knock sensor

mightybg · March 4, 2007

I have problem with my truck running badly it is a 91 k2500 5.7l. It is acting like the timing is way off on it and i have replaced just about everything you can unbolt or unplug from the engine. the truck backfires when the base timing is set at 0 btdc and you accelerate at high speeds lightly also hesitates when moving from a stop. the only way to remedy it was to put 5 degrees advance and you can tell the truck still isn;t running quite right. any ways i was thinking the knock circuit is bad so i unplug the sensor before i left from work drove it home 6 miles (it got up to temp though) and when i shut the truck off and checked for a code 43 there were no codes stored. Is my pcm bad or would I need certain conditions to set it off other than just being unplugged?

cambo · March 4, 2007

I have an 2001 and I need to replace my knock sensor also. But my performance or anything hasn't changed since I got it checked out. I would get it fixed but its like $800 to get it done. So I am just going to have to deal with the engine rattle when I press the accelerator for a while.

Wingnut · March 4, 2007

I have an 2001 and I need to replace my knock sensor also. But my performance or anything hasn't changed since I got it checked out. I would get it fixed but its like $800 to get it done. So I am just going to have to deal with the engine rattle when I press the accelerator for a while.

Yours is $800 because it's in the lifter valley under the intake manifold. His is $40 because it's in the side of the block. :/

cambo · March 4, 2007

Oh I didn't read his whole post. Whoops.

Yea, also I don't trust just anyone to tear down the top end of my engine and put it back together.

Wingnut · March 4, 2007

It's not a bad or tough job. Pretty straightforward.

cambo · March 4, 2007

Yea, but you also don't know the town I live in. No mechanic where I live has gone to school to do what they do. They just learn from trial and error.

redvett · March 4, 2007

I have problem with my truck running badly it is a 91 k2500 5.7l. It is acting like the timing is way off on it and i have replaced just about everything you can unbolt or unplug from the engine. the truck backfires when the base timing is set at 0 btdc and you accelerate at high speeds lightly also hesitates when moving from a stop. the only way to remedy it was to put 5 degrees advance and you can tell the truck still isn;t running quite right. any ways i was thinking the knock circuit is bad so i unplug the sensor before i left from work drove it home 6 miles (it got up to temp though) and when i shut the truck off and checked for a code 43 there were no codes stored. Is my pcm bad or would I need certain conditions to set it off other than just being unplugged?

The 91 has the knock sensor on the RH lower block drain. You need to get a new one (GM) and replace. Becareful with the torque 15flbs and do not drop sensor or its junk. Also there is a knock sensor module on the RH side under air cleaner its flat about 3"x3" and has 5 terminals with a 3 letter code it may have gone bad. If the ign module hasent been replaced since new replace only with a GM OEM since the circuitry is designed to control spark knock. There is no circuits in your ECM for knock control. I would start with the knock sensor first and the ign module next.

95Sierra2500 · March 4, 2007

You need to get a new one (GM) and replace. Becareful with the torque 15flbs and do not drop sensor or its junk.

He can get one from Advance or Murray's or where ever, they're just as good. However, I think your torque spec is a little high...we tried 15 ftlbs on my dad's truck and that junked the sensor...You actually have to go to about 12 ftlbs...or that's what we found, anyway.

mightybg · March 4, 2007

I got all of that, another thing is that the zone tried to sell me the wrong resistance knock sensor found that out withe the haynes manual and alldata, my knock sensor connects directly to the PCM no esc module. anyway I actually posted that I unplugged the knock sensor from the PCM and didn't get a code 43 that is what the problem is, after that is taken care of I can get to figuring out if my knock sensor still works, (which i think it probably will).

Norseman · March 5, 2007

Oh I didn't read his whole post. Whoops.

Yea, also I don't trust just anyone to tear down the top end of my engine and put it back together.

Then just do it yourself, it's an easy job.

cambo · March 5, 2007

I do not have the tools, experience, or any knowledge of what to fix. I am just going to go to a Chevy dealer to get it done.

mightybg · March 5, 2007

you guys hijacked my post.

Norseman · March 5, 2007

you guys hijacked my post.

Sorry! But, I thought your question had been answered.

mightybg · March 5, 2007

Did you read any of my posts in here? I said what the problem is and then this dude jumnped in and started talking about him needing to change his knock sensor and every body started giving him info. so i restated what my(the person who started this topic) problem was, and that was just flat out ignored. so my question really wasn't even addressed but I think cambo should be squared away by now.

mightybg · March 5, 2007

I have problem with my truck running badly it is a 91 k2500 5.7l. It is acting like the timing is way off on it and i have replaced just about everything you can unbolt or unplug from the engine. the truck backfires when the base timing is set at 0 btdc and you accelerate at high speeds lightly also hesitates when moving from a stop. the only way to remedy it was to put 5 degrees advance and you can tell the truck still isn;t running quite right. any ways i was thinking the knock circuit is bad so i unplug the sensor before i left from work drove it home 6 miles (it got up to temp though) and when i shut the truck off and checked for a code 43 there were no codes stored. Is my pcm bad or would I need certain conditions to set it off other than just being unplugged?

The 91 has the knock sensor on the RH lower block drain. You need to get a new one (GM) and replace. Becareful with the torque 15flbs and do not drop sensor or its junk. Also there is a knock sensor module on the RH side under air cleaner its flat about 3"x3" and has 5 terminals with a 3 letter code it may have gone bad. If the ign module hasent been replaced since new replace only with a GM OEM since the circuitry is designed to control spark knock. There is no circuits in your ECM for knock control. I would start with the knock sensor first and the ign module next.

the knock sensor on my truck goes directly to the ECM and then the brown/black wire goes the teh ign control module on teh distributor. I would have to say yes there is a knock control circuit in the ECM or it at least is conditioned through there. (alldata also says this)