mustangdaddie

Hi, new on the forum, first post.
Recently I bought a 2002 Mustang GT with 155k miles, pretty beat up body, running rather badly for 1100$.
When I bought it, there was a check engine light on for misfire in cylinder 2, and he had a printout from Autozone that was relatively recent.
On my way home, the check engine light started to blink, so I pulled over, and let it go away, then I drove it to my local pep boys and got the code read. Sure enough, misfiring in cylinder 2 but also misfiring in cylinder 1, as well as misfire on startup, and a fouled plug & helicoil on cylinder 7
Changed plugs and coils with all new motorcraft stuff, as well as a new helicoil, yet codes did not go away.
Changed injectors with stock 19LB ones, car ran a ton better, but still misfiring in cylinder 1, as well as on startup.
Sometimes the car doesn't misfire at all on startup, but half the time it will, I made sure all vacuum lines and everything is in check.
The car also backfires and runs incredibly rich. At my local mechanics shop, I asked for a manual emissions test, and on bank 1 the car was running incredibly rich. As soon as he removed the plug from the first injector, it leaned out and was more normal running. The cats are completely shot as well, and I think I might need to replace an 02 sensor.
What could cause this type of effect? Bent Valve? Stuck lifter? Head Gasket? Exhaust Leak before upstream sensor? Camshaft Position Sensor? Could the wiring be bad that its forcing the injector to dump fuel? If I did a compression test, would that show me either of those? The car sounds relatively smooth, and I don't hear any serious lifter ticks, but it also has a bad TOB which makes it hard to hear anything.
I just need the car to pass emissions, so I don't have to keep going to the DMV weekly to get new a temp plate.
The car makes wayyyy too much carbon to pass emissions without cats and with the misfire.

Anything will help.
Thanks guys.

Derf00

Could be anything at this point. You can test your injector/connector theory by swapping injectors from #2 and say #4. If the problem follows the injector then it's a stuck open injector. If not, it's probably something like a blown head gasket between cyl 1 and 2.

Start with a compression test then do a leakdown test to further determine if it's a valve (intake or exhaust) or head gasket, etc.

mustangdaddie

Just did a compression test. All cylinders on bank 1 came out the same, and the coolant looks completely clean. I'll try moving around injectors from 1-3.

mustangdaddie

Just switched the o2 sensor. Could bad catalytic converters CAUSE a misfire? I'm skeptical. Might be wiring? I'm going to try putting a test light to the trigger wire to see if its getting the spark at all.

Derf00

What were the readings of the cylinders? Also, a compression test is not a complete guarantee that the cylinder is ok. I've seen many times where the compression test is OK but, a leak down finds bad valves.

A bad cat usually causes a general lack of power, not misfires. Bad spark is easy to check, start the engine up when cold, run for a minute or two, shut it down, then remove the coil and spark plug. If you smell fuel and/or the plug has fuel on it you have a weak/non existent spark. Another way is with a code reader that has live data. Look at the fuel Trim. If it's way negative for both long and short trim then you most likely have a misfire from a bad spark and the engine is trying to cut the fuel way back.

I don't think it's spark related though because those kind of misfires thros a P035x (where x is the cylinder number). P030x like you have are are mechanical based misfires like head gaskets, valves, etc. P0316 can be found with both P035x and P030x misfires.