P0303 and PO174 on 3.0L OHV Engine

[brunnj]

I have a 2002 Taurus with the 3.0L OHV engine. I have noticed a miss on and off since I have owned the vehicle so I took it to Auto Zone to see if there were any pending codes. I got a code PO303, which is a misfire on cylinder 3.

While I was on my way to get new plugs and wires for the car, the check engine light came on and it turned out to be P0174, which is a lean condition on bank 2.

Could this be a problem with the PCV valve as noted in a post above this as I have recently noticed the last two nights it idled rough while the engine was cold. The engine also seems to lack power at times.

Thanks for any help you can provide.

[robroy55]

I had the same situation on my 2002 24 valve as you have, Rod came to my rescue and advised me to put new spark wires on and BINGO!! miss has gone now. Rod has never failed me!!
Give it a shot,
Rob Roy

[shorod]

Agreed. The PCV will not likely cause a misfire on a single cylinder. Fix the source of the misfire on cylinder #3 first and the P0174 will hopefully go away. Curiously, cylinder #3 is on bank 1....

Your misfire code would likely be due to either spark plugs, spark plug wires, compression, or the fuel injector. If the car has not had a tune up in quite some time, you may as well go the plugs and wires route first. Consider the fuel filter and air filter as well, and inspect all vacuum hoses, including the air intake plumbing.

-Rod

[brunnj]

Originally Posted by shorod

Agreed. The PCV will not likely cause a misfire on a single cylinder. Fix the source of the misfire on cylinder #3 first and the P0174 will hopefully go away. Curiously, cylinder #3 is on bank 1....

Your misfire code would likely be due to either spark plugs, spark plug wires, compression, or the fuel injector. If the car has not had a tune up in quite some time, you may as well go the plugs and wires route first. Consider the fuel filter and air filter as well, and inspect all vacuum hoses, including the air intake plumbing.

-Rod

I put new plug wires and plugs in the car on Friday. I still have the miss. I hope the problem is not compression related. An injector will be cheaper to fix than a compression problem.

[shorod]

It could also be the coil for cylinder #3. Also, did you make sure to get all the plug wires snapped on? Is the misfire code still P0303 after the new plugs and wires?

-Rod

[brunnj]

Originally Posted by shorod

It could also be the coil for cylinder #3. Also, did you make sure to get all the plug wires snapped on? Is the misfire code still P0303 after the new plugs and wires?

-Rod

I haven't had the codes set again since adding the plug wires and plugs. The code that was read previously was a pending code as it had not turned my check engine light on yet. I still feel the miss though, mostly at crusing speeds.

I checked the primary resistance and secondary resistance on the coil. The primary was about .8 ohms across each pin and the secondary was 11,800 ohms across each coil pack. My Haynes manual says the seondary should be 13,600 so I don't know if the coil is no good or not since there is no range on that spec.

[shorod]

If you have access to a high-end scan tool, you could check the component parameters to determine if there are misfire counts on one or two particular cylinders that have not set a code yet. With any luck, there will be only two cylinders showing a misfire and they will share a coil pack.

FWIW, if it were a compression issue the misfire feel would likely not be sporatic.

-Rod

[brunnj]

Originally Posted by shorod

If you have access to a high-end scan tool, you could check the component parameters to determine if there are misfire counts on one or two particular cylinders that have not set a code yet. With any luck, there will be only two cylinders showing a misfire and they will share a coil pack.

FWIW, if it were a compression issue the misfire feel would likely not be sporatic.

-Rod

Thanks to everyone for the information. I think I'll pull the coil pack and have it tested at Auto Zone or Advanced Auto (if they test them). My Haynes manual says the secondary resistance should be 13600 ohms and I am reading 11800. I don't know if that's close enough or not.

[Doug Tatham]

Check CAREFULLY for vacuum leaks. Almost every P0174 that I've come across was solved by finding a cracked vacuum tube.

[brunnj]

Originally Posted by Doug Tatham

Check CAREFULLY for vacuum leaks. Almost every P0174 that I've come across was solved by finding a cracked vacuum tube.

The hose the PCV valve is mounted into is cracked where it connects to the intake manifold. I plan to replace that along with the valve. I removed the hose from the valve cover while the engine was idling and felt vacuum but there still may be a leak.

[brunnj]

Originally Posted by shorod

It could also be the coil for cylinder #3. Also, did you make sure to get all the plug wires snapped on? Is the misfire code still P0303 after the new plugs and wires?

-Rod

I checked the resistance across the primary and secondary coils and compared the results to what is in my Haynes manual. What are the specs for resistance in the FSM and is there a +/- range? Sometimes the info in the aftermarket manuals is erroneous.

[shorod]

I did some looking in the 2002 FSM and was not able to find expected coil primary or secondary resistance numbers, even in the troubleshooting section for the Ignition System Secondary code.

-Rod

[brunnj]

Originally Posted by shorod

I did some looking in the 2002 FSM and was not able to find expected coil primary or secondary resistance numbers, even in the troubleshooting section for the Ignition System Secondary code.

-Rod

Thanks for looking. I appreciate it.