Random Misfire at startup and cylinder 3 misfire and O2 sensor

[Starjammir]

Lately this truck has been something else to me. 49k
Just got it back from the dealer for leaf spring replacement.
Now it's throwing a misfire at startup and cylinder 3 misfire. Just replaced all the plugs ( motorcraft) not 100 miles ago. Not sure where to go.
Checked the fan harness and I'm good on that.
Also, replaced upstream O2 sensor for no voltage and it's still the same. Used a motorcraft sensor too. Fuel trims are all over the place too, as to be expected.

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[Friday yet?]

I’ve no clue. But looking forward to some of the more knowledgeable folk’s responses.

 

[NotBudule2]

Now it's throwing a misfire at startup and cylinder 3 misfire. Just replaced all the plugs ( motorcraft) not 100 miles ago.

No code or misfire before you worked on it?

 

[Mighty Little Blue]

Seeing as how you just changed plugs I would double check that the coil is fully seated. You could also move coil to #2 and plug to #1 and see if the misfire moves. For the O2 sensor is the 0 voltage always or just at startup? They will read low until warmed up maybe an issue with the heater circuit to the sensor?

 

[Starjammir]

No code or misfire before you worked on it?

Yup I did have a misfire code before however I replaced the plugs and thought I fixed it.

 

[Starjammir]

Seeing as how you just changed plugs I would double check that the coil is fully seated. You could also move coil to #2 and plug to #1 and see if the misfire moves. For the O2 sensor is the 0 voltage always or just at startup? They will read low until warmed up maybe an issue with the heater circuit to the sensor?

Nope, it's always at 0 voltage. Drove 30 miles yesterday datalogging and it went from 0 to 0.030 and back and forth.
I'll pull the coil from one and swap it to 3 and such. See if that fixes it.

 

[Mighty Little Blue]

Yup I did have a misfire code before however I replaced the plugs and thought I fixed it.

Sounds like the coil, I just had one changed at 20k miles under 60/60,000 warranty out of 36/36000 warranty. Try switching them to isolate the problem.

 

[Mighty Little Blue]

Nope, it's always at 0 voltage. Drove 30 miles yesterday datalogging and it went from 0 to 0.030 and back and forth.
I'll pull the coil from one and swap it to 3 and such. See if that fixes it.

If the fuel trims are off the O2 might be a symptom from that which could be the misfire causing it. When mine went bad I had a whole bunch of random errors showing up. Is it the upstream or downstream sensor? Upstream should bounce between lean and rich, and downstream stay steady around .7.

 

[Starjammir]

If the fuel trims are off the O2 might be a symptom from that which could be the misfire causing it. When mine went bad I had a whole bunch of random errors showing up. Is it the upstream or downstream sensor? Upstream should bounce between lean and rich, and downstream stay steady around .7.

It's the upstream. I can't datalog the bottom one. Seems to stay between -7 to 14 on fuel trims but still shows no voltage on the upper one.

 

[Mighty Little Blue]

Short term will go up and down constantly depending on conditions need to check long term numbers also those will be more stable.

 

[Starjammir]

Short term will go up and down constantly depending on conditions need to check long term numbers also those will be more stable.

Any idea on no voltage to the 02 sensor?

 

[dtech]

Any idea on no voltage to the 02 sensor?

I beleive Ford uses a wide range sensor upstream of the cat and it is a heated sensor - if there is no voltage to work the heating element - then the sensor will not function properly

 

[Starjammir]

I beleive Ford uses a wide range sensor upstream of the cat and it is a heated sensor - if there is no voltage to work the heating element - then the sensor will not function properly

Where does the voltage come from?

 

[dtech]

Where does the voltage come from?

Afraid I don't know the answer - this board generally relies on the airline tech for that type of info. Usually a wide range o2 sensor has 5 or more wires, you might be able to search the internet for info as to which colored wires supply the current to heat the sensor.

 

[Mighty Little Blue]

Afraid I don't know the answer - this board generally relies on the airline tech for that type of info. Usually a wide range o2 sensor has 5 or more wires, you might be able to search the internet for info as to which colored wires supply the current to heat the sensor.

Agree with this, but I would get the misfire issue corrected before moving forward with O2 sensor those usually do not fail.

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