hardtailer

Not entirely sure but I believe the thin vacuum line in the picture goes from FPR to the crossover tube to get the needed vacuum reference.

ermandadana

One thing that has been apparent is that my fuel economy has improved, I no longer get the overly rich fuel smell in between short starts...

saxonthebeach

Think you may be right on manifold location based on the below parts diagram, although I believe the vacuum line is hard plastic, not flexible as it looks in your pic (note this is for a 996TT):

theprf

The 6TT is rather different, it's got a mile of vacuum lines in there. At least on the 6TT the line is nylon with two rubber end pieces (that have a 928 part#!).

saxonthebeach

yes I may have hijacked this thread inappropriately. I am dealing with a 996TT, not sure about the other posters here.

theprf

I didn't realize you had a 6TT. Yes the vacuum line to the fpr is very important, much more so than on an NA car. Run lean under high boost and you'll ruin the engine.
Lots of us 6TT guys put zip ties on each vacuum fitting to prevent them coming disconnected.

saxonthebeach

Yes I’ve intentionally kept off boost until I can sort out this starting issue for this very reason.

saxonthebeach

An update here:

Completed @hardtailer ’s test- I can reliably get a hard start after sitting for 6-7 hrs, but if I activate the fuel pump 30 sec before starting in this same timeframe, the car starts up no problem. I think I’m to interpret this as a likely failure of the fuel pump check valve. I now believe I have a few concurrent, not necessarily related, problems:

- fuel pump check valve
- disconnected vacuum reference on FPR (confirmed by feeling around the FPR by hand)
- malfunctioning fuel level sending unit (completely by coincidence- I was intentionally running the fuel low knowing I would need to pull the pump to replace the check valve. I think I may have run it lower than it has gone in a while because now the fuel gauge is stuck on empty. Suspect the sender is probably stuck in place- at least I hope so since I’d prefer not to go out the $500 to replace it)
- failing SAI pump (whines at startup)

Planning to:
- Replace SAI pump (had been putting this off but now that I have FPR issues the opportunity has presented itself)
- Replace FPR and reattach vacuum line (I figure the FPR is annoying to access so may as well replace if I have to get to it anyways)
- replace fuel pump check valve
- repair / replace fuel level sending unit

FPR arrives Monday so I have a fun project ahead of me this week!

mccahey

Hi, I had a hard to start problem when hot, after about 45 minutes after shutdown. It started fine straight after shutdown and fine when cold.
I replaced the hard pipe between the Fuel Pressure Regulator and the intake plenum which had snapped while I was changing the fuel injectors. All fine now.

saxonthebeach

Thanks. Could be all tied to the FPR after all...I may hold off replacing the check valve until I test the FPR replacement. Although I do need to go into the gas tank to fix the level sender...

hardtailer

Thanks for posting the results of the test and happy to hear it made a difference in how it started.
The missing vacuum line is not as big a contributor as the non-functioning check valve, obviously, as the vacuum line wasn't attached in either scenario tested. The difference in starting behaviour can therefore be entirely attributed to the non-working check valve.

Nonetheless reattaching the vacuum line will improve things further.

theprf

You have the 996 Turbo?
I would leave the original FPR alone, unless you are sure it needs to be condemned. The new ones are not nearly as high quality. Do reconnect the vacuum hose though.
The fuel level only needs to be below 1/2 tank to completely expose the fuel pump. There is a check valve in the pump plumbing octopus nightmare, it's a little silver thing. Porsche does not sell the check valve separately, you'd need to buy the entire fuel pump assembly. There may be aftermarket check valves available that could replace just the check valve, this one was recommended:
https://www.finjector.com/eng/sytec_...a-p-733975-153
My fuel pump, which I had to take out at Lime Rock during a track day to fix:

Also if you run the fuel level below 1/2 tank then add a small amount of fuel the fuel level sender can't see that and the "fuel level" shown on the dash continues to decrease. When the fuel is below 1/2 tank the dash estimates remaining fuel based on consumption. This is because the fuel level sender can only read down to 1/2 tank due to the tank's internal design.


I's also possible for the sender to fall apart. I fixed this on my car a few weeks ago, write up is here:
https://rennlist.com/forums/996-turb...l#post18877453
And this is what the sender looks like.

saxonthebeach

Very helpful reply and answers what I believe are all my issues.

I just got done with the FPR / SAI pump job. Wish I had read this earlier as I ended up replacing the FPR and it doesn't appear to have made a difference whatsoever. I did note the one I removed had a made in Germany stamp, while the new one is made in Brazil. Gave me pause, but I replaced it anyways. Was annoying enough to get to I wasn't going to turn back then...figure a 20 year old German part vs a brand new Brazilian one has to be at least a fair trade? I will save the original in any event.

Interestingly the vacuum line was actually connected. The looseness I felt by hand earlier before getting eyes on it was due to the fact that the nylon line it attaches to is very lightweight and easy to move. I have no way to confirm the other end of the vacuum line is in place since I couldn't trace to where it attaches, but I have no other reason to believe it's detached for now.

Other than getting rid of the annoying SAI whine at startup, my repair work today doesn't seem to have solved much of anything. That said I think my answer is in the fuel tank. Other than the hard start, would you expect this check valve to cause any other performance issues?

hardtailer

Answer to your last question: no, nothing else

theprf

The other end is connected just to the left of the throttle body (left, while looking at the engine standing behind the car). It's behind the oil filter.