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Multiple misfire?

Points70

Points70

New member
Ok so since I changed my LIM gasket and replaced the spark plugs a misfire occurred on the first start up. Then it stopped and went away until i drove it 900 miles to Montana. Then it misfired and had a code PO300, which is multiple misfire. Once I got to where I was going I was driving around town and on my way to the part store to clear the code it went away. And only when I drive at a constant 80MPH for atleast 50 miles the code comes back. But then after driving in the city for a while it goes out again. They are new spark plugs and wires. Anyone know what is wrong? Thanks
 


It's most likely either a plug or wire. Drive/scan and determine which cylinder is misfiring.

Quadruple check your wiring to the plugs. Make sure you didn't cross them.
 
As it goes like so...

From the top down on the coils...

6
3
2
5
4
1

and the engine if your standing in front of it looks like this...

2 4 6
UIM/TB
1 3 5
 
This could be a sign of your ICM going bad. when the motor heats up and tranfers heat to the ICM (which is connected to a steel mounting bracket and that bracket is connected to the cast iron head). When a bad ICM is heated up it will not function properly. It takes a while for this malfunction to occur because it takes a long time for the steel mounting bracket to become heat soaked.
 
Someone just reminded me the other day.

check the ICM connector to the coils. If you pulled it for any reason ..it might be loose.
 


I ran the code and it just says P0300 which is Random-Multiple Misfire. It does not say anything about which cylinders. So because of this it is probably not a plug or wire? And more likely the ICM? Not to sound like a complete noob but what and where is the ICM?
 
Just be sure to unplug the battery...because if your like I was the first time I removed it...I ground it out lol...and had to buy a new one regardless. $140 oops.
 


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