Just finished putting new exhaust manifolds on my 97 5.4. Prior to doing the job I degreased and pressure sprayed the area around the exhaust manifolds. I also lightly ran the hose over the whole engine to blow the dust off. I didn't pressure wash any of the engine except the manifolds from under the fenders. I started the engine in the car wash while I washed the rest of the truck and it had a miss. I know, cover the electricals with plastic bags which is what I always do except this time I wasn't planning on spraying the motor.
When I got home I sprayed all of the electrical connections with silicone. I got the manifolds changed and the miss is still there. In neutral the miss is less noticeable than when its in gear and I'm accelerating. It really shudders if I try to accelerate hard. In neutral it will barely be noticeable if I rev it up slowly. This makes me think its a vac leak. No Check Engine light. Any ideas? Thanks.

 

sound like you got some water around the coils and in the plug well. take off the COPs and dry them out. blow out the plug holes also.

 

Thanks for the quick reply. Would a COP problem or electrical miss trigger the CEL?

 

not always.

 

eventually yes... but not immediatly.. and even if u dont directly spray. the hottest part on the head is going to be the spark plug. so when u shut it off the humid air and surrounding water condenser to and around the plugs.. sux but we all deal with it. everytime it rains here i gotta pull my plug boots just about to let em dry out

 

I didn't have a CEL this time but the other times when a coil went bad I got a CEL right away when the miss started. Sorry for wasting everyone's time because I decided to put the scanner on it anyway and it came up with a missfire pending on cyl 5. The coil tested a .7 with the ohm meter set on 20. The new coil tested the same thing but it cured the problem. Did I put the ohm meter on the wrong setting? I didn't get any reading at all when I set the meter on higher marks.