jellonailer

Have a crazy troubleshooting issue can't seem to nail, neither could Porsche dealer.
Dealers been chasing vacuum leaks due to bank 1 and 2 lean codes, with misses on all cylinders were allegedly because of bad plugs and coils.I didn't believe that diagnosis so I changed all plugs and coils. Still throwing all the same codes and stumbling under load. here's what I have to share. I believe there is a fuel supply issue:
1) Put my fuel pressure gauge on bank 1 rail and get 2 bar. It holds after shut down for a long time, hours. I believe I should be getting 3 bars, min, but spec says 4 bars. I am 1/2 that.
2) Thought maybe one of my new fuels pumps was bad so I did fuse 13 and 14 test. First 2 times I pulled fuse 14 CTT fuel pressure quickly drops, stumbles and shuts down, no fuel pressure or fuel. Success! I have a bad NEW fuel pump. So I pull fuse 13, keeps running. Confirmed, On track here. Maybe because 1 pump doesn't work and both don't come on it never gets to 4 bar? I don't know, takes 2 pumps to build up pressure and 1 to maintain?
3) So now I want to pull my fuel gauge off the CTT so if I pull fuse 14 again the engine will starve, drain the fuel from the rails, die and I can pull the gauge off with no fuel mess. I pull fuse 14 and the it keeps running. So then I try 13 fuse and it keeps running. So then I pull BOTH fuse, 13 and 14 and the pressure drops to about 1.2 Bar and IT KEEPS RUNNING! With no fuel pump fuses. WTF?
4) Ok, those fuses work with the 404 relays.I think maybe if one of the relays is stuck - contacts closed to fuel pump, it wouldn't matter and it would run as if jumper ed. I checked relays, bench test good and then I swapped for new. Nope, thats not it.
5) So I grab my Durametric and think I can run a fuel pump test and the f'ing thing wont run actuation, again. Never seems to work right. Throw that aside and borrow my buddies Snap-On diagnostic tool and run the fuel pump actuation - BOTH work but neither pump gets over 2.0 Bar and his device does not let me do both at the same time. Pumps really do work as I could text them both through activation.
6) CCT off with fuel pressure gauge still hooked up and it holds 2.0 Bar when not running. Assume Fuel check valve must be good, pressure isn't bleeding down.
7) I go to start it again (starting has not been an issue) and it won't start, fuel pressure gauge never makes it past 1.2 bar. Just wont start fuel starved..
8) I'm disgusted now so I'm going to remove the fuel gauge from the schrader. Crack it loose and expect fuel to leak out for about 4 seconds and pressure drop to zero except it doesn't. Fuel rail schrader sprayes and hisses fuel and air for about a minute or more as if air is in there, about 1.2 bar. It isn't going down with the pumps offs.

Her'es what it feels like to me - something is wrong in fuel pump/FPR and delivery system. Maybe the FPR (brand new) isn't working right, maybe the fuel pumps are delivering the right output, or maybe the system is pulling air in, which is getting compressed, providing pressure to the rail long after the pumps stop running (that's why the car runs after fuses are pulled).

Needs some help, hopefully someone has seen something like this before?

BTW, won't even start now, can't get over 1 bar back in the rails...

Petza914

I would disconnect the battery for 10 minutes to try and get everything to reset and see if you can then start it.

With misfires in all cylinders, I might have started with the MAF as a potential culprit. Did you try running it with the MAF unplugged to see what it does in limp mode using default values instead of air metered ones.

J'sWorld

I feel like there is information missing here but you have a problem in the in-tank plumbing.

jellonailer

J's world. I agree, I think something is wrong in tank.
MAFs are good, did the test. There is a pressure issue.
I have disconnected battery and let it sit all night. Will get back into it today.
tks

deilenberger

https://rennlist.com/forums/cayenne-...p-routing.html

Dilberto

I resolved my lean codes(P2187/P2189) by using sticky red grease on: intake plenum Y pipe 0-rings, airbox charge pipe connections and lower intercooler boost hose 0-ring seal connections.

J'sWorld

Each pump does three things. Each pump has 3 outlets, 2 top and one on bottom. 1 on top feeds the engine, 1 on top feeds the opposite side of the tank's sucking jet pump, 1 on bottom feeds a venturi pump on the bottom of the basket to fill its own basket from that side of the tank. Each outlet on top has a check valve. Each pumps basket get's filled by its pump, return from the regulator, and the opposite side of the tanks jet pump via itself, or by fuel ingress from the top of the basket.

jellonailer

Thanks for the info. I would like to add more to this goofy situation from this mornings science project.

Today on start up (after all night negative ground removal reset) fuel rail pressure went to 2 bar, just like yesterday. Again I pulled fuse 14 and the pressure dropped until fuel starvation,put fuse in, pressure returned to 2 bar, pulled fuse and let the pressure drop until the engine died. Put fuse back in,noticed fuel pressure went back to 2bar without starting, restarted, pulled fuse 13 and engine kept running, fuel pressure at 2bar. Too low, should be 4bar I believe, but still ran. Fuel pump, fuse 13 is my best guess.

So thinking passenger side (left drive CTT), pump is the culprit I disconnect the ground, pull pump cover and check pump connections and electrical connection. (This cylinder missing issue started happening after dealer service for fuel tank seal recall and I wanted to check if something was messed with). Connections all good. So I button it up. Before connecting the battery and starting up I just happened to walk by the engine and glance at the pressure gauge. IT"S NOW 4BAR, with the battery disconnected and the car off!!! This is nuts, making pressure with both pumps off and no power?

So I start the engine and pressure drops to 2.0 bar. Shut off the engine and watch the fuel rail gauge - not only does it not go down, it creeps up to 3 Bar over the next 10 minutes, then after it's started the pressure drops back to 2 Bar.

Probably going back to the dealer next day or so.

jellonailer

Well, apparently all sorted. In tank fuel pump line issue.
How did that happen? I will never know for sure but - took CTT in to dealer for Recall on fuel tank seals. I know you have to disconnect a few lines to put the seals in. Lean codes and fuel starvation with low fuel pressure began after dealer service.
Dealer called said it's ready, runs great, a fuel line "issue" in the tank.
No charge...