I have a 2003 FX35 with 197K and an interesting issue.
First, this Vehicle sat for +2 years, and when pulled out of storage, the battery was shot, and the gas was very contaminated. The battery and fuel were changed.
The following was done:
Replaced all the injectors with new stock injectors
Replaced Ignition coils (New)
Replaced ignition coil plugs and partial wiring harness
Replaced Iridium Spark plugs (Proper gaps)
Cleaned MAF and check for proper operation
Checked for vacuum leaks...nothing.
Compression on all cylinders 181-185.
I pulled, checked, and cleaned both VVT solenoids, and checked them for clogging, and free movement. No issues there.
I disconnect every coil plug with engine running (one at a time), I plugged in an old coil and plug, and got a pretty good spark from every cylinder.
The Misfire is pretty evident when idling, however there's no distinguishable difference in RPM when the coil plugs are disconnected one at a time on Cylinder 2, 4, or 6. Basically, I can't tell which cylinder(s) are misfiring by removing the coil plug.
There is a strong (occasional) backfiring thru intake manifold when idling (or at least that's where it sounds like it's coming from). It doesn't really smooth out as the RPM's increase.
I was told that ECM has been replaced with a factory refurbished unit, because the shop that was working on this before couldn't figure out the issue. They said they were pulling P0302, P0305,(etc.) but it kept changing every-time the vehicle started. The only code I can pull is P0300, and it shows up every time in about 10-15 seconds after starting.
Fuel pump pressure at fuel damper is 45 - 48 PSI at idle, then 43-45 PSI@2000RPM (using Bosch J-44321-4 quick disconnect adapter). Fuel line stays pressurized for at least two hours after shut down. Most sources say I should be getting 51 PSI minimum at damper, but is that pressure difference enough to cause this?
I haven't inspected the the crankshaft, or camshaft sensors...yet. But there are no no codes, or history. Is that me just being ignorant?
Questions please! I'm sort of stumped by this.