False knock on 2002 S10 0411

I'm copying this from another forum in order of my posting.



262ci Forum (4.3)
Something feels like it is holding my truck back.
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Skylark
Skylark · Registered
Joined May 30, 2018 · 95 Posts
Discussion Starter • #1 • 6 days ago
Here is the truck, 2002 Xtreme 4.3, 5 speed, 3.42 gears, 8.5 with the G80. It currently has 130k, I've had it since 109k. Full synthetic fluids, all filters changed, NGK and AC plugs tried, I went back to the NGK because I prefer them. AC cap, rotor, wires, spider , O2 sensors and coil. The coil was because of a P0300 and I noticed that the coil was aftermarket and crusty. Everything else was replaced just due to my version of basic maintenance on a new to me vehicle. The fuel pressure is perfect all of the way through the top of 3rd gear. I finally got a little rattle in the front cat so I replaced both cats and the muffler. The distributor is at +1 over 1000 rpm. I've cleaned the mass air flow sensor with no changes. I've had 3 sets of tires on this truck, the stock 235/55/16, a set of 245/45/17 and now 275/40/17. It just hasn't ever felt "peppy". It refuses to break the tires loose unless if I dump the clutch over 2000 rpm. On the 245s I was routinely hitting 25 mpg on the flats at 70 mph and 18+ in town. The brakes aren't dragging and I don't drive like a teenager as evident by my mpg. I'm tempted to do a compression check just to see where it is at but with 130k it shouldn't be an issue. I haven't been shotgunning parts at it to fix anything but I'm quite surprised that it hasn't picked up anything.

Any suggestions as to what I could be looking for? No misfire on the scanner. It runs smoothly. It just feels like something is holding it back.

I've had 4.3 engines with 3.42 gears in full size trucks and 31 inch tall tires that were peppy. I had a 91 longbed on 245/75/16 that would leave about 25' of rubber at a 5 mph roll and actually scratch 2nd. My s10 just isn't in that league.

Here we go. I swapped the MAF with a known good one with no change. I grabbed the scanner and went for a drive. I noticed knock counts of 3-5 at full throttle and timing was 11-13 degrees. Under cruise I have 23-25 degrees, as soon as I give just a little bit of throttle the timing dropped to as little as -2 degrees with no knock counts.
Here is where it gets interesting. I unplugged the knock sensor and took it for a drive and it did the exact same thing complete with knock counts! I thought that maybe I unplugged something else but I verified the wire colors and connector style and it definitely is the knock sensor. Then I went to the pcm and depinned the knock sensor wire and drove it again and I have the exact same thing! I got frustrated and grabbed my ohm meter and checked the wiring between the pcm and the knock sensor and everything was perfect.

So how in the world do I still have knock counts???

Tomorrow I will borrow the pcm from an 02 Blazer (automatic, 4x4) and pop it in. Yes I know that it won't be right but it should run and throw a bunch of tranny codes.

I should add that the knock sensor was only unplugged for testing. I wasn't going to leave it that way.

I smoked it today. No leaks. Thanks for the idea though!

I did everything including the fuel filter as basic maintenance on a new to me vehicle within 1000 miles of purchasing. The only non AC Delco parts are the spark plugs. Nothing has changed the performance from my initial purchase although I just found out about the knock issue this week.

So this isn't a repost. Someone suggested that I smoke check the evap system so I did that. I've used 2 Snap On scanners and an OTC to verify the data. I didn't swap PCMs because I realized that I would have to do a security relearn on both vehicles and I didn't have enough time for that. I'm about to grab one of the $90 PCMs from evilbay because I'm 99% convinced that there is a programming error. I'm concerned that reflashing this one might not flash properly.

Quote:

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Originally Posted by Skylarkgp

I did everything including the fuel filter as basic maintenance on a new to me vehicle within 1000 miles of purchasing. The only non AC Delco parts are the spark plugs. Nothing has changed the performance from my initial purchase although I just found out about the knock issue this week.

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You unplugged the Sensor & are still getting Knock counts increasing?
Check the wiring between PCM & Sensor... (ESPECIALLY WHERE IT PASSES BETWEEN HEADER & BODY )
I had PCM out lots of times tracing this fault.


Terminal Crazy

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Originally Posted by Terminal_Crazy

You unplugged the Sensor & are still getting Knock counts increasing?
Check the wiring between PCM & Sensor... (ESPECIALLY WHERE IT PASSES BETWEEN HEADER & BODY )
I had PCM out lots of times tracing this fault.


Terminal Crazy

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I depinned it at the pcm and I still have knock according to the data. I also ohmed the wiring and wiggled the harness and it never flickered the ohmmeter.

Is it possible that the pcm isn't actually sensing knock but applying a knock value based upon engine parameters?

I know you have an 0411 so you aren't using EEHack, but I noticed--and confirmed from reports from at least as far back as 2017--that when EEHack has a communication error, it tends to show knock counts where there may be none. Just throwing it out there that the knock counts may actually be intermittent communications errors with whatever scanner you're using? Unless the scanner is actually pulling knock counts from a specific location in memory where the PCM itself is saving them, it's possible that these are false counts.

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Originally Posted by NomakeWan

I know you have an 0411 so you aren't using EEHack, but I noticed--and confirmed from reports from at least as far back as 2017--that when EEHack has a communication error, it tends to show knock counts where there may be none. Just throwing it out there that the knock counts may actually be intermittent communications errors with whatever scanner you're using? Unless the scanner is actually pulling knock counts from a specific location in memory where the PCM itself is saving them, it's possible that these are false counts.

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Would that account for the low timing? I've used 2 different Snap On scanners, solus and a newer one that came out a couple of years ago and an OTC Encore. The OTC is crap if anyone is curious.

Quote:

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Originally Posted by Skylarkgp

Would that account for the low timing? I've used 2 different Snap On scanners, solus and a newer one that came out a couple of years ago and an OTC Encore. The OTC is crap if anyone is curious.

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It would not, unless for some ungodly reason the scanner is altering timing without you doing anything, which it should never ever do. The low timing is being done by the PCM itself. Is "Knock Retard" an available parameter for you to inspect on the 0411 PCM? On the LT1 PCM it's a separate value from Knock Count. That could potentially explain the sudden drops in timing, though at that point it would also indicate that the knock is a real thing (or rather, that the PCM thinks it is).

Hi
What does EEHack show when it records a bad frame apart from knock counts. How can you tell from the log?

Mitch

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Originally Posted by Terminal_Crazy

Hi
What does EEHack show when it records a bad frame apart from knock counts. How can you tell from the log?

Mitch

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Hi Mitch, I would prefer if we didn't clutter this person's thread with unrelated topics, but to quickly answer your question, the log will give you data that makes zero sense in context. For example it may say that for a single frame of data you had a Check Engine Light for a random code, but then the frames before and after do not, which is impossible. It may say that you had the exact same data for several minutes without any parameter changing, which is impossible. It may say values like speed changed by massive swings within two frames, which is impossible. Now, the program itself while logging also keeps track of error counts, but these counts don't actually get logged with timestamps and the program doesn't discard data from bad frames, so while it should be possible to know with absolute certainty which frames are bad, instead you'll have to use your noggin' to sanity check what's there.