Maddening Running Issue

[willbrown]

Hello DDKers,

Would love thoughts on a running issue I am having.

All ignition parts are new. Cold start and thermo switches all working.

Basically the engine would run fine then just die as if someone had taken the king lead off. This was traced to a bad live to the CDI box which was fixed and seemed to improve things. Then the fault came back, but rather than die completely the revs would just hunt like mad and wouldn't settle no matter how much throttle was applied. Car undrivable. Then I had what i thought was a Eureka moment and found the CDI earth was not attached, sorted that and it seemed to do the job. Then the fault came back and i realised the CDI earth was loose, so snugged that up and the last time i drove the car in Autumn it was OK. That was wishful thinking as I've just spent over an hour trying to get it to run and no joy. Same symptoms (see vide link below). It's not the CDI as Gav P kindly lent me his which is known to be fine and i got exactly the same result. It's not injector spray patterns as the engine is basically new and all of that was done during the rebuild at Greatworth. So what do you think?? Gav suggested it might be the MFI internals sticking which seems 100% plausible. Any thoughts?

https://youtu.be/nscI2dDoXeU?si=Qkyvwr3AS8zC1HaJ note this is at constant throttle positions trying everything from part open to fully open. i am not pumping the throttle as it sounds!

Your wisdom as usual much appreciated.

Will

[Bruce M]

First test is always the same.

Spray something flammable into the intake (brake cleaner, Ezi-start, etc) and see if it runs better. Which answers the question of a fuel problem or not.

[willbrown]

Thanks Bruce. I can hear the cold start dropping neat fuel into the intakes so I don’t think that’s the issue.


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[hot66]

any black smoke ?

have you checked your rotor arm and cap

[willbrown]

No black smoke - checked rotor arm and cap. Both new.


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[Bruce M]

Thanks Bruce. I can hear the cold start dropping neat fuel into the intakes so I don’t think that’s the issue.


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The exhaust smelling of unburnt fuel should confirm that. I like to use the brake cleaner test because I might hear the injectors ticking but that doesn’t mean there is fuel coming out. It’s a simple baseline check that can eliminate a lot of distractions & validate assumptions.

[stretch]

How long has this been happening in relation to the engine re-build.? Are you getting enough fuel delivery to the MFI pump.? There's a 30 second test you can do on the fuel feed from the console to the pump which is in the workshop manual. I would work back from the MFI pump as it sounds like fuel starvation in the video.

[willbrown]

How long has this been happening in relation to the engine re-build.? Are you getting enough fuel delivery to the MFI pump.? There's a 30 second test you can do on the fuel feed from the console to the pump which is in the workshop manual. I would work back from the MFI pump as it sounds like fuel starvation in the video.

thanks stretch appreciate it - it ran fine after rebuild for about 6 months and then its been intermittent since then. since i'm pretty sure its not spark - it definitely feels like fuel starvation. do you know if that test detailed in the check measure adjust MFI docs or is it just in the workshop manual?

[Lightweight_911]

.

What is the internal condition of the fuel tank like - any rust which might be restricting the outlet ?

.

[satan]

Hi,

Have you checked points? I had similar but not exactly the same and my points had gone out of adjustment.

[willbrown]

How long has this been happening in relation to the engine re-build.? Are you getting enough fuel delivery to the MFI pump.? There's a 30 second test you can do on the fuel feed from the console to the pump which is in the workshop manual. I would work back from the MFI pump as it sounds like fuel starvation in the video.

thanks stretch appreciate it - it ran fine after rebuild for about 6 months and then its been intermittent since then. since i'm pretty sure its not spark - it definitely feels like fuel starvation. do you know if that test detailed in the check measure adjust MFI docs or is it just in the workshop manual?

I remember now that Grady Clay was an oracle on MFI stuff and his posts on Pelican are comprehensive. This appears to show where to measure fuel pressure and the correct plumbing for the fuel lines which were incorrectly shown in the workshop manual (apparently!)

https://forums.pelicanparts.com/porsche ... ost4302598

[willbrown]

.

What is the internal condition of the fuel tank like - any rust which might be restricting the outlet ?

.

thanks, andy. that is an unknown - will put it on the list.

[willbrown]

Hi,

Have you checked points? I had similar but not exactly the same and my points had gone out of adjustment.

points new and not long since run-in service at Greatworth so my thought was unlikely to be points, but ill get a gauge on them to be sure.

[stretch]

I remember now that Grady Clay was an oracle on MFI stuff and his posts on Pelican are comprehensive. This appears to show where to measure fuel pressure and the correct plumbing for the fuel lines which were incorrectly shown in the workshop manual (apparently!)

https://forums.pelicanparts.com/porsche ... ost4302598
[/quote]


This post gives you the test requirements. Get your other half to crank it over for 30 seconds. https://forums.pelicanparts.com/porsche ... ssure.html

If your not getting the required delivery, the next place to look is the check valve in the Fuel filter console. Hope it's not this as the part was nearly £100 quid from Porsche. This was the problem with mine. If all is well next check will be the fuel pump.

[willbrown]

[/quote]
This post gives you the test requirements. Get your other half to crank it over for 30 seconds. https://forums.pelicanparts.com/porsche ... ssure.html

If your not getting the required delivery, the next place to look is the check valve in the Fuel filter console. Hope it's not this as the part was nearly £100 quid from Porsche. This was the problem with mine. If all is well next check will be the fuel pump.
[/quote]

super helpful, thank you. will give that a whirl.