924Board.org

[Porver9two4]

Porsche brothers... I need help! I cannot get my 924 to run and am officially stumped.

THE PROBLEM:- My 924 is over-fueling. Catastrophically. To the point of hydraulic-lock. Needless to say, it won't start. The question is why has it suddenly started to over-fuel?

THE BACKGROUND:- I hadn't used my 924 for about 5 years. It had always been a good runner and starter. Following its slumber it was very difficult to start - the fuel had gone off, and once drained and refreshed with new petrol all was well. Hooray! It was driven into the garage for a full brake overhaul - new hard and soft lines, new slaves, full strip and rebuild and had lots of other love at the same time - new wheel bearings etc. - which took about 3 weeks to complete. Once complete I jumped in to drive it out of the garage again but it refused to start, refused to even fire...... which was odd.....

TROUBLESHOOTING SO FAR:- Initially I logically assumed it was no spark. Spark checked and confirmed as healthy - not that. Pulled out the plugs - all drenched in petrol - plugs cleaned, dried and cylinders left open overnight.
Next day, try again - still no start, not even a stutter, no firing at all. Pulled plugs again, all drenched in petrol. Spin engine on starter, petrol spewing out of plug holes. Its massively over-fueling. Assume 5th injector stuck open - check that (nope, fine) and disconnect electrical plug to avoid compounding issue.... Check airflow meter - plate moving freely. Reassemble everything and try again - still no firing, plugs still drenched.
So I have to suspect metering head - pull airflow assy. off and find, to my deep joy, that the piston in the metering head is sticky - AHA! Eureka, it must be that. Remove metering head to free piston (Polished with 1500grit wet & dry) and strip metering head to check for contamination. All as clean as a whistle and in good order - happy days. Carefully reassemble ensuring correct orientation of sandwich plate and ensuring fuel pressure regulating valve all free etc.
Reassemble to air flow meter and check piston operation with flap - all good. Reassemble to car confident it will now burst into life. Turn it over on the starter.... spins over but nothing, not even a firing before EUGHHHHH.... hydraulic lock! Remove plugs (all drenched), spin on starter and petrol geezers out of plug holes....
Assume I must have made a mistake on reassembly of metering head so strip off and strip down again to verify - nope all spot on. All assembled correctly, all o-rings fine, fuel pressure regulator working fine... nothing wrong. Reassemble to car, try again - still no firing and then hydraulic lock again.
Check fuel return line to tank isn't clogged - confirm all OK.
Check piston on metering head the right way up - confirm all OK.
Check WUR not clogged - confirm all OK (even though I knew this couldn't really be the problem, just going through all the components).
Check inlet manifold not blocked somehow - confirm all OK.
I have literally gone through everything each at least twice trying to get to the bottom of this and IT STILL WON'T START and is STILL catastrophically over-fueling..... I now have about 2 litres of fuel in the engine oil as an added bonus where it has washed past the rings.....

Can anybody suggest ANYTHING that might help..... I am at the point where I am stumped.

As I understand it, there is no way fuel can be reaching the injectors other than through the metering head via the metering slots as they are revealed by the movement of the piston, acted upon by the air flow meter flap. So how in the name of Ferry Porsche can a car that was driven into a garage 3 weeks ago with mechanical fuel injection spontaneously find itself defying the laws of physics and mechanical engineering?????

[daniel]

Did you renew the orings in the fuel distributor? Do you have a CIS pressure tester? If not get one, they are invaluable in chasing down these sorts of issues.

Also, all because you have disconnected power to the cold start injector does not mean it isnt still leaking fuel. Remove it from the inlet manifold and crank the engine, do the same with the 4 mechanical injectors. Be 100% certain where the fuel is coming from.

My guess is either cold start injector is leaking or the fuel distributor is leaking due to bad seals or worn out piston/bore or sticking piston.
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Over the top of skyline, total brake failure.... hit the wall at over 200 kp/h at the dipper, so anyone who has to brake for the esses is a pussy.
1977.5 Race Car, CAMS Group S Spec
1989 944 Cabriolet