Porsche Enthusiasts Club Forum

well after doing clutch etc over the past few months finally took her out for a test run and she broke down after @ 3 miles. Tow home - see earlier whinging post if your bored.
I've been trying to work out whats wrong on and off for the past few weeks. Did all the usuals DME relay etc. Bought a cheap oscilloscope on Ebay to measure the flywheel sensors. Speed sensor works lovely, nothing from the TDC sensor. Swapped them over to confirm dead TDC sensor. Still no output even with the "working" speed sensor. Adjusted sensor height as per Clarks Garage (really useful site) still no output. So decided to get a new pair of sensors incase they've lost some sensitivity. New pair arrive - (GSF) hurray!!!! stick them in still no output- what the ****!!!.

Nice sunny day today so try again. Connect 'scope direct to the new TDC sensor connector - maybe its a dodgy plug somewhere. Still no output. Hang on - the only ways thats possible is if the TDC grub screw that sticks out from the edge of the flywheel is missing - Not possible, it was there when I put everything back together and I haven't left any odd nuts and bolts in there either.

Turn engine over by hand and line up the TDC grub screw with the little viewing window at the back of the engine - there it is!. Hang on, no its not! thats a little shiny mark of whats left of the grub screw. Measure height with a long thin screwdriver - yes its been knocked off!

During the last mile of my test run, the back lane I was on had been resurfaced and still had a lot of loose stones. Didn't think anything of it at the time. However when I was disassembling the clutch etc, I noticed the rubber bung that blocks the clutch lever inspection hole was missing. Made a mental note to get a replacement soon as part of general tweaking and improving.
Today taken starter off - inside the clutch housing is a small stone that has removed my TDC grub screw.

So in the extremely unlikely possibility that this could happen to you - just have a quick check all your rubber bungs are in place underneath. Meanwhile I shall be mostly underneath my 944 taking the clutch and flywheel out again to repair it. In the words of Victor Meldrew "I don't bl**dy believe it".

that has got to be just about the most unlikely thing ever, what a pain in the ass big job too

Well spotted sir ... quite a bizarre cause as well.

It reminds me of my old Thema after it threw it's cambelt tensioner roller bearing ... after I'd replaced all 16 valves the car just wouldn't start - just cough splutter and repeat. What had happened was one of the bearing balls had shot down the front of the block and knocked off one of the crankshaft timing pegs on the ignition sensor, so what was happening was the ECU was counting pulses as normal, but 3 per rotation instead of 4.... hence it was firing once every rotations or something stupid like that. The next day I had a bump welded back on which I filed back to shape and resolved the problem ...

Glad you got yours sorted though...

G