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knock sensor replacement help

10005 Views 6 Replies 5 Participants Last post by  gmcintex
1999 silverado 4.8 ~145,000 miles
SES light came on, it was the bank 2 knock sensor. cleared the code, drove about another 50 miles, SES light came back on for the same thing.
i haven't washed my engine bay in about 3 years or gone under any water recently. i only drive the truck 1 -3 times a week.

i called the dealer and the knock sensors were going for $ 75 a piece and he said roughly $300 in labor to do it. i haven't called any other shops yet, but i think i want to try and do this myself.

from everything i've read between here, fsc, and, i think i should be able to manage it. i work at a stereo shop for a living, so i consider myself to be fairly knowledgeable with disassembly and such. i just have a few questions for those that have already done this themself.

1. should i stick with oem knock sensors? or get the $18 on ebay, or get them from napa, autozone, advanced auto etc? what about the manifold gasket, oem or parts store? and i think the sensor harness is a dealer only item, so i'll have no choice with that one.
2. from what i've read i should replace both of them? should i also replace the harness just in case. i really don't want to pull the intake manifold off more than once.
3. when pulling the intake manifold off, is it easier to take the throttle body off with cables, hoses etc. attached from the manifold? or leave the throttle body on and disconnect cables, hoses etc?
4 the only special tools i need that i don't have are the fuel line disconnect, and an inch pound torque wrench to re-torque the manifold bolts; should i see straight forward how to disconnect the fuel lines from the manifold once i have the tool? i haven't really looked at it close and haven't taken the top cover off the engine to get a good look at everything.
5. how do i relieve the fuel pressure from the fuel line before disconnecting it? or is that done just by disconnecting and letting fuel spray everywhere with the disconnect tool?

sorry for so many questions. i just want to make sure i have and know everything possible before i attempt this. i live in an apartment and i'll have to drive about 25 minutes to a friends shop where we can work on it and i want to get this all done in one day with the least amount of problems
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1) i'd stick with the oem sensors and i believe the oems come with a harness?.. check and see but if not yes get the harness and both sensors, i did this on a buddys truck and busted the harness pretty easily
2) yes
3) i'd take everything off of the throttle body and just keep the throttlebody on the manifold. if someone can chime in on a different method but thats the way i did it.
4) everything is pretty strait forward under the cover, if you think youll get lost mark the hoses/lines with some tape.
5) not sure of the proper way but i just poped the line and let the fuel spray out(wraped it with a rag n let it flow) and i actually used a flathead screwdriver on the tabs and pulled it out. no need for the tool.

I did this on an 04 4.8 but I think it should be pretty similar. Its not super hard for the mechanically inclined, took me a couple hours w/ a few smoke/beer brakes :) good luck
thanks for your help, this has cleared up some of my concerns. if anyone else knows anything please feel free to chime in
1. I'd get some from NAPA at bare minimum. I don't think you'd need OEM but I wouldn't get cheap ones from Ebay.
2. May as well replace them both while you've got the manifold off. There isn't any reason to replace your manifold gaskets. More than likely, your intake hasn't been pulled often and those gaskets will reseal fine.
3. I'd leave the tb attached to the manifold. Your cruise control cable will just pull off the side of the TB and the actual throttle cable has a cylinder that needs to be pulled out from the side of the TB to release it. unbolt the three bolts on top of the manifold to move the cables out of the way.
4 buy the disconnect tool. its only $5 and will save you the hassle of messing up a steel fuel line and/or rail. Also, I wouldn't worry about an in/lb torque wrench. Just tighten the manifold back down from center outwards using German torque specs...GuudNtite (don't bare down on them...getting them snug will be fine).
5. passenger side of the cross over tube has a schrader valve (like found in a tire valve stem). Just use something to depress it to relieve the fuel pressure from the rail. have a rag ready to cover it when relieving pressure.
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1) I ended up using one sensor from AutoZone and one from O'Reilly's. (AutoZone only had one.)
2) I replaced both even though the Bank 1 (front) sensor looked brand new. I didn't replace the harness, mine was fine.
3) I just disconnected the cruise control and throttle from the throttle body and unbolted the brackets holding them on and laid everything aside.
4) Go ahead and get the disconnect tools. I believe you'll need a 3/8" (supply line) as well as a 5/16" (return line) tool. I got mine from O'Reillys from $3 a piece.
5) The way I relieved my pressure was by pulling the fuel pump relay from the fuse box under the hood and I started the motor and let it die. (might toss up a SES code but you'll have no pressure in the lines when you disconnect the lines and you can clear the code.)

I just did this a couple of weeks ago and it took me about 6 hours from start to finish. It's not too difficult, just time consuming. Good luck.
I've got the same truck(01 gmc 5.3 ext cab 4x4) but the guy at the auto parts store acted like he knew what he was talking about and said the knock sensor is on the bottom of the block? was he just way off?
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