i have a built LT1 and isnt making the power is suppose to, on the dyno made 275 til 4500 rpm then falls to 189. i have changed valve springs, i have changed cap and rotor, i have changed spark plugs to NGK r 6, as soon as i get pass 4500 the car starts breaking up. and at time she stalls while im driving, ill roll to a light and keep it in N and just stalls out on me. can anyone point me on the right direction. i didnt change the opti on the cap.

 

im not real sure but have u check the fuel filter and have u put octane booster in it?

 

could be a number of things causing the high rpm miss

-icm
-coil
-opti
-plug wires
-fuel pressure

 

check for cracked plugs, replace fuel filter, replace your wires, then coil.

 

For MY car (96 LT1 M6) the answer was NOT the actual plug wires (which were good), but rather the placement of those wires.

Once I redid what the dealership monkey did and un-Zip tied my wires (!!!), then routed them with aftermarket wire seperators, MY car's high RPM miss was fixed.

I know our engine compartment is tight, but this might be what you need to try.

Oh, and I can tell you that zip-tieing three pass side plug wires (tightly!) to an A/C bracket will indeed result in a nasty high speed miss - even with new wires!

 

+2 onthe wire routing and also the fuel filter. I have had problems with a plastic fuel line kinked almost shut . Run a fuel pressure test while hammering on it and if it holds steady its not fuel related.
Another problem i had was a bad ignition coil.. The MSD coils are decent and like 40 bucks at autozone. And like mentioned before it could be the icm.

 

i have changed thos, and the cap. im starting to wonder if its tune related.

 

I don't think a tune will cause a high rpm miss unless for some reason your tune threw a **** ton of timing in the high or rpm or leaned the **** out of it which I don't see happening.

what gap are you running on those plugs?

the fact that you're saying it runs poorly after running for a while leads me to believe it is something else honestly:

heatsoak, which usually means old/bad electronics that are more prone to problems when being exposed to heat sources for prolonged periods of times. this could be anything like a fuel pump, icm, electrical connectors, grounds, wiring, coil, etc. I've seen opti connectors that run along the side of the intake cause this problem due to dry rotting. one time I even had an ICM not being bolted correctly to the coil bracket cause a high rpm miss.

 

Yeah could also be a ground issue. but i would recomend a fuel pressure test first. Also you can close your gap to a .035 and might bandaid a current problem. I think mine was due to some bad plug wires or cap and rotor wore out but did fix a similar problem i had at one time.

 

the plugs were gapped at .50 i should have went to .35 bc ill be on nitrous as soon as i get it running right. the car is turnning off on me and its popping like hell sounds like the 4 of july when ur driving by me and i let of the throttle and hit the gas again

 

im thinkin this problem is opti. all i did was change cap, i didnt touch the rotor either my low power is great ill spin 1 and 2 gear so i have good power low end only when i pass 4500 hp is 275 low end then hits 189 at 4500 rpm.

 

Oh one other possibility could be a dirty MAF sensor. You could try unplugging and seeing if that fixes it. Also you mentioned you only replaced the cap but not the rotor..The rotor actually gets wear on its tip.
Your Gap is awfully big. Do you have an aftermarket ignition box? If not , I would definiteley close the gap to atleast a .040
It could very well be the ol opti tho.. good luck man..these kinda gremlins can drive ya nuts lol

 

no luck man now she feels like she is skipping, i have no power and alot of vibration in 5 and 6 gear. i checked coil,plugs,wires. nothing starting to hate this car

 

Clean the MAF!