still misfiring

[Guest]

I've had an intermittent misfire with my 1988 3.2, for the last year, and still can not find the problem!

The car has been to both official and specialist porsche centres, but they just tell me the co2 is out, richen the mixture and claim to have fixed the fault. The car then runs OK if used every day, however if left for a period of time, say 2 weeks, then the misfire is back !

Completely frustrated, I paid my local porsche centre, to complete a full system diagnostic and they found nothing wrong! I have noticed that the problem sometimes goes away if I drive the car for 40 ish miles on the motorway at a constant speed. It also sometimes disappears if the car has been run for a day, then left for approx. 1 hr. and then restarted.

Based upon the above and assuming that I can rule of an electrical fault, I am wondering if it could be fuel starvation - anybody had a similar experience.

Does the 3.2 have a fuel pressure regulator / does anyone know how to check the pump ?

Thanks,

Scott

 

[Guest]

It might seem obvious, but are you sure it isn't a dodgy HT lead or connector, or distributor (or electronic ignition equivalent).
Arcing through the plastic due to damp or a carbon track being built up, might explin what you see. The OPC using a dry warm evironment might not see it, similarly when it is used regularly.
Try running it in the dark when it is happening and look in the engine bay, if you can see round the ducts, fan, etc. You may be able to see some arcing somewhere (look for a blue flash). (I solved a problem on a 1.8 Nissan Stanza this way once - not quite so glamorous, I'll admit).
It's worth a try and won't cost anything.

 

[bones]

Following on from Stuart's comments a light spraying with water (from a plant spraying bottle) at night with the engine running would show clearly any electrical arcing in the engine bay. It has all the annoying signs of an intermitent electrical fault. One other thing I would do next time this happens is to pull the plugs you should then at least be able to spot if it is one specific cylinder is causing the problem or all of them. Keep us posted.