Let me start by saying I have read the 10000+ posts related to others with this problem and have yet to solve it. I have replaced everything ignition related.
Opti - 3 of them (2 used and nor on a new one)
Plugs and wires (to many times to count)
Computer- did that too-Swaped with a guy that had a dyno tune on car with a simular setup, My car ran diffrent but the miss was still the same-no change at all!
Coil-had 4 different ones on the car
ICM-twice, one new and one used
MAF-3 of those suckers
Injectors - got 28#'s in their now
02 sensors-changed out more then a few
I have scanned the car hundreds of times with Auto tap (not the best scanner) and I don’t see anything that looks out of place or that changes from the lower rpm to the higher ones that shouldnt. Never got any codes besides the normal maintenance things that where all fix right away and never changed the miss.

The only thing that seemed to help at all was when I went to a .030 gap on my plugs. But that increased the performance through all of the rpm's and I still miss really badly up top.

The miss is like hitting the rev limiter at around 5500-6000 Rpm's, my shift points are set at 6200 Rpm's. At the top of third gear sometimes it is so bad it won’t even rev high enuf to switch into 4th for a few seconds. (Not a trans problem)

History
This all started when I bought this long block used (guy who I bought it from said it revved it to 6400 no problem but who knows). This motor has stock ported heads and a cc306 cam in it, I know nothing about the rest of the valve train
This motor has always done this, never in the last 2 years has it changed, never got any worse or better.
I am at a point where i feel totaly beaten by this car, every time i try something i pray it will work, but nothing ever does.

Some ideas I have that might be the problem. (And this is where I need your help also, most of this I don’t know how to check)

Springs, I hear allot of people talk about valve float causing this, however it seems like valve float would be more of a drop off of power not jerking of the engine. What do you think?

Fuel pressure, I have a drop of about 8-10 psi at around 6000 rpm,s. From what I understand this is caused by a loss of voltage at high rpm's and most likely is not my problem. However I think it should be tested, how would I go about testing this, Should I run 12 volts from the battery directly to connecter on the rear?

Crank position sensor or some other miss-match, my computer and harness is for a 97 and the motor is a 94. I have the CPS tuned out but I don’t know what that means. Is it possible that the car is still looking for that and messing up, up top because I don’t have it? Is their something else that the 97 computer wouldn’t work well with?

I read that a couple of people had the 3 screws that went into their cam come lose and caused a miss like mine, Could this be my problem? How do I check this?

Is it possible the cam was installed wrong? How could i check that?

Did i screw something up in the wiring harness when i swaped motors? The ground that normaly goes to the passangers side of the block is now grounded on the k-member becaue i couldnt get it to reach the block after zip tieing the wires away from the headers... I duno im just trying to throw everything out their.

What about valve lash, is this something you guys could walk me through checking and adjusting?

 

If I was you i would put a set of valve springs on it FIRST. B/c you dont know the guy who had it before you,how it was ran,how long it was ran,etc etc.

Loose cam bolts...could be but I doubt it...worth a check though since winter is coming anyway.

As far as setting valve lash,you need to run it and get it normal operating temp and shut it off. Pull the valve covers off and use a feeler gauge between the rocker arm and the tip of the valve and measure it (not sure what the lash is on a CC306,but someone else will). I still think you should throw a set of springs on it first though.

Fuel pressure could very well be a cause as well...8-10 psi is alot of drop,especially on an EFI car. Could be a fuel filter and maybe your fuel pump is too tired and old to keep up.

 

Having never been inside an engine before is valve springs something i should try to do myself, or should a pay a shop to do it? What springs would be the best to use?

Anyone have any other ideas i can try before i spend $$ throwing parts at this car?

 

Also from what i have READ it seems like bad springs would not cause such a bad miss that feel like i am hitting a rev limiter, it would be more like a big drop in power. My car still pulls hard between the misses. It feels like if you where to unplug the coil wire for a half second then put back while your pedal was floored the whole time. Its so violent it makes the car jerk forward.

 

Most common problem would be rockers adjusted to tight. I would also check the low-res jumper going to the opti.

Has the car been on a dyno before? Do you have the graph?

Dennis

 

I've had this miss but above 6000. 2 things that removed my miss, were less fuel around that rpm and or add more timing. I've played with this for a long time. It's not bad components just something that needs to be tweeked.

 

i was about to have it dynoed and when they pushed in the tune for the larger injectors the computer died

Going to try and get one done this weekend

 

The cheapest ($0.00 investment required) thing to do would be to check the valve lash as has been previously suggested. I would do it with the engine running and go about 1/4 turn past zero lash to start with (assuming you have 3/8" rocker studs).

If the lash is set too tight, the lifters can pump up at high RPM and go "solid", not allowing the valves to close.