Engine Misfire 4.6L Exhaust Leak?

2004 Ford Mustang Mach 1

I had a really bad exhaust leak, It caused my car to throw a o2 sensor code running “lean”. It made my car feel like it was misfiring, loss of power but never threw up a misfire code. I fixed the exhaust leak and o2 sensor code was gone but car still feels like its misfiring. Resetted the ECU, no luck. Then, I changed all spark plugs, no luck. I pulled each coil while the car was running and got spark on all cylinders. I don’t know what’s wrong, I feel like the engine isnt getting enough fuel and its causing my car to have symptoms of a “misfire”. Any suggestions?

McFly2 said:

You need to have your Air/fuel mixture (Short term fuel trims and Long term fuel trims) readings. A local Midas or any of the sort 0f local repair shop with live data scanner will be where you need to start. I just Paid $89 at Midas muffler for diagnosis. For that price a smoke machine was used to fill air intake and all vacuum lines to detect vacuum leaks. a scanner read was included. My EGR valve was open causeing a vacuum leak. I also had a air leak at the exhuast manifold to H-pipe connection. I had lived with the problem for 1500 miles (12 months) and was fixed today finally. I will give other info (issues) as I share this on the forum to give others helpful input of the irratic fuel/trim readings I incurred. Code P0174 bank 2 lean.

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Good input. I just did a diagnosis at a muffler shop and they found my exhaust manifold was cracked so I ordered a new one and getting it installed asap. Will update and see how it goes. I also replaced cylinder 6 fuel injector and that seemed to clear up the jerking and misfire symptoms. I guess it ran lean because of the exhaust leak and it made the car think it needed more fuel to compensate for the loss power and it probably pushed out lots of fuel and clogged it up to my assumption. Could be wrong though but it did fix the hesitation with the gas, and no misfire code anymore.

P.S. - Yes it did end up throwing a misfire code on cylinder 6. Changed spark plugs every cylinder and tested coil packs. Still misfiring then I changed the one fuel injector for cylinder 6 and worked like a charm. Still have loss of power though and O2 sensor code which might have to do with the cracked exhaust manifold