bogus

I am starting the thought process regarding the rebuild of my 1992 LT1.

The car is a 6spd coupe - see avatar!

I want to upgrade from the batch injection mine came with to sequential as used in 1994 on up.

My questions are:

1) Can a 1994 ECU be adapted to a 1992? I know there would be some harness changes, but I should be able to get those. My concern regards communications with the CCM and code extractions.

2) I see where Accel DFI is now available for the LT1. Is DFI sequential?

k99ja04

Wasn't sequential not added until 1996? An OBDII compatible computer was added in 1994 and changed from speed density in 93 to MAF in 94+, but I don't believe vettes became truly OBDII or SFI until 1996.

That being said if you could find the right computer / harness / sensors, it could be done. The only thing I don't know is will a 92 CCM talk to a 94+ ECM. I think you would reach a point of diminishing returns real quick. At WOT an SFI system acts pretty much like a batch fire system. The only real benefit to SFI is idling, and you can get pretty close with some good tuning.

I believe Accel DFI is sequential. tjwong is the guy to ask.

bogus

There has to be a reason why the 94+ models get better mileage then the pre 94 models.

That difference is the addition of sequential. That much I do know is that sequential came in for the 1994 model year.

I am hoping TJ chimes in. He knows his stuff.

Thanks!

Tom Piper

I've actually considered this myself.
There is no reason that it couldn't be done.
You would probably be better off starting with a '94 electrical harness.
You would have to get a MAF.
How many O2 sensors does the '94 use?
The '92 uses fusible links, I think the '94 has a fuse block.
I would think the CCM connections, etc woud work without a problem.
This is a project that I would want to do with the engine out of the car.
Plus, if you have stock '92 injectors, I think it would be a good idea to get the later ones.

Tom Piper

Lone Ranger

They went sequential injection for the 1994 model year. 1994 computer and ALDL were still OBDI. The OBDI ALDL is a 12 pin socket.

1995 they installed a 16 pin OBDII style ALDL, but everything else is still OBDI. 1996 they went to full OBDII logic for the PCM and sensors.

I didn't know the sequential injected 94 and up got better MPG?

tjwong

Boy thats going to be alot of work. It would be best to get a complete 94 or 95 wiring harness. For a PCM you need a 16181333 service number. As for CCMs, I beleive that they are the same but you can call your local dealer to make sure of the correct CCM for a 94/95 car. It can be done but its going to take a lot of work to install.

An Accel system is sequential. But it requires a dual sync distributor. While Accel totes true sequential capability, it will not be anywhere near the accuracy of a GM opti-spark as far as timing resolution goes. That opti, while everyone hates it. Is a highly accurate timing sensor because of its high resolution sensor. a few model years earlier in the GM truck line which used a 4x crank sensor. The opti-spark uses sensors with many many times the amount of "windows" to tell the PCM where the cam and the crank position is. An Accel dual sync uses the same 4x and 1x crank and cam sync signals for its position. It works, and works well but not as well as the opti-spark system.

VR'92

Bogus,

I am currently semi rebulding my 92 (new cam, 95 style opti, and head gaskets) so I might be of some help to you if you need any pics or anything I got a bunch.

bogus

Gang - THANKS!

I had a feeling it could be done.

As for underhood harnessing, that's not scary to me. Converting to a MAF doesn't worry me, but, I wonder if CA emissions would have a cow... or even notice? I mean, the numbers should be better, if anything.

And aren't 1994 ECU's ALDL updateable? Meaning, no chip burning?

I agree TJ, the Opti is one of the best timing monitors around. That's exactly why I would rather keep the Opti around then go DFI. Now, comparing DFI to say, HEI, DFI kicks ***...

I have the parts fiche, so it won't be a stretch to get the part searching done. I would rather not mess with the CCM, if only because of mileage issues. But I would suspect it's the same. I mean, they still use the single UART and the redundant wire for communications? If so, they are the same. Besides, the codes didn't change for another 2 years. The ALDL did change in 1994, I think.... It is upto the 16 pin, versus the 12. But I need to confirm that. If it was the same, Gordon Killebrew would not have stop at 1993 for his diag book.

1992 LT1, like all OBDI LT1s has 2 O2s and 2 knock sensors. the third O2 appeared as a dummy in 1995 and became real in 1996.

I already have FMS 24# injectors. So that's covered.

Sequential does a much better job of metering the fuel to the cylinder. Smooths out idle, improves idle emissions and improves fuel economy. The best I get on mine, average, is in the mid-20s, Those with 94+ models are getting nearly 30. Plus, the drivablity gain seems to be worth it.

I don't honestly know when this project will start... so I am getting my ducks in a row now. It will be months, tho. I am still not working, damnit.

Thanks!!!!

MaxLean

This isn't entirely true. I believe that early '94s may have had the 12 pin ALDL but my late '94 certainly has the 16 pin. In any event any '94 (even with the 12 pin) is flash programable.

MaxLean

The third 02 is there in '94 as well but it isn't really used for anything. As far as emissions testing, nobody would ever notice the change (assuming it's all functioning correctly). And don't forget that the MAF system is generally superior.

bogus

I didn't realize that 1994 included the dummy O2.

And yes, MAF is better!

TwoFast4Lv

I know for sure 94s with the upgrade A/C system have the OBD-II connector and the third useless O2

94 was first year of SFI on a LT system and flash programing rocks

Harness on the other hand....OUCH!!! $$$$$

Tom Piper

Just an added note to this subject:

It seems to me, for better fuel mileage, it is more important for a "batch-fire" system to have matched fuel injectors than a sequential fire system. Because a sequential fire system controls each injector pulse width individually, it can compensate better for each cylinder's fuel mixture.

The Charles O. Probst book, "Corvette Fuel Injection", has a section (page 124, Figure 6-18) where it states the batch fire systems have a different fuel delivery from one bank to the other because one side is on the inlet side of the fuel rail with more fuel pressure than the outlet side of the fuel rail and this system does something to compensate for that effect.

Tom Piper

tjwong

Bogus, if you do a good job installing the harness and PCM from a wrecked C4. I doubt that the inspection station people would even notice that you change it over. Everything that is in your car now would plug in directly into the new harness. The only issue really is the CCM communications. That one thing is what you need to really look at. The CCM in the case of the 94 to 96 cars is what provides the fuel enable signal to the PCM. Without that the PCM will not allow the engine to run. There is a workaround, which means I can flash the PCM with an F body calibration, that way the PCM won't even look for a CCM. However I think that it can be made to work with the CCM provided that either the CCM you have now is the same as a 94 or you get one from the dealer. They are about $275 and there is no exchange meaning no more core charges on them. I am fairly sure that the 94 and 95 CCMs are the same as the PCMs are the same for both model years.

k99ja04

tjwong,
Doesn't the CCM contain mileage etc? I thought I heard if you replace it, you only have 100 miles before a dealer needs to flash it.

tjwong

That is absolutely correct. And I can tell you that I can't flash the CCM using a TECH2. For some reason GM didn't incorporate that into the TECH2 I have to use an old TECH1a in order to configure the CCM.

bogus

That an the fact the CCM is used to transfer data to the EBCM. Without that, the ABS/ASR might not work.

I would rather get a CCM from a 94/95 then try to bypass processes.

As far as harnessing is concerned, I ain't afraid of some wiring...

k99ja04

best of luck bogus, let us know if you tackle this project how everything turns out. I'm especially interested if you really do see mileage gains with 94+.

bogus

This ain't happening anytime soon... just getting my knowledge base established. And go from there.

REDC4CORVETTE

Just use LT1 edit and shut off the features on the computer you don't
need.
And 94 has a 16 pin conector,not all of them are live.
If you order a 12 pin ADL it won't work.
I use TTS LT1 edit and Tuner Cats.