Possible sensor going south ???

[kenny-1907]

I will try and make this brief. About 2 months ago or so my 2000 silverado with the 4.8 developed what seemed to be an engine miss, took it to garage , no codes but they did admit that there was something wrong. Changed plugs, fuel filter, no change. (58000 km on the truck now) had it into GM , it is the #5,6 cylinders that are stumbling , #6 is real bad and they think that #5 is just doing the same cause it is next in the firing order. But no codes. poured 2 bottles of injector cleaner into it (i know i know , too much) the more i drove it , the better it got , so i figured the problem was a dirty injector, not so after i refueled, the problem returned. Took it to a garage and had the injectors purged and combustion cleaner ran though it , problem still there. It only occurs after the truck is up to operating temp and i am sitting idling at a stop light ect, it feels like someone walks up to the truck and kicks the bumper as hard as they can. I Read on here about resetting your computer, disconnected the battery and let it sit all day at work. Problem went away YAYYYY...........not. About 2-3 weeks later it started again, so today i disconnected the batttery at work again and let it sit ,and on the drive home all is fine again ......probably till about another 2 1/2 weeks of driving My thinking is that it could not be a faulty plug... it would not get better after resetting the computer, same for a dirty injector , would not get better.....especially after cleaning them after only 58000 km's. My question is , could this be a sensor somewhere that is starting to go bad , i heard that a faulty temp sensor will cause wierd stuff to happen but mostly on colder engines and as i said this problem only happens after the truck is @ operating temp. ANY sugestions would be appreciated.....ANY . thankyou

[GMMerlin]

I would first do an injector balance test..these injectors don't take much to plug.
Most of the injector problems I have seen have been caused by contaminated gas. It doesn't take much to plug the screens on top of these injectors.
if I do find one that has a plugged screen I recommend first replacing the filter and flushing the fuel rail.....if it is bad enough, I have gone as far as dropping the tank and flushing it out, flushing the lines and replacing the pump.
There are some other things that can cause your concern like a vacum leak, wiring issue or sensor problem, but most of the time on these vehicles I look at the fuel system first...all based on experiance

[skipr]

Originally Posted by GMMerlin

I would first do an injector balance test..these injectors don't take much to plug.
Most of the injector problems I have seen have been caused by contaminated gas. It doesn't take much to plug the screens on top of these injectors.
if I do find one that has a plugged screen I recommend first replacing the filter and flushing the fuel rail.....if it is bad enough, I have gone as far as dropping the tank and flushing it out, flushing the lines and replacing the pump.
There are some other things that can cause your concern like a vacum leak, wiring issue or sensor problem, but most of the time on these vehicles I look at the fuel system first...all based on experiance

I heard the balance test isn't always conclusive on locating a bad poppet. I stress the words "I Heard". I hear alot of things that are bull sh%#.

[kenny-1907]

Well for starters i was wrong , i had to go out tonight and it is still doing it. as for the comments you made GMMerlin , i already have had the injectors cleaned as well as the combustion chamber. If this were an injector issue would it not do it all the time and not just once the vehicle warmed up ? also , the fuel filter has already been replaced approx 2.5 months before this problem started. Don't get me wrong i am not doubting you or your expierence , but i would think if it is an injector plugged in anyway , i would think it would do it all the time <shrugs> I odo know that a person can almost put money on it that it is not a plug case if they go south , they will always act up once warm. as for possible vaccum leaks or a wiring problem , would something like that not show up on the scanner especially if they had their scantool hooked up at the same time that this problem was there ? <shrugs again>

[GMMerlin]

Originally Posted by skipr

I heard the balance test isn't always conclusive on locating a bad poppet. I stress the words "I Heard". I hear alot of things that are bull sh%#.

Well since the 00 Silverado 4.8 is not equipped with poppet style injectors..once again you have heard wrong

[gschretter]

Do a compression test when your engine is warm.
See how close they are to the other cyl.