Misfiring Mishap


#1

I have a 1998 Chevrolet Z71. When i bought the truck this March the guy i bought it from handed me a box and said he did’nt know what it was but the guy that he bought the truck from gave it to him so he figured he’d give it to me. It was a hypertech programmer. I am an avid truck customizer and i always love making additions to my truck, whether it is getting custom tailights and headlights to a new grille and hood to a sound system. Well i bought a new set of wheels and tires, and the tires i bought were 2 inches shorter than my previous tires. When i put them on i noticed my speedometer was off slightly so i decided to hook up my power programmer to recalibrate the speedometer for the shorter tires. The second it was finished programming i went on a test drive to see if it worked. When i started it up i noticed it was misfiring. I took it to the Chevrolet dealership i work at and scanned tested it and found cylinders 2 and 3 were dead and were not firing at all and it had a P0300 random misfire code, nothing else. So i put new spark plugs, wires, cap, and rotor on it and the problem persisted. The check engine light begins to blink when you reach about 30 mphs. I put new injectors in for cylinder 2 and 3, because i found they were stuck open due to the gas soaked spark plugs, and cleaned the other 6 injectors and still the problem persisted. I ruled out the ignition module by swapping mine with a friends that has a truck like my own, and the problem persisted. I checked the timing, fuel pressure, and compression and all tests came back okay. I even removed the valve covers and made sure the valvetrain was operating properly, and it was. Im wondering if something may have happend to my computer when i hooked up the programmer. What do yall think?


#2

Do the injectors for 2 and 3 operate properly now? Maybe the driver circuit is no good.


#3

Have you talked to the driveability guys at your dealership? Confided in your shop foreman? Hope you don’t say they are all stumped.How about a PCM reprogram with GM software.


#4

Well after i replaced them and noticed it wasnt running any different i took the intake off again and the new injectors were stuck open like the old ones.


#5

Well i tried flashing the computer and that didnt work. I couldnt even get it to communicate with the tech 2. So i put a new computer in it and no difference. But now i could communicate. I pulled numbers 2 and 3 the plugs out, attached it to the plug wires and watched the spark pattern, come to find out at idle the spark was erratic for about 5 seconds then would quit for a second and do the same thing over again. So what had happend was the programmer fried my computer, in turn messing up my ignition module causing my distributor cap to fail. Sure enough when i put a new cap on it ran fine after the new computer. So now its hitting on all 8 and no complaints here.