stereomandan

I searched but couldn't find anything for this exact mod... I know it's been discussed a lot, but I can't find the answer.

Anyone have a diagram of how to do this? I'm converting from OBDII to OBDI, and want to keep my '97 knock sensor in place. I have LT1 Edit, cable and OBDI PCM, but need to modify the PCM so that I don't have to swap knock sensors.

Thanks,
Dan

jaguar5822

I have found a couple solutions to this, but I'm not positive they work and don't want to fry a pcm, so I posed the questiont to Injuneer in a pm with the solutions I found, and if they actually work. When he gets back to me I'll post it in here.

Injuneer

I responded..... "I don't know".

jaguar5822

damn, thanks anyway. Someone has to know.

stereomandan

Well, I have an OBDI PCM coming in on Tuesday that was used for a OBDII to OBDI swap and may have the internal modification. (The seller wasn't sure if he just swapped to the other knock sensor or if the PCM was modified). If the PCM was modified, I may be able to see what was done. I'll let you know what I find out.

Dan

shoebox

Send an email to Ion. He will know.

96flame

Unless you're skilled in soldering electronic circuit boards wouldn't it be cheaper and safer to just change the knock sensor? Especially if you've already got a OBDI computer to use.

Black97SS

I have spent hours searching and am pretty sure that what is needed is a 3.9k ohm resistor soldered between pin 22 on the blue connector and ground. I have also seen that pin 32 on the gray connector is ground.

Many people say "just switch the knock sensor", but I want to have the capability of easily swapping from my stock PCM to the OBD1 PCM and back, at will.

"Easily" does not include swapping the sensor in the block everytime, imo.

I have not actually done this mod yet, and would be interested to see a definitive answer.

I'll see if I can find the posts that I used to piece this info together and post links to them.

jaguar5822

The posts I found said to bridge 21 and 22 together, and connect them to ground with a 2k resistor. I emailed Ion, we'll see what he says.

jaguar5822

OK, Ion says that the 3.9k resitor from 22 to ground is all you have to do. Thanks to him for the quick reply.

stereomandan

jaguar5822 You are a little quicker on the gun. Here is what I found.

Well, here is the proof. This explains it visually. I just opened up the modded OBDI PCM that I got.

The 3900 Ohm resistor is the correct value, as shown by the ring colors on the resistor. Here is exactly where to solder it:





Dan

jaguar5822

is that red hi temp rtv?

stereomandan

I don't know, but it must not be conductive. Otherwise, it would really mess with the circuits because it covers a few.

It looks like it is there simply to hold the resistor from vibrating loose over time.

Dan

jaguar5822

yea I figured that's what it was there for, it would just be a little funny that they would use high temp instead of clear. Should be pretty easy for me considering I have soldered resistors in my cell phone that are about the size of a piece of .9mm pencil lead.

Black97SS

I finally got the last piece I need to do the swap from OBDII to OBDI, the PCM.

The one I got had been used in a swap before and the seller said the knock sensor did not need to be changed. When I got it today I opened the case to see how it had been modified. It also has a PCMforLess sticker on the outside of the case.

Since I had so much trouble finding info on how to modify an OBDI PCM to work without changing the knock sensor, (and apparently I wasn't the only one), I thought I would post pics of the internal mods on mine as well.

This is the back side of the blue connector

Pins 21 and 22 are shorted together and go to the leg of a capacitor that comes through from the other side. 3.9K ohm 1/4 watt resistor.