MatthewMiller

I have a new-to-me 1996 LT4 C4, and it runs quite well on a tuned OBD1 ECM that was swapped in. The reason the original OBD2 ECM was swapped out by the previous owner was that it failed. The problem is that I can't pass emissions in my state (MO) because there is no more sniffer/dyno test - only a plug-in scan. And the scanner now communicates with the state's system in real time, so the car has to have the correct ECM to pass. The OBD1 computer won't cut it. I will always be able to fall back on the OBD1 computer to actually drive the car if needed, but I have to pass the inspection to legally drive it. I think that means that, at minimum, I have to be able to drive the car on the OBD2 long enough for it to test everything once (50-60 miles?), and then get it inspected, without throwing any codes.

So, I have an OBD2 computer on the way. At the very least, I expect I will have to turn off the downstream cat test in the OBD2 (it will pass with no more than two tests disabled, per regs). Almost certainly I will have to do some tuning to get it to run well enough to not set codes (i.e., to pass the test), due to the mods the engine has (396, serious head porting, custom cam with real overlap, etc). I'd really like to use the OBD2 computer all the time, given its greater ability to diagnose. But that is not an absolute requirement. What is a requirement is that it has to run well enough to pass emissions.

So with all that said, I am searching for tuning/scanning software for the correct OBD2 computer. My questions are the following:

• Are my choices still limited to LT1/LT4-Edit and Tunercat (now Jet Performance)? It looks like other products such as HP Tuner start with the LSx engines.
• Of the options available, is there a clear favorite? Does one allow more tuning options than the other? Is the interface easier to use with one vs the other?

I appreciate any info that you all can provide.

bjankuski

I have never used LT1/LT4 edit but I have used Jet and it works well, you will be able to pass inspection with the OBDII computer and it will operate the car fine.

MatthewMiller

Okay, I'm about to dive in with Tunercat/Jet.

What data-logging software will work with my OBD2 system? As far as i can tell, DataMaster only works on OBD1. What should I use to data-log my OBD2 LT4 car?

QCVette

Sorry I don't have info for you, but your situation made me wonder what is involved in swapping the computer from a '96 OBD2 to a '95 OBD1 on a '96 car? Is it as simple as just plugging in the other computer? (and probably a different tune) or other things too?

I have a '96 Corvette and a Caprice and it would be nice to be able to play with the tune. I recently bought some of the Moates stuff to work on my '95 so it might be fun work on the '96 also since it wouldn't cost too much.

MatthewMiller

It has an OBD1 computer on it now, and I think it is plug and play. In my case, the OBD1 module certainly needed a tune, but this is on a 396 stroker with seriously ported heads and a cam with real overlap. On stock or near-stock engine, it might work okay.

That said, the OBD2 PCM is a lot more capable. I understand if you already have OBD1 tuning software. However, if your car runs well on the original OBD2 PCM, I think you'd be better of leaving it alone. Since the 96/OBD2 cars have a MAF, they should adapt better to smallish mods.

pkincy

Best of luck to you. I am going to expect that there is going to be major sensor work you will need to do, to go back to OBD2. At least spend a lot of time investigating some of the old data on OBD2 to OBD1 differences on the Y body pcms. My guess is that to do the swap, the 396 was built for an OBD1 computer with all the appropriate sensors. So you may have to go back in and redo many of the sensors to get the proper handshake to the new to you OBD2 pcm. I would spend a fair bit of time with the Helms from 94 and from 96 to see what you need to change. Keep us posted.

Edit: Specifically do you have an early timing cover or does yours have the 96 with the Crankshaft Position Sensor? My guess is when they did the swap they put in a complete 94 wiring harness with the OBD1 computer and built the engine to 94 specs. To go the other way you will need a complete 96 wiring harness and the hardware that houses the additional sensors fpr that harness.

AgentEran

Resurrecting an old thread here.. but im curious if you ever figured this out, and more curious about how that 396 is running!

MatthewMiller

Yes, I did figure it all out. I was right back then about the two options for tuning software. I'm hearing that LT1-Edit may be history now, too. I went with Jet DST in part because it allowed multiple cars to be tuned under one license, and in part because it's literally the same as Tunercat (but just made for the OBD2 system), which would allow me to easily copy the settings from the OBD1 PCM (using Tunercat) into the same tables for Jet DST. It worked fine.

More importantly, the Jet software allows one to set any diagnostic test to "do not report," so that it is not tested and not counted against it in the emissions check. That was a key to easily passing emissions. And even though the old OBD2 computer had a problem, I was still able to lift the calibrations off of it with the Jet software, and upload them to the replacement PCM. It ran more than well enough to pass emissions. The OBD1 computer still runs the car better, so at some point I should get off my *** and copy over the settings from it. These have to entered by hand, though, so it will take an evening to do it.

Lastly, I have decided to probably keep using the OBD1 PCM for everything except inspections. Even though I should be able to set all the running parameters the same in either PCM, the OBD2 PCM cannot be flashed with a BLM (block learning module) locker function. That means that even in open-loop running (near WOT - essentially when you want it to never deviate from the fuel:air numbers you set), it will learn and gradually adjust itself to a (most likely) leaner, more emissions-friendly setting. That's not ideal for either power or longevity. The OBD1 PCM can be set up with a BLM locking function using Tunercat, so I'll probably stick with it. It's trivial to swap the PCMs out, so I don't mind making the swap every two years for testing.

AgentEran

Thanks for the info!

btw, im enjoying your work on the troll I brought out the wood works..

MatthewMiller

LOL, it's one way to be entertained. I haven't done any of my own actual tuning with either PCM - I've relied on the previous owner's calibrations of each so far, and only fiddled with the emissions diagnostics to pass inspections. So I'm not expert. But you are welcome to ask questions any time, if you're traveling down the same road I did.