P0301 - Misfire - Help

[diehonda]

Check out this mess:

* Ignition coil replaced (second 1.8 coil after replacing those crappy 2.0 coils three times)
* Spark plugs cleaned and then replaced with long reach plugs
* Seafoamed the tank and intake system
* New air filter
* Cleaned EGR valve
* Replaced the fuel pump and filter(screen)
* Wires are about a year old.

No hesitation until I hit half a tank and then Misfire Cylinder One. Plus it hesitates on hills and curves. If I fill up the tank the problem goes away.

A friend owns a shop and stated that the injector doesn't know how much fuel I have so if it was bad I would have issues from get go. I say this because I thought about swapping the injector from cyl one to two.

It has over 180K miles so I always smell a hint of oil when I park. When I have had the hesitation is smells a lot stronger, to the point that you want to pop the hood and expect a mess everywhere. No leaks other than my oil pressure sending unit that leaks a little but that can't be the issue as I am holding solid pressure.

Any suggestions?


Pump and filter are new, maybe 400 miles on them.

I am thinking either:

* #1 injector
* fuel gauge sending unit(the stopper on the fuel pump) because it shows few issues until it gets at or below half a tank
* fuel pressure regulator because the acceleration isn't up to par throughout the power band
* Or drive it off of a cliff

[Beerizfood]

Its hard to believe that a single cyl misfire is related to the fuel level,it really sounds like two problems .One being related to the pick-up in the tank and the other being a coil/injector/oil control -fouling type thing.
However thinking outside the box the fuel level sender is wired to the PCM as are the injectors.If there is a short between injector one wire and the fuel level sensor it is possible that with the fuel sender being a varible resistor could cause the cyl one injector to act up if shorted together.

[diehonda]

I swapped the 1st and 2nd injectors and replaced the o rings on all of them. Car idled pretty rough afterwards, didn't do that before. Wonder if it is the fuel dampner.....

Will have to drive it down to a half a tank to see if it throws P0302.

[MazdaNoob]

water in the fuel tank ... you don't start sucking any till 1/2 tank or less . pull the sending unit out siphon some fuel from the bottom of the tank and let it sit for a while in a clear container .. the water should separate from the fuel letting you see whats in there

[Beerizfood]

you can narrow down the bad cylinder by unplugging them one at a time to see if one inparticular makes no impact on idle quality while unplugged.

[diehonda]

I will check those things out. Thanks!

[dtatham]

With the engine cold, start it and spray a small amount of starter spray where the intake manifold and head come together at the number 1 cylinder. If the gasket is leaking and you're losing suction, it should rev.
Check for unusual appearance of the number 1 spark plug, rust to indicate coolant leak, or carbon buildup to indicate oil.
Is the valve cover gasket in good order? Oil leaking into the pit where the spark plug sits can cause a misfire.
Check the compression.
If the swapping of the injectors doesn't do anything it will rule them out.