Engine failure

[Rawbert]

New to the post so pardon any omission with protocol. I live in Jamaica and there are few mechanics with experience working on Porsches. I recently acquired a 1983 911 Sc and while exiting the highway the engine quit. After second attempt engine restarted and mechanic said he changed a fuse and gas pump relay to resolve About 3 weeks after engine quit and restarted after about half an hour. Drove for about a mile and then quit again. Called wrecker and it's now at garage where mechanic said he is checking ignition system (module). My only concern and not sure if related is car also has a "flapping" not quite misfire or popping coming from exhaust after changing gears out with rev building up for another gear change. Almost like an exhaust or gasket leak though muffler shop said no leak detected (by putting hand over exhaust). Prior owner said sound came after he installed after market bursch exhaust. Just curious on both points as I await my mechanics diagnosis on both which could take some time as parts have to be ordered overseas he doesn't want to take any chances until his diagnosis is more absolute. Know it's like calling up your doctor on the phone with your ailment but would appreciate any pointers.

[47silver]

first thing i would check is your air box. did you ahve a backfire?
then i would check ignition: check for spark at the plug with spark tester.
if you dont have spark then you have to examine each component to determine why,, if you have spark then
check for fuel pressure with a fuel pressure gauge.
if you have fuel pressure then
check for compression or leak down.
have to do it methodically so you can slowly eliminate each problem..

[Rawbert]

Appreciated. There was no pop or backfire prior to shut down engine running and then quits. Will perform the elimination test as you suggested.

[tirwin]

Let's talk about the "flapping" sound. If you take off the air box cover do you see something like this installed? It looks like the flapper valve in a toilet.



Problems with the engine cutting out are not uncommon. There are unite a few possible problem sources but diagnosis starts with figuring out whether it is fuel delivery or spark related.

[fred cook]

If you haven't done so already, remove the lower rocker covers and check for broken cylinder head studs. Broken studs are very common in these engines. If you are unfortunate enough to have two studs broken on one cylinder, compression gasses can cause the cylinder head to "flap". In this case, continuing to run the engine can cause damage to the cylinder head and cylinder. Good luck getting your car sorted out!

[Rawbert]

Appreciated. Have the head studs on my list as well. Will advise of the final diagnosis

[Bob Kontak]

Originally Posted by Rawbert

After second attempt engine restarted and mechanic said he changed a fuse and gas pump relay to resolve About 3 weeks after engine quit and restarted after about half an hour. Drove for about a mile and then quit again.

It is common for the female relay socket connection to get loose. A little motion and the legs on the round fuel pump relay do not touch the side walls of the female socket tube or the relay slides out a little dropping the connection.

You can fix this yourself. Get a single edged razor blade and slide it down into the slots of the red relay legs. Even if it's brand new. Just slightly open them up with a small amount of sideways stress applied by the razor blade. All you need is the size of a human hair bigger to assist.

May not be the problem but it's inexpensive and fast. My car has died several times because the relay just slowly vibrated out of the socket.

Can you describe the "flapping" noise differently. Does it happen at idle or only when shifting?

[Rawbert]

Thanks Bob. Flapping in exhaust doesn't occur when idling. Happens when I am going from low revs to high and more common when the engine is more settled in third gear and shifting to fourth. Not a loud irregular popping but Ana almost "fluttering" sound that similar to when the exhaust pan has a hole. My mechanic believes it could be connected to the Ignition relay or cd box being bad.

[Rawbert]

Mechanic narrowed problem to CD Box. Switched out on another car and didn't work. Bought refurbished box and car started and ran after a few turns. Car ran for about 10 minutes and then revs started falling and car shut down. Ignition module got hot. After allowing to cool car restarted and then died after about 10 minutes. Engine didn't just stop immediately but started losing revs then slight popping then shut out.

[timmy2]

Sounds like the refurbished box needs more refurbishing...

[Rawbert]

Any recommendations on a reliable supplier for refurbished boxes. This is the second one I am sending back. I take that bosch doesnt sell this part new ? Appreciated

[Targalid]

Sounds to me like a plugged fuel filter. This is inexpensive to replace and explains many of your symptoms. A plugged filter will allow the car to start and run for short periods before the engine shuts down from fuel starvation.

[john walker's workshop]

silver coil or original black? silvers have issues.

[Bob Kontak]

Originally Posted by Targalid

Sounds to me like a plugged fuel filter. This is inexpensive to replace and explains many of your symptoms. A plugged filter will allow the car to start and run for short periods before the engine shuts down from fuel starvation.

I would try the fuel filter. Can you tell where the popping is coming from? Exhaust or airbox? Popping can indicate lean and occurs through the intake normally.

Regarding my previous post about the fuel pump relay, when mine disconnected, it died pretty quick. Also, I don't think you have an ignition relay.

There is a member hear named lorenfb. He fixes boxes. If you find his older posts I believe he has a website linked. If you read the threads he likes to argue a little and folks like to argue with him. However, in the years I have been here, I have never read one unfavorable word about his work.