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1991 F100: runs very rough, no power. Rebuilt the carbs, and now it starts! I'm thinking maybe the ECU is bad: spark on all 4 cylinders is very weak.Checked with a spark checker and it's very orange to yellow, set @ 1/4". I do not have a DVA/harness to test. Could this cause the engine to be enemic? Everything else seems good. New plugs, good compression (only 120 hrs) . It was running great, then just started this the next day. Thanks
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Yellow fire on that engine may not mean an ignition problem, when testing a engine with no power you need pull spark plug wires while running engine with insulated (plastic is the best) pliers to isolate which cylinders not running, you should be able to hear the spark jump the gap when pulling wires from plugs.
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