The timing changing is really bothering me. Can anyone answer what could cause the actual timing to change when the PCM is commanding 35 deg. It is like the PCM thinks it is actually firing at 35deg and doesn't know it is actually firing more like 15deg advanced.

If something was actually pulling the timing through the PCM, the commanded timing would show that.

 

Perhaps you have high voltage induced spurious signals in the Opti wiring, or in the white wire to the IC module, that is corrupting the correct signals.

 

in the 3rd gen camaros the icm used to controll ign timing and timing curve and max ign timing but in the 4th gen the ecm/pcm controlls timing the opti tells the pcm where the timing is at then the icm sets the spark timing and dwell ,

do u have a pic of your dyno graph , one way to tell if you have valve float is to mark one exhaust and one intake valve spring with some kinda marking paint put the valve cover back on then go out and do a WFO 1-3 run all the way to redline in each gear then take it real easy back home trying to not get above 3k rpms and pull the V-cover again and see how much the valve springs that u marked have rotated. you valve springs should not rotate at all in a lt1 with the proper springs. rotation of valve springs in a lt1 indacate valve float and bounce.

some v-springs will start to bounce then stop at certain rpms because of v-spring material harmonics and ramp rate of cam , but with PROPER valve springs for your setup and redline you should NOT have any valve float and bounce.

this is why spring selection is SO IMPORTANT for a cam /valvetrain setup , every thing comes into play ,valve size, ramp rate on cam, coil bind, cam max lift , closed spring pressure ,open spring pressure, retainer and keeper weight,
,
the key is to key is to keeping your valvetrain light and have enough spring pressure to keep your valve from floating and bouncing on the seat with the rpm range you plan on redlining at,

 

What?! Valve springs rotate like crazy!

 

I agree, valve springs do rotate. Check out the link from PAC. http://www.youtube.com/watch?v=019Jy...layer_embedded

So..thinking about what Injuneer said about high voltage interference. I had that thought too. The plug wires are routed away from the opti harness, the ICM, and the coil low voltage wiring. It's a good thought, but I took care in routing them well away from the low voltage wiring.

There is a picture of a dyno graph here.
http://s819.photobucket.com/albums/zz117/wilsoncd2/

I have a ton of dyno graphs (~50). They all look pretty similar.
I also have a bunch of logs in efi live and Autotap formats.

 

i have nothing but a bump...

 

I am posting some follow-up to this post.

Since my last posting, I converted the car to a LS1 PCM (EFI connection) with coils on each cylinder. As soon as the car fired up you could immediately tell there was a difference. The car performed flawlessly with no misfire on the top end (compared to the high rpm misfire that was present before). It ended up making 345rwhp on a dyno dynamics chassis dyno. The best number we could get in the original state was 307rwhp. This was with a hot cam, long tube, CAI, and mildly ported stock heads. I think those are pretty good numbers

The downside to the long endeavor is that I really don't have the root cause of the original misfire problem except that it was in the ignition system. As posted before, there were 3 optis on the car (all GM units) 3 new LT1 coils, new ignition control module, new plugs and wires.

I do plan on doing some follow-up on another LT1 car with an opti to scope the signals for comparison to try and nail down the root cause.

I will say that I have been very happy with the performance of the EFI connection setup. I installed this last year on my personal car (93 formula) and on this 97 camaro.

-Chris

 

It really sucks that you couldn't nail this one down. To put in all that work, and not find the root cause, that is a tough one to swallow. You seemed to really try and troubleshoot, and not just replace parts, like so many on the internet looking for help. I applaud your efforts and hope that this thread will atleast help someone in the future.

A look at the graph for a perfectly working low res signal on an opti would give us all something to compare to as well.

 

Chris, what timing chain are you using with the EFI setup? Stock?

 

Right now on my car I am currently running a stock timing set. But I am going to be installing a 383 so I am not sure what I am going to run.

I guess EFI connection makes timing covers for running a double roller, but I doubt I will go that route.