Fuel Pumps

[Mike80911]

Thought I would post this and maybe help someone else with a similar issue diagnose their car. So I go to start the Cayenne the other day and it starts but running very rough and than stalls, start it again idling then searching and stalls again. After doing some research I pull the fuse controlling the left side fuel pump and the car actually runs. So the conclusion was bad left side fuel pump. I go to Porsche to get a pump and the parts guy says replace both because the other one is going to go real soon. He says we always replace both when either goes. I tell him not necessary I will only be needing the left one which he gives me for an excellent price as I shop there a lot. Get home and get ready to replace the pump and the right side goes out. Back to Porsche buy the right side and the fuel pump and replace everything and now she is back to normal. Should have listened to him in the first place and would have saved 2 hours of time running around.

[Travis84]

The secondary (right pump) doesnt always run. it has variables to kick on such as fuel level, temp of engine when starting and engine load. This doesnt mean that your pump wasnt bad, but always verify that the pump is being commanded on before assuming its not running because its bad.

[Mike80911]

Thank you for the input Travis. If the left side pump fails the car will run using only the right pump is that correct? After I got back with the parts for the left pump the right pump stopped working. I know the dealer wants to make as much money as they can when changing any parts. But I was doing the work and they gave me a nice discount on the parts so they were not making a fortune on the repairs. I know the parts guy and the service manager and they both said replace both and they even called in the foreman that agreed. With 110,000 miles on the car I guess replaciing fuel pumps is not an unexpected surprise.

[Travis84]

Mike,

If the left pump fails, the right pump will not automatically operate to run the vehicle. I know of other dealers that always recommend them as a pair, but I believe this is to prevent another failure in a short period of time. This would results in a car and customer stuck somewhere, possibly even on the side of the road, which is not a good situation for anyone. The left pump fails much more often since it runs all the time. If the right pump failed, you might not even know unless it is bleeding off pressure. It is a very complex design. If i get some free time, I will write up a article on it.

[LanceGT4]

After reading the above posts and checking my fuel pressure I removed the fuse for the left pump. The engine started up and I have driven about 70 miles to draw the fuel level down in the tank.
Seems to be running OK during normal driving.
I did notice that at one point when I had to merge with highway traffic from a left lane on ramp power was down for high throttle use. Almost to where I thought the other pump had died. Eek!

Really don't want and can't afford the second pump right now. Durametric was next on my list not parts not fuel pumps. Besides it's the C4's turn for work.
If I can get some decent, safe lighting I'll take pictures get something written up to share.