Ok i need some mechanical help!!

[MEMPHISFLEX 10+ year member]

I been working on cars since i was a lil guy, worked at ford as a mechanic for 2.5years, went to school for this sort of thing, along with body work, and paint work, but this truck has me stumpped!

Truck is a 1999 Chevy 2500 (lightduty not HD) with a 6.0L V8 in it, 4wd, 216,000miles on it, its my grandpas farm truck.

The problem with the truck is, when it was cold outside it started acting up, it would fall on its face, run out power, full throttle 35mph was max, then it would come out of it, and run fine?? Now that its really warm out side, its doing the same thing, will be ok untill the truck gets warmed up, then it will run out power totally, 35-40mph max speed, and wont go over 3000rpms, so i hooked up our Snap-On diagonistic scan tool to the OBD II out put under the dash, and got a oxygen sensor code, bank 1 sensor 1 which is a down stream O2 sensor on the left side, so i had my grandpa get a new O2 sensor, changed that out a few days ago, still doing it, and that was the only code in computer, it doesnt have any miss fire codes either, so we said piss on changing all the plugs, and all the coil packs, since these new vortec chevy motors have a coil on plug, and they cost alot. So then we thought maybe it is a fuel problem, so i hooked up the fuel pressure tester, tested the fuel pressure, runs at around 55-63psi, which is about right for these newer vortecs, then thought maybe its the fuel filter, so i had grandpa get a new one of them, put that on today, well the fuel filter i took off i couldnt blow threw at all, so i was like well thats a big problem right there, i put the new fuel filter in, and it seemed to be ok, so he wanted to go out and drive it and see how it was out on the open road, since all i did was put a load on it in the shop, he comes back and its doing the same thing, i have ran out of options here, it has good spark, fuel pressure, no other codes in the computer, what should i look into, i have never ran into a problem like this, maybe it has a bad coil but it should miss if it does, you would think?? But the truck just runs out of power, just like somebody put a governor on it, wont go past 3000-3300rpms, at most, and just wont go, any input fellow mechanics out there???

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[Joseph M 10+ year member]

very odd. the ECU's in those newer chevys are funky. My brother had a 01, and the security dil would mess with em everyonce in a while and not let the truck start. and i notice it does the same on my girlfriends step dad 2500 hd but his doesnt have near as many miles. and the spark plugs on newer chevys are only supose to be replaced every 100k so i am lost also

 

[MEMPHISFLEX 10+ year member]

Yeah i have ran into about every issue with vehicles, but this one has everybody stumpped, we even took it to a local Chevy dealer ship and they cant figure it out, i need some input here!! HELP PLEASE

 

[liftedcj7on44s 10+ year member]

Try cleaning the MAF meter. Clean the Throttle body real well also!

 

[Fear Of Theive 10+ year member]

My dad has been a mechnic for 30 years and he said check the wiring on the o2 sensor,may have bad wiring.

 

[liftedcj7on44s 10+ year member]

o2's just gonna cause it to run rich more than likely. A faulty MAF meter wont let the truck run over a certain RPM!

If you have any carb cleaner(which isnt suggested but i use it) take and clean the resistor off real good and try it, should take no lnger than 10 minutes to do.

 

[liftedcj7on44s 10+ year member]

also if it said bank 1 sensor 1 then what i am reading right is you changed the downstream sensor which is the one after the cat. Bank 1 sensor 1 is the one b4 the cat!

 

[sickofsoyo 10+ year member]

check engine temp and coolant... could be in overheat mode, where the car will run on only a few cylanders and only rev to a certain point. I know in my monte carlo SS hand book it says it does this as a precaution to the engine.

 

[Fear Of Theive 10+ year member]

Hey if he gets a o2 sensor he has to have a problem around that area that will kick it up so CJ

 

[liftedcj7on44s 10+ year member]

not necessarily fear of thieves. Ive seen plenty of Bad MAf's and vacuum leaks throw a O2 sensor code. also stated above a bad CTS will cause the truck to run rich. anytime you have a lean or rich condition the o2 sensor will throw a code because the 02 is reading too lean or too rich because something else is a miss.

 

[Fear Of Theive 10+ year member]

So your still alive?

Also Thank you Mr.GoodWrench

 

[MEMPHISFLEX 10+ year member]

also if it said bank 1 sensor 1 then what i am reading right is you changed the downstream sensor which is the one after the cat. Bank 1 sensor 1 is the one b4 the cat!

That was a miss type, it was before the cat, up stream bank 1 sensor 1, and yeah the O2 sensor shouldnt have a effect like that, but it was weak so I changed it, and im going out now to rip the air intake system off and see if it has something to do with that, maybe the throttle body is really dirty, or the MAF is dirty, i know fords would pull a check engine light on and run like shit, with the littlest piece of dirt on the MAF! I just really dont know what to say, ill go rip the airintake system off of it, clean up the TB and the MAF and then see how that is!! Keep me updated with ideas tho!

 

[liftedcj7on44s 10+ year member]

fear of thieves i am a mechanic as well so dont make assumptions on people like you did. Just because a certain code is thrown out doesnt always mean thats the problem. If you make a living as a mechanic you would find that out real quick.

 

[MEMPHISFLEX 10+ year member]

not necessarily fear of thieves. Ive seen plenty of Bad MAf's and vacuum leaks throw a O2 sensor code. also stated above a bad CTS will cause the truck to run rich. anytime you have a lean or rich condition the o2 sensor will throw a code because the 02 is reading too lean or too rich because something else is a miss.

Exactly and on the Snap On scanner, you can monitor every O2 sensor and bank 1 sensor 1 was acting up, and pulled that code! But i didnt think it would be something like that, making it do what it does, i mean you can run cars with out 02 sensors, not smart, and they run wierd as hell, but this thing runs out power totally and then all of a sudden comes to life, but it might act up for miles then come out of it! Im going to check TB and MAF, thanks for the help so far, keep the opinions and thoughts coming!! The O2 sensor was just a gamble, i knew that was not going to do the trick but my grandpa wanted it done, since it was acting up!

 

[MEMPHISFLEX 10+ year member]

Nobody needs to argue here, i just need some help from other mechanics, thanks so far ill be back in a few!