ok, i have my moms 98 blazer hat has a random misfire, that is the only code my innova scan tool shows. i personally changed the plugs, used ac delco, put new wires on it, from advanced auto, and a new coil. it made no difference at all. i waited till dark and started it and under the hood the plug wires jump fire, and fire jumps from the new coil all over the coil itself to the closest ground. gets worse as you rev it up any. so i took to a guy who worked for a cheverolet garage for the last 15 years, he put new plugs, wires, cap and rotor, checked timing, he cant figure it out. he said he went to go in and look at the ignition info on his snap on computer and it kicks him out of it, he tried several times and it wont let him into see this info. all it gives him is a random misfire. he cant get in to see the injector info either. he said maybe the ecm is bad. i have a computer off another blazer i had, it was a 98 4.3 same as te one im working on now. he said i cant put that computer on till i take it to a garage and have it programmed. if it is the same computer, off the same model balzer with the same motor why does it have to be programed?the blazer ran fine before we had a trans put in it, then it has this mis we cant get out. we have put a new tps, and mass air flow sensor on it as well as a map sensor. egr seems work right, temp sensor is new, fuel pressure is 65psi prime and 62 running, it leaked 10 psi over a four hour period. all fuses are good. can anyone point me in a direction to a possible fix? she has been out about 500.00 in parts and labor and it has made no difference. here is another thing, it starts everytime, idles good, but when you take off it spits and sputters, push the pedal down half way it takes off with no misses, plenty of power. thanks for any help you can give.

 

Sounds like the distributor position is off, or maybe it skipped a tooth (worn gear on the dizzy or worn/loose timing chain).

You need to look at the CMP Retard or CMP Offset in the live datastream. A good, higher end scan tool should read that. It's a GM "manufacturer specific" PID, so it won't show on a "generic OBD-II" scan tool. The Android app "Car Gauge Pro" will read it with a good bluetooth OBD-II connector.

Is there any contamination (oil or especially anti-seize) on any of the high voltage ignition bits? (wires, coil, dizzy cap inside or outside).

When the coil fires, the spark will go by the lowest resistance path to ground. From your description, it sounds like the rotor isn't positioned on the distributor cap post when that happens, except at higher RPM's (which should have more timing advance). If the rotor isn't in contact with a post, the coil energy will have to find another route to ground. The path it picks is usually not good.

 

he had already checked the timing with his scan tool, it was -1.. well with in range