Help diag my misfire
03-02-2016, 05:20 PM
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Help diag my misfire
Been chasing this misfire/stumble for months now. I've done everything I can think of to remedy this issue.
Replaced plugs and wires, checked tps, all engine and chassis grounds are good. Did find one ground missing from cylinder head to firewall. Replaced that. ecu sensor grounds are good. I've also replace the o2 sensor, ect sensor, fuel filter. Removed the plate off the AFM and adjusted it to enrich. I actually got it to stop missing but it was so far out it are like ˟˟˟˟. Wouldn't even stay running. Pueking Black smoke. But when revved over 2000rpms the miss clears up. this engine has been rebuilt ie new crank pistons rings timing chain water pump alternator. head gaskets and intake gaskets been replaced as well. I checked the distributor cap and there were no obvious signs of misfiring improper timing or excessive wear. I have also adjusted the valves and set the timing numerous times.
this is what the engine is doing when it misfires: you can feel it stumble at idle and when revved over 2000 rpms or so it stumbles and misses bad but not enough to effect drivability. I only started to notice it when I did a tune up. Obviously I thought it was something that I did or maybe the parts I used. Double checked everything I touched. When I was still working in a shop I convinced the head tech at my shop to help me. We first used the modus scanner to look at the live data. Found that it was constantly switching from open to closed loop operation. The ect and upstream o2 sensor had no effect. Hooked it up to an engine analyzer and the tech who was helping me determined the misfire was not mechanical or ignition related. Then we did an injector balance test and found one or more injectors were failing mechanically. So I replaced them with rebuilt OEM ones. Did not change anything. I also replaced the AFM with a used one but still no chance. if anyone can help me go through this I will gladly give more information. please help I love this truck and right now it's my only means of transportation
Replaced plugs and wires, checked tps, all engine and chassis grounds are good. Did find one ground missing from cylinder head to firewall. Replaced that. ecu sensor grounds are good. I've also replace the o2 sensor, ect sensor, fuel filter. Removed the plate off the AFM and adjusted it to enrich. I actually got it to stop missing but it was so far out it are like ˟˟˟˟. Wouldn't even stay running. Pueking Black smoke. But when revved over 2000rpms the miss clears up. this engine has been rebuilt ie new crank pistons rings timing chain water pump alternator. head gaskets and intake gaskets been replaced as well. I checked the distributor cap and there were no obvious signs of misfiring improper timing or excessive wear. I have also adjusted the valves and set the timing numerous times.
this is what the engine is doing when it misfires: you can feel it stumble at idle and when revved over 2000 rpms or so it stumbles and misses bad but not enough to effect drivability. I only started to notice it when I did a tune up. Obviously I thought it was something that I did or maybe the parts I used. Double checked everything I touched. When I was still working in a shop I convinced the head tech at my shop to help me. We first used the modus scanner to look at the live data. Found that it was constantly switching from open to closed loop operation. The ect and upstream o2 sensor had no effect. Hooked it up to an engine analyzer and the tech who was helping me determined the misfire was not mechanical or ignition related. Then we did an injector balance test and found one or more injectors were failing mechanically. So I replaced them with rebuilt OEM ones. Did not change anything. I also replaced the AFM with a used one but still no chance. if anyone can help me go through this I will gladly give more information. please help I love this truck and right now it's my only means of transportation
Last edited by Yomanchu; 04-19-2016 at 05:08 AM. Reason: Add more information
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