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Thread: Code 43 Knock Sensor Circuit Failure Issues

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    Code 43 Knock Sensor Circuit Failure Issues

    I decided to start a new post for this situation since it's very specific. But background here on my '7060 to '7427 conversion if it's helpful. Still lots to resolve on the conversion, but I think the most important thing right now is to get the KS issue resolved.

    So the weird thing about the code 43 I'm getting (in TunerPro and SES illuminates) is that it will set either immediately after starting the engine OR it will set after about 30 seconds of key on, engine NOT running. For both tests I'm sure the code is cleared by unplugging both ECM connectors for a minute and restarting TunerPro to clear the flag there. And both tests are consistent. Is it strange that the flag will set without the engine running? Stuff I've seen says that it does not do its diagnostic until after engine is running. Does that point to a possible ECM or Memcal issue? I will go through the FSM diagnostic procedure on the KS circuit, but wanted to check here to see if maybe that's not necessary based on the above observations.

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    do you have correct knock sensor? i believe on 7427 knock module is with the memcal, you can try reseating the memcal.

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    Quote Originally Posted by Daveo91 View Post
    I decided to start a new post for this situation since it's very specific. But background here on my '7060 to '7427 conversion if it's helpful. Still lots to resolve on the conversion, but I think the most important thing right now is to get the KS issue resolved.

    So the weird thing about the code 43 I'm getting (in TunerPro and SES illuminates) is that it will set either immediately after starting the engine OR it will set after about 30 seconds of key on, engine NOT running. For both tests I'm sure the code is cleared by unplugging both ECM connectors for a minute and restarting TunerPro to clear the flag there. And both tests are consistent. Is it strange that the flag will set without the engine running? Stuff I've seen says that it does not do its diagnostic until after engine is running. Does that point to a possible ECM or Memcal issue? I will go through the FSM diagnostic procedure on the KS circuit, but wanted to check here to see if maybe that's not necessary based on the above observations.
    Check the cables aren't rubbing the bodywork between sensor & PCM. If it's in a 4th gen F body, it runs up the side of the tunnel in silver foil next to the header. I don't think the diagnostic checks cable against ground.

    Mitch
    '95 Z28 M6 -Just the odd mod.
    '80 350 A3 C3 Corvette - recent addition.

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    duplicate post
    Last edited by Daveo91; 08-05-2021 at 10:18 PM.

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    Quote Originally Posted by Terminal_Crazy View Post
    Check the cables aren't rubbing the bodywork between sensor & PCM. If it's in a 4th gen F body, it runs up the side of the tunnel in silver foil next to the header. I don't think the diagnostic checks cable against ground.

    Mitch
    Thanks, it's a '91 squarebody suburban, but I'll check for any wire issues. I have previously checked for continuity between the PCM and KS - good, but maybe there's a persistent problem with a ground wire somewhere.

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    Quote Originally Posted by tayto View Post
    do you have correct knock sensor? i believe on 7427 knock module is with the memcal, you can try reseating the memcal.
    Pretty sure I have the correct KS: Delphi AS10016. As recommended by @daveW and it's what shows up for a '94 350 truck. I'll try and reseat the memcal - thanks great suggestion. I really think it's something along these lines since it flags as soon as engine starts or even after 30 seconds with key on. Also, KS appears to have been working for my first few runs after the conversion.

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    pretty sure 7060 and 7427 share the same knock sensor, but it's an easy check to do with DMM.

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    Quote Originally Posted by tayto View Post
    pretty sure 7060 and 7427 share the same knock sensor, but it's an easy check to do with DMM.
    Yep, you're correct, they are. I tested resistance on both, old one was around 100K ohms which AFAIK is right within spec, but the new one was only testing around 2K. So I swapped them and am running the old now. But I'm still having the same problem with the flag setting within 30 seconds, engine running or not. I'm wondering if the low resistance could have killed the memcal or something in the PCM?

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    I might have solved this issue with the KS, but not exactly sure how.

    First, I'm fortunate to live in the same city as Dave W (Vancouver, WA) He let me try a different 7427 and memcal. Exact same issue, no change at all so we were both mystified. In the course of this, Dave informed me that the KS with the much lower resistance - that I had taken out - was indeed the correct one. So tonight I reinstalled the correct (Delphi AS10016) KS, and, lo and behold, no code. I have not driven it yet, but left the key on for twice as long as it was taking to set the flag before, and then started engine and let it run for a bit. No code. Before it would have flagged within 20-30 seconds of either just key on or engine running. Won't know for sure till I drive it which won't be for a week or so now.

    With the correct KS installed I back-pinned a paper clip in to the B15 terminal so I could check voltage on the KS circuit to engine ground: 2.43 (key on) and I think 2.48 or so engine running. Do those voltages seem correct?

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    Not sure if this covers your year PCM...

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    That's a great fault tree, thanks for posting. Is that for the 7427 auto pcm or for the '95 manual ecm with a 2732a and not a memcal?
    -Carl

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    Not 100% certain but do seem to recall the latter would accompany escm and the fault tree would make some sort of reference to it.

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    I can't remember if it had a knock module. I put a whipple on that '95 manual and quickly converted it to a 7427 'puter. Sheesh, I want to say that was in 95 or 96 so, a couple days ago
    -Carl

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    Quote Originally Posted by stew86MCSS396 View Post
    Not sure if this covers your year PCM...
    Awesome - thank you for the fault tree. So sounds like the consensus is that this is for a '7427 auto truck?

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    So I'm not entirely sure what I did other than re-install the correct knock sensor, but now my code 43 problem has shifted to intermittent. It does not come on within 30 seconds of key on or engine running like previously, now it comes on after about 10 minutes of driving. Both times it was after a decel event, coming to idle. One of those two times, the SES light went out on the way back home, the other time it did not.

    Even while the flag is set, the knock sensor circuit appear to be working and showing knock counts in TP. A lot of them in fact, 10s of thousands per drive. A single acceleration event can trigger thousands and consistent 10 degrees plus of retard. There are no audible knocking sounds, and no unusual mechanical sounds ,that I can hear at least. I do have a roller cam (stock L31 complete set up including cam, lifters, heads, spider, retainers, etc. And I used a new set of Comp Cams stamped steel, roller-tip rockers. Could the knock sensor I'm using be incompatible with roller cam? A Google search indicated that can be an issue. If so, thoughts on which KS to use?

    I have not done this yet, but I will remove a couple of plugs to check condition. I would think tens of thousands of knock counts would be pretty obvious by looking at the plugs?

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