3.0 Misfire

nhf0549 · Sep 2, 2013

My 1993 Ranger has a '94 3.0 V6 with a manual transmission. I started getting a misfire a few weeks ago, so I replaced all the plugs and wires, cap and rotor. The misfire lives on! I re-checked the gaps on all the plugs, thinking I may have bent an electrode when I installed it, but to no avail. (Also, my code reader tells me there are no error codes.?) So I bought a compression tester, and the numbers range from 160 to 179 on all six cylinders. Good. However, I noticed the No. 2 plug was wet and black, not dry and brown, and it looks like it hasn't fired at all. I also poked around with a stethoscope- I heard a clicking from the other injectors when I touched them with the scope, but no clicking from No. 2 injector. Also, cylinder number 2 had the highest compression reading. Does this indicate a bad injector, bad coil pack, or something else?

RonD · Sep 2, 2013

If plug #2 is wet then it must be getting fuel, but could be too much fuel...

I would swap #1 and #2 plugs.

Ford fuel injectors should have approx. 14.5 ohms when tested with connector removed.
An injector is just a coil of wire wrapped around a metal cylinder, when power is passed through this wire it becomes a magnet, this pulls open the metal needle valve of the injector letting fuel pass, when power is cut a spring pushes the needle valve closed.

I would turn on the key and unplug the #2 injector, listen for a click, plug it back in and listen for a click, if it is clicking then it is working but there is a grounding issue or a PCM issue with that wire.
I think the '94 3.0l has sequential fuel injection, so one ground wire for each injector that runs back to the PCM(computer).
Earlier Ford systems used Batch fire injection, so on a V6 3 injectors fired at the same time, so there were only 2 ground wires back to the PCM..

With injector unplugged check its OHMs
And with key on check connector for 12v on one wire, if you have 12v on both you have a Batch fire system, the 2 other injectors still connected are passing the 12v thru the coils, which is normal.
If the other wire doesn't have 12v then switch to OHMs and test that wire for a short to ground, if that wire is a ground then either the wire back to the PCM has a short or inside the PCM there is an issue.
with 12v and a ground that #2 injector would be open when the key is on, flooding #2 cylinder.

Or injector needle or spring could be damaged holding injector open, so no click and a wet cylinder.

nhf0549 · Sep 2, 2013

Thanks, Ron. Great information! I'll do some more investigating ASAP.

3.0 Misfire

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