Saaboteur

Here's the whole story. I have another thread on my recurring alternator/battery warning light, and occasionally it would reappear. I could shut the car off, restart, and the light would disappear. The whole time I'd be getting 13.6-7-8 voltage, it would momentarily drop, causing the light. I fabricated my own alternator to chassis ground strap, also fabricated a new cable going from the junction point under the hood to the alternator, still had the issue with the warning come up.

Anyway, several weeks ago, the warning came on a few times in several days. On the way home one day, I had more difficulty starting again - cranked for 30-40 seconds it seemed before it would start. This happened twice on the way home, the second time taking even longer to start. Managed to get it home and left it for several hours.

Came back, tried again, still no start. Now more worried. More cranking and cranking but still no start. Finally, the battery drained too much such that it wouldn't even crank. hooked up the battery charger and charged it up over night. Next day, cranked perfectly, but still no start.

I tried the fuel pump fuse thing, and pushing the shrader valve in on the fuel rail allowed fuel to spurt out, still nothing. Figured it flooded, so took the plugs out, left everything overnight. Coils look good, plugs look good (but smelled of gas). Put it all back together, fired up right away.

Next day, same symptoms - wouldn't start, cranks fine. Hooked up Durametric and monitoring live/actual data for engine speed shows the crank sensor picking up crankshaft rotation when cranking.

At a loss. Ideas?

Rob VN

Are you getting any codes? The wet plugs might point to no spark, can Durametric show anything? Can you look at your fuel pump pressures in Durametric? Good luck.

endless_corners

Damn Saab. What's with this CTT? The universe knows you like to tinker and so you've been given a worthy adversary.

Dilberto

I'm betting fuel pump(s). They just fail with no codes....

CAVU

Something is amiss internal to the alternator. Either one of the two brushes is worn to a point that it is having intermittent contact (you'll see the voltage drop from your 13.6 down to 12 or less while it's running. If you see it drop even lower I would suspect a diode but those tend to fail and not come back. Could be a short internal to the alternator but my money is on one of the brushes. Change out the voltage regulator (hope it's available) and have a good look at the old brushes. There will be part numbers on the VR. One brush will be markedly shorter than the other. I have had excellent luck soldering in new brushes and reusing the VR.

Saaboteur

I put in a new alternator in the fall! And I dunno about the fuel pumps either - it doesn't explain how it fired up after I took the plugs out and let it sit overnight.

I caved and had the thing towed to a Porsche index shop last night. It's got them stumped too. They took out three plugs and said they looked oily and gassy, so they're going to take out the others, let it sit and see what happens Monday. I bet it'll fire up, but I do hope they find something.

bigbuzuki

Suspect engine harness / connectors.

Saaboteur

Just to revisit this sordid tale and to tie up loose ends, along with my other thread here:

https://rennlist.com/forums/porsche-...-issues-3.html

I didn't post again in February after the car was examined again by the shop, mostly out of spite and frustration. They said 'alternator!!' - I was skeptical because I put a fresh one in last fall. I told them about the bypass wiring I ran - their response 'nope, it's the alternator'. So out of a feeling of general pissed off-ness, and also not wanting to do exploratory surgery during the winter months (notwithstanding that we had a very, very mild winter), I drove my AMG instead.

Brought the car home on battery power only - it did fire up immediately with a full charge. The shop is only about 10km from my house, and weird electrical sh*t started to happen about halfway back - stereo and instruments cutting out. I just kept praying it would last the trip and not to get stuck at any red lights for too long, but fortunately had my neighbour give me a lift and we did it in the evening so there wasn't much traffic. All the way back, my little plug in voltmeter showed under 12V. Got it home and parked it. A few checks on it while I waited for the snow to melt showed the battery as pretty dead. Didn't look at it again until the snow melted in April. Charged it up and it fired up right away, and then drove it into the garage.

Anyway, my thought process was to have the alternator tested first. If it was wonky, then I was hoping to get a new one under warranty. Tore into the car and had the alternator out in about 3.5 hours - front bumper removal and moving the rad support to the 'lock position' and everything. Fortunately, the alternator tested out fine. Must be wiring harness, right?

Turns out bigbuzuki was right. Picked up a low mileage wiring harness from eBay, got the whole thing back together. Curiosities - there is a Mercedes star logo on the electrical connector on the passenger side, can't remember what it is - side of the block, up above the pan; and then the plastic covered nut holding the positive cable to the alternator has a BMW logo on it!

Anyway, car fired up basically right away and instantly 14V! Very happy. Now in everyday driving it typically is 13.9 or 13.8. The only other cable that could be in issue is the one from the distribution block by the battery through the firewall to the junction point under the hood.

So I don't know what happened to my fabricated positive cable, somehow it must have failed, somewhere. I suppose it's not a perfect piece. I used good quality battery cable and solder on eyelets. After soldering, I tested them too - put the eyelet in a vice and pulled, hard.

I'll update my other thread with a link to this post/thread too.