i have an 93 z28 with the lt1 and optispark distributor. i replaced the optispark with the msd pro billet after the water pump went and fried the original. since that repair it stumbles under load like a clear miss. i have replaced many things to try and solve the problem. for instance, msd super conductor wires, msd blaster coil, ignition module, ngk iridium plugs gapped to .045 for assurance of spark to no avail. new fuel filtler, accel injectors, trickflow intake, hypertech thermomaster chip, built trans from monster transmisions and 22oo stall converter. motor has high mileage but never ran so poorly since the distributor change. scanner said quad driver module fault and vats fuel enalbler problem. im at a loss.... dont know where to go from here. what oould cause the stumble?

 

So the engine ran fine until the water pump rained on the old opti? Are you sure you didn't cross any plug wires when you put on the new opti? Also make sure you didn't forget to hook up any sensor wires, etc.

 

ran great till the msd relplacement. a shop did it so im trusting they did everything right?

 

honestly? i've heard some bad things about MSD opti's...i would personally check all the wire routing and make sure that's rock solid, then i might point a finger at the opti unit

 

Everything except for the stumble, but that may or may not be their problem. Was the MSD your part or theirs? If you supplied it, they aren't responsible for your stumble issue. And for what it's worth, I put an MSD on my Vette this summer right before a 2,000 mile road trip, and it didn't skip a beat. Bad parts (if that's what it is) can come with any brand. But looking at it logically, you didn't have a stumble when the old opti was still working, and now you do. That means it has to be either the opti itself, or something else was missed or messed up, so stop throwing parts at the car left and right. For fun, check the temperature sensor on the bottom left of the water pump, it's easy to break when removing the belt (don't ask)!