Running Out of Ideas!! Help Please!

[Blue_01_Z28]

Hello guys/gals, Thanks for your help first of all.
I have this problem with my car where it seems like at WOT it looses spark or fuel, it just stumbles around 4k - 6k. It first happened passing an 18 wheeler in 4th gear on the highway. Its like a pause in firing then it picks up where it left off then it does it in and out till i shift.
The car has full bolt ons heads, Erson cam 620/620 int/exh on a 108 LSA. It ran fine for a year and it just stated acting up.
Here are some of the things i have done. I changed fuel pump to a granatelli 255, fuel filter change it was dirty, temp sensor because a friend suggested, I tried to test the coils but not really sure how. Injectors are stock and they are running about 11% duty cycle according to my EFILive software. Another friend of mine suggested to change the knock sensors to fix the problem, what do you all think about that idea, because I really have no clue if a bad knock sensor would kill my fuel or spark like that. If you guys need more info let me know. Thanks again.

[Spaz]

your cats could be clogged...

[pajeff02]

If your knock sensors were causing issues you should be able to see the PCM pulling timing under acceleration with your tuning software. In addition to clogged cats, you should also check for a dirty MAF and verify fuel pressure with a gauge. Any codes being thrown?

[Cutlass]

sounds like it might be leaning out. Check for low fuel pressure, MAF problem, dirty injectors, or O2 sensor problems.
If it is spark related, check the plugs for deposit buildup, worn out, improper gap, or carbon tracking (cracks) on the insulator. Might also be a crank position sensor problem causing erratic spark.

[Blue_01_Z28]

sounds like it might be leaning out. Check for low fuel pressure, MAF problem, dirty injectors, or O2 sensor problems.
If it is spark related, check the plugs for deposit buildup, worn out, improper gap, or carbon tracking (cracks) on the insulator. Might also be a crank position sensor problem causing erratic spark.

You sir, are a genius thanks man, I had already checked everything, plugs cleaned MAF sensor, wires, Fuel pump...But when you said the crank could cause eratic spark i knew that was the problem. I also noticed a couple days ago that the engine stumbled but the RPM shot up to 6k, didn't make sense since the motor really never went that high. A bad Crank position sensor did though when u mentioned it, I just changed it our few hours ago and fixed the problem. Thank you guys for your replies and help, I love this site! I think its been bad for about a year now but it never stumbled on me till a month ago. But during the winter when the car was cold it started to backfire but only till it reached operating temp, so i never thought much of it, since it was the first winter with the big cam. Ahh well its all better now thanks to you guys

[c5z28]

Since you figured the problem is that 620 the lift? What's the duration, what kind of hp numbers is it?

[Cutlass]

Glad I could help!!

[Blue_01_Z28]

Since you figured the problem is that 620 the lift? What's the duration, what kind of hp numbers is it?

Yea Lift @ .50 Int/Exh. 236/242. numbers aren't that great it pushes about 410 or so.