3.2 No Start When Hot

[DSPTurtle]

Pelican Brain Trust,
I have an odd one here in the shop that is kicking my butt. 1988 3.2 Carrera. After about 30 minutes driving (engine good and warm), she won't restart until you let her sit and cool off. I have changed the DME relay. I've run three days worth of fuel pressure checks (all well within spec) and the worst part is that it is intermittent. It doesn't always exhibit the no start. The engine runs smooth as silk up until you turn it off... so no cutting out which would point to the sensor. The only modification is a Steve Wong chip... but I don't think that should be affecting this. Any ideas on what I am missing or how I can run a better test to narrow this down?
TIA

[JJ 911SC]

Originally Posted by DSPTurtle

... she won't restart until you let her sit and cool off.

... but the starter work?

[Driven97]

Does it crank and not start or does the starter not even try? My starter solenoid stopped working when hot recently, once it cooled off it was fine. I replaced the whole starter and no more issues.

[proporsche]

JB ..check for some alarm relay ..ask the client if he one aftermarket in the car ?
i assume it is a clients car,right?
Look under the dash on the ignition switch plug if you see if someone has tappet into the big yellow wire ....this would lead you to the relay.
Ivan

[RL technical]

Just had the same problem on a 85 3.2 we mechanically restored. Every time I’d park it in the sun, it wouldn’t start.
Replaced the ignition coil, and it hasn’t missed a beat since.

[88911coupe]

Also check the speed and reference sensors...they can fail sporadically...work one day, not the next. I think they are temp sensitive somewhat when the start to go bad. Use the BWM equivalent which is MUCH cheaper.

[DSPTurtle]

Originally Posted by RL technical

Just had the same problem on a 85 3.2 we mechanically restored. Every time I’d park it in the sun, it wouldn’t start.
Replaced the ignition coil, and it hasn’t missed a beat since.

What lead you to the coil? No spark or was it leaking?

[DSPTurtle]

Originally Posted by Driven97

Does it crank and not start or does the starter not even try? My starter solenoid stopped working when hot recently, once it cooled off it was fine. I replaced the whole starter and no more issues.

Starter is brand new and works like a champ. It just cranks and cranks and cranks.

[DSPTurtle]

Originally Posted by 88911coupe

Also check the speed and reference sensors...they can fail sporadically...work one day, not the next. I think they are temp sensitive somewhat when the start to go bad. Use the BWM equivalent which is MUCH cheaper.

Sweet! Do you have a xref part number on the sensors? Thanks for the idea!

[McLaren-TAG]

Originally Posted by DSPTurtle

Sweet! Do you have a xref part number on the sensors? Thanks for the idea!

on the speed reference sensor, that's my guess as well. an easy way to check is to let the car cool off so where it does start fine. then heat up the metal around the area where the sensor sits and it should then not start.

[kmoush]

Check the CHT sensor. That was the solution to the exact same problem in my 86 3.2. You can test by jumping using a resistor in the plug located in engine bay at the left of the engine....see the Bentley manual for proper ohm for desired warm engine temp rage.

[GH85Carrera]

Originally Posted by RL technical

Just had the same problem on a 85 3.2 we mechanically restored. Every time I’d park it in the sun, it wouldn’t start.
Replaced the ignition coil, and it hasn’t missed a beat since.

If it is the original black Bosch coil it might be be leaking. If you need to replace it, it is a challenge to find a good coil. The new Bosch coil from Pelican, or even your local Porsche dealer is junk. Most aftermarket coils are not the right voltages and can cause your DME to have issues, or just not work anymore. The ultimate cure is find a good working 30+ year old black Bosch coil. The Brazilian made ones are just not good, even if you get them from Porsche direct.

[steely]

Originally Posted by DSPTurtle

Sweet! Do you have a xref part number on the sensors? Thanks for the idea!

12-14-1-708-619-M14 here at PP

[steely]

Originally Posted by DSPTurtle

Starter is brand new and works like a champ. It just cranks and cranks and cranks.

Do you have spark and fuel?

[DSPTurtle]

Originally Posted by steely

Do you have spark and fuel?

I think I have narrowed it down to no spark. The fuel pump is doing it's job perfectly. I pulled #3 last time I was able to replicate the problem and could not see a spark. Two new ref sensors are on order. I just don't want to replace parts until I can show a pattern of the no start condition as opposed to it being intermittent.

[JJ 911SC]

Originally Posted by DSPTurtle

I think I have narrowed it down to no spark...

To confirm, spray some "Quick Start" (ether or even brake cleaner) into the intake while cranking, no coughing = no spark.

PS: In Florida "Quick Start" might not be very popular but its good at -40...

[brujo65]

CHT check it out

[kmoush]

Forgot to mention on my earlier post (CHT). My warm no start issue was intermittent and when it occurred I only had to wait at least 30 to 45 min for it to cool down and it would start no problem.

[ischmitz]

I'd determine if you miss spark only or fuel and spark. If it's only spark it's pointing towards the coil of DME. If both are missing it's more likely one of both of the sensors.

Let us know what happens once the sensors are replaced.

Happy New Year,
Ingo

[DSPTurtle]

To close this out... I changed both sensors and reset the gap. So far, so good. It was odd that the car ran fine and everything worked normal except for when it was hot. The problem was repeatable after the car was up to temperature, shut down and then allowed to heat soak for 20-30 minutes.