[edm]

Little help guys,

 

             1993 968 Cab Tip, cold start no problem, drives GREAT, here the problem starts once I drive non stop city, highway driving for approximately 45 minutes to 1 hour, I shut off the car, let it sit for 10 minutes and I try to start it HARD ENGINE STUMBLING occur to the point that you cannot drive it. Once parked overnight NO ISSUES, until you drive it again for at least 45 minutes, then I shut off the car and in 10 minutes I try to start the car, ENGINE STUMBLING AGAIN.

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[edm]

forgot to tell you that I just got it back from my mechanic and he replaced the fuel filter, cleaned throtle body and mass air flow sensor.

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[Waylander]

Replace the fuel non return valve in the fuel pump


If the fuel pressure drops to fast when the engine is hot, the fuel boils in the injectors and causes vapour lock, this will cause stumbling misfire lack of power, also be hard to start, but will clear after a few mins driving

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[edm]

Thank you for the quick response Waylander, I will pass it on to my mechanic when I bring it back tomorrow. MUCH APPRECIATED...

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[ds968]

Replace the fuel non return valve in the fuel pump


If the fuel pressure drops to fast when the engine is hot, the fuel boils in the injectors and causes vapour lock, this will cause stumbling misfire lack of power, also be hard to start, but will clear after a few mins driving

 

+ 1.    

 

( and  I would not have remembered this without Waylander’ s post, but that was also the case ( and solution ) with my tiptronic.

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[edm]

Thank You ds968 ....

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[ds968]

No absolute guarantee that’s the problem, there’s a bunch of other  things that can cause that , but at least this is one of the likely culprits .. 

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[Waylander]

And cheap, about $25 Goethe part

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[snova]

Little help guys,

 

             1993 968 Cab Tip, cold start no problem, drives GREAT, here the problem starts once I drive non stop city, highway driving for approximately 45 minutes to 1 hour, I shut off the car, let it sit for 10 minutes and I try to start it HARD ENGINE STUMBLING occur to the point that you cannot drive it. Once parked overnight NO ISSUES, until you drive it again for at least 45 minutes, then I shut off the car and in 10 minutes I try to start the car, ENGINE STUMBLING AGAIN.

I had something similar related to oil leaking past the spark plug seals.  Once the oil warmed up, it became thin  enough to pass through the aging seals.

Easy to check. 

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[edm]

THANK YOU ALL for thee help...

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[94SilverCab]

DME Relay...it's always the DME Relay....

 

Jay

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[ds968]

DME Relay...it's always the DME Relay....

 

Jay

Crap, forgot about that possibility .. all sorts of inconsistent and odd manifestations when the DME relay starts going bad .     Good news is that it’s not too expensive ( $ 80 nowadays , I think .. ?  ) and you always must keep a spare in the trunk or glove compartment anyway .. 

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[edm]

I replaced the DME relay ( I always keep a spare ) with the same results. My mechanic has it now and will change the non return valve on the fuel pump, we will see if this fixes the issue. Thank You and will update when replaced.

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[edm]

UPDATE....Replaced the fuel non return valve in the fuel pump as suggested by Waylander, to no avail, same issue, to make a long story short, the culprit was the MAF itself, after replacing, the car runs GREAT with no remnants of the HOT start issue. A BIG Thank You to all that contributed.

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[ds968]

Glad to hear the problem is solved.  It’s surprising to hear a bad MAF only had that one manifestation, I’d think it would cause more problems , at idle, on acceleration , etc.  

 

Once every couple of years I spray a little  CRC MAF Cleaner on the wires, not sure if it’s really necessary but my mechanic recommended I do that and after a couple of decades it’s still functioning very well, so I think I’ll just stick with that routine ..

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[edm]

funny you should say that Advocate, I cleaned it with CRC MAF cleaner 3 weeks before I had the issue, I also cleaned the throttle body with CRC throttle body cleaner the same time, I usually do this once a year. My mechanic only works on Posches, all models from a 356, all the way to a 959 and he said that was the 3rd 968 that had this issue since he opened many years ago.

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