[Adambbur]

I have a 98 12 valve last when I started building the motor I started with Afc live(no max travel spring), valve springs and 4k Gov springs. everything was fine at that point. Then once I did 5x14 injectors, T3 3 piece manifold, and a 63/68/.83 turbo, if i free rev it or full throttle in 1st and sometimes 2nd it would almost backfire out the exhaust and spit out grayish smoke. Under normal load 3rd through 5th it would drive fine but Exhaust temps would get a little hot under heavy acceleration or large hills. I have ordered the 35-45psi max travel spring from PDD but havent installed yet dues to waiting for a new clutch. I've thrown around lots of ideas like too much fuel(but it doesn't smoke a lot), too much back pressure from the smaller exhaust side, and not enough lift pump pressure but wanted to see if any one else has experienced this or has had any ideas.

 

[GAmes]

In order to backfire an intake valve has to be open. Have you set the valve lash correctly? Do you know what your timing is set at?

Edit; Reread your post. " almost backfire out the exhaust" What the heck does that mean?

 

[Adambbur]

Not sure if Backfire is the right term or not but timing is at 18 and valve lash is correct. Its almost like fuels combusting in the exhaust or in the turbo if that's even possible. It reminds me of cars with 2 step if anything

 

[Brewski5.9]

Maybe gotta try running without AFC.

 

[GAmes]

Let me guess. This phenomena happens when you suddenly release the throttle after heavy input? Try to put gas engine things out of you mind. It is not combusting in the turbo with only 18 degrees of timing.

 

[Adambbur]

no,it happens during throttle snap, or full/near full throttle in 1st or 2nd. popping starts around 2000 rpms and kinda slows the engine from revving too fast for a few seconds before hitting 4k and smoothing out for the most part. the only reason i care about it is because since it does it during throttle snap and it makes gray smoke I can't do emissions

 

[GAmes]

What is your fuel pressure while this is going on?

 

[Adambbur]

Haven't been able to put a guage on it yet but is that a possibility? Wasnt sure if fuel pressure being low would be an issue as it smoked so much

 

[GAmes]

You bought an AFC live, but no gauges. Incredible.

 

[Adambbur]

I just don't have fuel pressure as i was told it wasn't very important on a 12 valve. truck came with boost, egt, and a trans temp

 

[GAmes]

I just don't have fuel pressure as i was told it wasn't very important on a 12 valve.

Now you know better. It wasn't a concern 20+ years ago when most engines were stock and lift pumps were still working (since they were fairly new).

 

[Adambbur]

I have planned to get one soon out of curiosity, but i guess ill get one when i get the new clutch

 

[Mudram 5.9]

I am having the same problem mine didn’t start until I advanced the timing to 18°

 

[Destroked 450]

Check for boost leaks, my old engine would do it whenever i had the intake off working on the afc.