My last stand!! Please let me know if im correct

[jkrustchinsky]

Ok, this is my last shot at getting the porsche running. There is no spark, not at the coil and not at the plugs obviously. The Tachometer does NOT bounce when i turn the car over. Is it the reference sensors that are bad? If so i will order two of them from paragon tomorrow. Is there a quick way to test them.

Here were the symptoms before she finally quit last week:

Monday, driving at 60mph, sudden loss of power, then regained power, then completely stalled. I stopped and she restarted and didnt do anything wrong for the rest of the time i drove it which was about 15 minutes.

Monday afternoon, stopped to fill up gas tank, she started then died immediatly and wouldnt start for 5 minutes.

Tuesday morning, 35 degrees outside, 6:30 in the morning, i start her and she back fires and grunts and will hardly idle then die, VERY VERY LOUD( neighbors complained ), after 10 or so minutes i finally got her to start and idle, if i gave it any gas it would want to die and grunt and stall. Then when she warmed up she ran fine unless i started driving on the freeway and she cooled off then she startwed hiccuping again.

Tuesday afternoon, hardly made it home same deal until it warmed up. when i got home, i tried to restart her and she refused, hasnt started since. Has no spark and tach doesnt bounce when turned over. Am i correct in my assumption of the reference sensors. Thanks so much for your time and help, Josh

[hpservertech]

Really dumb question on my part, but are you sure they afm/tps are plugged in?

I sent you a PM about the sensors.

[Techno Duck]

Jiggle / clean the connectors for the speed and reference sensor. Sometimes there are intermittent connection issues.

[jkrustchinsky]

I cleaned the reference sensor AND bam, she fired right up, i drove her around and she drove great. I went home, turned her off, added some coolant AND NOW IT WONT ****ING START AGAIN, except this time the tach does move so its not the sensors.

Im going through everything again,

[hpservertech]

your getting there! Could be a loose connection somewhere.

[jkrustchinsky]

ive gone through everything, its getting spark, i havnt tested for fuel but im sure its getting it, ive cleaned and made sure every wire was connected. Its just refusing to start. ive check all the fuses tapped on all the relays.

[Scuba Steve]

Originally Posted by jkrustchinsky

Ok, this is my last shot at getting the porsche running. There is no spark, not at the coil and not at the plugs obviously. The Tachometer does NOT bounce when i turn the car over. Is it the reference sensors that are bad?

Per your decription here, the problem lies with either of the two speed / reference sensors or the DME. The coil rarely goes out from what I've seen. The only way to truely test the sensors is to follow the procedure at clark's garage ( http://www.clarks-garage.com ). This will require a multimeter AND an oscilloscope.

There is no way to test the DME except to swap in one that is known to be good. I was in the same situation you were in 3 years ago. Replaced both sensors one by one, but the problem was still there. The only place left to check was the DME. I removed and resoldered it, and that fixed everything.

My guess - you probably don't have an oscilloscope so I would recommend making sure the connectors at the sensors are clean first and test their resistance per Clark's Garage. If they pass, go ahead and check the wire continuity between the sensors and the connector at the DME. I don't remember which pins to test, however but the pinout may be available at Clark's Garage. Odds are this will be good too but you never know.

You *may* be able to test the DME by knocking on it while you crank the engine and watch the tach to see if anything happens. If that does anything to bring even a glimmer of life to the tach needle you've found the culprit.

Maybe someone around could loan you the part(s) to swap in something that's known to be good just to test things. I'd volunteer my old sensors but they're in questionable condition. If this was a year earlier I could've just gone over to check things out but I moved to Seattle from San Antonio.

edit: you never know you have spark until you see it. The still tach needle makes me really skeptical... If you somehow have spark but no movement at the gauge it's pretty much certain that the DME is the culprit. They can easily be resoldered.

[jkrustchinsky]

i have spark and movement at tach though just no start,

[hpservertech]

Sent you a PM.

How do you know you have spark though? Did you use a spark tester or just assuming you do since the tach is bouncing?

[jkrustchinsky]

i pulled the plug and grounded it and had somebody turn the car over, i can see spark between the gap on the plug, josh

[mikepellegrini]

Originally Posted by jkrustchinsky

...Then when she warmed up she ran fine unless i started driving on the freeway and she cooled off then she startwed hiccuping again.

Tuesday afternoon, hardly made it home same deal until it warmed up. when i got home, i tried to restart her and she refused, hasnt started since. Has no spark and tach doesnt bounce when turned over. Am i correct in my assumption of the reference sensors. Thanks so much for your time and help, Josh

If I read this correctly, you say once it warms up, it runs better, except when you got on it?

I'd vote for a vacuum leak. Something's loose when cold; when it warms up (and metal/plastic expands), the hole is sealed (at least partly) and it runs better.

Spark or sensors wouldn't be affected by a hot/cold engine, Neither would fuel (except maybe the injectors).

But vacuum leaks ARE affected by whether the engine is hot or cold... Backfires and what not are common as well, when you have a good vacuum leak.

Just a thought.

[jkrustchinsky]

ok heres where ive gotten, i have movement at my needle, ive pulled the dme and when i turn the car over there is no movement at the needle and everything is exactly the same, but when its plugged back in the tach does move, So... my reference sensors are probably working seeing as the needle clearly moves which leaves me with the DME.

Im talking to a nice fellow on pelican forums who says he has a Known working DME from a 1987 924s, from what ive read it should be interchangable, correct me if im wrong on that one. so what im going to do is get this dme from somewhere and see if it makes her run.

Thanks, Josh

[speedracing944]

Sounds much like the problem I had with a huge vacuum leak on the underside of the intake manifold. Can you get it to start and run by feathering the throttle?

Speedy

[jkrustchinsky]

nope, refuses to run at all, i think the stumbling and stuff i described earlier was because one of the vaccuum lines coming from the air boot had come loose, when i drove it yesterday right before it refused to start it ran perfectly, just refuses to start now.

and ive had the refusal to start problem happen many times before and then it would just randomly start running again, so it has to be somthing on its last leg

[Scuba Steve]

The DME was removed while you cranked the engine?

[jkrustchinsky]

i pulled the dme and cranked the motor, the tach didnt move, when the dme is plugged in the techometer does move when i crank the motor so does this indicate that the dme is good?

[nynor]

no.

[jkrustchinsky]

ive looked all over the forum, exactly why would the tach move if the dme was bad and not when its removed, is it just completing a circuit or is there a certain part of the dme that can go bad and cause the car not to start but still make the tach needle move. thanks josh

[nynor]

um, the DME is more complicated than simply registering that there is a signal from the reference sensor. it also has to pulse the injectors and the coil, among other things. if it was that simple, it would be computer as such, but could be a simple relay.

i am not saying that the DME is bad, just that this 'test' is not conclusive. i'd try a different DME.

[jkrustchinsky]

Well will a dme out of a 1987 924s work in my 87 with and 86 motor, thanks josh