chief455

iTrader: (21)

I am looking at a modded 94 with a 383,700R4 trans, headers, 3.73, etc. The guy selling bought it this way. How can I tell if the legal guys plug into my OBD I port the cars VIN will be correct? What if it's been changed?

Also - if this car had a tune done to run as good as it does
can I change just the gear ratio (tire swapping) with a HPP or something?

I need to know if I am getting in a bag of snakes...

Ls1Bait

Ive replaced my pcm and the dealership had to reflash my vin into my new pcm. I use lt1-edit to tune and the vin and all the other numbers have to line up to use my software. I did have it running on a spare pcm I have tho and it was never programed to work on my car, so it may be possible this car doesnt have the original pcm. I dont know how to tell if it was original on your car, someone will chime in.......

Boodyrider

iTrader: (2)

VIN: who cares, nobody reads OBD1 computers.
That car will not be emissions legal most places. (LT headers are not legal by definition most places if emissions are required because cats are not in stock location)

Changing tune for gear ratio: depends on who/what was used for the tune. A very few tuners, specifically at least ONE mail order tuner, locks the PCM so no one else can modify it. Typically a program such as LT1edit or Tunercat can make that change easily; HPP may or may not be able to.

transam5.7lt1

iTrader: (18)

1994 f-bodies came with 4L60E's and not 700r4....

Formula350

iTrader: (3)

To be fair, a 4L60E is basically a 700R4 that's electronic. Except no one calls it that, since it'd be like 700R4E heh. But he's right, the only year 4th gen that had a 700R4 is 93, and it's called a 4L60 in that year.

chief455

iTrader: (21)

like I said - it's been modded
trans and convertor from Yank....
the education I'm seeking is PCM related -

LiENUS

You could find someone near you with tunercat (or similar) and a cable to read it for you. But most emissions stations don't plug into the odb1 computer, its relatively useless for emissions checking. It lacks many things but the biggest is the catalyst efficiency checking rear o2 sensors.

rbrcka

You can d/l Tunercat and you get a free 30 day trial. Then you will need a aldl cable that you can get from several places. I got mine from PCM Performance for $43. Once you have those two things you can "read" the vin from the pcm to make sure it matches your car. If not, it is simple to change it. There is also a section for setting your tire/wheel size, gear ratio so the speedo is correct.

Obviously, there is a lot more you can do with it too, but the things you mentioned Tunercat could do easily do for you. It is also nice to be able to backup the config out of the pcm and save it on your computer in case the pcm would ever die. That way you could get a used one and flash the good config back in. Good luck!

LiENUS

He'd need to purchase the data file for the $EE pcm as well. and 43$ for an ALDL cable sounds awfully cheap (unless it lacks the molded connector in which case its a decent price). The ALDL cable is not the place to skimp when working with a flash memmory based pcm.

rbrcka

Yeah, I forgot about the definition file. They are $20 from Tunercat. I actually have two different aldl cables, but I like the $43 one I got best. It has a led light on the db9 end where it plugs into the laptop so you can see it has stable power.

The safest route if you are going to be doing a lot of pcm flashing is to get a benchtop harness and a power supply. That way you can do it in the house and take the cars battery/electrical out of the mix completely. Just less chance to have something go wrong.

LiENUS

Heh Il'l say. I am currently birdless due to a flash gone wrong. But I disagree about that being the best method to flash. The best way to flash is to desolder the chip and flash it in an eeprom flasher.

rbrcka

Can you solder in a eprom socket and then just plug and play with different eprom chips like the earlier pcm's? That would be safer for sure if so.

LiENUS

Not exactly http://www.mindspring.com/~amattei/flashfix.htm You can solder in that socket however.

LT1Falcon

iTrader: (3)

i agree

rbrcka

I know with my skill level of soldering my odds are better with the benchtop. lol

chief455

iTrader: (21)

M lordd - you guys are WAY too smart for me!

I'm getting from this:
1. If the PCM is stock and has been tuned(I think it was sent out) I could change speedo calibration with some different types of cables and software.
Any hand held units?
2. If the PCM was changed and the cars VIN is not in there, who cares - nobody at DMV or emmisions will be plugging in.
3. I must be careful not to lose the tune "flashed" into the PCM - not sure how I can save/back it up?

thanks all..

Boodyrider

iTrader: (2)

You're pretty close.


Clarification to 1: As long as the PCM is not locked by whoever/whatever was used for the initial tune, you can do really simple stuff like changing for gear ratio with most handhelds. However, you need a more sophisticated program to change VIN.

2 Dead on except you might want to have it match for purposes of being able to use all tuning programs.

Clarification to 3: The tune in your PCM is 'read' by ANY tuning program, and stored as a file on your PC (laptop or whatever). This copy is then edited by the tuning program. The edited copy is then 'written' back into your vehicle PCM.

The hazardous part is during the writing process; reading your PCM CANNOT harm it or the program stored in it. Occasionally, particularly when a cable is defective or power is interruted to either the car or the PC during writing, or if there is a bug in the writing software, the PCM in the car is made useless by the process of attempting to write to it. This is RARE... but does illustrate the need for some caution during the writing process.

a) Use a GOOD quality cable and take good care of it, don't just throw it in the trunk under a cinder block.
b) Make sure the car's battery is in good condition and fully charged
c) Ground potential between the car and laptop should ideally be even. A good cable ensures this, and some cables use optical coupling to isolate the laptop power from the car power.
d) Don't play around while flashing (writing) the PCM in the car. IE, don't flip on and off the 600 watt sound system in the car, and don't play frisbee through the car; you might knock the cable loose or create an electrical issue.

I personally like the cable/laptop/tuning/datalogging approach; it's about the same cost as a good handheld, and will do FAR more, incl;uding allowwing you to monitor in realtime a LOT of engine parameters the computer doesn't normally show you, a useful thing for catching problems on a modified engine before they get to be big problems.

chief455

iTrader: (21)

ok, thanks! this is sounding just like the HP tuners I had bought for my LS1 with a basic laptop a few years back. I used the precautions they - and you - recommended, but I logged, watched and edited - but never felt a thing. I never fully grasped what I was looking at in those data tables and nobody ever really gave a good explaination.
However - for my 94 - what cable/laptop/tuning/logging software would you suggest? If it's locked by the tuner - I'm screwed?
On a budget - probably won't need to tune the car as it's an animal and was tuned by pro's already.
Just looking to save the data and be able to write a new tire/gear combination.
thanks again!