#7 misfire

[prodigal stang]

Thanks in advance for any advice.

I have a 1997 5.0 AWD explorer.

I went to one of those pay and wait car washes after work earlier this week. The kind you pull up tell them what you want and then wait inside. I paid for the cheap-o wash, meaning they didn't pop the hood to clean under it. Went to drive a way and it's misfiring. I pretty much had my eye on it the whole time so I don't think they did anything malice but that was the only veritable in this equation. The water jets in the car wash might have done something but I don’t know what.

I’m getting trouble code PO307 and a check engine light. I've pulled the spark plug and replaced it, checked the coil packs with an ohm meter and they were within spec. Check the spark plug wire for any damage and ohmed it out and it didn't seem bad. I have cleared the code and swapped the coils and ran it until the check engine light came on. Still misfire in #7. So this should completely eliminate the coils from being the culprit. I pulled #7 plug and did a compression check it came back 165ish I then reinstalled the #7 plug and pulled #8 and did a compression check. It came back also at 165ish. Given these are similar #'s to what the mustang did and that they are about the same from each other I’m going with compression OK, I'm at least getting compression. However, I don't have a leak down tester to be conclusive. I have also pulled #7 plug stuck it back in the wire and grounded it while my wife turned it over and it was getting spark, did the same with #8 and it was comparable spark.
The last thing I haven’t done is mess with the injector but the new plug is amber in color like it’s burning some fuel. This explorer is my daily driver but I’ve been turning wrenches on my 89 mustang for years and I just haven’t come across a faulty injector story so I’m not sold on that idea unless someone says this is a common issue with the explorers.

My last hope is that there is some common issue with the explorers that I’m not aware of or someone might know what the car wash might have done. Could it have knocked some other sensor outa whack that could cause this?

At this point any ideas would be welcome.
Many continual thanks,
Jon

 

[prodigal stang]

Ah one other symptom that I almost forgot, after it warms up it will start to back fire and I get a rotten egg smell.

 

[Cobraguy]

Well, it takes three things to make combustion. Compression, spark, and fuel. You've confirmed the first two. Check your injector electrical connection. Do you have a noid light? If you don't have the diagnostic tools to check injector patterns, I would try replacing that injector.

 

[prodigal stang]

Thanks, I’m saving the injector for last, #7 is back up under the plenum. I’ve got a new plug that smells like fuel as well as a burnt fuel appearance and under the stethoscope the injector sounds the same as the others. Unfortunately I don’t have a noid light.

I’m starting to think it may be a cam sensor or something that might throw the firing off.

 

[Turdle]

I would replace the #7 plug wire.

It is possible the moisture caused a cracked wire to start arcing and develop a carbon track which is allowing it to become worse.

 

[prodigal stang]

I would replace the #7 plug wire.

It is possible the moisture caused a cracked wire to start arcing and develop a carbon track which is allowing it to become worse.

Hmm this I was not aware of. So are you saying that just the heat of the motor could cause the wire to start arcing? In other words it'll run fine when cold but after it heats up it goes to crap?

 

[Cobraguy]

Oh wow...I thought you had swapped wires to see if the problem followed the wire. If you haven't, you should do that before anything else. Good suggestion JT.