Misfire CEL on 4.0 sohc wont go away

[UnorthodoxCreat]

Today I got a CEL for misfire on my 97 V6 4.0L SOHC. Once I got the 300, random misfire, but generally I keep getting 301, 302, and 305. I changed out the coilpacks since I had an extra and that didnt do anything so I went and bought a set of plugs and wires. Idle seemed to smooth out a little but it didnt take long for the CEL to come back. I just broke 97K miles today. The engine is totally stock. Any ideas what to try next? It seems to drive perfectly fine but I dont like driving it with a CEL on.

 

[dogfriend]

I know that you swapped out the coil pack, but I would test the primary and secondary resistance of the coils to make sure they are in spec. I was having a misfire problem and it turned out to be high resistance in the coil pack.

If that checks ok, then I would test compression to make sure everything is ok .(e.g. the head gasket isn't blown)

P.S. If you drive with a bad misfire for too long you can trash your cataylic converter(s), so I would try to resolve it soon.

 

[UnorthodoxCreat]

How do I test the coilpacks? What kind of specs am I looking for? Changing out the coilpack for another made absolutley no difference(once i put the plugs on in the right order )

It seems pretty odd that it would be a head gasket. It does not leak or burn a bit of coolant or oil and does not ever smoke either. The engine definitely feels a strong as ever. Also the 2 codes I get the most 302, 305 are on different banks. 301 comes up often but no quite as much as those 2.

 

[dogfriend]

See post #32 and on in this thread:

http://www.explorerforum.com/forums/showthread.php?t=90340&page=2&pp=20&highlight=coil+pack

If you have a Haynes manual, there is a good section in Chap 5 on testing the coil pack. You test the secondary resistance between Coil towers that are connected together (e.g. 1 and 5). The specs are in this thread:

http://www.explorerforum.com/forums/showthread.php?s=&threadid=96320&highlight=coil+pack

 

[UnorthodoxCreat]

Thanks for the help, hopefully I'll have time to look into it tomorrow. I also need to check for blown fuses. The only other problem i've ever had with this vehicle was trying to fix an O2 sensor code and then it turned out to be a fuse.

 

[UnorthodoxCreat]

I had some time to check all the fuses tonight and nothing wrong there. I'll check the coilpacks tomorrow but I have my doubts considering I have the exact same codes with 2 different coilpacks. Any other ideas. Camshaft positions sensor? I think I saw something along those lines in a thread I found searching but now I cant find that.

 

[dogfriend]

Here are some other threads discussing misfire:

http://www.explorerforum.com/forums/showthread.php?t=85474&highlight=misfire

http://www.explorerforum.com/forums/showthread.php?t=108712&highlight=misfire

http://www.explorerforum.com/forums/showthread.php?t=147350&highlight=misfire

 

[UnorthodoxCreat]

Now the CEL and codes have all gone away. I've made 3 trips now from 10 minutes to 20 minutes and no codes. Prior to this it has always come on within 5 minutes and stayed on till the engine is turned off. Call it coincidence but I pulled out my right rear brake light bulb to confirm it was blown as I had been told it was. I didnt replace it but put it back in. On the trip to get a bulb, to a friends house, and then home no CELs. I replaced the bulb tonight. Hopefully the problem is gone.