Misfire Under Load

Engine idles smooth and sounds good. I’m getting the flashing CEL and P0302 code (misfire on cylinder 2) when the engine is reved and reaches 1800-2000 rpm. Plugs and wires are relatively old, but not high mileage. I swapped the #2 and #4 plungs and the miss stayed the same. I also switched the #2 and #1 wire. The miss did not move.

I have a few questions:

1. How do I test the coils to eliminate them as being bad?
2. Although they don’t seems to be bad, should I replace the plugs and wires anyway since they are getting old?

Edit to add: Truck in question is a 2000 DII.

Thanks, Ed!

I?m suspicious of a failing injector or o-ring considering I appear to have fuel and a spark. The engine is just shy of 102,000.

Well, I finally got around to changing the plugs and wires. Kingsborne 8mm wires and Champion 7070 (rc11pypb4) plugs. The misfire is still there. I also gave it a Seafoam treatment as a long shot, but no luck. Going to do a compression test this week and see what I find.

Compression tested the engine today. Frankly, the results surprised me as I was figuring on a head gasket leak. Results are as follows:

1. 150
2. 155 (misfiring cylinder)
3. 145
4. 165
5. 150
6. 145
7. 150
8. 155

Now for a few questions...based on the test results am I safe to assume it's not a gasket or valve issue? How do I test for a bad injector or injector O ring?


Edit to add: test was done with the throttle closed because I'm and idiot and forgot to hold the pedal to the floor...

Finally got it sorted out this afternoon. To recap what I had done:

Initially I had multiple codes so I changed the very, very old O2 sensors. This fixed all issues expect the misfire on #2. I tired swapping plugs and wires around to diagnose and the miss remained on #2. Next step was Seafoam through the intake along with new plugs and wires. (8mm Kingsborne) Still the miss remained. I then ran a compression test that the engine passed. After that I swapped in a "new" fuel injector from an old overheated engine. No success. Finally bought an Allmakes 4x4 coil from AB on sale. Put it in today and success! No more misfire and no codes. The old Disco is back up and running. I also determined that he misfire was constant and not under load. However, it took about 1800rpm to trip the flashing CEL.

Now for a new wiper motor and rear door lock actuator. Then I guess I'll tacked the frame and undercarriage rust that appear to probably be terminal after that...