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4.0L OHV & SOHC V6 Tech General discussion of 4.0L OHV and SOHC V6 Ford Ranger engines.

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Old 11-29-2008
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I'm stumped?! Trouble Codes

Got codes P0304 (misfire #4) and P0153 (bank 2 O2 sensor)

Now, since this bank O2 is for #4 cylinder these have to be related? Correct?
I've pulled the plug (it was fine) AND replaced it anyway to no avail.
I've tried different wire/s to that plug from the coil.
If it's the coil I'm 90% I'd get a least one other misfire on diff. cylinder.
Check oil for coolant and coolant for oil, suspecting head gasket/cracked head.
Checked for oil on plug of misfiring cylinder suspecting valve guides/rings.

Would a bad O2 cause it's cylinder to misfire?? Found a sensor for under $30 on the net w/free shipping (that's about $20 less than Advance wants) so it's prob. worth buying anyway, seeing as Ranger has 93k on her.
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Old 11-30-2008
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Originally Posted by wickerham View Post
Would a bad O2 cause it's cylinder to misfire??
No. The 02 sensor is for the whole bank (or side) of the engine. These are narrow band sensors and can't identify an individual cylinder misfiring. A good quality wideband could.. but not the stock one. The 02 sensors are only *part* of what the PCM uses to adjust timing, fuel, and the IAC. It also has adaptive learning which semi-overides immediate inputs like a cylinder mis-fire.

IMO.. I'd go looking for a intake gasket leak. Or possibly a flaulty injector. You might try swapping injectors and see if the problem follows it.

Last edited by wydopnthrtl; 11-30-2008 at 07:29 AM.
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Old 11-30-2008
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Originally Posted by wydopnthrtl View Post
No. The 02 sensor is for the whole bank (or side) of the engine. These are narrow band sensors and can't identify an individual cylinder misfiring. A good quality wideband could.. but not the stock one. The 02 sensors are only *part* of what the PCM uses to adjust timing, fuel, and the IAC. It also has adaptive learning which semi-overides immediate inputs like a cylinder mis-fire.

IMO.. I'd go looking for a intake gasket leak. Or possibly a flaulty injector. You might try swapping injectors and see if the problem follows it.
Rich, wideband sensors are much faster than the "standard" O2 sensors, but the location of the O2 sensors measures an average of all the cylinders in the bank. To be able to measure individual cylinders, the O2 sensors would have to be located at the cylinder exhaust port. The O2 sensors have NOTHING to
do with the IAC control voltage....

The PCM looks at signal phase shifts from the camshaft position sensor to determine which cylinder misfires.

Last edited by Takeda; 11-30-2008 at 07:57 AM.
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Old 11-30-2008
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Originally Posted by wydopnthrtl View Post
IMO.. I'd go looking for a intake gasket leak.
I agree. The Ranger 4.0 OHV is famous for leaking just enough air or coolant into the #4 runner to cause a P0304 misfire code. If that's it, a new set of lower intake-to-head gaskets will take care of it.
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Old 12-04-2008
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^might done been their with those problems a year ago replaced all kinds of gaskets come to find out it was a cracked head so 400.00 for the head and i done the work my self might want to get the head checked
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Old 12-05-2008
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Originally Posted by Takeda View Post
To be able to measure individual cylinders, the O2 sensors would have to be located at the cylinder exhaust port.
I used to think the same thing.. before I had a high quality wideband sensor. (innovative LM-1)
It's true that the farther away the the sensor is, the more unlikely that you'd pick up individual mis-fires. But in the stock upstream location (in exhaust manifold) You can indeed pick up them up. Now, you have to be data logging other parameters at the same time. But you can clearly see it.

If you spent a little time in application.. you too might change your mind. Fat chance there...

Rich
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Old 12-05-2008
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Originally Posted by wydopnthrtl View Post
I. Now, you have to be data logging other parameters at the same time.
Rich
Exactly! The signal from the camshaft position sensor, which is used to detect a misfire!
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Old 12-06-2008
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Well, I pulled the correct plug this time and it looked fine. I replaced anyway and now the truck's running fine. Could my thin (0w30) synth. oil have leaked past the vavle guides or rings a caused a misfire? Went back to stock oil (motorcraft 5w30) and put a qt. of Lucas in to help stop any blow by. (man that stuff's THICK!!)

Ordered the oil test kit from Blackstone, so I'll find out if any coolant's in there soon.

Also, could an exhaust leak downstream from the O2 sensor still set off a code?
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Old 12-06-2008
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A valve seal that's leaking won't cause a foul becuase 99% of the oil that gets in, only happens after shut off. If it's bad enough of a valve seal leak, you'll see a puff of white/grey smoke right after start up. (cold motor starts)

I don't think any leaks downstream of the last 02 would cause a code. A donut thats between the header and the cat/mid pipe is notorious for causing it though.


Rich
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