Brandon 95 Z28

Hey,

Ever since my heads/cam install this past winter, the car hasnt been able to pass 6k rpm. It acts as if it is hitting a rev limiter, but PCM4less swears that they set it to 6700. I dont have a way to scan the car right now to be sure, so is their anything else I can look for as a culprit, could it be valvetrain related?? I really want to fix this since I finally got the new fuel pump in, and the car is finally near where it should be, thanks for the help.

Brandon

LWillmann

I supposed it could be a bad coil or Opti. Doesn't the Opti typically start to break up in the upper RPMs when it begins to fail?

1racerdude

It could very well be your valve spring's. What is your seat & open pressure.You have put a new pump in it and that was my next guess.Fuel filter?

Brandon 95 Z28

Yeah, I was wondering if it could be the valve springs as well. I am running the 987's, and Lloyd set them up for me. I thought others were running the 987s with this cam without issues. I havent checked the pressure on them yet. It definitely isnt the pump or filter, and it doesnt feel ignition related. Thanks for the replies.

Brandon

mrz28 73/97

I notice in your sig that you have Comp R lifters, what do you have the lash set at? These lifters like from 0 to 1/8 turn lash, if you have them any tighter your engine won't want to rev.

NightTrain66

MRz, that is the same thing that came to my mind.

The R lifters are VERY picky about rocker arm adjustment. Most have the best results running these VERY close to zero lash or even at zero lash. Even at 1/8 of a turn past zero, they can still "pump up" at high RPM and hold the valves off of their seat. If the valves are doing this and not trapping cylinder pressure, the engine will NEVER run right.

Fuel pressure, opti, etc, would be some other places to check but I would start with the rockers. This is a simple thing that you can do pretty quickly and it is cheep. If this makes no difference, find someone that has some tuning equipment that can help you check things out better and you can see if it is A/F, fuel pressure, opti, timing, etc.

Do a search on the R lifetrs and you will see what kinda problems they have given people when adjusted too tight and how things are MUCH better when adjusted correct.

Lloyd

NVMYZ28

I agree - it could be that your valves were adjusted too tight - causing the lifters to collapse or "pump up" in the higher RPMs. I had followed the "factory recommended" setting on tightening my valves - but that caused the lifters to collapse or "pump up" - car acted jus like it would when hitting rev limiter. Once I backed off and only tightend the valves 1/4 turn past 0 lash - all was well.

Edit: I too have the "Comp R" lifters.

Brandon 95 Z28

Thanks for the replies, I will be sure to try re-adjusting the lash on the lifters this weekend. Do you consider 0 lash to be the point where you can feel a resistance being placed on the pushrod while spinning it with your fingers? I just went to the track and was trapping 105mph because I couldnt rev above 5800 in any gear and I was having to shift into 5th near the end

1racerdude

I'll put my money on springs.