let it sit for probably 20 minutes, came back, car started up, idled and died before I could walk back into the house.

I seem to remember that I could hear the fuel pump run with the ignition on, but I'm not 100%. I definitely don't hear that now. I replaced the DME (OEM Porsche) at VIR, so I don't think it could be that.

Would like to try my hand at fixing this myself before bringing the car to my trusty guys at Powertech.

Now for a few pics!! Also looking for a ducktail if anyone has one used they'd like to part with, not too picky on color.

Day I picked her up

Made it home.

At NJMP Lighning

Proper wheels

VIR with my Dad's Martini Carrera and friend's Turbo, all '86's!

Proper Headlights

Thanks in advance!
Old 12-02-2017, 10:50 AM
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sugarwood's Avatar
Join Date: Apr 2014
Posts: 4,302
Nice car!
Intermittent stuff seems like a pain to track down.

I would probably replace the fuel pump, just because.
Do you know if you have the 1986 fuel pump in your car, or was it updated with the 993 motor?

Also, should you measure your fuel pressure?

Originally Posted by sugarwood View Post

I ran the fuel pressure test with the gauge I got from AnnWorx.
With the key turned to Acc position, the fuel pressure was 0.
Once the engine was actually running, the pressure immed. read 32-34 psi.
1986 3.2 911 coupe.

Last edited by sugarwood; 12-02-2017 at 07:58 PM..
Old 12-02-2017, 07:54 PM
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Registered User
Join Date: May 2008
Location: Grapevine, TX
Posts: 193
First thing I'd do is check to see if you are getting spark. Just grab a spare plug and connect it to one of the ignition leads and have some one watch or crank the engine and see if you are getting spark or not. If you don't have spark start there before you spend much time trying to diagnose the fuel system. If you do have spark, than your fuel system is suspect.
Old 12-02-2017, 09:01 PM
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Plays with cars's Avatar
Join Date: Nov 2001
Location: Southeast of Seattle
Posts: 410
Hard to diagnose from the armchair, but your symptoms seem to point to an electronic component breakdown. As they get warm they start to fail, but early on will recover if cooled; it will get progressively worse until complete failure.

Does '86 use a CDI box? Coil? Crank position sensor? I'd be looking at these as suspects before I spent too much time on the fuel pump. Fuel pump failure is more binary (yes/no). Follow 76FJ55's advise and check for spark when it won't run. I'm putting my money on ignition issues.
Mark B
'73 911S (long term ownership) '70 914-6 (long term project) '74 914-2.0 (sold)
Old 12-03-2017, 09:59 AM
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Registered User
Join Date: Nov 2010
Location: Mountain Lakes, NJ
Posts: 28
Hey Guys,

Thanks for the responses! Finally got a chance to take a look today. I first pulled the cover off the fuel pump, found no power there. Then checked power at the fuse box, nothing. Jumped the fuse and the fuel pump ran.

I remembered that one of the times the car cut out was while moving the seat, and I know the wiring is a mess under there so I decided to pull the seat out. Confirmed the DME is good by throwing it in my Dad's car (started right up).

We found there is power to the DME plug and we jumped the DME with a piece of wire and the fuel pump runs. At this point I'm a bit confused- The DME is good, power to the DME is good but with the DME plugged in the fuel pump doesn't run.

Any ideas?

Here is a picture of the mess I've inherited under my seat (after opening up some suspect areas to check connections). Any idea what the transformer is for?

Old 12-26-2017, 03:22 PM
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Join Date: Jun 2009
Location: St Paul MN
Posts: 2,065
Generally a fuel pump will only run when either youíre cranking the engine or the engine is running- safety issue in an accident so the fuel wonít be pouring out.

Are you checking the pump without trying to run the car?
Rutager West

1977 911S Targa Chocolate Brown
Old 12-26-2017, 04:36 PM
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Join Date: Sep 2013
Location: La Mesa CA
Posts: 138
That transformer and itís associated wiring would worry me, the bare wires on the left side of picture go to transformer. Is it in the seat power circuit? Trace that stuff and get rid of it or figure out if its useful. Part of owning one of these things is learning. Good luck perhaps itís speaker or stereo related?
Old 02-08-2018, 07:40 PM
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