robphilop1029
Newbie
Hi all,
I'm a relatively novice car guy, and this is my first truck, so bare with me as I try to explain some of these issues.
I have a 1994 c1500 GMC sierra 5.7L V8. It's got a little over 200,000 miles on it, and for the most part it's running strong and it's easy to work on. There are, however, a few strange issues. There is no check engine light or codes, so it makes these things difficult to pin down.
1.) When I am cruising down a road or highway, and I depress the accelerator about 5% of full throttle, it will sometimes cause the engine to make strange noises as if the actual combustion process is reaching some sort of 'resonate frequency.' The RPMs jump up and down, oscillating back and forth about 150 rpm in either direction, and the car will start to shake as I'm going down the road. I don't know how to search for the cause of this problem or even how to word it, really.
2.) When im in reverse, the engine does not want to accelerate steadily whatsoever. It idles real low, 500rpm. One time the engine stalled on me trying to back into a spot. That hasn't happened but one time, but I'm curious to know what might be wrong.
3.) When I let off of the accelerator, there is another combustion that happens in the engine after I completely let off. Not a big deal, but i'm wondering if it's related in some way to the other two problems i'm having.
Some ideas i've had reading through Haynes repair manual or on the internet is possibly a dirty throttle body, bad fuel pump, bad fuel injectors, or general ignition system issues like worn spark plugs, faulty ignition coil packs.
I'm wondering if there's some wisdom on this issue out there that will save me the time of checking all these things out and wasting money and time replacing stuff that's not going to fix the issues.
Thanks for your time!
I'm a relatively novice car guy, and this is my first truck, so bare with me as I try to explain some of these issues.
I have a 1994 c1500 GMC sierra 5.7L V8. It's got a little over 200,000 miles on it, and for the most part it's running strong and it's easy to work on. There are, however, a few strange issues. There is no check engine light or codes, so it makes these things difficult to pin down.
1.) When I am cruising down a road or highway, and I depress the accelerator about 5% of full throttle, it will sometimes cause the engine to make strange noises as if the actual combustion process is reaching some sort of 'resonate frequency.' The RPMs jump up and down, oscillating back and forth about 150 rpm in either direction, and the car will start to shake as I'm going down the road. I don't know how to search for the cause of this problem or even how to word it, really.
2.) When im in reverse, the engine does not want to accelerate steadily whatsoever. It idles real low, 500rpm. One time the engine stalled on me trying to back into a spot. That hasn't happened but one time, but I'm curious to know what might be wrong.
3.) When I let off of the accelerator, there is another combustion that happens in the engine after I completely let off. Not a big deal, but i'm wondering if it's related in some way to the other two problems i'm having.
Some ideas i've had reading through Haynes repair manual or on the internet is possibly a dirty throttle body, bad fuel pump, bad fuel injectors, or general ignition system issues like worn spark plugs, faulty ignition coil packs.
I'm wondering if there's some wisdom on this issue out there that will save me the time of checking all these things out and wasting money and time replacing stuff that's not going to fix the issues.
Thanks for your time!
