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Thread: Code 43 Knock Sensor Circuit Failure Issues

  1. #16
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    Idk if this is what you’re describing. I’m thinking it wouldn’t throw a code if it is.
    http://www.gearhead-efi.com/Fuel-Inj...o-knock-counts

  2. #17
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    do you have another memcal you can try? also f found wrong heat range, or fouled/worn spark plugs can cause high knock counts. also if you have exhaust touching the chassis or a worn motor mount is a good place to check. other thing i should mention, what did you torque the sensor too? IIRC, 14 ft-lbs. tightening it to much can cause issues as well.

  3. #18
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    As others have alluded to, changing the knock sensor isn't going to change the outcome. The only thing the ECM cares about regarding the sensors is the resistance. It uses that resistance to check if the sensors are physically in place, but nothing else. The sensors will continue to operate properly even if the resistance is out of spec and Code 43 gets thrown. This is very common; the resistors inside this type of knock sensor tend to fail well before the sensor element itself does.

    But the actual thing that's taking the signal from the knock sensor and telling the ECM that it's knock? That's the knock module, which on your ECM is integrated into the memcal. To change how your ECM interprets knock, you would have to change that module to a different one. Or disable knock feedback entirely, forget about your knock sensors, and just make sure your tune is up to snuff. Or I guess run some sort of external knock feedback rather than relying on the ECM.

    Best of luck.
    1990 Corvette (Manual)
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  4. #19
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    Thanks everyone. I went out and poked around tonight. My PS exhaust manifold has a heat stove around it (the kind that sends warm air up to air intake for cold operation) that is loose and may be rattling on the manifold. Could that cause a knock signal? I don't use it any more so I think I will remove it to be sure that's not causing the problem.

    Also pulled four spark plugs to take a look. 3 of the 4 looked pretty normal to me, but the one from #1 looked silver-ish, like maybe it's too hot. First pic is representative of the three plugs that looked similar, while the other two are from the one I'm thinking is showing hot. I'm thinking I'm going to replace them with one heat range cooler. Currently have Delco R44LTS, probably going to go to 43s.

    IMG_2254.jpg

    IMG_2250.jpg

    IMG_2251.jpg

  5. #20
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    can stuff the heat shield with steel wool dish scrubbers.what compression is your engine? i had a sbc 10:1 compression with vortec heads and went from 44LTS to 42LTS and nearly got rid of my knock counts that were maxing out every datalog.

  6. #21
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    Quote Originally Posted by tayto View Post
    can stuff the heat shield with steel wool dish scrubbers.what compression is your engine? i had a sbc 10:1 compression with vortec heads and went from 44LTS to 42LTS and nearly got rid of my knock counts that were maxing out every datalog.
    Thanks, great input. My 383 has about 9.5:1 - I agree I think the 44s are too hot for it. I also have a Vortec 355 with similar compression in my '76 Corvette and I've always run 43s in that. But it's got a q-jet and no knock sensor.

    Should I be worried about going too cold on the plugs though? Low RPM truck motor...could foul plugs more easily?
    Last edited by Daveo91; 08-19-2021 at 08:11 AM.

  7. #22
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    yes if they foul then too cold

  8. #23
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    dave, any update on this? I was getting 1000s of knock counts just idling. Found the knock sensor connector was broken, fixed that and also replaced my knock sensor w/ new ac delco. torqued to 14 ft-lbs per FSM. counts have gone down considerably but still there. i can get it to active the knock retard by just reving it in park. thought it might have been a belt accessory, but with belt removes there is still a racket. since this is a high mileage rig, 211,000 miles, i am thinking the timing chain is slapping around. i will be replacing along with new cam this winter, owner needs truck back soon.

  9. #24
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    Quote Originally Posted by tayto View Post
    dave, any update on this? I was getting 1000s of knock counts just idling. Found the knock sensor connector was broken, fixed that and also replaced my knock sensor w/ new ac delco. torqued to 14 ft-lbs per FSM. counts have gone down considerably but still there. i can get it to active the knock retard by just reving it in park. thought it might have been a belt accessory, but with belt removes there is still a racket. since this is a high mileage rig, 211,000 miles, i am thinking the timing chain is slapping around. i will be replacing along with new cam this winter, owner needs truck back soon.
    Sorry for the long delay in reply - I was out of town with no access through Sunday night. After changing plugs and fixing the things I think were causing noise, I haven't driven it much - no serious data logging yet. I really just drove it to get it warmed up to set base idle/min air. I did have the computer monitoring on at least one of those drives and I was watching knock counts a little. It looked like I was still getting some knock, but not near as much as before. And it seemed like it was not doing much knock retard any more. I hope to do some data logging this week or if not, this weekend. I'lll post results.

    Will you just turn off knock retard / Code 43 error in the BIN for now?

  10. #25
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    no, i only get SES if i hold higher rpm @ idle in park for extended periods. i had to work at it too get code to set. should take my own advice and replace plugs, the current ones look ok but i didn't install them so you don't know if they've been dropped or overtightened and porcelain has a hair line crack. drivebility seems ok, i should disconnect knock sensor and datalog to see if i'm still getting counts....
    Last edited by tayto; 09-14-2021 at 06:45 PM.

  11. #26
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    Quote Originally Posted by tayto View Post
    no, i only get SES if i hold higher rpm @ idle in park for extended periods. i had to work at it too get code to set. should take my own advice and replace plugs, the current ones look ok but i didn't install them so you don't know if they've been dropped or overtightened and porcelain has a hair line crack. drivebility seems ok, i should disconnect knock sensor and datalog to see if i'm still getting counts....
    I finally got a chance to do some data logging tonight. 27K knock counts in about a 10 minute drive. Watched the whole datalog so at least I know it didn't turn over in that time frame. So it's less than it was before I put new plugs in and tightened stuff, but still significant. I'm getting a lot of knock retard in the 3 deg or less range, but also getting some up to 10 deg in heavy accel or load. And it was showing 3 deg on the freeway at steady 60 mph, no hill. (but it was only a mile on the freeway)

    How do I know if this is real knock or it's just hearing something mechanical? Truck has stock L31 valvetrain (roller lifters) and also Comp Cams stamped steel roller-tip lifters. Would either of those cause noise?

    In your case, how would it register any knock at all if the KS is disconnected? (Not being a smart ass, I just want to know) Should I do that test?

    One last question, I have PE turned off for narrow-band VE tuning. Should I turn it back on? Maybe a lean condition during accel is causing knock? I'm about to switch to WB tuning so I think it should be on anyway for that?

  12. #27
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    mine wasn't registering knock with sensor disconnected. If it was i would suspect ECM. I worked on a '727 swapped into an older car that was running funny. found if you tapped the ecm case it would detect knock. replaced ecm and problem went away.

  13. #28
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    How do you know if it's real knock? Put high octane fuel in and pull all the timing. It won't make much power, but it also won't knock. If it says you're knocking anyway, it ain't real.
    1990 Corvette (Manual)
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  14. #29
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    Quote Originally Posted by NomakeWan View Post
    How do you know if it's real knock? Put high octane fuel in and pull all the timing. It won't make much power, but it also won't knock. If it says you're knocking anyway, it ain't real.
    I'll try that - eventually. I just put $100 of 87 octane in, as I was pumping I realized I should have put in 93 to see what it does. But I am going to pull timing and see what that does. I found this thread with the '98 vortec timing tables. They are all lower values than the ones in my BIN, up to 7 or 8 degrees. My engine is a 9.5:1 vortec 383 so I'm going to see what happens with those timing values.

  15. #30
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    Switched to the L31 timing tables (all cells at least 3 deg less than what I had before, many up around 7 or 8 less) and still getting high knock counts and lots of knock retard. Attached is a screen shot of knock retard running average values from about a 20 min log with freeway driving. It seems like it might be mostly fake knock? I'm also still getting an intermittent code SES light with Code 43 showing up in the log. Light comes on after 15-20 min of driving while coming to a stop. Usually turns off after a minute or two more.

    One thing I've been thinking about: I switched knock sensors a couple of times due to confusion about which one is correct. A new in box sensor has the orange teflon tape for sealant, but after a re-install I didn't trust that so I used a dab of ultra black Permatex. Could that be part of my problem? What is the proper sealing method after re-installing a KS?

    knock_retard_092921.jpg
    Last edited by Daveo91; 09-30-2021 at 08:23 AM.

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