How to find a misfire?

[semperfi]

This is on my '96 Z71 with 5.7l vortex.
I have noticed what appears to be a miss when running about 50mph in 4th gear (lock up), and I apply the gas, gently applying pedal, and just before it shifts down (out of lockup) and almost feeling like lugging the engine, I'll get a jolt at the same time or maybe slightly before the transmission shifts down to 3rd. To me it feels like a miss from one of the spark plugs. On a side note, if I do a HARD pedal push to cause a down shift, the transmission shifts very smooth. That's what leads me to looking for a miss.
Is there a simple way of determining which plug or circuit is the problem?

The CEL does not come on & checking for possible codes with Torque lite shows NO codes. I don't have a reader to check transmission codes.

Truck has 75k miles, I'm the original owner. I changed the spark plugs with ACDelco 41-993 Professional Iridium @ 73k. I just replaced the Distributor cap & rotor last week @75k, Plug wires are originals and all look good. I even moved any wire that I thought could be arcing to ground & double checked that they were all the way down on the plugs. I do not have any missing happen at any other time.

Transmission is the 4L60-E. I have added a deep pan @ 51k, with new filter & add 7.5 qts Dexron VI. Did a drain & fill @ 57k with 5.5 qts.

I have also updated the fuel injection with the Delphi FJ10566 Fuel Injector MFI Conversion Assembly when I replaced the intake gaskets back at 58k

Do you feel this is an ignition issue that I'm chasing or a problem with TCC issue? Any suggestions are appreciated.

 

[grey wolf]

Initially I'd say it sounds more like something going on in your transmission. You could try keeping the truck in 3rd gear and matching the RPM you have at 50 mph in 4th and lockup, then apply the gas as you would normally do when experiencing the misfire type problem. If it doesn't happen the same way, then you probably have some kind of problem with the transmission, like a TCC related problem. Maybe some kind of build up of varnish somewhere in the valve body causing something to stick? I'm not really an expert when it comes to automatics, but to me this doesn't really sound like an ignition misfire.

Nice looking truck by the way!

 

[Redneckgeriatric]

beautiful truck! quickest, easiest, cheapest over the long run? have a good mechanic put it on his scanner and take him down the road and reproduce the problem. he can see it real time and recommend the fix.

guessing? adjust the tv cable. it sounds like the lugging may actually be lugging. a temp gun pointed at individual headpipes can show a missing cylinder sometimes. the coolest temp will be the least efficient cylinder.

redneck? lock er in 4high, shifter in 2nd gear and put bumper against a tree, hold throttle till miss starts, find miss. lololol dont really do this. the mechanic with a scanner is lots cheaper and more accurate.