Hi,
i have a 92 camaro z28 with a 357 (Stock Vette Alum 113 heads, Crane Compucam 2032 http://crane.carshopinc.com/product_...d/15861/104224, roller rockers 1.6 ratio, Tri Y 1 5/8 headers) and a few other mild mods. it has the stock TPI (speed density) from a 90 iroc. The problem is it will miss very bad when accelerating normally, or when cruising down the road, at above about 45mph it will backfire every so often too. but when you put your foot to the floor it runs good (it sometimes feels a little weak) but overall runs better the more your in the gas. Also when the engine is cold it will run better. And since we put the 1.6 ratio roller rockers on it it will idle erraticly once it is warmed up it will idle fine cold though, vaccum seems to be ok when it is idling fine. this problem has been bothering me for a while, i have checked the plugs, wires and distributer and all seem to be ok, i also have changed the injectors thinking that maybe a couple were not always working (it didnt help). The old ones were stock ' LT-1 and the new ones are a set of 1 year old Accel 26Lbs ones. fuel pressure is 45 Psi. I am not sure if it is emmission related since we toke off all the emmision stuff without doing anything but plugging up the holes, or if it is electrical related. any help would be much appreciated. if you have any questions please ask me, i have described this the best i can but im sure i forgot something.
Thanks
Kenny

Data log file at... http://www.masontroop763.com/underconstrution.htm

Edit by Ken's Dad

Attached below is the data logging we did back in August. I hope that this will be some help for sorting out what to look for...
The motor is fresh .040 over has in addtion to the mods Ken has listed a crank scraper and a roller timing chain.
The car is one that Ken and I redid last winter from the ground up with parts for a '90 Iroc and the '92 Z-28
L98 700R4 3.45 9 bolt Edelbrock TES 1 5/8" into 2 1/4" pipes to a 3" Flowmaster cat back Cat were replaced with plain piping. Stock dist with a MSD cap stock coil and newer stock wires. I forget what plugs are in it at the moment.
Only concern I have is the balancer is small 6" +- rather than the bigger one like on my '88 IROC that might make my initial timing off because the tab is some distance from the balancer I think that I am close but I could possably be off it is set for 8 or 10 degrees initial. I do not recall for sure what one I used... Vacuum Is 18" and steady at idle.

If someone has a data log of a speed density L98 that they can e-mail me PLEASE do as I would like to compare another car since mine is mass air flow.
My e-mail is 1988IrocZ28@gmail.com

Thanks!!!
Dave

 

Have you checked continuity on all the plug wires - even brand new wire sets have bad wires.

Have you made 100% sure all the plug wires are seating on the dizzy and plugs all the way?

 

Yes we have checked that all of the plug wires check out ok with the ohm meter and the wires did "snap" on to the plugs and dist. Thanks for thinking of the little things as I am out of ideas! I also for got to mention that it is a 730 ECU with the stock chip
AUJP as I recall. We did have bad grounds when the harrness was reinstalled ran a new ground lead to the back of both heads and the dignosis connector from the battery (car would not start until we did that) Also to make it a little more clear at wide open throttle the car runs strong but at part throttle lets say a 50MPH cruise is runs rotten. What I am confused with is why it is good at wide open.

Thanks
Dave