Running lean? huh?

[BlackbirdOfPrey]

I did a few logs today and it turns out I am running lean and this is causing a knock problem once I get to about 5k rpms. I am running at 16psi and I am pulling about 139% in my lows and 114% on my highs. Mids are pegged at 100% solid. IDC reached 94% at the highest. The reason I'm confused is that I don't have any boost leaks (I checked a half dozen times, and I hold boost well) and I'm using the high pressure 255 walbro (rewired) WITHOUT an AFPR, so if anything I should be running rich shouldn't I? Anyone know why this is? I don't want to compound a problem by installing more parts if there is already an existing one.

 

[95blackGsTurbo]

You are running LEAN because you are overrunning your FPR and just bleeding off the excess fuel back into the tank instead of keeping the line pressurized.

 

[BlackbirdOfPrey]

Uh wouldn't overruning your regulator make you run RICH?

 

[megadeth0]

Uh wouldn't overruning your regulator make you run RICH?

No, he is right. The return line is there for that reason among others.

 

[Boost95]

You should be running an AFPR for starters. Secondly you need to get your fuel trims closer to 100%. Also check to see what your TPS is registering at WOT. Thats a start for you

 

[steve]

You are running LEAN because you are overrunning your FPR and just bleeding off the excess fuel back into the tank instead of keeping the line pressurized.

No, he is right. The return line is there for that reason among others.

Sorry guys, that's incorrect.

Fuel pressure regulator overrun causes the fuel pressure to increase because the return port in the regulator (or the return line to the tank) can't flow enough fuel back to the tank.

The regulator starts out with the return port closed and no fuel flowing, that how fuel pressure is created. Once the pressyre rises to match the regulator setting the port opens a bit and enough fuel flows out that the pressure drops and the port closes. Increase the pump flow rate and you get the case where the port open more and regulates the pressure. Once you pump more fuel than the engine is using and the return port can flow back, the fuel pressure will begin to rise and be unregulated. Kind of like boost creep and the wastegate.

BlackbirdOfPrey,
Unless you have hacked your MAF the fuel trims suggest a pre-turbo leak or a bad 02 sensor. Keep in mind that the turbo can keep the boost pressure up even with leaks so that data is meaningless but not going rich under boost lowers the likelyhood of a boost leak.

Steve

 

[BlackbirdOfPrey]

Sorry guys, that's incorrect.

Fuel pressure regulator overrun causes the fuel pressure to increase because the return port in the regulator (or the return line to the tank) can't flow enough fuel back to the tank.

The regulator starts out with the return port closed and no fuel flowing, that how fuel pressure is created. Once the pressyre rises to match the regulator setting the port opens a bit and enough fuel flows out that the pressure drops and the port closes. Increase the pump flow rate and you get the case where the port open more and regulates the pressure. Once you pump more fuel than the engine is using and the return port can flow back, the fuel pressure will begin to rise and be unregulated. Kind of like boost creep and the wastegate.

BlackbirdOfPrey,
Unless you have hacked your MAF the fuel trims suggest a pre-turbo leak or a bad 02 sensor. Keep in mind that the turbo can keep the boost pressure up even with leaks so that data is meaningless but not going rich under boost lowers the likelyhood of a boost leak.

Steve

My MAF is a stock unit (upgrading to a GM over spring break unless more problems show)unhacked. And my O2 sensor seems to be reading ok (was .17v and when knock set in it was .89v) I also did a leak test and the pressure seems to hold well. ECU is a brand new EPROM. Where does that leave me? Low fuel pressure perhaps?

 

[megadeth0]

Sorry guys, that's incorrect.

Thank you for the info. I have been under the wrong impression for some time now. Good to know!

 

[AL92]

I think you can have high idle trims from the o ring seals in the throttle shaft.The car will still boost but leaking air thru the shafts can whack things out..change out those seals if you haven't already..

 

[andytalon]

I got a similar problem, I have 139% low trim, and I hear a little pissing sound off my TB, but the gaskets are new and everything. It is only when I give it a lilttle gas u can hear it. kinda stinks I just got new TB gasket too . But do you really think it can knock it out that much????