I'm probably going to do the resistor mod for the knock sensor on my car. I'm going to use switch, so that the KS can function normally 99% of the time, and then be bypassed when at the track.

My car has an OBDI conversion PCM, that has been internally modified to work with my OBDII KS. So I'm assuming that I'll be doing it much like the following pic. Anyone care to confirm this for me?

Thanks to "FASTLT1" for the original pic (which I modified).

 

That should work except for the resistor value. Yours might need a 3.9K value at least that is whats on the L98 speed density cars. You can measure the resistance with an ohm meter to find out for sure. The 100K value is for a L98 MAF car.

 

why dont you just tune it right? Before a GOOD tune mine knocked all over. Now after jeff at carolina automasters tuned it, no spark anywere, and lots more power! Just a thought though.

 

The idea is to leave the conservative tune intact, along with the knock retard that it occasionally has due to valvetrain/header noises. That will protect the engine in the event that I get a tank of bad gas. But for the track, I can flip the switch for racing.

I do plan on sending a datalog to Bryan Herter (tuner) so that he can fine-tune things a bit. I guess that this switch/circuit may or may not be necessary after that's done. That is a good point about the tune, firebirdStud, and I'll be getting that done as well.

89TramsAmGTA: I was under the impression that 100K was the correct value for OBDII LT1 KS's, and 3.9K was for OBDI LT1 KS's. Hopefully someone who's done this before will chime in and verify which is the right one.

 

I did it several years ago and have the same setup as you... a "hardware modified" OBDI PCM to work in an OBDII car (96SS) in that the 100k ohm knock sensor is kept in the car. I can switch between the OBDI PCM and OBDII PCM just by unplugging one and plugging in the other.

Your graphic looks just like I did mine. You only use the 3.9k ohm resistor if you ALSO swapped out knock sensor with the OBDI conversion. Since you have a hardware modified PCM you need to use a 100k resistor (or combination to get to 100k).

Also, question for you While I know my PCM is internally modified, I bought the car used and never did much research to know just how this was done. Now, my PCM might be flaking out on me and I may need to change it... do you (or anybody else) know exactly what gets done to internally modify the PCM for the 100k knock sensor? Thanks!

 

Thanks for the help, Brent!

Sorry, but I don't really know what is done internally to modify the OBDI PCM to work properly with the OBDII KS. Mine was done by Bryan at PCMforless. Their OBDI conversion PCM (for '96-'97) cars is $100 more than a programmed standard OBDI or OBDII PCM, so I'd hafta assume that whatever they do involves a bit of work and parts.

Maybe PCMforless or MadZ28 could help you... but they might consider their modifications to be a trade secret.