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Porsche-O-Phile's Avatar
Join Date: Feb 2004
Location: A Rock Surrounded by a Whole lot of Water
Posts: 32,458
951 electrical problem

The good news: I just acquired an '86 951 in good shape.

The bad news: It died right after I picked it up. Here's the story:

I had the little "!" lamp illuminated while driving it and figured it was just because there was virtually no fuel in it (the thing was well into the red - on fumes). I pulled into a gas station close to my place, put go-go juice in, checked the oil again, and went to start it up. . . click. Nothing. Again. Click. Nothing. DAMMIT!!!

Tried pop-starting. Engine turned, fired a couple of times, then died. Nothing. I had a guy help push to get a little more speed for the pop-start - same problem. I asked a kindly guy in a van for a jump-start, vroom! It started right up, but as soon as the jumper cable was removed, RPMs dropped and the engine died again.

Soooooo, I went home, grabbed the (known good) battery out of my 944 that's up on stands right now and went down and transplanted it into the 951 - vrooom. It started right up, but the damn "!" light is still on and voltage is showing very high on the scale (up over 14 it looks like). This seems to be an alternator / charging system problem of some sort. This bugs the crap out of me too, 'cause the car was PERFECT when I test drove it before. I'm guessing this might be an overvoltage relay problem that's tripping the alternator off-line (?) Where is this located? What are the first things to check? Voltage regulator maybe? How do I check it? Where can I get a replacement and how much is it?

Thanks all!
'74 911 Targa 2.7 (in storage, hoping to finish "someday"), 2001 Mercedes SLK 320 (with a few AMG fun bits), '85 BMW K100, a few surfboards

Black Cars Matter
Old 08-29-2004, 04:57 AM
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Join Date: Jul 2001
Location: Edmonton, Alberta, Canada
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"You asked on the other board"

Here are another couple of questions for all you 951 people out there:

(1) what are typical boost indications? I'm showing 0.4 or less at idle / RPMs up to about 1500-2000 or so and light throttle (makes sense I guess) and as high as 1 bar (maybe a little higher) with the throttle mashed and the RPMs higher in the band (3K-5K).

(2) There's a small "L" hose by the a/c receiver-drier that comes off of the pipe by the BOV. It looks like a hose of some sort should be connected to it, but there's nothing (just the metal "L"-shaped nipple). Anyone know what this is? I'll post a pic later on.

(3) Are the dash lights always that dim on the new style car dashes? I've heard people complain about this, but MAN!!! Driving home from the gas station last night I was wondering if I had the little rheostat all the way up or down - it didn't seem to make a whole lot of difference! .......

1. the stock boost guage is not the most accurate thing in the world..... but the numbers are close. 1 bar on your stock guage is if it reads 2 bar you would be running ~14.7 psi. So the 0.4 at idle is ok (vacuum).... you should read at least 1.75 bar WOT dropping to 1.5 bar

2. need a pic for that one but it could be the hose that goes into jboot........ which is not a good thing. Intake leaks are bad for boost. Its the only L-shape connector that I can remember from the stock setup ...but post a pic.

3. Yes the dash lights dim over time. Its probably the reflectors in the guage clusters. A few options to brighten things up.

BUT your current problem....... ~14 v at the battery while charging is actually fine. I find it odd that your stock system can actually pump that out..... Try putting a volt meter on the battery.......and rev it up. Does the Voltage go higher ~15v........ it should stay relatively constant.

Turn on some accesories and see what the voltage at the battery is as well. You may have some corroded or loose grounds that are giving you intermittent problems.....

Let us know what else you find.

! symbol is so misleading so check your parking brake switch and brake fluid level just in casel.........
Alex - PCA Polar Region - Boxster Muncher
86' 944 Turbo - Megasquirt - 326 rwhp/340lbft @ 18 psi SOLD
Old 08-29-2004, 07:41 AM
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