Hey everyone, I have a 94 z-286 spd that I can't get to run right. I have tried everything I can think of andjust can't seem to solve theproblem. The car seems to start fine and idle fine, but under acceleration it speratically misses all through the RPM range.A time when it really seems to miss bad is when I am cruising at about 2000 RPM in any gear and try to accelerate. Also, under hard acceleration it will be pulling hard, then studder and fall flat on its face for a second then pick right back up. I have checked and/or changed all of the obvious things but it has not helped it at all. I hooked a diagnostic up to it and drove it last week and most of the readings seemed to be fine, and the check engine light does not come on. Two things I saw that seemed to be off were that the manifold absolute pressure seemed to be high and the timing was screwy. The diagnostic said that the MAP reading should have been between 29- 48 and it was consistantly between 48-54 while under power. The timing was the thing that really through me off though. The timing was set at 3 degrees retarded but when it would miss it was reading up to 40 degrees advanced. Some of the modifications were not done by me so I am in the process of fixing another persons issue and I am still trying to learn about these motors. I am totally confused by this, if anyone has any sugestions or anything it would be awsome. Below I listed all the mods on the motor if that helps.

Engine Mods

Isky valve springs
Isky locators
Isky titanium retainers
Comp cams #305 hydraulic roller cam
Holley ignition box
Taylor 8 mm wires (new)
Crane fireball coil pack
TPIS optispark
Moroso cold air intake
Granatelli mass air flow meter
Lingenfelter LT-4 intake plenum
BBK shorty headers
LT-4 Knock sensor

 

Did it ever run properly with all those mods? Chances are it needs to be tuned. The 40 deg advance is OK under low load condition, but should pull back into the low 30 deg range unde full load (WOT).

 

No, it has never run right since I have owned it. I have delt with issue after issue, so it has never run how it should. I used a power programmer to reset the ecm but that is the extent of ecm work on it. I have decided I am going to have it tuned at somepoint soon I just want to know that I am taking it to a shop to get it tuned not have a whole bunch of other problems worked on. I am on quite a limited budget right now and don't want to pay for them to do mechanical work as well as tuning. Thanks for the input though.

 

I know it may sound stupid but this could be really simple. I recently had to buy sparkplug boot protectors because my headers would get so hot that the wires couldn't take it and the engine would start to miss fire. Then it got so bad that the headers were melting the wires and the car ran just as you described. About $50 and a little time and your problem can be solved. Hope this helps, let me know.

 

You shouldn't run that much timing, for a motor like yours on pump gas it should be at least 34 and not more than 38 degrees max. Good luck finding the problem.