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Q: #1 cylinder is misfiring.

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My #1 cylinder is misfiring fairly consistent (occasionally #5)...primarily at idle. im pulling code 0172 suggesting a faulty fuel pressure regulator. I have replaced all ignition parts with factory brand (plugs, wires, cap &a rotor). I am leaning more towards a faulty injector rather than a regulator. What are your thought? Can a regulator cause a misfire? By the way the plugs are not fouling out ... they look fresh as the day I put them in.

My car has 225000 miles.
My car has an automatic transmission.

Hello - I think your diagnostic skills are working well on this one. If the misfire is consistently a particular cylinder, that plug, wire or injector is certainly more suspect than anything else. A faulty fuel pressure regulator would have other symptoms, misfiring is possible, but less isolated and more random. Given your mileage, check the distributor for slop in the shaft that could cause "wobble" and misfiring as well. For additional technical expertise on this one, I would recommend having a Engine is Misfiring Inspection completed by a mobile, professional mechanic, such as one from YourMechanic, to diagnose this problem, get an accurate assessment of damage and cost estimate for repairs.

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