MFI troubleshooting - high idle, pops and bucks at part throttle

[Arne2]

Originally Posted by Jonny042

So without reading 13 pages of posts, the short version of the story is you didn't check the fuel pressure at the MFI pump head?

Yes, the fuel pressure was checked at several spots early in the process. But results were inconsistent, which was part of the puzzle.

Apparently, one (or more) of the early service docs from Porsche for MFI cars have a diagram of fuel line routing that was wrong, and that erroneous diagram was picked up early on by other publishers, and so it lives on in some older 3rd party manuals (like the Haynes I have). I had "verified" the "correct" hose routings very early in the process using the bad data. This bad info was pointed out to me by Mark Jung (MFI Werks, 356RS ).

[tobluforu]

Originally Posted by Arne2

Yes, the fuel pressure was checked at several spots early in the process. But results were inconsistent, which was part of the puzzle.

Apparently, one (or more) of the early service docs from Porsche for MFI cars have a diagram of fuel line routing that was wrong, and that erroneous diagram was picked up early on by other publishers, and so it lives on in some older 3rd party manuals (like the Haynes I have). I had "verified" the "correct" hose routings very early in the process using the bad data. This bad info was pointed out to me by Mark Jung (MFI Werks, 356RS ).

OMG,. back when you started this thread I was going to ask if you setup the fuel lines in regards to that diagram which is wrong. But decided not to because to sounded like you had done your due diligence already.
Don't you love those easy fixes?

[cmcfaul]

I would run a can of Techron or something similar through it now. Prob sucked dirt out of the fuel filter and into the engine / injectors.

Its a common mistake. Did it myself once.

Chris

73 E

[Jonny042]

Originally Posted by Arne2

Yes, the fuel pressure was checked at several spots early in the process. But results were inconsistent, which was part of the puzzle.

Apparently, one (or more) of the early service docs from Porsche for MFI cars have a diagram of fuel line routing that was wrong, and that erroneous diagram was picked up early on by other publishers, and so it lives on in some older 3rd party manuals (like the Haynes I have). I had "verified" the "correct" hose routings very early in the process using the bad data. This bad info was pointed out to me by Mark Jung (MFI Werks, 356RS ).

Oh my. What a pain.

For me, there's no replacement for understanding how something works, so you can just look at it and verify that it's assembled/adjusted/connected/working correctly, so you don't have to rely on 50 year old documentation that may not be correct.

In the case of the fuel filter console, how it functions is not immediately apparent. It's actually a pretty wondrous little bit of clever engineering, but I didn't understand exactly how it worked until I had one on my MFI test stand, flowing fuel, with clear hoses.

Posts #453 & 454 of my build thread is titled "Mysteries of the fuel filter console - revealed!" which sounds pretty dramatic but I had not seen anything explaining how it works before:

Project Heavy Metal - an all steel classic, remastered

Project Heavy Metal - an all steel classic, remastered

It's worth a read. I've been meaning to post the text and pics in the MFI resources thread.