Intermittent No Start
 

I'm having a weird intermittent no start problem. Every so often (seemingly at random- I've not been able to pick out a pattern) I'll turn the key and the car won't crank. Lights/ electronics turn on as normal. When the car starts normally there's no drama. Starter sounds strong and it starts right up. When it won't start all it takes is touching jumper cables to the battery and it'll immediately start right up like normal. I've read every no start thread I can find so I've tried a bunch of things but the other day I drove the car to dinner and when I came back to drive home I was stuck so here I am hat in hand looking for what I'm missing. So far I've:

-Replaced the battery
-Replaced trans ground strap and cleaned attachment points
-Both flywheel sensors are new
-Swapped DME relay

My best guess is there may be high resistance somewhere and the extra juice from the jump provides enough amps to overcome it? Still seems strange that it happens randomly if this is the case. Anyone have any ideas?

Stock 84' 3.2 Targa.

failing ignition switch.

Long shot but it could also be that the cast connection between the mechanical and electrical portion of the ignition tumbler into the switch could be starting to fail.

no start
 

1987 carrera....I had a similar issue and was found to be the yellow start wire between the ignition switch and the engine compartment connection 11 wire plug. a short that could not be identified. We disconnected the yellow wire on both sides and added a new wire and welded it on both sides. This was a much cheaper way then replacing the whole 11 wires strand.

+1 with Jp..also check you ground connection on no.1 intake
Ivan
https://www.porscherepair.us/porsche...48_431_755.jpg

PO replaced the ignition switch not too long ago but I think it was an aftermarket unit. It doesn't display the behavior outlined in the 101 projects book (hard to turn key/ flickering head lights) but this could be the culprit.

I will check out that engine ground as well.

I'll be tearing into this this weekend so if anyone has other ideas please keep them coming.

did you check the yellow wire connector at the starter if it is tight?
Ivan

Is the trans. ground strap actually connected to the car chassis?
My car suffered the same random no start when i bought it. Turned out the PO had the ground strap bolted to the trans. mount:rolleyes:

Also, check the big ground wire from the battery to the chassis. I had one that looked perfect but would intermittently develop some electrical resistance, so the car would occasionally refuse to crank at all.

I believe so but its been a few weeks since i was under there so I will check again.
I believe so but will double check this as well. If this ground was not in place properly I would think I'd have more issues but its certainly worth a look.
I did not check this so I will look there as well.

Thank you guys very much, this is very helpful. These intermittent problems are the most frustrating.

If anyone has any more ideas keep em coming.

How many miles on that starter? It's a PITA to replace, so make sure you do the easier stuff first...

It would be worth removing the yellow wire at the solenoid and checking that you are getting 12.25 volts with a meter. Not easily done as you will need to attach the meter probe to the yellow wire and the black to earth and at the same time operate the key in the ignition switch to start position and observe the meter!

85K miles. I know that top bolt is a PITA to reach. I need to get one of those long hex key sockets.

That's a good idea. I'll have to recruit a helper.

I had an intermittent no start that drove me crazy. Turned out to be a failing relay that was part of a P.O. alarm install. Got rid of it and the problem went away.


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Was it draining your battery or was there some other cause? I've been keeping an eye on the battery with my multimeter and there doesn't seem to be a parasitic draw issue.

Agreed on checking the yellow wire.

Intermittent No Start
 

In my case the battery level was not affected. It was simply a starter circuit cut-out that was malfunctioning. Once removed it was back to original. It was a special circumstance in that it was caused by the aftermarket alarm system. Irrelevant if yours is all original. As said by others, go through all the basics, chasing all the wiring to be sure it’s all sound, especially where it passes through connectors, fuses or fusible links. As frustrating as electrics are, the Bosch harness in these cars are very logical and robust. It’ll probably turn out to be something simple that you’ll kick yourself for not seeing sooner. Do you have the wiring diagram for your car? It’s best to start out with a good understanding of how the circuit is laid out.


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My 87 had the same issue. One time I wiggled the main DME harness plug under the seat and sure enough she started right up. After more investigation, it turned out to be the DME. Fractured old solder joints. Had the DME inspected/repaired and it never happened again.

Thanks for everyone's help so far. I checked out a few things and nothing looked too out of sorts but I had limited time so there's still more testing to do. Took it out to dinner again and it fired up just fine both there and back so maybe its all set? Time will tell.

So I finally had some time to dive into this. I cleaned the battery ground, engine bay round and transmission ground. No change.

I just had my brother help me with the above: I disconnected the yellow wire from the starter, connected that to one probe of the multimeter, connected the other probe to the transmission ground, and had by brother turn the ignition.

I'm not sure what to make of the results:

With the battery connected but no key in ignition I was reading 10.4 volts but it was jumping around a lot. Shouldn't I read 0 until the key is turned?

When the key is turned the voltage would shoot up to 16 or 17 and then back down.

Not sure what to make of this. Any ideas?