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Q: Misfire - 2003 Ford Expedition

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My check engine light came on. A scanner read from Orileys read Bank 2 o2 censor & Misfire on cylinder 3. Shortly after, I got the plugs and wires changed. During this process my mechanic discovered an issue where one of the plugs got stuck inside of the motor. So, I ended up replacing the head, because he said it was damaged. He also replaced the head gasket, intake gasket, & timing chain pulley all together. After he finished, there was still a misfire. So I was adviced to have the coil on cylinder 3 changed. Did that, well guess what, there is still a misfire. Took it to him again and the same exact code came up on the diagnostics monitor. He then got under and swapped plugs and coils from other cylinders and discovered that none of them got any spark from cylinder 3. At this point I do not know what else to do. What else could possibly be causing this misfire??? The truck does not drive smoothly. I also checked the transmission fluid. The color and the levels seemed to be fine.

My car has 193000 miles.
My car has an automatic transmission.

A: Hello and thanks for your question. When di...

Hello and thanks for your question. When diagnosing a misfire, you would need to determine all of the factors for what could be the problem. When you mentioned that you had switched a coil out from another cylinder to number 3 and saw that that coil did not energize up, then there is a problem with the harness to the coil.

Check the harness plug that connects to the coil on cylinder 3. Look for any broken or pulled out wires. Look inside the plug and make sure that the pins on the wires are pulled all the way out. Get a paper clip and put it into the plug on one pin. Use a digital volt meter and check for power with the key on and engine running.

Check all of the pins for power with the key on and engine running. If there is no power, then take a knife and open up the wire protection around the wires to the harness plug.

Be sure not to cut the wires. Look at the wires for any breaking points. Follow the harness to the plug to the main harness on the engine. Cut back some of the protection cover where the harness to the plug meets the harness on the engine. Check for any breaking points on the wires.

If you cannot find any problems with the wiring harness to the plug, then I recommend replacing the entire engine main harness that is has the coil packs tied into. There may be a break in the harness somewhere causing a no power situation. If you need assistance fixing the wiring harness or diagnosing the misfire, have a certified professional, like one from YourMechanic, diagnose the misfire and assist with any repairs that are needed.

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