Could also be the ignition module I guess?
Random misfiring would generally mean that the wires are working, randomly misfiring would suggest that they're skipping intermittently on random cylinders - which would be caused by the ignition module I believe.
I am the original owner of a Pontiac Grand Prix 1997 with 113K miles. Recently the car started shuddering... sort of like hesitating or 'misfiring' without any noise whatsoever. It usually does this when I am attempting to accelerate uphill in between 40 to 60 miles per hour speed. NO - it is definitely not a transmission issue because I recently (just two days back) put in a new GM GOODWRENCH transmission because the car also started slamming in gear, we thought that the shuddering led to the slamming but now with the new trans and all the slamming and harsh shifting is gone but the shuddering remains. My mechanic says it could be a wiring, coils, spark plug issue based on the diagnostic code that says RANDOM MISFIRING... Can someone pls provide some insight, I am sick to my stomach shelling money trying to retain this car. Thanks in advance.
Bad plug wires.
Same problem on my 95. It was the plug wires.
It's been my experience with the GM DIS waste spark systems that if one section of the module goes bad it tends to stay bad. I've had coils go on and off though. I've found that when one or the other goes, you really feel it because two plugs turn off. Been several times I've had to limp back on 4 cylinders instead of 6. All the while sending raw fuel to the cat.
Bad spark plug wire(s).
-- GW - note incorrect email address "It's good to yell at people and tell them you're from Tennessee. That way you'll be safe." - Gary Busey
NSS wrote:
I had two different problems that caused the same symtom.
First was a worn through vacume hose that went right down by the battery torward front fender. Just had the battery replaced months ago and the protective sheild slid down and away from the batt. Took two months to wear through.
Second one drove me nuts. The mechanic had replaced both spark pack all wires, the plugs were new. I was bleeding the coolant over the water pump and a spark like hell hit. Turns out the plug had a cracked procelain. Replaced it and instant relief.
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