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Stupid knock sensors

This is a discussion on Stupid knock sensors within the General Help forums, part of the LSx Technical Help Section category; 05 Z71 5.3 truck. I have had knock sensor drama with this thing since I got it 2 years ago. ...

  1. #1
    Junior Member Z28dryva's Avatar
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    Stupid knock sensors

    05 Z71 5.3 truck. I have had knock sensor drama with this thing since I got it 2 years ago. The previous owner replaced both and the pigtail. I replaced both and the pigtail. I had my moron former tuner tuned them out because he said he could. Of course that's not true (so my new tuner informed me of) and I've been getting shitty gas mileage ever since. #1 is constantly throwing a low voltage code and #2 has been known to from a time to time. I recent ran a wire straight from the PCM to the pigtail for #1 (pin 51 on blue connector) and had 0 results. It came on faster it seems from me using a lower guage wire as a jumper. I have tested the KS's themselves and they both have 100 ohms of resistance. Same on the pigtail and the PCM pin (100.1 ohms at the actual PCM pin) I'm completely stumped as to what will continually make a knock sensor throw a low voltage code when everything (including PCM) has been replaced twice. Only thing I can do now is pull off the valley plate and make sure the grommet isn't leaking oil onto the sensor. My 01 Trans Am pulled that code because of this. I would greatly appreciate any info anyone has about this problem

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    Sound like parts store knock sensors -- throw a set of GM's in there and be done with it.

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    Junior Member Z28dryva's Avatar
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    They are but the Trans Am has them and has never had a problem. Different engines respond differently to off brand knock sensors?

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    Junior Member Z28dryva's Avatar
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    Also, if I use GM knock sensors, do I need Delphis or Delcos?

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    Whatever they have at the GM parts counter. So long as your wire harnesses are in good shape -- no breaks or corrosion, you should be good to go.

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    Junior Member Z28dryva's Avatar
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    Well I was getting it off of Rock Auto so that's why I asked. My Tuner said Delco's the only way to go. Like I said, I jumped a wire directly from the PCM to the knock sensor and it still threw a code. The fact that the pigtail has been replaced 3 times pretty much rules that out.

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    Spaz is My Mentor SMWS6TA's Avatar
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    make sure you're getting 99'< KS sensors vs >98'. They look the same but the >98's have been phased out from GM but are still in Auto part stores inventory.

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    Junior Member Z28dryva's Avatar
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    Ok so I got Delco KS's and a Dorman KS harness from Rockauto. This harness made the Delco version look like a cheap piece of shit. I removed the intake and they old harness looked good. I replaced them right after I got the truck 2 years ago as the CEL codes were saying they were bad. I removed the harness and the knock sensors themselves look like they just came out of the box. I pulled them and noticed the front hole in the valley plate looked corroded or possibly water damaged. I pulled the valley plate and both KS grommets were seized to the little platforms the KS's sit on. Luckily I thought ahead and picked up a couple of new ones at the dealership on the way home. I noticed the platforms were extremely rusted and covered in crap. I spent and hour with WD40 and a wire brush and got the KS mounting platforms as well as the holes in the valley plate back to spotless. I then took one of the old KS's and ran it in and out of the KS platforms 5 or 6 times apiece. I tightened the hell out of it every time I cranked on it in an attempt to clean off the threads. I installed the new KS grommets, KS's themselves, as well as the harness. I slapped the intake back on and plugged everything back in then took it for a test drive. I immediately noted 10 more degrees of timing advancement then I had previously. It runs around 28 degrees now at WOT. It never went over 19 before, even dyno tuned. I expect to see a great increase in power and gas mileage once the engines starts to learn it has timing advancement once again. I'm taking it to my new tuner tomorrow to have an off-the-dyno tune put in it. Looks like rust and moisture were to blame for my knock sensor tribulations

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    I pinched a front KS wire when I reinstalled the intake on my engine swap over a year ago. I had 1000 ohms R on my KS's. I had 0 ohms R on the front wire due to the fore-mentioned pinch. I fixed it last Dec. and it hasn't been a problem since. I'm careful and meticulous and it still happened to me. It's one of those things to watch out for and it's happened to more than a few of us.

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    Spaz is My Mentor SMWS6TA's Avatar
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    glad to see you fixed it. Some of us here have started putting a 1/8th of inch ring of RTV around the KS wholes to help make a barrier from the water. I know too late for you now but something to keep in mind for next time.

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    Smiles for 9.5 Years cammed goat's Avatar
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    I have read and heard that mositure can lead to corrosion thus causing a "false knock" condition. Also, if the KS is overtightened, that will cause a "false knock" as well. Keep us posted with progress or any other issues OP.

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    Junior Member Z28dryva's Avatar
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    Quote Originally Posted by SMWS6TA View Post
    glad to see you fixed it. Some of us here have started putting a 1/8th of inch ring of RTV around the KS wholes to help make a barrier from the water. I know too late for you now but something to keep in mind for next time.
    Haha this is LS motors we're dealing with here. I can yank that intake off and seal it up real quick in an hour or so. I did clean the hell out of the valley plate where the top grommet plugs into it to make it seal a little better but the hole in the middle where the wire goes in always lets a little in. If there was any kind of a reliability factor to the knock sensors,(only have to be replaced once in an engine's lifetime) I'd just fill the whole damn hole with caulk and call it done

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    Is putting caulk in the hole to remove moisture? Or another reason i have missed?

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    Water can leak down from the cowl and accumulate on the valley cover. If it gets to the sensors, they start to rust. Caulking around the plugs can help seal out water.

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    ok.....learn something every day!!! Thanks....

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    Ive had the same problem, replaced everything and still getting a code

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    Did you use parts store sensors or GM pieces?

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    AC Delco i think

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    Junior Member Z28dryva's Avatar
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    Quote Originally Posted by Spikito View Post
    Ive had the same problem, replaced everything and still getting a code
    Get on those mounting platforms with a wire wheel. Don't stop until they're shiny or the rust/corrosion/bull shit down there will create resistance for the sensor
    Spikito likes this.

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