bad head gasket-re use old plugs? msd??

[bigbadchev84]

i just got done replacing the head gasket on my truck, i blew the head gasket during break-in of a completely rebuilt motor, new everything. well i got pissed at it and just left it for about 2 months, well i just got it back together last night and fired it up and it runs really rough and will backfire intermitenly when you hold it at about 2500 rpm for awhile, i did re-use the old plugs, as they were new when i first tried to fire the engine, will a blown head gasket ruin plugs? they look good physically but should i replace them?? it sounds like it is missing, also this motor is fairly beefy, does an msd really make a noticable difference?

 

[dyeager535]

Forget the MSD, its not going to solve your problem. (or at least it'd just be a bandaid)

Pull plug wires one at a time while the engine is running. That will isolate the bad cylinder(s). You can then swap a suspected bad plug to another cylinder and see if the problem follows the plug or not.

Bad head gasket shouldn't hurt a plug, BUT, depending on brand, and how they were treated, they could still be a problem. NEVER hurts to check plugs with ignition problems. Make sure the plugs aren't all crudded up though either, you may need to clean them.

 

[bigbadchev84]

anyone else have an idea?????

 

[smalltruckbigcid]

Isolate the dead cylinder. Then.....
Step 1 switch the plug with one that is working if the miss follows the plug its a bad plug....if not then try swapping out the plug wire.

Step 2 if the same cylinder still misses.
run a compression test then a leakage test...if the leakage is fine but compression is low pull the valve cover and check cam lobes and valve lash, if compression is ok but high leakage the head has to come off at least because you have a compression leak in the rings, valves, or gasket.

Step 3 for multi port fuel injected engines...check electrical connections and swap injectors for known good ones.

Thats all that occurs to me right now
George