beedo

I am doing the LT1 swap and was wondering if there was something else besides lt1 EDIT to reprogram the pcm, it is from a 97 car. I know everyone is saying to go with the 94-95 pcm but money is really tight and I have to have the car asap. LT1 edit is 450.00. Im asking because ive done searches and con only find info on the obd 1 pcm. thanks

JPrevost

TunerCat offers an OBD-II tuner for the 96-97 years but it isn't exactly "inexpensive." At $300 for the program and $80 for the definition file. Still cheaper than LT1 edit.
For about $240 you could be OBD-I. The breakdown; $100 for pcm, $70 for TunerCat OBD-I, $20 for $EE tdf file, $45 for max232 cable for programming and datalogging.
The OBD-II Tuner packages out there for the 96-97 Lt1's don't appear to have scanning/datalogging abilities which means if you wanted to do any kind of serious tuning you would have to pump MORE money into getting the OBD-II to the same level as the OBD-I.

beedo

Thanks, I was thinking that the OBD II was going to be better as far as the data loging and such but guess I was wrong. Will the 94-95 pcm's plug into the existing harness or will there be more problems?

JPrevost

You need 2 resistors I believe, crack open the OBD-I pcm and soldier these 2 resistors in place to utilize both knock sensors. The reason for this little hardware modification is because the OBD-II used 2 knock sensors while the OBD-I used 1. It's really simple but if that scares you then ask me to do it for you (you pay shipping).

Dave_Jones

As far as datalogging, IMHO OBDI is much better for tuning purposes, due to the faster data output. However, the OBDII diagnostics do come in handy sometimes (individual cyl misfire, etc.).

F-body LT1s only had one knock sensor, even the OBDII cars. B-cars and 'vettes had two. So, if you're using an F-car program as your base cal, you'll only need to worry about one.

Also, you don't necessarily have to put the 3.9K resistor inside the PCM. I prefer to add mine to the engine wiring harness instead, so I can use unmodified PCMs. I also have the resistors wired inline with a toggle switch, so I can revert back to OBDII when I want. (this should answer your question as to whether the connectors are the same)

Another solution is simply to use an OBDI knock sensor in the block.

On occasion, I've also just disabled Code 43 in the PCM, which will at least eliminate the MIL caused by a mismatched knock sensor. I've only done that on a short-term basis, though, so I'm not certain if that hinders ESC functionality or not.

beedo

Thanks for the info, I belive ill be allright as long as I can get the harness wired into the car

junkcltr

iTrader: (1)

What Dave_Jones said is good.
I bought a 1995 "LT1" PCM from a Caprice (baby LT1) for $50 from the junkyard and used that BUT be vary careful. The knock module in the PCM defines if two or one knock sensors are used.
You will need an F-body knock module for using one knock sensor. The Vettes and Caprice use two knock sensors. Take a look at the "Street and Performance" website for the one and two sensor knock modules.
Also, searching the web you will find that some people are using the LT4 knock module NOT KNOWING what is really going on with the PCM but thinking it is good because they get less knock retard. The fools are installing them with the wrong amount of knock sensors and incorrect resistance knock sensor so the circuit doesn't work correctly and becomes deaf to knock. They pick up a tenth in the quarter thinking all is great........at the expensive of having the engine rattle more.

Also, some states are going to OBD-II engine monitoring at the state inspection. Nothing on the OBD-I because things varied so much. Something to keep in mind. It may happen everywhere eventually.

J

Z69

That might explain why I saw LT4 knock modules on the main page of GM Parts Direct yesterday. I thought that was an odd part to have up front next to LS2 crates and serpentine kits.

beedo

The inspection is for 96 and up cars, the 95 and lower have to run on the dyno with a sniffer. OBDII cars are only checking for the IM readiness and ses lights, If I use the OBDII pcm ill still have to run on the sniffer. I have the 96 pcm so con I change the knock module from it to the 95?? The mechanical side of the swap is easy ive been searching my butt off on here trying to figure out the wiring side of it with a lot of unawnsered?????????.