Having strange electrical problem
 

Hey, My newest problem started out to be(or thought it was) the starter going bad, when you rotated the key to the crank position sometimes it would click, and not engage the starter, then it pretty much stopped altogether, I thought the starter had went out, tried to roll it off a few days later, and it wouldnt hit, so I took a screwdriver and crossed the contacts on the starter fron under the car, and all it would do is rotate, and not hit a lick, at this point I thought, the starter must be good to crank at all but now i have no spark.. so I leave and after about an hour I returned, the car now rotates with the key, and this time starts up..... then a day or so later, I parked it and went back to attempt to move it, now spark again!!!

Anybody want to buy a porsche?

Clean your grounds, especially on the bell housing, clean your starter terminals and battery terminals, charge you battery.

If that's not it, post some more information.

The battery is brand new and when it cranks fine, when it doesnt click, could it be the key switch? I will check the connections and rule that part out.

If you jumped the wrong part of the starter to make it spin but not engage the throw-out solenoid, then, yes, it could be the ignition switch. Not a bad part to replace anyway - it's fairly easy, not to expensive and cured MANY intermittent electrical gremlins on my car.

Also....just because the batter is new doesn't mean its charged. If you have a charging system problem, it can still be dead. So just put a multi-meter on it and see.

So you had to replace the ignition switch on your car?

Not in relation to the issues you are having. I had gauges working one time I started the car and not others. And fans working sometimes but not others. Turned out wiggling the key a bit usually fixed both of those. A new ignition switched fixed it for real.

I have checked everything, I still have no spark .. changed coils nothing... are there any common failures on 944's that i need to check?.. I checked all fuses nothing there.

Bad solder joints on the DME - but that my not be the first thing to go for.

If you have no spark - have you checked for voltage at the coil? And have you cleaned those grounds yet? That's your #1 common electrical problem on these cars.

Ok, coil is good, crank sensor is good, I cleaned the connedtions on the battery, and am now cleaning connections on the starter, there is 12 volts to the coil, but no spark! I took the key switch out then apart, and it looks good, is there a way to hotwire the car at the key switch to eliminate the switch? I took the computer out and kinda smacked it as one method of checking it and nothing... whats next?

i cleaned the starter connections, still no spark.

Is there any cutoff switch somewhere that might cut off my spark?.. oil lever shutoff, that kind of thing..

You're not done cleaning things up yet...
 

First, clean the big battery ground wire where it connects to the top of the bell housing. That is the starter ground and is also the DME ground, so clean all the other ground connections you find on top of the bell housing as well.

See what happens and report back.

You didn't mention if you had any kind of alarm system in your car. Do you?

OK, the computer(DME) is bad, I have been researching options to fix this, I have read that certain BMW computers will replace my DME.. if I chagnge me internal chip. I dont want to put any more money into this car at this time and if any of my BMW computers will work it will save me some money... sadly she is becoming a money pit. I dont like "cobbling", but if the are the same...! Thanks

OK, I'll bite. How did you come to this conclusion??

I can crank the engine, and it will not hit(no spark), I can then lightly tap the DME while cranking it, and it will fire right up... also, as I drive it down the road, it intermittingly stalls, again i can lightly tap it, and it will pick up and go on. the computer is now at an electronics shop, but the last time i talked to the repair guy he said he couldnt find any traces bad enough to cause any real problems, so I am seeking other options.

Time for a new repair guy...
 

So, is he saying there are bad traces, but not bad enough to cause any real problems (in his opinion)? Any trace/solder joint that looks even a little bad probably is!

Heat, vibration and age can cause the solder joints to loosen on a minuscule scale, leading to intermittent connections. The wiring connections to the terminals should be inspected carefully for the same condition. The terminals themselves loose their springiness and get dirty with age. Happens a lot with BMW Motronic DME's it seems. These are cheap things to check before you go spending money or wasting time hacking in a BMW DME that probably won't work for many other reasons.

I dont think its a waste of time, education never is, plus I have them. I will check out everything I can with mine first of course, but I am open to options.

New territory...
 

Happy to help if I can. I am pretty familiar with Porsche and BMW DMEs. I am blessed with a good example of each.

Things to consider if you decide to use a DME from a BMW:
- should be from a four banger
- should have both a speed and a reference sensor inputs
- number of teeth the speed sensor sees in one revolution
- fuel injector resistance
- fuel/air maps will not be optimal for the 2.5L Porsche engine
- DME to wiring harness plug compatibility and pin designation
- ignition coil compatibility (internal vs. external ballast resistor)
- compatibility with Porsche AFM (5V or ~8V sensor)
- other things I can't think of right now, but you get the idea

You should be OK with sensors like TPS, O2, temperature and other switch contacts, but the big hurdles will probably be speed sensor trigger wheel tooth count and the AFS, but you might get lucky with that.

OK Update:

I picked up my DME-Computer from the electronics guy yesterday, and he said it had some bad(cold) solder joints, but he found a componant leg the had seperated, or pulled up from the board near a heat sink(one of the common things I had read about), he re-soldered it, and I borught it home and it runs fine now! No losing spark of having to bang on it to get it to work! In fact I think is might actually run a little better.