Possible fuel pressure issue?

[Kingx1]

Ok I've done some searching and can't find the same issue that I have, so I figured to ask in a post. I have a 2004 Yukon 6.0L . The truck starts no problem, but in the morning my issue is much more prevalent. If its real cold and I give the truck wide open throttle, it really falls on its face. When I lift off of the throttle a little, I feel it pull harder. The problem is still there when the truck is up to temp, but just not a severely noticeable. In general the truck is very weak due to whatever is going on. I took a ride in my buddies 5.3 L Tahoe and his truck has so much more lower than my 6.0L does so there's definitely an issue.

Ok so what we did so far was pull the o2 sensors to see if the cats might be clogged. It still had the same issue.

Then we hooked a fuel pressure gauge up to it. Good pressure at idle(around 60 psi), but when its under a load during hard acceleration the pressure drops off below 35 pounds. The weird thing is that I still have the symptoms of sluggishness before I see the pressure drop down in the guage.

Is it normal for the pressure to drop like that? Any ideas of where I should go from here? This thing is driving me nuts!

 

[01ssreda4]

No, your pump is failing. Pressure should NOT drop even during load.

 

[Kingx1]

No, your pump is failing. Pressure should NOT drop even during load.

So do you think that's my main problem with lackluster performance while accelerating? Its just so weird that I lift off the gas and it pulls harder.

 

[01ssreda4]

Yes, that will cause crazy issues. The computer can open the injectors longer to compensate for less fuel pressure (+trim) but there is only so much it will overcome.

 

[Kingx1]

One more thing. When I put the bullydog tune on it, it isn't anywhere near as noticeable. It actually runs decently. Why is that?

 

[retiredsparky]

Even using a tuner (which modifies how the ECM reacts to the various inputs from all the sensors) you are probably still running lean when the fuel pressure falls below minimum. A lean engine can end up being a dead engine eventually. The tuner gets it closer to the right fuel/air ratio, but I would not rely on that as a fix.

 

[01ssreda4]

Yep, I would agree

 

[Kingx1]

Even using a tuner (which modifies how the ECM reacts to the various inputs from all the sensors) you are probably still running lean when the fuel pressure falls below minimum. A lean engine can end up being a dead engine eventually. The tuner gets it closer to the right fuel/air ratio, but I would not rely on that as a fix.

I'm going to take a wild guess and say that's probably the reason why, even when I use higher octane fuel, the motor will still ping at high rpm. I ended up placing the order for a new Delhi fuel pump assembly from amazon. Got it at a great price of $224. I'm sure the labor will cost me more than the part.

I'm also trying to figure out where the fuel filter is on this truck. Is it in the tank along with the pump assembly? And if so, should it come with it?

 

[SnowDrifter]

I'm going to take a wild guess and say that's probably the reason why, even when I use higher octane fuel, the motor will still ping at high rpm. I ended up placing the order for a new Delhi fuel pump assembly from amazon. Got it at a great price of $224. I'm sure the labor will cost me more than the part.

I'm also trying to figure out where the fuel filter is on this truck. Is it in the tank along with the pump assembly? And if so, should it come with it?

2004 and up, the fuel filter, pump, and pressure regulator are all one piece. Prior to that the regulator is on the intake manifold and the filter is on the inside of the frame under your left foot as you sit in the driver's seat

 

[Kingx1]

2004 and up, the fuel filter, pump, and pressure regulator are all one piece. Prior to that the regulator is on the intake manifold and the filter is on the inside of the frame under your left foot as you sit in the driver's seat

Thanks. I got the assembly installed yesterday and I still have my issue with the power at wot from a dead stop. I'm gonna try to check the fuel pressure as soon as I get a chance too. Hopefully that's fixed at least. I'm wondering if the torque management is really that significant to where I'm thinking there's a problem and there really isn't.