1987Porsche944WithRealLongName

A few weeks ago I noticed my car starting to cut out occasionally while driving. It would lose all power to accessories and the motor would quit but it would start right back up. That is until one day it quit and I had no power to anything once again. Boosted the battery and it let me start, and proceeded to power the car long enough to get 2 miles up the road before quitting out again (after giving me a sputtering and bucking show). I replaced the alternator with a spare I had and got a new battery (couldn't do anything with the old one) and the car ran fine for another week or so until yesterday when it died again but this time left me with accessory power. I was able to turn the car over several times until I left it alone for a few minutes and then tried again and the starter was locked and wouldn't even turn once, which I found odd how it abruptly lost power.

So I towed the car home and put a multimeter on the alternator/battery. With the battery charged and car running voltage did seem to slowly go down from 13.8. I checked the voltage reading from the battery posts to the alternator case it and it was over a volt on each. Then as I was tying things up something from under the intake started sparking! Before I could even act the car turned itself off. As if all that wasn't alarming enough my interior started smoking at the driver's side seatbelt bolt to the floor.

I examined all the power cables coming from the battery and nothing seems to be touching the body. Where can I go from here to track this down?

[Edit: Solved but now a new issue]
Turns out it was the alternator cable at the back of the engine bay rubbing on the exhaust and charging the engine and body
Now I have an extremely lean situation at idle and throttle
Opened the DME and there was some broken contact on the circuitboard itself where the harness connector goes, I repaired and tested it but the lean issue remains
I've also tried unplugging the o2 sensor and knock sensor (where I'm pretty sure I saw sparks) to no avail
Tested the grounds from the dme plug and they all seemed fine

The wideband shows 15 when first started (I assume the sensor isn't warmed up yet) and it falls to 17 or above quickly
Car shakes and shutters and remains lean when revved. Fuel pressure is nominal and I do smell gas from the exhaust.
What can I test that would involve these symptoms?

Mister Quickie

There's the bucking/cutting out and the battery drain. My 944 has/had these problems too.
It's hard to get the negative terminal ultra-secure on the battery, any little slippage and the bucking/cutting in and out is the result so make sure it's tight.
The drain, for some reason the 944 has some process that sucks power. I can leave my VW for weeks and it fires right up. My 944, 4-5 days (pretty new battery) and it's dead so I make sure I take it on the highway every third day.

mytrplseven

Check the connections on the starter from the battery and the ground attachment on the bellhousing. Make sure all those connections are clean and tight.

Dougs951S

This shouldn't be the case, if you have a serious battery draw (draining a battery in 4-5 days is a serious draw) then you have a problem. I can leave my car for months and it still fires over on the first crank, every time. As a matter of fact, none of the 944's I've owned ever had battery drain issues, they could all sit for weeks and still have plenty of juice. Based on what you are saying, I'd say you're looking at a ~ 400-500 mA draw. The average 944 battery is rated at 50-60 amp-hours and if your battery is being drained in 100-120 hours of sitting, your draw must be around half an amp, which is a lot. For comparison's sake, in my car with the key out, my battery drain is ~30 mA.

1987Porsche944WithRealLongName

The grounds are fine and the negative terminal tests very little resistance to the shock tower bolt, as does the alternator case. I'm really at a loss on where to go from here.

Is it possible the alternator has a problem somewhere inside and is charging the case itself up slightly?

VirginiaF1

I'm equally perplexed at the smoking seat belt bolt..
Burning where bolt meets the carpet due to it being volted/grounded?

Johnboy4444

+1 on this, I have had 2 944's (not a great resume compared to some rennlisters... ) however, on both, (86's, one N/A, one turbo) the N/A i replaced most of the interior on it and with over a month sitting, fired right up, and the Turbo, due to some part compatibility issues (supplier) and some shipping times, equating to about seven weeks, no starting issue, first time, every time. seems you may have a loose ground or something staying on/shorted somewhere...

In response to the OP, with sparking under the intake, I'd check for an exposed +12v wire on possibly the Air meter, or another small connection, if the air meter is grounding, it may be causing the DME to receive a bad return signal, giving you the bucking/stalling issue, just my 2 cents though...

1987Porsche944WithRealLongName

Found power cable making contact with an exhaust pipe. Alternator now isn't perfect but does act a lot better.

BUT
At idle I'm getting anywhere from 16.8 to off the charts lean. Revving only makes it worse. I have proper fuel pressure and the post maf intake doesn't have any leaks.
I used to think this was because the alternator didn't have enough power to run things but I'm getting over 13 volts at the battery.

Van

Also make sure your grounds are OK - specifically the bellhousing and engine grounds to the chassis. If a seatbelt bolt was smoking, it sounds like the engine is trying to use other (smaller) wires for ground and overheating them.

1987Porsche944WithRealLongName

Injectors show proper resistance, injector harness gets 12v across the board on one pin and 10.4 on the other (DME side). No bad resistance on the dme plug to DME wire.
Swapped DME relay for fun anyway

Checked MAF signal at the DME while running and it also seemed fine

And just for the sake of mentioning I'm getting 15hg of vacuum on a very cold engine

???
I just really don't want to have to drop a few hundred dollars on a DME and wait for it to ship since the 944 is currently my only transportation

Van

Then open the DME up and look for broken solder joints - usually at the main plug.

1987Porsche944WithRealLongName

Already done that. The strip on the circuitboard where the plug connects looked like it had burned up a little and wasn't making contact. I repaired it but the problem remained. I couldn't find any capacitors that looked obviously busted and I reflowed all of the solder looking somewhat aged.

So far the only thing I've found bad was my KLR grounds in the plug. Testing each one to the ground showed all but #14 as infinite. All of the grounds on the DME plug tested fine however.

Does the KLR and DME share a ground wire?

1987Porsche944WithRealLongName

It's around 30 degrees now, had trouble even getting the car to start
Had to give it a fair bit of gas to even get it to run, didn't want to idle on it's own. I pulled the plugs afterwards and the 3 front ones were wet with fuel and #4 cylinder one was dry.

R&S sensors checked out

Bypassing KLR by jumping pins 9 and 16 didn't help

Van

#4 might have a clogged injector. Do you have an IR thermometer? Check the exhaust header runners right after you start it up.

1987Porsche944WithRealLongName

Let me just ask, what other possible suspects could there be besides the DME
I want to be 95% sure it's the culprit before I drop $250+ on one

I've had the thing open 3 or 4 times now and nothing looks obviously wrong