Truck Running Like &*&%&^#**%#*($^(!

MaForrest · April 23, 2010

quick and simple. 1997 Gmc Sierra 4x4 5.7L and 4l60-E. Truck runs awsome but cranks longer then it should when cold. Once started, it runs fine....untill you give it throttle. Even when warm, anything more then3/4 throttle is a waste. Truck will actually loose power and start slowing down...like starving for fuel after 3/4 throttle. I will be getting a fuel pressure guage and checking preasure. Anything else could be causeing this? Brand new plugs, cap and rotor, coil. What should my preasure read? From key on, to idle to half throttle to WOT.

Nytemare · April 23, 2010

quick and simple. 1997 Gmc Sierra 4x4 5.7L and 4l60-E. Truck runs awsome but cranks longer then it should when cold. Once started, it runs fine....untill you give it throttle. Even when warm, anything more then3/4 throttle is a waste. Truck will actually loose power and start slowing down...like starving for fuel after 3/4 throttle. I will be getting a fuel pressure guage and checking preasure. Anything else could be causeing this? Brand new plugs, cap and rotor, coil. What should my preasure read? From key on, to idle to half throttle to WOT.

You should read 50ish PSI I am pretty sure...all the time.

Check for actual WOT operation with the truck shut off...your cable may be screwed up and actually not doing anything past 3/4 throttle.

But yeah...if its bogging and everything is operating correctly...its likely fuel related.

Silverado4x4 · April 23, 2010

Yup I think your fuel pump is ready to take a poop. Have you changed the fuel filter on the driverside inside frame rail?

MaForrest · April 24, 2010

Oh ya, I changed the fuel filter about...ohhh...6 months or so ago. The fuel pump that is in it now is only a couple years old but that dont mean it aint producing enough volume to keep the fuel preasure at level. I will check the cable today. I know my pedel sticks usually when i let off it and have to tap it to break her loose again...usually with a loud chirp! But even if my cable is stretched...which im sure it is...got 185,XXX miles on it, it dont explain why between half and 3.4 throttle she will run decent but when pushed to the floor it feels like I just hooked onto a trailer. What about that stupid fuel spider GM just HAD to invent and stuff under the intake? Those have any known issues?

Nytemare · April 24, 2010

Oh ya, I changed the fuel filter about...ohhh...6 months or so ago. The fuel pump that is in it now is only a couple years old but that dont mean it aint producing enough volume to keep the fuel preasure at level. I will check the cable today. I know my pedel sticks usually when i let off it and have to tap it to break her loose again...usually with a loud chirp! But even if my cable is stretched...which im sure it is...got 185,XXX miles on it, it dont explain why between half and 3.4 throttle she will run decent but when pushed to the floor it feels like I just hooked onto a trailer. What about that stupid fuel spider GM just HAD to invent and stuff under the intake? Those have any known issues?

you could be pulling past the WOT position on the throttle lever and the butterflies are actually falling back to the half or less position.

Chances are though...your pump is likely the cause of this problem

kchasse · April 24, 2010

If your fuel pressure checks out good then it could be a partially blocked converter not allow good airflow at the higher rpms.

MaForrest · April 26, 2010

I was thinking about my cats as well. however I havn't thrown any codes for them, and it dont do it all the time. Granted, its getting worse but I can get on the throttle and the truck acts like it has no gas and then out of no where it will find that power again and off you go...and then poops out at higher RPMs.

ryan_hermanutz · April 26, 2010

I was thinking about my cats as well. however I havn't thrown any codes for them, and it dont do it all the time. Granted, its getting worse but I can get on the throttle and the truck acts like it has no gas and then out of no where it will find that power again and off you go...and then poops out at higher RPMs.

That is what I would have guessed, I had them go out once it was just like you explained. But I don't know jack and the other guys who already answered are far better at this than I.

Nytemare · April 26, 2010

I was thinking about my cats as well. however I havn't thrown any codes for them, and it dont do it all the time. Granted, its getting worse but I can get on the throttle and the truck acts like it has no gas and then out of no where it will find that power again and off you go...and then poops out at higher RPMs.

That is what I would have guessed, I had them go out once it was just like you explained. But I don't know jack and the other guys who already answered are far better at this than I.

Yeah...could very well be cats too...but the rear O2's should have picked up the issue.

Could also be an issue with your trans too man...there's a whole lot of could be's...

rodram · April 26, 2010

... first thing to do is get the fuel pressure checked...

... GM spec for these96-99 Vortec engines with Sequential Central Port Injectors is 61 to 66 psi, at all stages of operation

... some report that the engine will start and run at a little less than this, but once it gets down into the 50's that indicates that the pump is heading south

... if you need a new one then get a ACDelco or a Delphi brand replacement

Nytemare · April 26, 2010

... first thing to do is get the fuel pressure checked...
... GM spec for these96-99 Vortec engines with Sequential Central Port Injectors is 61 to 66 psi, at all stages of operation

... some report that the engine will start and run at a little less than this, but once it gets down into the 50's that indicates that the pump is heading south

... if you need a new one then get a ACDelco or a Delphi brand replacement

Yeah wasn't 100% sure on that pressure...Thought it was low 50s...sorry man.

MaForrest · April 28, 2010

Ok, ruled out the cats due to my o2 sensors not picking anything up and since it will clear itself out after a few seconds. Plugged cats will run like crap always untill replaced. Have had this issue on another chevy i owned. My fuel pressure is at 55. A buddy of mine checked it a while back when the truck first started doing it. Kind of forgot about it till the other day. That was right after the new pump was installed. My transmission was just rebuild by a well known shop in town and is A-ok. Only has a couple thousand miles on it maybe. Those two brand of pumps you mentioned, are they anything different about them besides quality? Do they sell a pump that will produce more then the range the truck calls for? I know they have a return line but dont know if it will harm anything by pushing a few extra lbs through there.

Nytemare · April 28, 2010

Ok, ruled out the cats due to my o2 sensors not picking anything up and since it will clear itself out after a few seconds. Plugged cats will run like crap always untill replaced. Have had this issue on another chevy i owned. My fuel pressure is at 55. A buddy of mine checked it a while back when the truck first started doing it. Kind of forgot about it till the other day. That was right after the new pump was installed. My transmission was just rebuild by a well known shop in town and is A-ok. Only has a couple thousand miles on it maybe. Those two brand of pumps you mentioned, are they anything different about them besides quality? Do they sell a pump that will produce more then the range the truck calls for? I know they have a return line but dont know if it will harm anything by pushing a few extra lbs through there.

No...your pump is likely fine...your fuel pressure regulator however is likely on its way out.