Barn996

That makes sense. My bad.

choogenboom

see my post above - problem is now isolated to the fuel pump/hoses/valves etc INSIDE the fuel tank.

re diagram - there are parts blow ups on the porsche usa web site but they are not enough as they are (1) missing some of the part names (ie there are numbers on the exploded view but now corresponding part number/name) and (2) the names are not adequate to divine the part function in all cases. Shop manual would be helpful. Note that porsche's we site does not specifically have a 996/C4 so had to go to 996 turbo to see what my fuel tank looks like, assume its the same as the C4.

re OBD codes - my reader is in my volvo which is currently parked at the airport - my wife took it. I doubt there would be any codes other than perhaps low fuel pressure assuming ther system has a fuel pressure sensor. Like I said above, fuel pump is unable to pump tank below about 50% level after which a hose from pump seems to be blowing bubbles in the tank. I think the pump must have a pressure relief valve which is faulty OR the pump sucks air when it gets below a certain level. Anyone ever had a similar problem?

Chris

Macster

Good job of checking pump action all the way down! I don't think I would have thought to be that thorough.

Suspect fuel intake hose/line has crack/split and the bubbling sound is air being sucked into fuel pump through crack/split in hose as level of gas gets to crack/split. If any air getting to pump it will make noises too.

Time to carefully remove fuel pump/filter assembly and inspect it and associated hoses/lines for any cracks, loose connections, etc.

I believe once you get unit out of tank source of problem will be obvious on inspection of assembly.

Sincerely,

Macster.

RAC

I had my C4 that died on me and would not start. Seemed like it was the fuel pump but was not. Turned out to be (can not remember the correct name) a fuel pick up jet, or something like that.

choogenboom

thanks Macster, RAC. Next step will be to pull the guts out of the fuel tank. I have to say I was expecting, when I opened up the tank, to see just the pump with 2 hoses one each to a high pressure side and a low pressure return. I was not happy to see a veritable rat's nest maze of tubes with, so far, unexplained functionality. Fortunately I have 4 children (9, 7, 4, and 2 months) so much like a socket set I should have just the right sized set of hands to get the stuff out of the tank Its _tight_ in there!

Chris

htny

That's too funny, here's hoping those kids are metric !

Out of curiosity, was your fuel level below the level of the pump when the motor stumbled initially (i.e. before you pumped out the fuel to isolate the problem?)

I'm trying t find the diagram and the pressure specs

htny

OK my apologies if you already have the info:

Actuate Fuel Pump
A) With PST2
B) or via fuel pump relay
Disconnect fuel pump relay from central electrical board and bridge contacts 30 and 87 (identified as 3 and 5 on board) with a fused shop made cable

Nominal Test Values
Stationary engine 3.8 +/- 0.2 bar
Engine Idling 3.3 +/- 0.2 bar

Flow Test from fuel return line should be 850cc / 30 seconds

PM me your email address if you want this section of the shop manual and don't have it

Best,
Hans

choogenboom

When motor died initially on freeway fuel guage was at 31 miles left so assuming about 1.5 gallons give or take. It will now not pump out below about 7 gallons, so guessing that the failure on the freeway was not gradual but more a falling off a cliff type failure - ie a hose came off a fitting, a hose burst etc. That the pump runs dry and blows bubbles inside the tank with the fuel level right at the top of the pump module is mighty suspicious - going in for a deeper look now.

Chris

choogenboom

I am a little worried I might be jumping to conclusions in that normally the fuel delivery system is closed - the pump pumps high pressure to the rails and whats not used is returned at low pressure to the tank. Right now for my tests I have an open system - ie the return line is open and disconnected so possible the pump is sucking air from it? In other words, is my test methodology valid, is the data point that I cant pump past 1/2 full valid, and the conclusion there is a problem in the tank with the plumbing valid?

Chris

savannah996

i think you are getting ahead of yourself and i hate to see you tearing your p car apart.

1. check for codes
2. do a fuel pressure test with ignition on, engine off.
3. good fuel pressure? check condition of plugs/color.
got to run--for now. will check back in later.

choogenboom

If pump supply/pickup hose (assuming there is one, I have yet to dissassemble) were to be loose that fits the clue that the pump quits pumping at 50% full but guessing that engine should run up to that point and it does not run at any level of tank fullness.

htny

Chris,

I agree exactly on this basis (reason for my seemingly stupid questions, just hoping to encourage you to take a step back and slow down!).

I would do this methodically even if it feels elementary and painful, just because the modern electronically controlled Porsche relies on so many feedback loops and signals and gadgets to run. First pull "pending" codes from computer (i.e. those that haven't hit the CEL threshold, but have been logged), and in the absence of any codes for guidance test all air (maf, throttle, ICV if applicable, the works), then basic electrical, then all fuel (starting at gas cap, then sender etc. before going to areas that require replacement parts just for testing)

I emailed you the manual chapter, let me know if you don't get it.

Hans

choogenboom

great pictures of 996/4 fuel tank - now I can see what I am dealing with ...

http://www.6speedonline.com/forums/9...-pictures.html

relevant quote from the link above

"It seems that one of the fuel pressure failure can be on those venturi tubes, if one fail, all fuel pressure goes to that pipe and back to the fuel tank and you get almost no pressure to the injectors. So it is a good time to inspect them if you remove your fuel pump from the tank."

Given I am getting bubbles blowing from the passenger side venturi tube, and RAC's comment about his car dying due to a failed "fuel pick up jet" I think thats the component I'll focus on.

htny

Also, from what I remember C4/TT tanks are only like 1/3 of a gallon smaller than C2, that front drive is pretty compact I guess!

htny

thats a great post, beats the heck out of the diagrams! keep us posted, and good luck!

-Hans