timdogg1313

I have a 97 4 door 4wd 5.7L Tahoe w/ 143K on it that has started acting up. Replaced 02 sensor on bank 1, sensor 1 and plugs in #2 & #4 as they showed on random misfire. It is running really bad with lose of power, bad gas mileage, shaking/motor tweaking and making a fairly loud thunk noise out of the exhaust. Any ideas? Since replacing 02 sensor bank 1, now giving me bank 2 sensor code. The CEL is blinking most of the time and then will stay on solid, then back to blinking(thought that might help). I've searched the forums and have gained some knowledge, but don't want to just start replacing parts. Took to mechanic yesterday to run codes and I have spark @ #2 & #4 and sounded like compression was good(per mechanic with no compression test done) only starting the engine with spark plug out. With the noise coming out of the exhaust I have thought about the cat or cats being bad, but like I said don't want to just start replacing parts if I don't need too. Is there any way to check to see which cat is bad and does anyone have a link to a website that shows in pretty good detail the labeled parts of the Tahoe? One other thing is that the fuel gauge isn't reading correctly. It pegs out way passed F and then will bounce all over the place until get close to empty. Have fuel pump replaced a little over a year ago.
Please help!

Thanks!

73shark

Sounds like the mech. didn't scan for the codes. That's the first thing you need to do. Probably plugs, wires, etc should be replaced. Run 2-3 bottles of Techron thru the tank at the same time might help.

timdogg1313

He did scan the codes and got the P0300. That's why I replaced #2 & #4 spark plugs as those where the 2 cylinders that showed as miss fires. I put a bottle of injector cleaner in today, so I guess I'll see if that helps. Do you have any experience with the injector system on this vehicle? My mechanic said it could be a cracked injector line, but I really would like to troubleshoot it first b/4 i tear into that. I'm hoping that it's the cat or wires, rotor or cap. I replaced all of them about 40k ago, so it seems unlikely that would be the problem.

Thanks,

Dirtbike768

I have a 1996 Chevy K1500 that is having the same problem, it also idles at 1000RPM when in park, i am getting the P0300 too. I replaced cap and rotor and that didn't help. I have been told it can be bad injectors, air leak into the intake manifold, burnt valves, or a leak in my vacuum system. There are a few more things that can be wrong with it i am going to try and test for manifold leaks tomorrow. Will post anything i find out.

Dirtbike768

I can also be the cat i forgot about that.

timdogg1313

Thanks Dirtbike! I will be interested to know what you find out. Like I said I really don't want to just start tearing the thing apart( i.e. injectors) if it is the cat. Let me know.

timdogg1313

I think that I might have said what the noise out of the exhaust sounds like. After listenting to it again it is more like a puff, puff, pop noise. Almost like a backfire noise but not as loud. Hope that will help with the diagnosis of my problem.

Dirtbike,
Is your 96 make the same noise out of the exhaust?

timdogg1313

Okay I cleaned the throttle body and that didn't help. The noise out of the exhaust is traveling thru the entire exhaust and seems like it "pops" at different locations. Please someone help!

Dirtbike768

No i not having the poping problem. I droped my exhaust down and cleared the codes then tested, checkengine light came on again so that didn't help. I tested my throttle position censor and i think that might be my problem i am supposed to have .6 volts with no throttle i only have .39 and full throttle is supposed to be 4.5 volts and i am only getting 3.19. Also tested the circuit and it was good. I would suggest testing the Throttle Position Censor

73shark

Might check for an intake manifold vacuum leak, especially around the area of the misfiring plugs.