Misfire/small backfire on my 89 gt.

[RawNotch]

Hey guys,
Well title says it all, stang is misfiring on left side of motor.(left side if your driving) New valve in number 5 piston(bent). it ran fine after that, just throwing it in there. I have an older spark plugs in that side but it does not looked fouled at all. I can hear the difference is piston firing listening to the tailpipes. THe left side is loping way harder, and more rough. When I rev it, I get a small backfire out of the left side. It running like crap. Do you think it could be that spark plug? It's a motorcraft, The other 7 are brand new platinum double tips. SHe did not misfire after I changed them. I droped one in the engine, never to be found, that's why ther are only seven new

Sorry it's so chopey, I'm tired as all H-E double hockey sticks. Thanks.

 

[bgjohnson]

how old are your plug wires? and I'm bettin the spark plug either went under the intake plenum or somwhere near your motor mounts. anyways, if your plug wires are old and you recently did plugs, you could have cracked or damaged an old plug wire, they can be pretty brittle with age and ground themselves out. and if that doesn't work do the rotor and cap thing. and if that doesn't work do a cylinder balance test( you unplug each wire until you find one that doesn't affect the idle i.e. one that doesn't make the idle go down.) and if it is not your ignition , try doing that cylinder balance to the injectors, one of them could be bad also.

 

[RawNotch]

Yeah, that plug is in there somewhere. The plug wires are pretty new (4 months), they are frpp 9mm. Iwas thinking it could be an injector, but they only have 28k on them(frpp 24#'s) Could be though. I wish I had a code logger, I could just run the codes, and she what she says. I'll try the wire test, don't know why Ididn't try that yet. Thanks alot for your input.
Bryan