I've been chasing issues with my 01' TT for 8 months. I never get any codes but the car runs rough/inconstant. It take for ever to build boost. At cold start up, it literally spits raw fuel out the exhaust So I decided to test fuel pressure while driving. At Idle and just driving easy I am getting 55Psi. At full throttle or when accelerating I am seeing 75psi. See video(check out after the 7:40s minute mark
Just about everything is new or has been replaced. New: O2's, plugs, coils, Cobb 1000cc injectors, 997 throttle body, IPD plenum, K16 billets, intercoolers, MAF, FPR, N75's, fuel filter, every check valves, solenoids & boost control sensor.

I've done many boost leaks...no leaks.

 

when you installed the 1000cc injectors did you have your tuner scale the injectors? sounds like its way off pumping to much fuel into the motor

 

I'll find out...I went with a reputable tuner. One would think they accounted for the injectors.

 

How much boost are you running? About 15psi or so? It's a rising rate regulator and should raise fuel pressure in line with boost and lower it with vacuum. Sounds like tune issues to me too...

 

Factory workshop manual gives 3.8 +/- 0.2 bar (55.1psi) for engine off fuel pressure -- fuel pump activated using PST2 diagnostics computer.

For engine idling fuel pressure should be 3.3 +/- 0.2 bar (47.8psi).

There is no call out for fuel pressure at any engine speed above idle. I would hazard a guess the fuel pressure should be in that 3.3 +/- 0.2 bar ballpark though.

Well, unless there is a fuel pressure compensation system to increase fuel pressure when boost is active and to increase fuel pressure in parallel with boost. IOWs, more boost, more fuel pressure.

There is a hose that connects to the fuel pressure regulator which suggests there is some, well, connection between intake manifold pressure and the fuel pressure regulator.

If fuel pressure is ok at cold start/idle and you observe raw fuel coming out the exhaust this suggests not a fuel pressure problem but a fuel supply problem, as in too much fuel is being delivered. (Granted too much pressure can result in too much fuel, but I said as long as the fuel pressure is ok at cold start/idle.)

In this case then one or more injectors are leaking or are being left on too long or there is an air metering problem. The DME is being misled regarding how much air the engine is consuming.

 

1.2 bar

 

Interesting... Logs are showing the DME is constantly making changes/compensations for some reason. The car feel like it is searching at all times. I've actually wondered if I have a bad DME? I've installed my DME(after uninstalling my tune) in my mechanic's 03' TT and his car ran OK so I am hesitant to buy a new DME but am wondering if there is something wrong with it.

 

Rising rate regulator, 1.2BAR is a 16psi swing from base. You can determine base by pulling the vac hose off the regulator, pressure will rise to base and go down with vac at idle.

 

Are you able to see the fuel trims? Short term/long term. What are the fuel trims under idle vs load?

 

Hey guys. Karl, I feel so bad for everything you've gone through with this car. Multiple gremlins. The tune is all good and it's been another cars. I even looked to Cobb for support and everything is where it needs to be. We discussed all the different things to try and Karl did everything. Changing and double-checking everything you can imagine. He found a really kind computer repair company where the gentleman honestly said he wouldn't do that yet. So we decided to go to checking fuel pressure. I think this is the culprit. What you thought was a 3.8bar fuel regulator could actually be a five bar regulator. As you drive the car and manifold pressure moves around it just is never happy. Car is definitely over correcting and going crazy trying to get it right. WOT is great as is idol because the car compensates. I think changing that regulator again is a good move. Or we can recalibrate. But I think it's too much and hard on the pump in your set up. Really hope this is going to be it buddy. Otherwise still an issue with air of some sort. Here for you as usual.

 

To check if it's a 5BAR is easy since he has a gauge - pull the vac hose off. This will remove the correction for vacuum and yu will see what the FPR was set for as a BASE. the fuel pressure is SUPPOSED to move as load varies. Under vac the engine is attempting to SUCK fuel from the injector, under boost it's trying to BLOW it back up the pipe. The FPR adjusts for this 1:1 so that the injector sprays the same amount of fuel per fixed opening time under vac or boost so you have one less variable to chase.

Hope that makes sense of what you are or should be seeing with the FPR. So far as I know the ECU in the 996 doesn't control the fuel pump other than on and off so the FPR is what varies.

 

You're right and that's a great suggestion. Pulling the line would make the car more friendly static feel pressure and shed more light. Log that Karl. Before you buy a new one and change it again.

 

I think sambo is right. My 5bar did the same crap and Tony at epl did a great job in adjusting it. Even Tony said he doesn't like 5bars just upgrade Injectors and I have never been happier.

But if your running a 5bar and 1000cc there's your issue.

 

Whoa! I'd pull the vac hose to check static base pressure to verify what FPR is in there but I sure would be VERY careful driving it that way. It could go pretty lean without the FPR pushing pressure up and you might hit the limit of the ECU's ability to compensate which would be "bad"...

He says it runs fine WOT so if the fuel trims are okay there and the tune isn't weird then the fueling is correct there. Maybe the FPR is sticking somehow? It's a mechanical device with an internal diaphragm and a plunger. Actually a ruptured diaphragm is a possibility and would push fuel into the vac hose but probably run WAY worse than it does now. I dunno', the ECU ran fine in another car but not with this tune right? Tune not matching the hardware seems likely. A bum FPR could do it, sounds like everything else has been checked. The readings don't seem too bad though, checking base pressure to make sure it's accurate seems like a good first move next.

 

No it's not running right he said its rich and boost takes for ever to hit and black smoke. You just can't run a 5bar with 1000cc on stock ecu.