So I skipped a few pages in my haste, but why are you not just using the EFI 24x kit, splicing the LS1 and LT1 harness and just piggybacking the LS1 computer? My opti just took a dump (this will be the third replacement on the car) and this is the route I'm looking into. I plan on keeping the car for as long as humanly possible (would love to hand it down to my son in 14 years), so I don't mind a little more money now to NEVER have to change the opti ever again.

 

For a few reasons listed above, but to reiterate:

1. EFI connections costs thousands
2. You lose the trip/fuel computer accuracy (if you piggy back, if you use just the 24x kit, you lose it completely)
3. You have to dissemble the front of the engine
4. EFI connections nor anyone else makes a harness that works for the corvette
5. You lose traction control information
6. You lose security
7. Its a sloppy solution.

 

For a few reasons listed above, but to reiterate:

1. EFI connections costs thousands
2. You lose the trip/fuel computer accuracy (if you piggy back, if you use just the 24x kit, you lose it completely)
3. You have to dissemble the front of the engine
4. EFI connections nor anyone else makes a harness that works for the corvette
5. You lose traction control information
6. You lose security
7. Its a sloppy solution.

 

Well, I can live with most of that. I'm already looking into what it's going to cost to build the harness as me an electrical work don't mix (color blindness doesn't help). Also looking into how much of the parts I can get used locally (LS1 harness, computer, LS3 coils, etc...). The main issue though is having to splice the LS1 and LT1 harness though right? Will the LT1 run ok on a stock LS1 tune, or will it need a complete retune? I'm assuming the latter.

 

You would not want to splice a harness... You want to re-pin. There is 1 wire to splice, and 105 wires to re-pin. 12 new wires to run and pin.

You dont need an LSx harness.

The wiring is the easiest part.

Yes you will need to re-tune.

LSx have a different firing order, need to fix injectors and coils

LSx injectors are different sized than your engine, need to calibrate

LSx has a different maf, need to calibrate

LSx has different VE characteristics, need to calibrate

There is more do it...

 

Damn, well I was hoping to have more fun with this C4 *****. I guess I'll get an opti on it to get it up and running again, follow along as you make more progress, then address it hopefully before this opti goes bad.

 

I've had 3 C4s and only one true opti failure. Another was cause by lack of locktite and spinning to 7k... Maybe try some lens cleaner and lint free glasses wipes on your opti LEDs if your missing resolution signals... and/or replace the cap. (probably left best for a different thread)


When I get the kit ready for production, I will announce.

 

all your cons are addressed with a retune and the MAF does not change, I kept the same MAF>

You need to rewire and you need a tune, that's it. It's not that hard and I did it in one weekend. I repinned my original harness on my 96 lt1. I spent $1000 in total on my conversion. it's as straightforward as it gets. you do need a retune for sure, but now you have a ls1 computer and you'll have more people that can tune it. With a c4, depending on the year, I could see the guages being harder to do depending on the year.

 

You are correct. The maf does not need to be changed. But the LSx PCM needs to be calibrated for the maf

All of the analog gauges will work just fine on all of the LT1/4 Corvettes.
But your trip computer, fuel computer, and digital gauges will not. Neither will your EBTCM, cruise, VATS...

Might as well be driving a Camaro at that point.

 

Straying away from the Y platform, ...

If I was to use a C4 cluster in the Fiero for a dash swap, would I need the computers to have the speedo, DIC info and the analog gauges to function properly? Even for a C5 cluster and/or dash swap?

Jon, you know fuel economy on that car would be pointless to monitor. I'm just feeding my brain. Don't worry, that black C4 in the garage isn't getting touched.

 

Yes. The digital readout on a 92-96 corvette requires serial data from the ecm to the ccm to the cluster.

A c5 cluster requires direct feed from data bus.

You touch my Vette, and I will lay down the

Back on subject.

 

I have been following this thread and others like it for a while now. I am not an electrical wizard so if I am over stating the case please forgive me. I do not understand why no one has come up with a "black box" that could be used to recieve a signal and convert is to a signal that the ECM on a LT engine could run on. Since the Opti is the problem why can't a crank triger system be used to send a signal to a black box to replicate the Opti signal? I understand that the 24X systems does that in some ways. But it too is not just a plug and play system. Is my understanding correct?

 

I think youre a little off there....

the opti-spark is not needed what-so-ever when converting to a lsx pcm. the opti has nothing to do with the rest of the car. you could throw it like a Frisbee when the engine is running on the lsx pcm.

the 24x signal is needed for the new pcm to run the engine. thats how it determines where the crankshaft is while its rotating. so it knows what cylinder to fire.

That signal usually comes from a crank trigger (reluctor wheel) on the lsx engines.

------------------------------------------

now what I am doing:

1 making a module to convert the information that the lsx pcm sends out so our CCM (this is what controls things in the body of the corvette) works properly. This has nothing to do with running the engine. engine will run fine without this information.

2 making a module so i can KEEP the optispark. yes. I am making a device so I can use my optispark to run the new pcm. making the new pcm swap completely plug and play.


------------------------------------------------------


I may have not understood your post entirely... but I hope this helps.

 

I think youre a little off there....

the opti-spark is not needed what-so-ever when converting to a lsx pcm. the opti has nothing to do with the rest of the car. you could throw it like a Frisbee when the engine is running on the lsx pcm.

the 24x signal is needed for the new pcm to run the engine. thats how it determines where the crankshaft is while its rotating. so it knows what cylinder to fire.

That signal usually comes from a crank trigger (reluctor wheel) on the lsx engines.

------------------------------------------

now what I am doing:

1 making a module to convert the information that the lsx pcm sends out so our CCM (this is what controls things in the body of the corvette) works properly. This has nothing to do with running the engine. engine will run fine without this information.

2 making a module so i can KEEP the optispark. yes. I am making a device so I can use my optispark to run the new pcm. making the new pcm swap completely plug and play.


------------------------------------------------------


I may have not understood your post entirely... but I hope this helps.

 

Just out of curiosity. If we want to ditch the Opti all together, would we be able to use the system you are developing with an LS crank trigger, like from EFI Connections? Or are you making an opti only version. You are just using the low-res signal right, which usually isn't the fault area of the opti?

 

Boy I'm waiting for the answer to this one! The high voltage side seems to be the problem with the opti's.

Does anyone know a company that can make a harness to use the LT1 ECM for body functions and the 24X to control the engine and trans functions?

 

Well yes, in that case you would just need a wiring harness and data conversion module.
I currently dont have any plans to make to make an lsx crank trigger.

I only plan to make an opti version as of now.

The high and low resolution sides of the opti are identical, mounted in the same plastic box, using the same input power, and do exactly the same thing. That side of an opti rarely, if ever, will fail on its own.
Water, ozone degradation, and high voltage are the most common causes of an opti failure. More often than not, its the cap that causes these issues and water pump failure on the non-vented opti's. These intrusions into the opti will cause the optical sensors to be clouded, coated with crap, or in the case of water, ruined. Along with the potential water ingress is water getting between the shutter wheels' holes. This will cause a problem on the high resolution side first, as the holes are very small and if it misses seeing a certain number of them over an amount of time, it will throw a code for high resolution failure. Many opti failures can be fixed by simply cleaning off the leds and shutter wheel. But since most people dont understand/care about how it works, they are more likely to buy a whole new opti and cuss the designers.


This would be piggy backing. And nope, no one is manufacturing a harness to piggy back. Or manufacturing a harness for the C4/24x period.
If piggy backing is done, the trip computer will be in-accurate, cruise control will not function properly, ASR will not function properly, and Pass-key/VATS will not function properly.

 

http://gearhead-efi.com/gearhead-efi/def/aldl/A275.DS

Win.

 

Jonathan,

I had all of this stuff ready to send to you, but never heard back from you on the Google Documents thing.

I've got the data stream info for the PCM, CCM, ABS, SIR, HVAC, etc. for all model years from 90-96.

You back on dry land?

I'm working on my wiring harness and the bus sniffer at the moment.

Jep

 

Jep,

Just hit land about 5 hours ago in Cameron Louisiana, now in Houston. Headed to OKC at 0530. As soon as I am home and situated I will be working on the google docs. Expect an update sometime tomorrow evening.