bobhorn15

my 93 z stumbles at low rpm and under load after msd opti replacement. waterpump killed the original. replaced both with plugs gapped to .045 to ensure spark, msd wires, msd blaster coil, gm ignition module. also had hypertch thermomaster chip, neew fuel filter and 24lb accel injectors. scanner said quad driver module fault and vats fuel enabler problem. i cant figure out why it runs so poorly and ideas?

Injuneer

There are three codes for the three quad driver modules on the 93. Which code did you get?

http://shbox.com/1/Dtcs.htm

Did it stumble BEFORE the Opti replacement? Is that why you replaced the Opti? If it only started to stumble AFTER you installed the Opti, are you sure you got the splined Opti drive shaft indexed correctly?

Is the chip programmed for the larger 24 #/HR injectors?

bobhorn15

it ran so strong before the water pump/opti went replaced it then the stumbling occured. i just found out it was chipped when i heard my ecm make wierd noises when i shook it its tuned for 22lb injectors (stock) im pretty sure but even after the injectors were changed to 24 ran fantastic for 2 years

Injuneer

In theory, the ECM can compensate for the 10% difference in fuel injector size, but the correction is limited to about 15%, so if you have a new problem causing it to run slightly rich, the combination of the new problem and the oversize injectors may be complicating things.

What about the possibility the Opti isn't indexed correctly?

bobhorn15

oh and i think the qdm has to do with the ac relay since my ac doenst work and the relay has been removed

bobhorn15

a shop did it there is a possibility i guess that was the second opti in a week that they put in so they could have half assed it to get it out of the shop.