3/4 spark plugs examine ok for timing, but one is way way off. One of the trailing spark plugs seems way off, and some of the tests in the FSM seem hard to follow. Is it likely that the coil is shot or could this be as simple as one bad plug? Thoughts?

 

Vehicle information needed.

If you're checking with an inductive timing light, a poor connection can throw the light off. Move the lead somewhere else on the plug wire.

 

Also trailing doesn't fire the same as leading. Leading fires waste spark (assuming 1st or 2nd gen) while trailing is independent. T1 is probably on the mark, T2 will be way off.

 

u only check timing on leading and trailing of the #1 rotor. what manual u got that has u checking timing on all 4 plugs?

 

Ah, first time dealing with ignition timing, and so I just sorta assumed you want them to fire as pairs. Thought the FSM was leaving that jump in logic to you, to repeat the check on the second set. As predicted, T2 is the one that's way off, the T1 and the leading pair are all dead on to their respective timing marks. So, I guess timing isn't the issue.

Been trying to track down the reason for 15 mpg in my 89 NA, and was hoping that had solved it. Time to keep searching, I guess.

 

Check the coolant sensor. If the car doesn't realize when it's warmed up, it will continually run rich.