Wet PCM plug
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Wet PCM plug
FYI, I developed a bad miss yesterday when I left work. The CEL started blinking on the way home and the code reader showed a PO307 code that is a miss on the #7 cylinder. We got an odd snow overnight and I was getting heavy water drainage from my roof (which I didn't clean off very well).
When I got home I checked the primary resistance against another COP and it was the same. I checked all the COP's for water and found nothing. Still the miss is there but still intermittent.
I started checking the rest of the wiring for any water and while checking the book saw that the plug for the PCM is in the engine compartment. I checked that and it was soaked. I pulled the battery and battery box to gain easier access to the PCM plug and dried it well with a hair drier. Problem went away.
Apparently the wires and plug were just wet enough to cause problems. This time it was a misfire on the #7 cylinder but it could be any kind of gremlin that crops up on a very wet day. So, when you are looking for a cause of something on a wet day check the PCM plug. It may be a much easier fix than appears.
Chris
When I got home I checked the primary resistance against another COP and it was the same. I checked all the COP's for water and found nothing. Still the miss is there but still intermittent.
I started checking the rest of the wiring for any water and while checking the book saw that the plug for the PCM is in the engine compartment. I checked that and it was soaked. I pulled the battery and battery box to gain easier access to the PCM plug and dried it well with a hair drier. Problem went away.
Apparently the wires and plug were just wet enough to cause problems. This time it was a misfire on the #7 cylinder but it could be any kind of gremlin that crops up on a very wet day. So, when you are looking for a cause of something on a wet day check the PCM plug. It may be a much easier fix than appears.
Chris
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Well, now I have a slight miss that gets steadily worse the longer I drive. When I start out in the morning it is fine and for my 10-15 minute drive to work it is okay. But, it will start to miss at about the 15 minute mark and the longer I drive after that the worse it gets.
I've pulled the PCM plug and dried it a couple more times since the first time this showed up. No CEL since the first time. The coils still look dry.
Anyone seen a bad coil act this way? Any suggestions?
Chris
BTW, this is a 2002 Expedition with the 5.4L motor.
I've pulled the PCM plug and dried it a couple more times since the first time this showed up. No CEL since the first time. The coils still look dry.
Anyone seen a bad coil act this way? Any suggestions?
Chris
BTW, this is a 2002 Expedition with the 5.4L motor.
Last edited by ResJudicata; Mar 30, 2011 at 03:15 PM. Reason: vehicle info
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Joined: Jan 2001
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From: Central NYS
Yes. As the coil gets hotter it is possible that the windings move slightly and begin to short out. When it cools it returns to normal. Might be interesting to compare your resistance between a coil when it is cold and when it is hot.
As I have pointed out in other posts, resistance testing a coil only tells if it is bad. It doesn't test it under load when current is going through the coils. A marginal coil will begin to break down as the current heats up the coils. To test it under load you really need an amp clamp hooked up to an oscilloscope so you can watch current pattern as the PCM pulls the coil to ground and then releases the ground.
Since you misfires seem to be more random, I wouldn't think all the coils are going bad, and would suspect your plug to the PCM. Be sure there is no green stuff growing in the plug and that all the pins are snug and not pushed back.
As I have pointed out in other posts, resistance testing a coil only tells if it is bad. It doesn't test it under load when current is going through the coils. A marginal coil will begin to break down as the current heats up the coils. To test it under load you really need an amp clamp hooked up to an oscilloscope so you can watch current pattern as the PCM pulls the coil to ground and then releases the ground.
Since you misfires seem to be more random, I wouldn't think all the coils are going bad, and would suspect your plug to the PCM. Be sure there is no green stuff growing in the plug and that all the pins are snug and not pushed back.
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Yes. As the coil gets hotter it is possible that the windings move slightly and begin to short out. When it cools it returns to normal. Might be interesting to compare your resistance between a coil when it is cold and when it is hot.
As I have pointed out in other posts, resistance testing a coil only tells if it is bad. It doesn't test it under load when current is going through the coils. A marginal coil will begin to break down as the current heats up the coils. To test it under load you really need an amp clamp hooked up to an oscilloscope so you can watch current pattern as the PCM pulls the coil to ground and then releases the ground.
Since you misfires seem to be more random, I wouldn't think all the coils are going bad, and would suspect your plug to the PCM. Be sure there is no green stuff growing in the plug and that all the pins are snug and not pushed back.
As I have pointed out in other posts, resistance testing a coil only tells if it is bad. It doesn't test it under load when current is going through the coils. A marginal coil will begin to break down as the current heats up the coils. To test it under load you really need an amp clamp hooked up to an oscilloscope so you can watch current pattern as the PCM pulls the coil to ground and then releases the ground.
Since you misfires seem to be more random, I wouldn't think all the coils are going bad, and would suspect your plug to the PCM. Be sure there is no green stuff growing in the plug and that all the pins are snug and not pushed back.
Or, the wet plug could have happened coincidentally when the coils started going bad.
Chris
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From: Omaha, Nebraska USA
My number 4 miss acted this way It would hardly miss a beat untill it started to warm up, then as it the engine got warmer the missing got worse. I put in all new cops and runs as good as new.
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Well, I replaced the plugs and replaced the #7 COP and the truck runs great. All the plugs looked okay considering they had 130,000 miles on them. The gaps were a bit big but not too bad.
I checked all the coils and compared them and the primary resistance as well as the secondary resistance all matched very very closely. But, replaced the #7 anyway since that was the cylinder that threw the miss code.
I'm still going to replace all the coils with the Ebay set as a precaution. They should be here next week.
Chris
I checked all the coils and compared them and the primary resistance as well as the secondary resistance all matched very very closely. But, replaced the #7 anyway since that was the cylinder that threw the miss code.
I'm still going to replace all the coils with the Ebay set as a precaution. They should be here next week.
Chris
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I replaced all 8 coils over the weekend with a set from Ebay. $85'ish shipped for all 8.
The truck runs great. I think one of the other coils has been intermittent because I would sometimes have a slightly rough idle. Not so bad that it was a problem but just barely noticeable. The truck seems smoother now with all the coils replaced.
BTW, the second time pulling all the coils and replacing with new took about 1 hour. Recent experience certainly helps speed up the process.
Chris
The truck runs great. I think one of the other coils has been intermittent because I would sometimes have a slightly rough idle. Not so bad that it was a problem but just barely noticeable. The truck seems smoother now with all the coils replaced.
BTW, the second time pulling all the coils and replacing with new took about 1 hour. Recent experience certainly helps speed up the process.
Chris
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