I have been having a problem with my car for the last month. Most of the time it will not rev past 4500 rpm, it will break up and backfire through the intake. I also know when it is going to happen b.c it doesnt idle right. Sometimes it will rev tho, but I feel down on power. I went on my computer at work and went through the trouble shooting chart for fuel first b.c it is esier, and everything checked out ok. I have also replaced the valve springs...not related, and the ignition coil b.c I had an extra...neither had any affect. I have chip from pcmforless and I took that out....still nothing....but now I have no rev limiter on my stock chip when it does rev. Im not someone who buys parts and just throws them at a car....I want to no whats wrong. I have a scope at work....but i dont have a dyno....so there is no way to check it. It only happens under load. There are also no codes. Does anyone have any ideas??? The opti is about a year old now. MSD makes a cap and rotor for the opti....does that really solve the opti problems???

 

You didn't mention checking the plugs and wires.

 

Sorry, plugs and wires are brand new...checked all the plugs when i did the springs and they were fine....Im not saying the wires arnt a possibility, but if they were bad you usually can feel it under any load.....this does it consistantly at 4500.

 

ANSWER at the end!

chance that your PCM is broken less than 1%

chance that your opti is broken
two part answer,

pt.1 you have trigger / CPS crank position sensor signal since you have spark so the opti CPS is GOOD

pt2 your cap and rotor could be bad with spark scatter, loose rotor, free torx screws, bad cap and rotor....POSSIBLE

Here is what's wrong with your car.
......Rockers are down too tight....

too much pushrod preload into the lifters
when you rev and oil pressure builds the lifters pump up
and now you have lift on the cam base lobe
then cylinder head pressure leaks out the intake on the compression stroke...hence the backfiring
the motor is so inefficient at that point it can not rev

At www.Race-Prep.com we offer performance lifter adjustments done on the dyno with before and after dyno results. It is typical to see 7-15 hp across the rev range on heads and cam cars and a widened rev range of 500 RPMs in your case alot more.

TAD

 

Its possible, but not likley to be the rockers/lifters. It reved fine from the moment i got the car till now. Like it tell everyone the car is a freak. Its in the 12's with very few mods...and this week i went to the track and my mph dropped off by 5 and i went a 13.4 at 105. I was in the 12;s without the valve springs, but im doing a cam and put them on b.c i had some time. I had the problem before i did the springs....and it just started happening out of the blue. The rockers are ajusted 1/2 turn on all of them....and i double checked them just to make sure. I really think it has something to do with spark b.c of how random it happens. if it was the lifters, I think it would happen all the time....also when it happens it wont idle right and wants to die which would have nothing to do with the lifters. Also when it happens im down on power....but I could drive the car the next day and it could be almost completely fine.

 

There is a very good chance it is the lifter adj.

The is an ouside chance that it is the opti.
Sometimes cars will backfire theu the intake when the spark advance is way off. this would suggest that the opti is not propperly engaged and indexed into the cam. I had a friend that got a cam with a dowel pin that was too short, once.

TAD out

 

my car does the EXACT same thing, right down to the point, I couldnt have explained it any better...the popping comes at around 4500 rpm, and my car is deffinatly down on power... the problem is also, SOMETIMES intermittant, but most of the time it does it....... I've heard that sometimes it could be the IAT sensor, but not in my case..... PM me if you find anything else... my assumption is that its just the opti... my brother also had a 93 z28 and his opti went out, but it didnt pop like mine, that I know of.. just stumbled... anyone? I might try the rockers as well........ thanks guys,
Adam

 

I havent put the cam in the car yet...and the same opti has been in my car for a year with No problem at all....The problem didnt happen when i did the lifters....it just started happening...so i doubt that they are adjusted to tight. Im going to try a cap at rotor from msd....if it doesnt help then i guess i will try the computer.....i hate to throw things at it but there really arnt many tests that i can do. I will let you know how it goes.....and thank....Im going to check my rockers for the hell of it tonight