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Registered User
Join Date: Oct 2011
Location: Minneapolis
Posts: 154
'86 Carrera fuel pump symptoms?

First off, I'm searching, but figured I would post in hopes that someone who has had a known bad fuel pump might verify my symptoms.

I purchased my car after it had sat for nearly three years so I'm discovering all sorts of little fixes, but the fuel pump was the main reason it wouldn't initially start after getting it all back together. I pulled it and hooked 12 volts to it on a bench to see what would happen and to my surprise it came to life and shot fuel everywhere. So, I put it back in and the car started, but runs a little rough at idle. It will rev ok but under load it cuts out around 3k or so and gets worse as the engine warms up to temperature. The pump is pretty noisy so logic tells me it's shot, but does this sound like what anyone has experienced? My thinking is that the pump runs enough pressure to get the car started and running but not enough to do much more and as the pump gets hot it performs worse.

I checked the reference and speed sensors and will probably check the cylinder head temp sensor as well. I didn't have the right fitting to check fuel pressure, but since I plan to just replace the pump anyway I didnt figure it was necessary. I could always do the test to see how much it pumps in a certain amount of time.

I'm not trying to over think a simple part, but there's too many horror stories about going through all of the sensors motronic uses and I don't want to just throw parts at the car.

Thanks for any help!

'86 Carrera
Old 08-17-2012, 06:55 PM
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pete3799's Avatar
Join Date: Nov 2008
Location: Vermont
Posts: 6,231
The screen in the bottom of the fuel tank may need to be cleaned.
New fuel filter may help also.
79 911SC RoW
"Tornadoes come out of frikkin nowhere. One minute everything is all sunshine and puppies the next thing you know you've got flying cows".- Stomachmonkey
Old 08-17-2012, 07:21 PM
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kidrock's Avatar
Join Date: Jan 2009
Location: Coastal PNW
Posts: 3,054
Fuel pump sounds like it's on its way out. Drain fuel and fill with fresh fuel and a can of Sea Foam or Techron. Replace fuel filter.

FWIW, I recently had a similar running condition which you described. When car is warm, pull the cylinder head temp sender plug from its harness and jump the female end of the plug with a paper clip. If this smooths out your idle, you have located your issue.
'88 Cabriolet, using EP Slick 20w50 partial synthetic Snake Oil...just as Rommel intended.

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Old 08-17-2012, 07:55 PM
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Registered User
Join Date: Oct 2011
Location: Minneapolis
Posts: 154
Thanks, it has a new fuel filter and fresh fuel with Techron added. I will probably check the screen but fuel seems to be flowing fine from the tank. Hadn't thought to jumper the cylinder head temp sensor, that's next!
'86 Carrera
Old 08-18-2012, 05:35 AM
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