I have a 1999 Silverado 4X4 with 185,000 miles. Gradually over time the engine started "bucking" at around 2000-2500 rpm. This is really annoying when during normal driving it does this all of the time. I checked the MAF sensor and it is clean. I also had a Motorvac treatment done to it thinking it might be dirty valve related. No change. Could it be related to emmisions, EGR, etc? No check engine light has come on.

Thanks to any and all replies to this posting. Any help offerred is greatly appreciated.

Dave

 

Dave, I also have a 1999 two wheel drive that just rolled over to 85k miles. I am experiencing the same problem. My truck does it anywhere from 2000-3500 rpm's. But it runs fine full throtle or below 2k rpm's. It's driving me nuts, I have done a complete tuneup, new plugs, wires distributer cap and rotor button, and new fuel filter and air filter. Also replaced both catalytic converters and all four oxygen sensors and still doing it. I can smell that the truck is running really rich and have know idea why. Also no Service Engine light at all???? Let me know if you get yours fixed and I will do the same.

Thanks
Sean

 

i havea 1999 silverado 2500 4x4 also and i had the same sorta problem.... my fix was a coolant sensor. Took a while to find the problem because no check engine light would come on. This may not be a fix for you but just an idea.

 

Are you talking about next to the thermostat or is it located somewhere else, also what was the approximate cost of fix. If that is it, is it the sensor, is it's purpose to sense the temp. of the coolant and adjust the air/fuel mixture accordingly? Maybe that would explain it running rich. Also, I forgot to mention but I have the 4.3L in my 99 silverado. Thanks for the help.

Sean

 

Ok, i have the 6.0 V8, it is located near the front on the engine on drivers side by the very first spark plug. You will see a connector that plugs into engine right above the first plug. This sensor is supposed to get the temp and adjust the fuel and air to the temp, if it is raining or damp outside it will probably act up more than normal. This is jsut an estimate but probably cost around $50? Let me know wh at you find out.

 

If you're running a cold thermostat that will cause it to run rich, also.

 

some of the 5.3 and 4.8 have had a problem with dumping mudd like or peppery like carbon into the #7 injector, the fuel rail will have be taken out to completly clean it, trust the motorvac is an excellent machine, but ive had 5 of these trucks to do this with me and thats the only way to do it, the motorvac just breaks it up and moves it around.

 

I have a 99 silverado with a 4.3. V6 and the check engine light came on. I had it checked and it said catylist effeciency below threshold. What does that mean?

 

Hi guys just been reading all your post's,i havethe same problem with my 96 gmc ex cab 4x4. I have done just about everything you can do to this truck with no change.the truck will run good for 30 min's or so then start runnning like it's going to run out of gas.most of the things you have all done i have done,even changed the fuel injection unit under upper intake, ran good for10 days or so and now doing it again.what the hell.someone please help.the last owner changed tires from 245s to 265s and took the tranny out. I was told to change them back because this is whats doing this, i don't know if this is it or what. helpppppp [:@]

 

I had the same problem wit mine, but my check engine light did come on. It turned out to be the knock sensors that went out. I just replacedthe sensorsand the wires that go to it(It all burned out)and it worked great after that.