Ok well, I didn't know how many miles were on the new cat. Are you sure you do? Anyway, since the plenum is blown, it is more than likely just carbon on the valves. Seafoam the crap out of it before you do the plenum, and use Techron+ after you fix it.

 

You mention the transmission was recently serviced (dropped), right? It could be the #8 plug wire was bumped and is now mis-routed, thus causing "crossover" or "noise" from one of the wires. Check the routing of #8.

 

Yeah .....Dropped twice! I could have disturbed # 8 pretty easily while reinstalling CKS possibly - of shoving trans fill tube back in.

zman - BIL replaced cat in May, I picked truck up in June and have only put about 300 miles on it myself (as it has been sitting in garage with transmission issues). He only drove it around the small town where he lives a little. So estimate on miles is possibly high. But I will have a better idea when I pulll intake I suppose.

I guess my real question is why can't I hear or feel it misfire? Can it be that subtle? I don't feel any loss of power, but then I haven't driven it enough to know how it should feel, but I don't feel a miss at any level - idle, pulling out quickly into traffic, etc.

 

Fix the damn plenum first, then lets talk.

 

zman has a point, it may just be a lean-burn miss, due to the leaking plenum.

 

Decided not to work on truck tonight. Took wife out to dinner and put about 150 miles on truck to check mileage before plenum fix this weekend. I could feel the miss a little at 70 mph. Will pull intake tomorrow morning and get as far as I can go. Gotta take one of my grndsons to the World Series games this weekend - so I can be the "bestest grandpa in the world" as he puts it. Should be able to get everything pulled off and maybe start back together on Sunday. Anxious to see improvement in mpg and performance.

 

Found the cause of the misfire:



Tensioner installed:



Timing set:



Timing cover and water pump back on:


Didn't get the intake pulled and swapped yet - too many ball games this weekend! May have to slip off work early tomorrow.......

 

When my #8 plug was misfiring I couldn't get the truck to go faster then 45MPH, felt like I was in the middle of an earthquake it shook so bad.

 

That is what I expected. 4 other plugs were nearly as bad, and although it got CEL running aound town (30 - 40 mph) I did not feel anything until around 70 mph. I am surprised it was running as well as it was with plugs in that condition. With new plugs, rotor, wires and tune, this thing ought to really feel like a different truck - hopefully tomorrow.

 

I'm sure it will! I gotta do the plenum on my truck too. It still has good power, don't know how bad the O2 Sensor is or the Cat. Really the only time it doesn't have any ***** is when the valves start rattling.