2001 2500hd 8.1 Misfiring

[Matavichos27]

Need opinions....

 

Truck has been running rough. Scan at the repair shop shows P300 (general misfire), P307 (#7 misfire), and P308 (#8 misfire). They told me I needed new coils on those two cylinders in addition to new plugs and wires. Plugs and wires haven't been changed in the 13 months since I bought the truck, so I've got no doubts about changing those. Is it likely that the coils are not actually bad, but that the plugs and wires were causing the misfire? Any harm in doing the plugs and wires and seeing if the problem is fixed before doing the coils? I don't want to screw up the new plugs.

 

 

FYI- They wanted $1200 to do the above work plus changing the left front wheel bearing, so I told them to go park it out front and I would come pay for the scan. I've already got the wheel bearing done and getting ready to start on the misfiring issue.

[dewfpo]

How many miles are on your truck/spark plugs.

 

My approach to something like this....... I always like to work from simplest/cheapest fix first and then move up, so.......If it were me, I'd run a bottle of Techron thru the fuel system to clean the injectors. If the engine runs a little better, consider running a can of Seafoam thru the intake. Those two things may solve most/all of your problem. After that if you still has a miss, then I'd consider change the plugs, if that doesn't solve the problem then I'd change the wires, if that didn't solve the problems, then I'd consider replacing 1 coil and seeing if that solved the problem on that cylinder, if it did I'd replace the other bad one.

 

DEWFPO

[Matavichos27]

How many miles are on your truck/spark plugs.

 

My approach to something like this....... I always like to work from simplest/cheapest fix first and then move up, so.......If it were me, I'd run a bottle of Techron thru the fuel system to clean the injectors. If the engine runs a little better, consider running a can of Seafoam thru the intake. Those two things may solve most/all of your problem. After that if you still has a miss, then I'd consider change the plugs, if that doesn't solve the problem then I'd change the wires, if that didn't solve the problems, then I'd consider replacing 1 coil and seeing if that solved the problem on that cylinder, if it did I'd replace the other bad one.

 

DEWFPO

 

Thanks for the input. I too don't want to do anything unnecessary but if I change the plugs I 'm going to go ahead and do the wires. Truck has 147k on it. No idea how old the plugs/wires are but the shop said they took one plug out and it was fouled (i think). Ran 3 bottles (STP/Lucas) through before I took it to the shop. No real change.

[yukon25008.1]

I agree with the techron in the tank, and then the seafoam, that stuff works great and it will feel like a new truck after a proper seafoam treatment,

just inspect the wires, msd makes a real nice perfect fit set.

[Kirkathon25]

to test the coil packs swap them out with another cylinder and see if the misfire moves

[tim73]

Id go ahead and swap the wires/plugs. You are having missfires...plus you dont know when(if) they were done. I know my 8.1 acted ugly a while back...and a set of plugs/wires straightened it right out.