LT4 Knock module questions

[Dannyac500]

Couple questions about the LT4 knock modules, but first a little background info. So we recently switched our 96 Z over to an OBD1 PCM. We were running the factory PCM with a PCMforless tune up until the motor rebuild and the car was deadly consistent. Over the winter we rebuilt the engine (bad head gasket). The engine was all reassembled with stock parts with the exception of adding the LT4 hotcam. We purchased an OBD1 PCM from MadTuner (ordered as 94-95 PCM compatible with 96 knock sensors). The engine was reassembled with the 96 knock sensor. The PCM was supposed to be programmed to reflect the new cam, tire size and set shift points to 6k. Made some passes with the car and was bouncing off rev limiter @ 5850-5900 and not shifting. I pulled the tune with tunercats and the fuel cutoffs were set to 5825 (SWEET.) I upped them to 6275 and it now shifts fine right at 6k. I found that there was also NO entry for tire size at all in the PCM, so i added it in myself. Now that we got the car shifting fine my data log showed it pulling 12* of timing running down the 1/4 mile.

From all my research on here i have to come to the following conclusion, and feel free to correct me if im wrong. To make the OBD1 PCM compatible with my setup, i need to EITHER: A: have the LT4 KM installed in the OBD1 PCM.....OR B: install an OBD1 knock sensor correct? So i pulled the OBD1 PCM from the car and found the stock (#16177700 OBD1 KM) installed. I opened up my old PCM (OBD2) and found the LT4 (16214681 KM). This was installed by PCMforless when we put the 1.6 rollers and headers on the car. So the moral of this story is that I dont believe the PCM purchased from MadTuner was what it was supposed to be. There isnt anything internal to the PCM other than the KM that would be modified to support the 96 knock sensor right? Unless you desensitized the knock tables, but why would you when you can easily change out the KM? So in the end i swapped the KM's and now i have the LT4 KM in my OBD1 PCM and its reinstalled into the car. Im assuming this was the correct move on my part? The KM is a stand alone unit correct? meaning i shouldnt have to do anymore tuning to the PCM for it to recognize the new KM? Planning on taking the car to the track friday to make some passes to im interested to see if its still pulling all the timing out @ WOT.

Sorry for the novel, but id love to know what you all think
Thanks

[SSlowBoat]

You still desensitize the knock tables a lot of the time, lt4 knock module doesn't make tuning issues go away, it just desensitizes the physical record of seeing the rockers or things of that nature etc. Meaning false knock.

I'd say it was the correct move, but don't be suprised if you still see knock being pulled. That's where you desensitize it. Also, lt4 modules aren't the end all be all fix, there have been cases (myself included) where if it's a really early obd1 computer, it literally will be worse than a stock knock module. Something in the programming of the early revisions causes it, and you will see max knock retard constantly. I'd be leery of that tune you have in there more than anything

[Dannyac500]

Yeah i wasnt expecting 100% resolution from the KM, but hopefully i see a little difference and can go from there. However, from what i have read, it seems to me that paying 275 for the obd1 PCM to be compatible with 96 knock sensors, versus the 150 for general tuning of a OBD1 PCM, the extra $125 would have been for something like changing the KM. If i see no gain ill look into getting a tune from someone with a similiar tune and tweaking it to my liking so i can run the car and get a stock tune to modify as i have time.

BTW: the OBD1 PCM i have is from a 94 T/A, built in Canada

[SSlowBoat]

Get the service number off of it, and I can check it against my two early revision pcm's tonite.

[Dannyac500]

Not sure if this helps
vin: 2g2fv22p9r2204717
sequence# 204717

I dont have the PCM here with me tonight its in the car across town.

[Injuneer]

To make the OBD-1 PCM compatible with your 96/97 100kOhm knock sensor, I believe they add a resistor in parallel across the knock sensor ground and signal wires, so the PCM will "see" the 4kOhm resistance it expects from a 93-95 sensor. The knock module is apparently a filter, to eliminate noise signatures that are not representative of actual knock. The LT4 KM is intended to filter out the sounds from the LT4's Crane Gold full roller rockers.

I found the LT4 KM to be totally compatible with my stock (late) 94 PCM and 4kOhm sensor.

Check for code DTC 43 for the knock sensor. That would indicate a problom with the knock sensor circuit. When DTC 43 sets, the PCM pulls timing, based on engine operating conditions, rather than using the knock sensor.

[Dannyac500]

Thanks Injuneer, not getting any codes, put the LT4 KM in. Going to make some runs and see how it looks on the datalog.

[SSlowBoat]

Yeah both mine were early revisions, manufacture date of October 93.