Wanted to post on open forum an issue I'm having with my 91. Have had a pulsing/surging and low power under load the past few days, getting worse over time.
Slight unburnt fuel exhaust smell, idle is okay, slight shake, free rev is good but under load theres a noticeable misfire. Spark plugs, wires, cap/rotor all 6mo old and less than 10k miles. O2 sensors, air filter and 1 new injector on #2 at that same timeline, it cracked the top and was non functional. Ran amazing the last 7k miles but rig has 280k on it.. presuming original drivetrain.
Unhooked each wire at idle and each cylinder had some amount of fire, stronger on 1,3,5. Pulled cap and wires, nice even wear on rotor and posts (OEM denso, plugs were NGK coppers and wires were Standard)
Pulled spark plugs, plugs 1,3,5 nice and chocolate colored, no weird deposits or anything. 2,4,6 were black and wet showing overfueling, no weird deposits from oil burning.
Thought O2 sensor went bad, but those are split 1,2,3 and 4,5,6. The issues on 2,4,6 is the same set of injectors during batch fire so I'm thinking input sensor for fuel system (coolant temp sensor is new denso, AFM checked good 6mo ago.. but suspected issue when hot) or wiring short. Desmogged everything a few months ago and didn't have any wiring issues stand out.
So I'm suspecting AFM, its original and had a problem with low power under throttle on hot days going slow on trail rides this summer. If you shut it off and restarted the problem would go away for varied times. Is there anything else that would affect only 1 of the injector firing banks outside of a computer issue?
I'm an engineer so I assume I'm wrong until proven right