My 88 ranger started missing (1 cylinder) after pulling a large load of hay up a long hill (driveway), in 4 wheel, on gravel, and not spinning any wheels,1500 RPMs, with foot mashed to floor. Ranger has 200,000 + or - . I completely rebuilt the engine. started engine and it still misses.on 1,and getting worst. I replaced plugs, wires, cap, rotor, stator & pickup ,and module. I also cleaned all injectors, Engine idles so rough it wants to jump out. put a timing light on all cylinders and all are firing. no check engine light has ever came on. im at wits end.

 

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Have you done a cylinder balance test to see if you can isolate the misfire to one cylinder?

 

I would do a cylinder compression test. You may have burnt a valve pulling that load.