Advice!!! Engine Knock - Loss of Power

[msimmering]

1st gen mint original 1991 Explorer 4.0 w/268K. Intermittent engine knock started 100 miles ago and ended with same knock but now with misfire and loss of power. Pulled upper intake & valve covers to verify valve train/rockers/pushrods look and function well (was hoping for broken pushrod or rocker but all is fine on top...).

Before I tear the engine down any further, any suggestions on next steps and/or when to give up and consider an engine R&R? If R&R is recomended, what newer engine/tranny combos will fit my '91 Explorer with minimal mods? Thanks!!!

 

[sparky2263]

Is it engine knock or pinging (valve rattle, spark knock, detonation, etc.)? BIG difference.

 

[msimmering]

Strong metallic knock, there was a small amount of valve train rattle prior to the loud internitent knocking. Even then, all was good (power and performance) with the louder metallic knocking but when the engine started missing, I felt it was serious enough to park and begin tearing down.

 

[savagefan]

Was the knock speed or load sensitive? I would do a compression test next. Try a vacuum test and use some kind of stethoscope to pinpoint noise location if it will do it in neutral etc. Good luck.