Mystery misfire on cylinder 1

[Simon P]

Hi,
I have a mystery 993 C2 misfire, with cylinder 1 not igniting the fuel going into it. Started to slightly lose power when out for a drive recently and then suddenly got dramatically worse with unburnt fuel igniting in the exhaust. V scary! Got trailered to the Porsche centre. Technician has replaced the distributor heads, checked the plug leads including changing them round, good spark in all cylinders, fuel flowing correctly and borescope showed cylinder 1 in perfect condition with valves working normally. Timing was spot on and the small. drive belt between the primary and secondary distributor was fine. HELP! Any suggestions v welcome on other things to check!
S

 

[IndischRot]

Hi,
I have a mystery 993 C2 misfire, with cylinder 1 not igniting the fuel going into it. Started to slightly lose power when out for a drive recently and then suddenly got dramatically worse with unburnt fuel igniting in the exhaust. V scary! Got trailered to the Porsche centre. Technician has replaced the distributor heads, checked the plug leads including changing them round, good spark in all cylinders, fuel flowing correctly and borescope showed cylinder 1 in perfect condition with valves working normally. Timing was spot on and the small. drive belt between the primary and secondary distributor was fine. HELP! Any suggestions v welcome on other things to check!
S

An engine needs spark (at the right time), fuel and compression to run. Sounds like the spark is OK and the fuel is OK. I would do a compression and/or leakdown test to make sure there is nothing amiss with the valvetrain or rings on cylinder 1.

 

[993C2EX]

Christian Sanger previously looked at my car, a C2, and said that one of my HT leads was breaking down when hot. One runs very close to the exhaust manifold I think.
also there are two spark plugs and leads per cylinder not just the usual one and so if you have no spark at all rather than only one spark then either both leads might be heat damaged or it a fault further back at the distributor.
im no expert, just sharing that thought.
best of luck

 

[MoC2S]

Given the process you've already been through, the problem sounds like an injector sticking open.

Assuming that it has not escaped the engine wiring loom recall somehow, if eligible - that can certainly generate this sort of thing.

HTH, cheers, Maurice

 

[IndischRot]

That is a good shout and worth checking. But the OPC technician should have spotted plugs that were wet with fuel, perhaps even dripping with it.

IMHO find a good indie that knows the air cooled cars and can do old school diagnostics that don’t rely on a computer.

 

[Simon P]

Thanks for these thoughts. Plug is getting wet with fuel. They have switched injectors round and still not solved the problem.. Now think it is the DME which is horrendously expensive! Is it possible to get lower cost replacements or repairs?

 

[IndischRot]

Have they checked that the wiring harness recall has been done?

 

[Simon P]

Forgot to close this by telling people it was the DME. I sent it off to a DME refurb place near Birmingham to try and get it repaired but unsuccessfully. This only succeeded in putting clouds of smoke into Porsche Centre Sheffield when it was returned and refitted. Fortunately the refurb people gave me my money back! In the end I had to get a new DME from Porsche, so I am now much poorer but at least the 993 is now fighting fit again. Sheffield Porsche were excellent by the way. They were really fair with the bill and got me a decent discount on the part.