2001 Ranger 3.0

One week ago, I put a gallon of bad gas from my snowblower into the ranger. It started to run rough but went away with a full tank of gas. Fast forward three days, I'm driving it all day and it has no CELs, running normally. Then all of a sudden that night, it gets a grade A misfire in cylinder 2 and 3, CEL flashing. Only codes are: p0302 and p0303. Compression is 150psi. Changed out all spark plugs on bank 1. Changed out plug wires on 2 and 3. Changed fuel filter. Drained 5 gallons of gas hoping to get any water sitting on the bottom out. Injectors are getting 14v at the harness. Running it on starting fluid, it seemed to run normally so I turn to the injectors. Bench tested injectors and ran carb cleaner through them reinstall. No difference so I tear it down again and swap injectors 2 and 3 over to the other bank. The misfires do not follow the injectors, also they do not stay there. They go away. Wha? But the truck is still idling extremely roughly, and stalls on minor inclines from a stop. But now there are no codes thrown. Just fuel trims at +20%. Oxygen sensors seem functional. What happened?

Going to pick up a fuel pressure tester tomorrow, any other suggestions are welcome.

 

Good idea to perform a fuel pressure test & while doing that, since your +20% fuel trim reading maybe suggests not enough fuel, from lean squirting injectors, also consider a fuel flow / volume over time test of the pump, via the gauge pressure relief hose into a measured container of choice. Flow Volume should be something like half a pint / 15 seconds pump run time.

If the fuel tank pump pick-up pre filter sock, fuel filter, or the fuel injectors internal centered filters are clogged, that can cause the injectors to give a lean squirt. So, when the O2 sensors detect & report a lean cylinder bank, the ECM will + up the injector squirt time to try & get fuel trim back in tolerance. A bad vacuum leak can also cause this + fuel trim problem. So, still a number of suspects on the list. Are Both cylinder Banks reporting + fuel trims???
More thoughts for consideration, let us know what you find.

 

Fuel trims are: bank 1 ST +16%, LT +22%, bank 2 ST +1%, LT +22%. Before I swapped around the injectors, only bank 1 was +. Now that they are on bank 2, both sides are +.

I tested the fuel pressure and it's 62 psi at idle. Tested volume and it's pitifully low at the rail. I get half a cup of fuel after 1 minute. The pump gives 3/4 gallon after a minute both before and after the fuel filter. No fuel in oil, no puddles on the ground so I don't think it's going anywhere except maybe back into the tank. The pressure regulator is in the pump assembly but I don't know whether that could cause this. Maybe a restriction between the filter and the rail? Your ideas are welcome.

 

I take it back, it was the fuel pressure tool that was causing low volume at the rail. Took out the schrader valve and pumped directly into a hose and got the proper volume.

 

Sorry to spam the thread, but it’s getting dark here and I noticed that the cat is glowing red. I think the misfires are gone but the cat was damaged. Sadly, I think I’m leaning towards a new cat to fix the concerns. Again, your thoughts are welcome

 

Ok, good observation on the cat showing overheating signs from the misfires, question is, if its suffered a internal matrix melt-down thats causing excessive exhaust back-pressure???
So lets think about this some more. You can perform a restricted exhaust test by feeling how wimpy the exhaust Flow is at the tailpipe, when a helper brings the engine rpm up above idle.

Safer, If you have a vacuum gauge, hook it up & note idle vacuum, then note vacuum as rpm increases & if it drops off & stays low as rpm is held steady, its restricted.

Replacing a melted cat converter matrix can fix its exhaust back pressure problem but does nothing to address the root cause of the converter damage, which was running the engine with a bad misfire long enough for it to damage the converter. So just replacing the converter without putting the misfire root cause of all your current woes right, will cause damage to the new converter. So be sure you've found & fixed the misfire problem Before replacing the cat converter.
More thoughts for consideration, let us know how it goes.

 

Vacuum reading was good, vacuum holding at 20 at high rpm so that threw the clogged exhaust theory into doubt so I looked elsewhere.

The positive fuel trims went away on bank 2 at high rpm’s indicating vacuum leak so I retorqued the upper intake plenum and it went away.

Now I was at a place where the fuels trims were max positive on bank #1 throughout rpm range. Unplugging cylinder 1 fuel injector bogged down engine, but unplugging 2 and 3 made no difference. So as a known good injector, I swapped #1 and #2 injector. However cylinder #2 still was not firing even with a known good injector. Now I think bad spark even though I could see spark.

Unplugging the #2 and #3 plug wires at the coil pack, there was no spark jumping. This happened last year with the factory coil pack and replacing it fixed rough running. Replaced the coil pack and now it’s running like a Swiss watch. I guess the spark was there, but weak

 

Ok, good trouble shooting, find, fix, feedback & to hear all now seems well & your "on the road again"!!!