97 Explorer V8 - Getting Code P0308

[Dan Ouellette]

My Explorer started running rough w/CEL on. Code received P0308.

I replaced fuel filter, air filter, spark plugs, wires, coil pack. When removing Cyl 8 plug, there was moisture on internal end of plug. Plugs looked fine, but replaced any way.

Vehicle idles fine when in park. Runs fine when first driving. Runs fine at 70 mph. Runs rough at 25 - 45 mph.

Misfire is erratic. It will drive smooth at times and rough at other times. IE: misfire does not appear to be consistant.

 

[storlied]

I don't know off the top of my head what the code means, someone will chime in soon about it. But did you check your MAF?

 

[Cobraguy]

That code is telling you the PCM detected a misfire on a cylinder...and guess which one. Yep...#8. I guess you need to find out what's going on in there. Was it coolant on the plug or gasoline?

 

[storlied]

What does it mean if there's coolant in the engine? I keep seeing people mention this. I also keep seeing it in tear down pictures of a 5.0L..

Is there something horrible I should know about my engine?

 

[gavin]

coolant on a spark plug usually means a head gasket leak. Which should be fixed ASAP, or there could be catastrophic failure.

 

[storlied]

Found no coolant on my last spark plug change. *wheW* Just oil and ash...

 

[Dan Ouellette]

That code is telling you the PCM detected a misfire on a cylinder...and guess which one. Yep...#8. I guess you need to find out what's going on in there. Was it coolant on the plug or gasoline?

It was gasoline on the sparkplug.

 

[Dan Ouellette]

What does it mean if there's coolant in the engine? I keep seeing people mention this. I also keep seeing it in tear down pictures of a 5.0L..

Is there something horrible I should know about my engine?

I've been told that if there is coolant in the oil or oil in the coolant, then there is a leak in the headgasket. But, I don't have either problem.

 

[Cobraguy]

It was gasoline on the sparkplug.

That could be from a defective ignition system (coil, plug, wire, etc) or a leaky injector, a partially plugged injector (too lean to fire, but enough fuel to wet the plug) or a loss of compression. Loss of compression would be a consistent miss. You have replaced the ignition components. If this were mine, I would pull the plug and make darn good and sure I haven't cracked the insulator when I installed it. Sometimes, those cracks are almost impossible to see, so you might just throw one of your old plugs in it for testing purposes if you still have them. Check and make sure your plug wire isn't shorted anywhere. If everything checks good, the next place to look is the injector.

 

[Dan Ouellette]

I just replaced the crankshaft position sensor. No luck. I rechecked the plugs & wires, even swapped out cylinder 8 plug with yet another new one.

Still getting code P0308.

 

[Dan Ouellette]

That could be from a defective ignition system (coil, plug, wire, etc) or a leaky injector, a partially plugged injector (too lean to fire, but enough fuel to wet the plug) or a loss of compression. Loss of compression would be a consistent miss. You have replaced the ignition components. If this were mine, I would pull the plug and make darn good and sure I haven't cracked the insulator when I installed it. Sometimes, those cracks are almost impossible to see, so you might just throw one of your old plugs in it for testing purposes if you still have them. Check and make sure your plug wire isn't shorted anywhere. If everything checks good, the next place to look is the injector.

How would I check the injectors?

 

[gavin]

before you swap injectors... have you tried swapping the coils?
see if the issue stays with cyl. 8, or stays with the coil.

 

[Dan Ouellette]

before you swap injectors... have you tried swapping the coils?
see if the issue stays with cyl. 8, or stays with the coil.

I replaced the coils with new ones and still had same issue.

 

[Turdle]

Before swapping injectors--
try cleaning the Cam position sensor.

 

[Dan Ouellette]

Before swapping injectors--
try cleaning the Cam position sensor.

I replaces the crankshaft position sensor, is there a cam position sensor also?

 

[Turdle]

Yes--it "times" the fuel injectors, and is located where a distributor should be on the front of the engine. Under the coil packs

It also drives the oil pump

you can remove the 2 top screws to look inside, and clean the sensor without removing the synch drive unit--( distributor shaft for lack of better description)

Check out this thread-

http://www.explorerforum.com/forums/showthread.php?t=161590&highlight=squeak+chirp

 

[Dan Ouellette]

before you swap injectors... have you tried swapping the coils?
see if the issue stays with cyl. 8, or stays with the coil.

I swapped out the coils and still have P0308 code.

 

[Dan Ouellette]

OK, I just replaced the Cam Position Sensor and still P0308 and mis-firing...

Any other ideas?

 

[Turdle]

Boy--
At this point I am stumped.
You know, the weird thing is I had an obviously bad spark plug wire with a constant miss, and no misfire code.

This tells me that the only "misfire" which will set a code is fuel related.

It would be easier at this point to check the compression on #8 , then, if compression checks out look at the injectors.

 

[steve968]

Have you tried to see if you are getting spark on that cylinder? Plug in a spark tester on #8 wire.