Starting issues

[gbstu]

I've been having a tough time starting the car since changing the primary pump last month. The engine will not start unless I put my foot on the gas and also takes "longer" to start, sometimes it will not start during the initial cycle but will always start the next cycle.

I've also changed the fuel filter and purge valve (948-110-202-01) since replacing primary pump.

I'm at a loss to what the problem is. Any ideas?

Thx, Stu

[deilenberger]

Stu,

Do you have a fuel pressure gauge kit? It would be interesting to see what the retained fuel pressure is. Had a problem like this on my '06 when I got it. The former owner had it to a dealer several times, who couldn't figure it out. I bought a $29.95 fuel-pressure test kit from Harbor Freight, screws right onto the fitting on the fuel rail, that showed pressure dropping immediately on shutting the engine down. The system is supposed to retain pressure up to I think several hours so there is pressure to start the beast.

After the new dealer was presented with the problem - both pumps got replaced (didn't help), the pressure regulator was replaced (didn't help) and finally the fuel filter assembly, which apparently has a check valve in it that wasn't sealing. It could be that part, or one of the other check valves in the system isn't sealing, or your hoses between the pumps and other components in the tank have a leak, allowing pressure to bleed down.

A fuel pressure test will tell you if this is the problem, and $29.95 is a lot cheaper then throwing parts at it hoping they'll fix it.

BTW - knowing the year/model/engine of your P!G would probably make it more likely to get an intelligent answer.. just a thought..

[ekstroemtj]

Stu, Do you have a fuel pressure gauge kit? It would be interesting to see what the retained fuel pressure is. Had a problem like this on my '06 when I got it. The former owner had it to a dealer several times, who couldn't figure it out. I bought a $29.95 fuel-pressure test kit from Harbor Freight, screws right onto the fitting on the fuel rail, that showed pressure dropping immediately on shutting the engine down. The system is supposed to retain pressure up to I think several hours so there is pressure to start the beast. After the new dealer was presented with the problem - both pumps got replaced (didn't help), the pressure regulator was replaced (didn't help) and finally the fuel filter assembly, which apparently has a check valve in it that wasn't sealing. It could be that part, or one of the other check valves in the system isn't sealing, or your hoses between the pumps and other components in the tank have a leak, allowing pressure to bleed down. A fuel pressure test will tell you if this is the problem, and $29.95 is a lot cheaper then throwing parts at it hoping they'll fix it. BTW - knowing the year/model/engine of your P!G would probably make it more likely to get an intelligent answer.. just a thought..

Great how you discover this !!!!

[gbstu]

That is interesting, I actually have that Harbor Frieght guage and use it on my old 911.

My Cayenne is a 2005 Turbo.

Thx again

[gbstu]

Measured the fuel pressure today.

It was about 55psi when running, however, as soon as I shut the engine down the pressure drops to zero (the gauge was NOT leaking).

As I mentioned before, the primary pump, fuel filter and purge valve have been changed.

Any thoughts?

Thx, stu

[bigbuzuki]

Sounds like you may have to inspect and confirm the disturbed plumbing inside the tank whilst changing the filter has indeed been installed securely.

There is no "primary" pump on the vehicle.

It's either left or right.

With the activation of drivers outer door handle - left pump primes fuel rail.

starting procedure: left and right pumps on

Fuel tank qty >60 L

right pump on

full load: left and right pumps on.

Fuel tank qty < 60 L

left pump on.

full load: left and right pumps on.

[gbstu]

It was the left pump that was changed....i also think it was the independant that failed to install correctly or broke a line.

Thx, stu

[coleta]

bigbuzuki, can you give the reference on where you got the info on the pump operation? I'd like to read more.

[bigbuzuki]

bigbuzuki, can you give the reference on where you got the info on the pump operation? I'd like to read more.

Publication is called Service Information Technik.Note, pump operation is for non DFI engines, the DFI operation is similar with a few extra parameters included.

[deilenberger]

There are lots of check valves in the fuel system, not all of them documented. There is a check valve in the fuel-pressure-regulator (basically the regulator functions as a check valve), plus one in the fuel filter (not documented by Porsche, but it was what caused my problem.)

Porsche also added an elbow to the fuel filter to eliminate a leak caused by a sharp bend of one of the plastic internal pipes hooking up to the filter. I believe it was the port side pump..

Also as bigbuzuki said - it could be a leak internal to the tank plumbing, Lots of lines and lots of connectors in there.

Here is the info on the elbow:

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955 620 911 00 angled pipe

see technical information service group 2 KD-NR.2066 13/10

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If you're a paid member here I believe you can look up that service bulletin.

Here are the fuel test specifications:

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Switch on both fuel pumps using the adapter P 9479 and read the pressure on the pressure gauge. The fuel pressure should be approx. 4.0 bar. Then switch off both fuel pumps and check the steady-state pressure. The fuel pressure must not drop below 3.0 bar after 10 minutes.

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You don't need adapter P-9479. You can power on the pumps by starting the engine. To power on a specific pump, pull the fuse for the other pump from the underhood fuse box. The pump that still has power will automatically be switched to. Obviously your P!G failed the pressure-drop test.

Attached is a diagram I found helpful in understanding the fuel system plumbing:

Good luck!

[gbstu]

Found the problem.

The fuel line in the tank was cracked at the elbow quick disconnect. Cut back the tube and re-crimped the elbow, now the system holds pressure and starts with ease

Thanks for the help, stu

[mbagge01]

Does anyone have the technical service group information for the angled fuel pipe listed below. I looked throughout the wiebsite and in the TSB available and it is not listed. I am trying to figure out which connection that this goes to.

955 620 911 00 angled pipe

see technical information service group 2 KD-NR.2066 13/10

[Loren]

Does anyone have the technical service group information for the angled fuel pipe listed below. I looked throughout the wiebsite and in the TSB available and it is not listed. I am trying to figure out which connection that this goes to.

955 620 911 00 angled pipe

see technical information service group 2 KD-NR.2066 13/10

Perhaps this will help...

[mbagge01]

When I replaced my fuel filter, I had that angled connector but I never used it. Also one of the connections from the fuel pumps would not click on. I believe that the inner snapping piece of the connector was not working properly but I slid it on and zip tied it up to hold it firm. Is it possible that I could have some fuel pressure issues if the connector is not secure. My idle is fine but I get some issues on occasion with hesitation on acceleration or WOT. No CEL codes with durametric. I am going to check the fuel pressure this weekend, and wondering if I would notice something with a bad fuel filter connection.

[Faceman]

Hey guys,

I am changing my left pump and there is a tube that is connected to my old pump that doesn't have a release on it.. It is glued maybe? And when I reach into the tank there isn't another connector that I can feel, I am assuming it goes to the right pump.. If I open the right side and find the connector, will I be able to connect this tube to my new pump or is there a different hose I need to buy?? I will take a picture if this is too confusing..

Thanks!!!