Wondering if anyone (especially JDS Porsche) can advise me on the following, : I have an intermittent problem where my engine can cut out suddenly after startup or whilst driving at slow speed (low revs). It appears to lose all power to the instrument cluster gauges but if i switch off ignition and immediately restart in neutral, the engine fires again immediately. I would be most grateful for any advice which would help me diagnose the problem and how to sort it.

Generally, the car drives like a dream otherwise. I have spent the last year having engine etc fully restored, but my mechanic admits to not being up to advanced electrical fault diagnosis.

 

first place I would start is the battery,
Clean all of the connections,
if your ground cable is original now is the time to replace it,
also replace the running relays and the fuel pump fuse,,
best to also do a CE panel cleaning, and clean the 14 pin connector at the jump post
make sure to use Deoxit

 

Thanks Stan, you are always one of the first to offer advice and I thank you for that. Thanks also to John Speake from whom I had similar advice by email and I have therefore done as you both suggested, starting at the battery terminals and then going on to relace the x-relay, ignition relay, fuel pump relay and injectors relay and fingers crossed, so far I havent had the problem recur. I probably need to give it a week though to be absolutely sure that the problem is fixed. You are two great Rennlisters !!!

 

make sure to replace the fuel pump fuse with a new fuse and make sure the fuse is gripped tightly in the holder

 

Yes Stan, I also replaced the fuel pump fuse also but unfortunately, I still have this intermittent stalling problem. Could it be anything to do with the MAF or ECU I wonder. The fuel injection system is LH-Jetronic and I have installed Greg Brown's adapters using the 24lb injectors. Apart from this intermittent cutting out, the car is driving and accelerating really well.

 

Just a guesstimate but this issue sounds most likely to be related to an issue at the jump post, so I would pay extra attention there.

 

Is it possible that the problem might be in the ignition switch?

That's only a guess based on your observation that, "It appears to lose all power to the instrument cluster gauges but if i switch off ignition and immediately restart in neutral, the engine fires again immediately."

 

Thanks for suggestions. I still have this problem after changing relays, fuel pump fuse and cleaning jump post and battery terminals. Today whilst driving at about 45mph the engine cut out again. The car is automatic and all power to the instrument cluster was cut. I quickly turned the key off and on again, the cluster gauges came back to life and the engine fired immediately without having to use the starter. It is as if a phantom is turning off the ignition whilst driving !!
I am expecting a new battery ground strap to arrive tomorrow but I have my doubts as to whether that can solve the problem. Is it possible that the ignition modules part no. 928 602 706 01 (Bosch p/n. 0 227 100 124) could need replacing ? Be very grateful for your thoughts.

 

mdkelly1 asked about your ignition switch. Have you replaced this already?

 

I'm not sure what is the part number for the switch he refers to. Ive been looking at the rennlist "how to re ignition switch". It says part number for all models is 928 613 017 01 but on searching for this number in the pet for my MY 1985 28/22, it is not listed.

 

Think Ive found the correct part number now 964 613 012 00 , but do people agree that this might cure my problem ? Should I also look to replace ignition modules as mentioned previously ?

 

Yes - for your symptoms as described (especially the "fix") I'd say the ignition switch is the most likely cause by far.

Next time it happens - just wiggle the key in the switch without switching it off...

Get a good quality switch from a known vendor. You do not need to mess with the ignition key barrel - the ignition switch electrical part just bolts on the back of the lock part and the wiring connector just pulls off.

Alan

 

There is enough room if you put the steering column all the way up to undo the connector at the back of the switch just pops off and pull the harness down enough to plug in another electrical switch which you turn with a Philips screw driver..... that way you can test to be sure it is the switch before you pull off the steering wheel and pod to see the two screws which hold the switch to the back of the ignition lock and they are tough to get to

 

Bad crank position sensor and/or wiring to same will cause this. Ask me how I know. . . Anyway try idling the car while playing with the cable to the CPS. If you can make it die that way, then you know. . .

 

In this case since a CPS issue cannot cut power to the Pod it's not really consistent with the symptoms listed...

For a CPS issue turning the ignition on & off (while still moving) would not likely change things much... but since here manipulating the ignition switch already makes the issue resolve - while coasting after it dies... I think the most likely by far is the ignition switch.

John - If you can further determine that just wiggling the key can restore running - that would be more definitive still.

Alan