My son recently bought a 2003 Dakota SLT 4-door with the 4.7L V8. It was a one owner truck with only 76K miles on it and is in really nice condition. The problem is that it has a constant misfire on #7 cylinder. Actually, there were other problems (i.e. heater core leak, coolant temperature guage reads full hot (which is not the case) and a severely clogged air filter) that I don't feel apply to this situation, however, after replacing the heater core and discovering and replacing the clogged filter it has run normally except for a constant misfire on #7 cylinder. The temp guage problem may be due to a pinched wire from removing and reinstalling the dash, but I can't see how it is relevant to the misfire, however, due to the guage problem and the fact that the clogged filter would cause all the plugs to foul and kill the engine after only driving a few miles, I replaced the ECM. Unfortunately, the refurbished ECM was not the fix for either problem. I replaced the engine coolant temp sensor then, but had no better luck there.

Once it stopped quitting from fouled spark plugs, a misfire was then noticeable, so I checked for codes and found one for the #7 cylinder misfire. Having not worked on anything with individual ignition coils until now, I replaced the #7 coil pack and spark plug, but got no better result. This was all done at my brother's home about 80 miles away, but once I got it home I did the following: Replaced the remaining spark plugs with standard Champion plugs as was in it. They were obviously the originals. After a test drive and checking for color of deposits on all, the #7 spark plug showed no deposits whatsoever. Checked compression. #7 was 175 psi, which was close to others I checked. Ran a head gasket leak test through the radiator. No combustion gases detected. Replaced the #7 fuel injector. Checked for signal to #7 injector with a NOID light. All of these checks showed normal, so I even reinstalled the original ECM, which made no difference either. I'm grasping at straws now and wondering if the port in the cylinder head might be clogged. I would like to know if anyone else has had a similar problem and what they found. Thanks.

 

Verify the PCM is controlling the coil as well. Noid lite *should* work for that too.

Verify you are getting power TO the coil, engine running. (coils will only have power for about 3 seconds at initial key on..... so, best to test when you KNOW the coils should be powered.)

 

Thanks HeyYou. Actually, that thought came to mind about a half hour after I posted. My mind is kinda like the character in Cars II, the one that looks like a Challenger. As he and his buddies are traveling through the night and need to speed up, when he hits the gas he's misfiring on a cylinder or two, but soon hits on all eight again. I did check and #7 was not getting any power. I have since traced down the power wire to that cylinder and although it isn't shorted to ground or broken, still has no power, even right at the ECM connecter. I also swapped the OEM and the reman unit I bought and same result. I'm of the opinion that both ECMs are faulty. Nothing else makes sense. Would you agree?

 

The issue may be mechanical, such as a stuck lifter or valve issue. Does it tick quite a bit?

 

Definitely not mechanical. No abnormal engine noise at all. Also, low miles (76K). Have determined that there's no power to #7 coil with factory PCM or reman unit. Reman company is sending another. This year was apparently the first year of this PCM (four connecters as opposed to three), so I suspect this was a common problem. Will let you know soon.

 

Not to my knowledge and I've been here a while. I've got the same truck here, 340K & original PCM.

 

POINT taken. Doesn't change my diagnosis, though I've got two units with same symptoms.. No power to #7 coil. I've checked the wire from connecter to connecter for continuity or grounding. No faults found.

 

Wasnt really trying to make one. Anyway, it would be highly unusual for the two computers to fail in the same exact way, as to affect #7. That is unless something is blowing them, for lack of a better term. Maybe a short somewhere.

 

I finally got to the bottom of this. I determined at one point that there was no power going to the #7 ignition coil. After replacing the ECM with another reman unit, there still was no power. Finally, I thought maybe the ground is the problem and BOOM! There it is. The ground wire wasn't making connection to any of the other ignition coil grounds. Since the grounds for the coils all use a common wire from the ECM, it finally made sense. I had been checking for power to the coils using my test light and connecting one end to battery ground. Apparently just any old ground won't do. It has to come from the ECM. And, since the coils share the same ground wire as the fuel injectors, it explains why the spark plug wasn't even getting wet. That little 4.7 has plenty of power now.

 

There you go! So the problem wasn't a short as I theorized, it was an open. If you don't mind, can you state the exact location of the failed ground and maybe post a pic of it?