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Engine misfires

Hi Car nuts,

My 91 Isuzu trooper with the 2.8L V6 has been misfiring increasingly frequently for months now. It seemed very much like an ignition problem, so Ive changed the plugs, wires, distributor cap, rotor, ignition module, and coil. No luck. The computer is not storing any fault codes. Its an elderly trooper with 248000 miles. Any suggestions appreciated.

Have you run a compression test? You need compression to get the “fire”. You seem to have replaced all the pertinent components to provide the spark. Then you need the fuel and air and it all has to get compressed. Perhaps its all there but not enough compression to light it off.

Low and erratic fuel flow/pressure can cause misfire and stuff. What is the fuel pressure when the engine is under load (like during acceleration and hill climbing)?

Thanks for asking, no not yet. I forgot to mention the trooper does fine typically for about 30 minutes before the problem starts happening. Never cold. One person suggested a sticking valve. If I could do a compression check at the moment it occurs, then maybe I could isolate the problem. Thanks