I have a 2.8 in my '93 s10. I don't think the engine is exactly the same as the 2.8 in the f-bodies, but I was hoping someone here could help out. I'm getting knock during part throttle operations under load. But when I go full throttle it goes away. The engine is completely stock with 130,000 miles. I would have thought that the ecu would back off the timing until the knock went away. Could I be running lean? If so, what should I do? change the O2 sensor?

thanks,
Chris

 

sounds like spark knock to me. probably from a carbon build up on top of the pistons. get some GM top end cleaner and try that. from what i hear, its some good stuff.

 

I'll look into the cleaner.

Is there a knock sensor on this engine? I'm wondering why the ecu doesn't correct it or throw a code.

 

The engine should have a knock sensor, but how do you have a '93 with a 2.8??? They switched over to the 4.3L in '91 for the S-Series truck.

The knock doesn't go away @ WOT, you just can't hear it. If you hear WOT knock, then you are damaging the motor. My money is on leaness. We see that all the time at the shop I work at. 99% of all the cars that come in and fail smog due to emisions, do it because they are running lean.

 

Well there is rumors to be allot of Chevy truck that do not have the right 4.3 motor. Not sure where or who made them but I assume they ran short n stuck in anything that fit.

Buddy had a 91-92 from the original owner. It was also suppose to be a 4.3 truck but had a 3.4. The guy had paperwork to take it back to get the right engine but he never did. I changed the smog pump on that sucker. Its was a 3.4, should of been the 4.3

 

The engine is definitely a 2.8 and its the original engine.
If it is running lean, how do I correct that? O2 sensor?

 

I thought there wasn't a knock sensor on the 2.8?

edit: https://www.thirdgen.org/techbb2/sho...hreadid=244978

 

The 2.8 that came in the S-Series truck was TBI, not MPFI, so it got a different computer. by 91, Gm "did away" with the 2.8 and went to the 3.1L. At that point, they were all Speed density(MAP) systems and had a knock sensor, the 2.8 didn't.

 

Sounds good.

 

Where can you get GM Top End Cleaner? None of the stores around here have it...

 

GM...

There is also a product made by a company named BG, we use their cleaner all the time, it works REALLY well.

 

Hey if you want to clean carbon off of your pistons just floor that sucker and keep the revs up high, you'll burn it right off. I believe carbon buildup usually happens when you baby the motor and keep the revs down really low.