Hello all. Tonite, I changed my spark plugs and wires (only because I ruined one trying to remove it) and I now have a wonderful misfire. The SES light is not on however when I press on the throttle, it stumbles and then goes. It's fine at steady throttle and while cruising but if I get on it to accelerate, it stumbles a couple times before accelerating. I've checked to make sure the plugs are torqued properly and I gapped the plugs to .055in which is at the wide end of spec. I also did a visual and audible inspection of the vacuum lines for leaks but have yet to perform the propane test which I will do as soon as I'm done typing. The truck was fine before I messed with it except that my mileage has been decreasing and the plugs and wires have 83k on them. Oh yeah, I poured a bottle of Lucas fuel injector cleaner into half a tank before all of this too.

Any ideas what's causing my misfire??

 

Check to see if any of the plug insulators are cracked, Tom. That's easy to do when changing plugs, especially if your spark plug socket cushion has seen better days. The symptom can be a dead miss or one that misses under load like yours.

 

Hmm.. Interesting. I hadn't considered that. I'll have to pull the plugs tomorrow and see what I find. I did the propane test and didn't detect a vacuum leak and even tried creating a leak which had no effect on the symptoms. I checked for spark at each end of the plug wires and have good spark at each end.

I'll check the plugs tomorrow for cracks. I checked my plug socket and the cushion is missing so it's very possible I cracked a plug. Especially since the only way to get the plugs tight was to use a 3/4" wrench on the end of the plug socket.

 

i did that on my 92 when i changed the plugs on it... and it really sucks when you have to change 8 plugs on a 4 cyl and then have to go check them...

 

Bob, you were exactly right. Thank you!!

 

Glad you got it fixed, Tom!