well .... lets see , i have a 1995 3/4 ton silverodo 8600 pounds plus. i have just rebuilt the motor, 0.30 over, msd ign. box , stock dist. , new crane cam, new intake, flattop pistons, new off-road chip, all new sensors, headers, flow masters. well anyways i cant seem to get timeing right .... it runs like crap, and i cant seem to make it run smooth! i know most people hot-rod there motors without computer, but i keept mine, so there must be someone out ther that has done this and had same problems! well i get a code 42  ( EST) electronic spark timeing is grounded , or open , or bypassed, is this maybe because i installed a msd box?

I am running an MSD6A box on my 92 k1500 with the 305. The MSD box was one of the first engine mods I did. It smoothed out my power band and has never triggered an error code. Now I have done several other mods over the last 20,000mi and seem to have confused my ECU.

What i'm saying is I wouldnt blame the MSD. I would blame the fuel delivery, a friend of mine bored his 94 350 30 over with a good cam and needed to switch to a 750 holley carb and ditched the TBI cus it couldnt supply the fuel.

But on the other hand, I have seen TBI 383 strokers with stock GM electronics.

Good luck.