Shifting/revving problem

[98 Centurion Z71]

Ok, I have a 98 GMC Z71 w/ a 350 vortec....it drives fine with no problems unless you "get on it"...then the rpms rev up but it won't hardly accelerate. However if I let off a little it will pick up speed. I noticed this on the interstate do around 65-70 but it also does it in lower gears too. Any suggestions as to what this could be? My friend's dad had his dually put in the shop today for the same thing and he was told it's something to do with his fuel pressure, is this possible? Any help is appreciated.

[PapaShlapa]

My first thought would be that your clutch is fried

[98 Centurion Z71]

It shifts fine during normal driving, it is just when I "get on it". Could this still be the clutch?

[herefordman]

If the engine revs up then its unlikely a fuel problem, my guess would be clutch, if its slipping like that you won't have to wait long to find out.
Smell anything under the truck ?

[Lucky87531]

I have a 98 Sierra Z-71 Offroad doing the exact same thing. My fuel pump and alternator crapped out at the same time so I just spent $1500 getting that fixed. I took it to a tranny place and they said it was a fuel or exhaust problem. I had the cadalidic converters checked but they're ok. It has to be a fuel problem. No check engine lights or anything, and my mechanic just informed me that he didn't change the fuel filter while he was changing the fuel pump which he was supposed to. I guess that could be a problem since i have about 130,000 miles on it!!!! Maybe thats even why my fuel pump crapped out, because it was working extra hard from my fuel filter being clogged!! I will let you know if this helps even a little! Let me know if you find the fix!

Annie

[MSpring]

I have a 1996 g.m.c. with a 5.7 and had the same problem. It turned out to be a bad check valve in the fuel pump.

[Lucky87531]

Is that the Pulsator Dampner Valve?

[Lucky87531]

Ok, I just got a call that my truck is done at the shop and they said my fuel filter was clogged solid. I guess that's a good reason for my fuel pump crapping out and my truck having no power. A little clarification about what my truck was doing... I thought that my tranny was slipping because it was fine in low RPM's but super slow in high RPM's so I took it to a transmission place and they said the fluid was good, no metal shavings in the pan or anything and no codes. They drove it and said it was a fuel or exhaust problem. After driving it broken for a while, I noticed that I couldn't get my RPM's over about 4500 RPM. I tested the exhaust and it was fine, so i just changed my fuel filter and the mechanic said it was driving really well now. (I have to pick it up still). I have a feeling it's a problem with your fuel pressure. Don't take it to a dealership to have them test the fuel pressure because they will only test it at idle, not under load. Take it to a real mechanic. I have started to notice that if your car is not throwing any codes and telling the mechanic what is wrong, they have no idea what is wrong. As said in a previous post, it could be a valve, could be a pinch in the gas hose some where, or it could be as simple as a fuel filter. But checking the fuel pressure is a good place to start, if you haven't started already! Good Luck!

[beenydu]

Wait a minute! Easy with the dealership stuff. How many "shadetree" mechanics do you know with a Tech2 ECM reader and can even tell you the codes that are posted? We are dealing with a completely controlled electrical device. It is not all about valves and hosing anymore. GM does a great job supporting the mechanics that want to diagnose the customer's problem. It is not the lacking of a dealership, however that of the individual servicing your vehicle. There is no need of shooting off about the BEST auto manufacturer in the world!

Originally Posted by Lucky87531

Don't take it to a dealership to have them test the fuel pressure because they will only test it at idle, not under load. Take it to a real mechanic. I have started to notice that if your car is not throwing any codes and telling the mechanic what is wrong, they have no idea what is wrong.