New to the forum, knock sensor question

[bp71k5]

Hello,

I'm a new member and have a question about tuning around knock sensors. I'm about to get a new tune done and I've had my chip tuned a while back but always seemed to have issues with getting a knock signal error code from the ECM so I had the timing dialed back in the chip. It doesn't have any codes much anymore but has issues with stumbling and misfires before it warms up in the morning. If I increase the base timing to about 4 btdc, the cold start issues go away, but I don't want to keep it that way. I'm wondering if my knock sensor is picking up too much drivetrain noise and retarding the timing too much. I used a knock sensor from an 89 automatic, but I'm suspecting I should get one from a 92 manual trans since that what trans I'm using.
I get horrible mileage as we'll (8mpg on the freeway)

The specs for my truck is below.

1971 Chevy K5, 350 ci
7747 TBI system from a 1989 blazer (knock sensor too)
TBI adapter plate on an edelbrock carb intake
corvette exhaust manifolds
tbi "salad bowl" power charger.
nv4500 trans from 92 chevy 1 ton
dual transfer cases (they are noisy)
big heavy axles and 37" tires.

[steveo]

definitely could be false knock, what are your knock counts, and are they fairly constant?

you can always tune it out and see if it runs better

[bp71k5]

The knock counts read around 19-ish when I had the timing advanced, and went down to 4-ish when I put the base timing back to 0. I only rarely got a SES light about it under heavy throttle+load though.

Im going in got go through all the maintenance stuff like fuel filter, check injectors, vacuum leaks and then get someone to look at the tune. Not so interested in tuning it myself so I plan to have Eaglemark do some tuning for me. I'm wondering of anyone had a similar issue and noticed difference between the manual trans sensors and the automatic trans sensors

[Woods]

The knock sensor is actually matched to the ECM, not the transmission. GM used different ECM's, PCM's with different transmission applications later on. I believe that's where the different Knock Sensors come from.

From what I looked up the 89 Blazer used only one Knock Sensor for both applications. As long as it worked before, you should be fine.

[EagleMark]

The knock counts read around 19-ish when I had the timing advanced, and went down to 4-ish when I put the base timing back to 0. I only rarely got a SES light about it under heavy throttle+load though.

That's wehn the ESC forced knock test is done. With the CEL coing on then I'd say it's failing the test for some reason? You may have a bad wire, ESC module or knock sensor.

Is it a code 43? Do you have any data logs?

There is a difference in newer TBI trucks with manual and auto knock sensors. But they are also different ECM/PCM as well.

[bp71k5]

Honestly, I can't remember if it was a code 42 or 43. I used to check it a while back,but it would go off after about 10 minutes of driving so I stopped bothering to check it. I never got a code right after startup, only after driving a while.

So I swapped in a the new 1992 sensor (different P/N from the auto that year) and did some driving. Only get 8 knock counts when I first start it up and then no more through various driving styles. I tried lugging it a bit and giving it big throttle in a higher than normal gear to get it to knock but no luck (that's good luck I guess). No codes or anything odd so far, but I did find a overheated spark plug boot that needs to be replaced. Would posting a log be worthwhile before fixing that wire?

[bp71k5]

The knock sensor is actually matched to the ECM, not the transmission. GM used different ECM's, PCM's with different transmission applications later on. I believe that's where the different Knock Sensors come from.

From what I looked up the 89 Blazer used only one Knock Sensor for both applications. As long as it worked before, you should be fine.

I did the swap before I got this reply so I wanted to make sure I replied. My thought process (right or wrong) was that GM may have changed the knock sensor in 1992 with the introduction of this transmission on large trucks since the trans is so much more noisy than an auto. Hopefully it'll work ok cause it wasn't fun getting coolant all over the place swapping it.