Help requested with diagnosis - 02 Sensor?

DrWizard · #1 12-28-2015, 09:55 AM

I'm hoping someone here has seen my problem before and can help me diagnose it. I am on a very limited income and can't afford to buy a bunch of parts I don't really need.

My problem started with my 2003 Ranger 6 Cyl 3.0L Flex after I had been out of the country for 7 months. The truck was parked at a friends house, and only occasionally started to move it out of the way for something. When got back and picked it up, it ran fine - for only about 3 miles. Then started running really rough and misfiring. I thought stale gas, and put in fresh. Did not help. (I have since been thru a dozen tankfuls). Next thought was fuel filter clogged with sediment from sitting so long. Changing the fuel filter did help -- some. I've also run several bottles of injector cleaner thru it. I got one of those bluetooth OBDII adapters and paired it with my tablet. Here's what I've found:
Misfire codes P0301 (Cyl 1) mostly, and sometimes P0303 (Cyl 3). No codes so far on any other cylinders.
O2 Sensor 1 readings are all over the place, from .1 to .9, constantly up and down. Sensor 2 readings are much more stable. So I suspect sensor #1 or the connection to it. Have not gotten any trouble codes related to O2 though.
Runs rough when cold, a little better after warmed up. I'm in Fla. and we don't have much in the way of hills here, but it tends to misfire when accelerating up an incline (what we call a 'hill'). Gas mileage is still normal, about 17 MPG. Plugs were changed less than 20K ago.

Other theories are that the new fuel filter also got clogged with sediment, or a weak fuel pump. My engine apparently does not a have fuel pressure sensor readable via OBD. Pressure always shows 0 via OBD. I suppose it could be a plug, wire, or coil. I'm not technical enough to know what other OBD values I should be monitoring.

The truck is driveable, and gas mileage is OK, but I wanna get this fixed. Just need to fix it cheaply.

Suggestions????

Jeff_Birt · #2 12-28-2015, 12:48 PM

The O2 sensor should change rapidly between .2V to .8V (approx.) that is a sign that it is responding properly. If your getting a misfire then you will have raw gas/air going through messing up the O2 sensor reading. So the misfires you are seeing correspond to the 'stable' O2 sensor, i.e. they are on same side of engine I'm guessing.

Pull the plugs and see what they look like. I would look at plugs-wires-distributor cap to see if all looked well. Look under the hood at night, if you see sparking around a plug wire you know it is bad.

GSF1200S · #3 12-31-2015, 10:44 AM

Quote:

Originally Posted by DrWizard

I'm hoping someone here has seen my problem before and can help me diagnose it. I am on a very limited income and can't afford to buy a bunch of parts I don't really need.

My problem started with my 2003 Ranger 6 Cyl 3.0L Flex after I had been out of the country for 7 months. The truck was parked at a friends house, and only occasionally started to move it out of the way for something. When got back and picked it up, it ran fine - for only about 3 miles. Then started running really rough and misfiring. I thought stale gas, and put in fresh. Did not help. (I have since been thru a dozen tankfuls). Next thought was fuel filter clogged with sediment from sitting so long. Changing the fuel filter did help -- some. I've also run several bottles of injector cleaner thru it. I got one of those bluetooth OBDII adapters and paired it with my tablet. Here's what I've found:
Misfire codes P0301 (Cyl 1) mostly, and sometimes P0303 (Cyl 3). No codes so far on any other cylinders.
O2 Sensor 1 readings are all over the place, from .1 to .9, constantly up and down. Sensor 2 readings are much more stable. So I suspect sensor #1 or the connection to it. Have not gotten any trouble codes related to O2 though.
Runs rough when cold, a little better after warmed up. I'm in Fla. and we don't have much in the way of hills here, but it tends to misfire when accelerating up an incline (what we call a 'hill'). Gas mileage is still normal, about 17 MPG. Plugs were changed less than 20K ago.

Other theories are that the new fuel filter also got clogged with sediment, or a weak fuel pump. My engine apparently does not a have fuel pressure sensor readable via OBD. Pressure always shows 0 via OBD. I suppose it could be a plug, wire, or coil. I'm not technical enough to know what other OBD values I should be monitoring.

The truck is driveable, and gas mileage is OK, but I wanna get this fixed. Just need to fix it cheaply.

Suggestions????

What do you mean by sensor 1 and sensor 2? These engines have upstream oxygen sensors and I believe 1 downstream sensor as well. The upstream sensors will fluctuate from .1 to .9 as youve mentioned- that is perfectly normal. This happens because the o2 sensor is constantly "checking" to see if the fuel mixture is correct; .1 volts indicates the mixture is lean so the PCM adjusts short term fuel trim (STFT) to richen the mix while .9 indicates rich and the PCM adjusts STFT to lean out the mix.

The downstream o2 sensor should remain stable and near .4-.6- this indicates the catalytic converter is doing its job and removing excess emissions.

So, can you tell us what all three sensors are doing? There should be voltage readings for: o2 Bank 1 Sensor 1 (B1S1), o2 B2S1, and o2 B1S2 (possibly B2S2).

Quote:

Originally Posted by Jeff_Birt

The O2 sensor should change rapidly between .2V to .8V (approx.) that is a sign that it is responding properly. If your getting a misfire then you will have raw gas/air going through messing up the O2 sensor reading. So the misfires you are seeing correspond to the 'stable' O2 sensor, i.e. they are on same side of engine I'm guessing.

Pull the plugs and see what they look like. I would look at plugs-wires-distributor cap to see if all looked well. Look under the hood at night, if you see sparking around a plug wire you know it is bad.

+1 on this. I would especially pay attention to the plugs on the cylinder reporting misfires.

I would rent a fuel pressure tester from Advance or Autozone and start there. Its free as you get your money back when you return it. It should read in at least the 50s psi and preferably around 65psi. Given your situation, dont condemn the pump to the trash if fuel pressure is low- I would pull the pump and carefully inspect the fuel sock where the pump sucks in gas from the tank. Perhaps varnish developed in the tank from sitting and has clogged up the sock?