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i have a 90 lincoln mark 7 engine mounted on a 70 mustang.
idling is rough, power is low and i cant run the koer test with the snap-on.
what checks should i do in order to replace the right part and not all electrical parts?
the hego sensors works fine ( i checked them with avometer to see they switch fron lean to rich).
map gives me 2.5 v with koeo.  

Check all the vitals: Timing, compression, fuel, and spark. Were you able to pull any hard codes out? If everything looks ok then do all your engine off/on tests. I just fix my son's mustang 5.0 but he had it alt off 180 degrees. Same Symptoms, rough idle and no power.