Looking for a tune / L18 454 4L80E 12212156

L21/L29 wasnt used with the LS1 PCM, it was Black Box only to my knowledge as that's what all GMT400 trucks used. It also has the original BBC firing order where L18s have the LS style.

You may be able to find one, like 99.9% sure that combo with the OS you're looking for never appeared in the US.

I guess I'm not sure what or why you want a factory combo here? Guessing either for a swap or for COS5. I'd say just make your own "factory" tune, just use all the factory values. Most, if not all, of the tables exist in both those OS' so just copy/paste between and you should be good.

Thanks for the info. I'm chasing down a problem with the trans segment in my express van tune on my 99 L18 and no matter what I segment swap, it's just not right. I thought maybe there is a better base tune. I have a 2002 6.0L 4L80e 4x4 tune I will play with. It's the closest thing I can find. Now to find some time! :)

I've attached the tune out of my stock 2003 suburban 8.1L 4L80e 4x4. It should be similar to what you need as the motors were very similar with return vacuum FPRs and EGR. The timing sets were different, but only a hardware change the computers couldn't care less. I know this is the year break when the changed the throttle body style from the LS1 style to the 03 and up truck style. Not sure if that is evident in the tune or not. I have a few more tunes I'll attach for reference. I have 7 of these engines laying around in various states of assembly, so ask any other question and I'll try and help. I'm not strong on the tuning side, but have plenty of hardware scars.

-Alex

I appreciate these bins. I will compare the 2002 bin to the one I made using a 2500 silverado and seg swapping in the system from an express van tune.. the ladder got me better but not perfect first-second shifts and 4lo shifting too! This will likely be even better. thanks!

You might want to look at an 02 3500hd. They were still the older gmt-400, but had the 8.1l in them as GM discontinued the 7.4l in 00. I don't know if they were dbw or dbc, but I think they switched to the 0411 pcm in them from the earlier black box when they switched to the 8.1l in early 01, and they came with either a 4l80e or nv4500. Not sure if you can find a 4x4 cal as all 4x4 gmt-455 3500hd's were conversions.

I've looked at everything I can find and it looks like the factory never used 12212156 with a big block. My solution was to start with a 2500 6.0/4L80e/4x4 tune, swap in the system segment from an express van tune and set the platform parameters to low res crank, etc. So far it has worked very well. 4LO shifts, first-second upshifts correctly and the engine seems to run smoother than before with the express van as a base OS. The last part is probably just my imagination but so far with around 1000 miles on it, it's a winner.

You must have done the idle yourself. Mine is a mish mash of 350 and 454 stuff. Truck works well enough as is and fuel trims are minimal so I haven't been forced to prioritize cleaning up my idle on the 3500. In the warmer weather it idles around 1100 RPM in park/neutral despite being commanded lower. I figured it should trim itself, but I guess there's something fundamentally wrong. I was able to hack a good stock VE table though, likely why fuel trims and driveability are so good.

I extrapolated the tune from the black box computer way back when I first did the 0411 swap and it's done pretty well.

I believe the 1998-2000 L21 is a regular 512k type ecm and not the black box. Part numbers 16238212 and 16238212 show they could be used in a 1999 5.7 camaro to gmc topkick with the l21 7.4 liter. Does not look like any black box from say the 1996 vortec black boxes that I have seen. Didnt the l21 7.4 have cnp and a 24t reluctor under the front timing cover?