I just finished putting my new 383 together for the second time. I had this motor together once and running in the car already and put about 150 miles on it before I had to pull it for an unrelated reason.... Now that I've got the motor back together and running again I have a problem with it missing badly under load.

The car starts right up and idles great. It also seems to rev smoothly when out of grear with no real signs of a miss or anyhing. The problem is when I'm driving the car and it's under a load. It seems to run fine at light throttle and under easy acceleration though it may be a little short on power but when you get over say 50% throttle the motor starts missing horribly above about 4000 rpm...

Also, I went out for a short 5 minute drive last night and when I got back home I opened the hood with the car idling and the #4,#6 and #3,#5 header tubes were glowing red!

I'm wondering if this could be the opti going bad that's causing these problems? I've already tried a new coil and everthing else is new (wires, plugs, etc). The fisrt time I had the motor together it had the same miss but it didn't occur until about 5200 rpm...

The motor is a fresh 93 383 LT1 with CC230/236 cam, ported heads, ASM headers, no Cat, TR-55 plugs gapped at .050", vented opti, 11:1 compression, etc...

I was originally pretty confident that the opti was the problem, but now I'm reconsidering since I saw the glowing headers. Is it possible for Opti problems to cause the headers to glow red?

When I originally installed the opti, I first disassembled it and everything inside was spotless clean so I assumed it was a low milage unit and decided to use it.

Any help with this would be greatly appreciated.

Thanks,
Rob

 

It's possible. Whatever it is, your engine is running pretty hot I would say- lean condition, perhaps?

It's gotta be either ignition or fuel, but I'm not confident enough to say which.

Your missing above 4000 rpms sounds like the opti, but problems like that could be fuel related as well.

 

Typically when your headers are glowing red you are encountering a lean condition. What kind of fuel setup are you running? Also did you get you chip reprogrammed for the motor? It sounds to me more like a tuning issue than an opti issue.

 

I've done most of the prgramming for this combo myself and I have been leaning away from fuel problems since the BLM's are all within the acceptable range (120-135).

Now that I think about it, if it was the Opti going bad should the missing still occur in neutral? It only happens under load for me.... Can a bad opti only show up as a miss under load?

I guess I'm going to have to put the fuel pressure guage back on it tonight and see where it's at.

Thanks again,
Rob

 

same exact thing happend to me when i did my cam install. i figured it was a result of all the oil that had spilt on the manifolds along with it running too rich/lean.
so i cleaned the manifolds off and readjusted my rockers. never happend again.

 

Just a thought but if you have a cat convertor you might want to check to make sure its not clogged as well.

 

I'm going to check the rockers again too but i'm 99% sure they're fine.

And there's no cat converter on the car....

-Rob

 

Quick update:

I hooked up the fuel pressure gauge and went for a drive tonight and it holds a steady 43 psi right up to 4000 rpm where the motor starts missing horribly. It feels as if it's blowing out the spark, but if I accelerate slowly in 2nd gear and only use about 25-50% throttle I can run it right up to 5500 rpm no problem. It's only when I got WOT that it misses so bad the car no longer accelerates over 4000 rpm...

Any other advice would be appreciated.

Thanks,
Rob

 

TTT, any other advice would really be appreciated.

One other question too. If I had installed the timing chain 1 tooth off on the cam and the cam was then retarded could that cause the problems I'm having? I doubt it would cause the miss, but only a reduction in power, correct?

Thanks,
Rob

 

I know its possible to install the old style optis off by a tooth or two because the teeth and keyway are so small. Is it possible you actually installed it a tooth off in the retarded direction and the timing is way retarded now? A friend told me he did the opposite once and installed one and it started spark knocking cause it was advanced way too far.

 

No, I've actually converted to the vented opti and I'm sure that it's on correct.

Thanks,
Rob

 

Yeah, its damn near impossible to screw that up. Oh well, keep digging.

 

Well, after talking to a few other people i've decided to try changing out the Opti to see what happens. I just ordered a new GM opti from Dal so I'll let you guys know what happens when i get it installed.

-Rob

 

that would have been my advice. a buddy of mine had the same exact problems out of his 383 after he got it finished. It was the opti. New one installed and all is well.

 

Just wanted to let you guys know that I changed the opti last weekend and now the car runs perfectly!! Thanks for all the suggestions and now I can finally get around to tuning the new setup and getting it out to the track.

-Rob