Code 43 Knock Sensor Circuit Failure Issues

**Daveo91** · 08-08-2021

Originally Posted by tayto

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?

**Daveo91** · 08-09-2021

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?

**stew86MCSS396** · 08-09-2021

Not sure if this covers your year PCM...

**In-Tech** · 08-09-2021

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?

**stew86MCSS396** · 08-09-2021

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.

**In-Tech** · 08-09-2021

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

**Daveo91** · 08-10-2021

Originally Posted by stew86MCSS396

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?

**Daveo91** · 08-17-2021

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?

**stew86MCSS396** · 08-18-2021

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

**tayto** · 08-18-2021

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.

**Daveo91** · 09-30-2021

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

**NomakeWan** · 09-30-2021

Generally adding more sealant makes a knock sensor less sensitive, not more. Also usually when looking at knock I look at a scatterplot; it's what Trimalyzer does really well, for example.

**tayto** · 09-30-2021

Originally Posted by NomakeWan

Generally adding more sealant makes a knock sensor less sensitive, not more. Also usually when looking at knock I look at a scatterplot; it's what Trimalyzer does really well, for example.

dave just curious but what datalog cable are you using?. i read an old post on thirdgen that may be something to consider.... https://www.thirdgen.org/forums/diy-...when-aldl.html

Basically it's saying to use 10K resistor to connect then turn it off once connected. i know mine was always on 10k...