Fuel Pressure Values Please

DSN46 · July 31, 2010

Hello,

I have a 04 Suburban 1500 Vin code "Z" Flex Fuel. I have recently had idle problems along with "almost stalling / low rpm" problems when at a stop. I have a cheap sears fuel pressure tester (may not be most accurate) and have tested the pressures at the Schraeder valve as follows:

KOEO= jumps to 52 at first then drops to 46 immediately.

After 10 min = still holds at 46 psi.

After 30 min = still at 46 psi.

Engine running at Idle = 42.

1000 through 3000 rpm it holds at 42 to 41 psi.

When I stomp the accellerator, it jumps to 52 then drops back to 42 again quickly.

Could someone please look at my numbers and tell me if they think I have a fuel pump problem or maybe FPR problem? (no gas leaking at FPR by the way) Are these numbers okay for a flex fuel engine? I know the flex fuel should be a little lower than the regular engines. If these numbers are okay, then where would you look next for possible causes of low idle rpms? Oh yeah, it does it whether AC is on or not, but MORE so with AC on.

EDIT: I forgot to mention that I have removed the throttle body and cleaned it thoroughly as well as cleaned the MAF sensor and replaced the MAP sensor. Also, Intake Manifold Gasket replaced by dealer.

Thank you all very much!!

James

txab · July 31, 2010

For a T code engine KOEO value is 55-62. I would think your engine would be similar. You could change the FPR. If problem still exists change the pump. That's where I'm betting your problem is

DSN46 · July 31, 2010

For a T code engine KOEO value is 55-62. I would think your engine would be similar. You could change the FPR. If problem still exists change the pump. That's where I'm betting your problem is

Thank you for your fast response! I knew the pressures for a VIN code T engine, but I read somewhere on another forum that the Z code engines had less pressure in them.... however, I cannot seem to find exactly what that pressure is, or if my "immediate Key-On of 52 then drop to 46 and hold" with engine off is acceptable or not. Hoping someone with experience with the Z coded engines will know exactly.

Thank you again!

James

txab · July 31, 2010

Have found conflicting info on fuel pressure readings for a Z. I'm sure 46 is too low. What about the fuel filter? IIRC '04 "Z" code still has an external serviceable filter on the rail. Might check it for sure

DSN46 · July 31, 2010

Have found conflicting info on fuel pressure readings for a Z. I'm sure 46 is too low. What about the fuel filter? IIRC '04 "Z" code still has an external serviceable filter on the rail. Might check it for sure

Thank you again! I agree with you that 46 is too low. What I am not sure of, is if it is the Fuel Pump... or the Pressure Regulator like you mentioned before. Since it starts at 52 - 54 psi. right when key is turned on, then about one second later, it drops to the 46... it leads me to believe that the pump is doing it's job, but the regulator may be hindering things. I am going to replace the regulator tomorrow and see if any change occurres. Also, I considered the filter also, but I just changed it about 15,000 miles ago, I cant see it being the problem yet.

I appreciate your help on this as I dont want to just keep throwing parts at... something I think alot of us are guilty of, unless you happen to own your own, personal Tech II Programmer.

James