Fuel regulator or Filter Issue

[mbagge01]

On my 04 cayenne TT, I finally checked the fuel pressure and noted that each fuel pump holds above 4 bar which is what should be expected but when I turn the engine off, the pressure slowly drops to just under 1 bar in less than a minute. According to what I have read, it should hold at least 3 bar for about an hour. According to other posts, this brings up the question of either my fuel pressure regulator being bad or the fuel filter with its check valve. I will mention that I changed out my fuel filter a couple months ago and one of the connections from a fuel pump did not snap on firmly so I ended up zip tieing it up to hold it. Could this be my issue if I have a slightly bad connection at the fuel filter. I have no CEL codes and idle is fine but my issue really is with acceleration which leads to some hesitation and I notice timing being pulled at WOT. Recording with durametric, I found that the injection times were significantly high which I have been told is a fuel pressure issue. Even though my pumps seem to be putting out over 4 bar at idle, when the car is under WOT or accelerating can a bad connection at the fuel filter cause pressure issues. Isn't that what the regulator on the other side is doing. Is there a way to tell between a fuel pressure regulator and fuel filter issue in these cars? Thanks.

[clarksongli]

Based on what you have described, i would take a look at the regulator first.

To answer your question, unless the hose connection is leaking....a lot....it doubt it could cause the issue you're describing. Maybe the fuel hose popped off the FPR in the tank?

I haven't ever really heard of a FPR failing.....they are really simple devices.

[mbagge01]

If one of the hoses from the fuel pumps to the fuel filter had fallen off, would the vehicle still drive or what would I expect to see. When I isolate each pump, it idles and revs ok so I would assume it is connected fine unless the fuel pump has a bypass to still get fuel to the regulator since there seems to be connections between the fuel pumps themselves per the diagrams.

[clarksongli]

no...if it fell off the fuel filter you would have a serious issue.

I'm thinking if the vacuum/boost SENSE hose popped off the regulator in the return to the tank.

[deilenberger]

As far as telling the difference given your symptoms - probably only by replacement. Mine may be the one you found a write-up on.. luckily the problem was covered by CPO. Either one could cause the pressure leakdown. The fuel filter might be considered a consumable item (although there is no change interval specified.) If you watch on eBay these can be found for "reasonable" prices - ie - less then the dealer price. Since it's an ugly smelly messy job to change them, I'd be tempted to change both at the same time (especially given your driveability symptoms and the fact that the one hose didn't connect correctly to the fuel filter.) If I had to only change one - I'd go for the fuel filter, and the hose fitting that is giving you a problem. There was a right-angle add-on connector added to one of the fuel filter hoses due to problems with the angle it connected to the filter - did you have, or did you install the right-angle extension connector? If not - this might be the cause of your problems. And I would guess - a leak at the fuel filter could cause pressure problems, particularly under high-demand conditions.

Also - what caused you to change the fuel filter?

[mbagge01]

So I went ahead and reinspected the fuel filter connections and played with the loose connection from the left fuel pump, closed up and now the fuel pressure will hold around 1 bar for at least 10 minutes now and the car runs dramatically better with just a few hiccups. I still have the angled connector but did not install it to the line from the right pump. What problems does the ooriginal connection lead to why the angled one was develped. Can it decrease fuel pressure and flow and maybe still another small issue for me. My fuel filter was replaced last year prophylactically when first trying to diagnose my timing issues bein pulled

[deilenberger]

The angled connector relieves a pull on the hose where it fits to the filter. Without it there is the possibility of a leak caused by the pull on the connector to the filter. Yes - it could cause some running problems.