How do I tune my supercharged pre obd2 LT1 Camaro?

Posted by Life-uhfindsaway@reddit | projectcar | View on Reddit | 23 comments

I bought a 95 z28 from the family of the original owner who passed away a year or so ago. I don’t know a lot about it because of this. But, it has a Vortech V1 supercharger, headers, magnaflow exhaust, some sort of fuel system and I’m guessing injectors.

It runs okay and idles okay, but I get an occasional backfire in the intake at idle as well as feeling a little down on power.

It has an old school crane cams hi-6 ignition box that may be the culprit. I’ve called a few shops and nobody knows how to tune a pre obd2 car with an analog ignition box, so I guess I’m gonna have to figure it out myself.

Does anyone know where to even start? Should I just upgrade the ignition system to make it easier for a shop to tune it?

[-]

phate_exe@reddit

The separate ignition box makes me think it might not actually have bigger injectors and an ECU tune, I know a lot of the old forced induction kits used an FMU (rising rate fuel pressure regulator) to handle the added fueling by increasing fuel pressure by 6-8+psi for every pound of boost. Then the ignition box is there to pull timing with boost.

You might be able to do some old school eeprom tuning on the stock computer, but since it's probably not getting plugged into the computer for inspections (between being 30 years old and OBD1) you also have the option to change to whatever engine management you want. Either one would likely eliminate the need for the separate ignition box.

[-]

Life-uhfindsaway@reddit (OP)

Thanks for the info! Yeah, it’s gonna be a journey to undo some of what’s been done to redo it with modern tech. Almost sacrilegious in some ways since it’s kinda cool to have all the old stuff…. But also, leaving power and reliability on the table isn’t great.

[-]

phate_exe@reddit

I get the desire to keep things original, especially if there's some sentimental value involved.

But the only reason people ran janky setups like that back in the day was because better tuning solutions were less available/less understood/pricey, if they even existed. FMU's, piggybacks, extra injector setups, etc worked well enough to keep the engine from blowing up, and under at least sometimes you probably can get the fueling/ignition timing pretty close to where they should be under some rpm/load ranges. Oh, also they were doing all of this on top of whatever the stock ECU (tuned for a naturally aspirated engine) is doing.

But nobody building a car back in the 1990's or 2000's thought this was the best way to do it, it was just the most reasonable option at the time.

I saw in another comment that there are options available on the stock ECU, which would allow you to get rid of the janky stuff (FMU or piggyback, separate ignition box, etc) and have ignition and fueling directly controlled by the ECU.

[-]

Life-uhfindsaway@reddit (OP)

Yeah, I think that’s the route I’m gonna go. 42lb injectors, 255 fuel pump and remove all the other crap then get it tuned.

[-]

Banhammer-Reset@reddit

Cool, my time to shine. The 94 and 95s specifically can very easily and cheaply be tuned, the only thing you need is a USB-ALDL cable and a laptop. Source: I have a 95 firebird track car and reflashed it literally yesterday.

[-]

Life-uhfindsaway@reddit (OP)

Thank you for this info! Is there a program/tuner you recommend?

[-]

devilpants@reddit

When those vortech kits originally came out, tuning ECUs was considered voodoo science, so they did all sorts of crazy fueling stuff to "tune" the car.

If you are going to retune that car, you probably want to remove all the old fuel system modifications that were originally done if they are still there. I think they came with a secondary fuel pump inline after the in tank pump as well as a little device that would spike fuel pressure when the car would go into any boost. Both of these only kinda sorta worked. I also vaguely remember they would put ignition modules that would pull timing based on boost pressure as well so they car wouldn't blow up.

If you wanted to tune the car using the factory computer without all that stuff, you would probably want to start with a larger volume in tank pump and possibly larger fuel injectors and then I'd spring for a wideband oxygen sensor. I don't know if there is a way to tune the factory computers referencing boost pressure but if someone has created a workaround, that would be ideal.

[-]

Life-uhfindsaway@reddit (OP)

This is helpful!

[-]

Banhammer-Reset@reddit

Tunerpro RT or tunercats for BIN editing, flashhack for actuality writing the new calibrations. As for the crane box, not sure there.

Another good program is scan9495 for code reading all the modules, as well as EEhack for data logging. Which is where I would start on this.

[-]

Thorappan_0111@reddit

swapping to a Holley or FAST standalone ECU would ditch that old ignition box and let any tuner with a laptop dial in the blower setup. Dynosty in Louisville also tunes LT-platform cars on their dynojet if you'd rather not DIY it.

[-]

trashlordcommander@reddit

PROM/EPROM/EEPROM burning is old school but it’s still possible. There’s been tons of improvements in ecu technology and honestly if you can swing an upgrade to a more modern standalone you’ll make your engine safer realistically.

With all that said, like another user said this problem is more than likely unrelated to the tune. If the vehicle sat for awhile, I highly recommend you remove the injectors and get them cleaned and flow tested. Pulling the plugs and putting in a fresh set to then drive and check is also advisable so you can see if there is any outliers. If you have an inferred temp gun, let the vehicle idle and while it’s popping check the exhaust primary temps if it has headers. One that is hotter or colder than the others can help you find which hole is having the issue.

These older cars and ECUs require a bit of hands on diag but they can be learned just the same as anything else. Good luck!

[-]

DefEddie@reddit

94-95 LT1 is OBD1-ish but no chip burning, some of the 94-95 GM stuff was the first flash programable including the LT1/Fbody (even the 3.4 those years was flash programable instead of memcals!).

[-]

Life-uhfindsaway@reddit (OP)

Thanks for all the info and agree, I have plugs and wires on the way. I’ll pull the injectors as well. Good call out on checking the header temps, I didn’t think of that.

[-]

zeed88@reddit

The forgotten era

[-]

thickanvil69@reddit

Hey check this out, call your local speed shop with a dyno and get it do e professionally tuned based how it performs on the dyno.

[-]

meata@reddit

I didn't have a supercharger but I got my 93 vette tuned by this guy and was happy https://lt1pcmtuning.com/ It's old school and has its limitations but a hell of a lot cheaper than a standalone! To be honest, I think your car would have had to have a chip tune done already to run at all (you should take a peek at the ecu and see if there's a new chip in there), and you'll probably want to give it a tune up to rule out any low hanging fruit, while a backfire would seem fuel/tune related but could just need a new fuel filter for all we know. Good luck

[-]

Life-uhfindsaway@reddit (OP)

Thank you for the info! I’ll check him out and yeah, I will do a tune up and replace all of the “easier” stuff before making a mountain out of a mole hill. Fingers crossed.

[-]

Reddit-mods-R-mean@reddit

You might have a piggy back ecu attached to your factory ecu, that should have dip switches on it.
Those dip switches rich or lean different areas of the RPM band.

You’d have to look up a manual for that piggyback to decode the dip switches.

The other possibility is a socketed ECU with a tuned chip installed, that would require someone burn you a new chip with a new map.

But it’s highly unlikely this is your issue, I doubt this car was supercharged and never tuned.

You have a malfunction that you need to diagnose, you need to open the ECU and the piggy back if present and check the capacitors, then go through all the basics to figure out what’s actually happening and fix it.

[-]

Life-uhfindsaway@reddit (OP)

Thank you for this info! I’ll check the ecu to see what it has.

[-]

Fakeone040@reddit

Go standalone. New tech will do that old thing wonders. I have an OBD1 LT1 as well, but I converted mine to carb and HEI. I had it running on a megasquirt for a couple of years but something happened and it let the smoke out so I went “backwards” with stuff I already had.

[-]