P0307 Misfire has been detected in cylinder 7

wrldky

Well-known member
Apr 21, 2004
410
7
Raleigh, NC
Was hoping someone could give me some advice based on symptoms and what I am considering as mu course of action.

Threw this code a couple of months ago. I replaced it with a new Bosch spark plug. The plugs and wires are about six month old. The plug looked fine. I didn't see this code for a while after the new plug and then it started occasionally. I changed the plug again but it didn't help and it will stay on now.

I have SAI so it's kind of a PITA. I'm thinking coil pack. I am thinking I will pull the top of the engine and replace the two coil packs confirm everything is tight and put it back together. That seems like the cheapest thing to do (after spark plug and cable)

Anyone elses feedback would be great. I did get a MAF code a couple of weeks ago but I don't recall what it was and it hasn't come back.
 

mlnnc

Well-known member
Mar 23, 2008
266
31
Charlotte
From my personal experience plus a lot of years reading on this and other DII forums a misfire on a single cylinder is most often either the plug or the wire. Double check that the #7 wire is firmly seated on the coil terminal. I changed plugs and wires a month ago and found I had to be very careful to make sure the wires clicked into place on the coil.

There are several on this and other forums who swear by replacing the coils, but at last report P.T. said he has yet to see one fail and he's seen a lot of DIIs. And if it was a problem with the coil I'd expect to see misfires on more than one cylinder, especially the cylinder paired with #7, which is #6.
 

SGaynor

Well-known member
Dec 6, 2006
7,148
162
52
Bristol, TN
Check that the wire didn't come in contact with the block and melt the outer rubber layer - I've had that happen. On #7.
 

wrldky

Well-known member
Apr 21, 2004
410
7
Raleigh, NC
Pulled the #7 ignition wire and sure enough the metal on the spark plug end had pulled away. The cables are not even close to being a year old. I had an old STI wire that I used to replace it. Thought that would do the trick. Still thru the code. Now I'm really confused. I put a spark plug wire tester on and the light on it burned a flashing orange like it should. Pulled the spark plug. Now here I noticed that you could tell on the threads that it had night been screwed down enough. Put it back in and tightened it until I couldn't turn it anymore. Still thru the P0307I code. I'm going to pull the plug again tonight to see how far it was screwed in. Maybe I cross threaded it. Wise it always have to be the hardest plug to get to? Plus I have SAI which is a complete pain in the ass.
 

squirt

Well-known member
Nov 13, 2008
824
13
Los Angeles
Under what conditions do you get the code? Cold/hot? High RPM/cold start? Do you get a flashing CEL, or does it just turn on?
 

SGaynor

Well-known member
Dec 6, 2006
7,148
162
52
Bristol, TN
You put an old wire on it - you sure it's good? Did you try the spray the wires with water at night to see if you are getting electrical current coming through?

The fact that you had a KNOWN bad wire, I would replace that with a KNOWN good one. Just because the tester is showing current, doesn't necessarily mean you are getting enough current.

FYI, I always use http://kingsborne.com/ wires. When my #7 melted, I was able to order just the one from them.
 

best4x4

Well-known member
Mar 1, 2015
595
72
Beaumont, TX
I had a bad coil pack causing P0300 & P0307 faults. Swapped plug wire, swapped plug, and still had faults. Finally said F it, and replaced both coil packs while I had it apart. Zero faults after replacing the coil with original plug wire (checked it), and original spark plug. OEM coils lasted to 230K so not gonna complain.

A coil can die on just one cylinder. As a rule of thumb I now recommend new coils (very reasonable price wise now) whenever I’m installing new plugs/wires onto someone’s P38/D2 vs having to tear it all down again if an OEM coilpack dies.
 

wrldky

Well-known member
Apr 21, 2004
410
7
Raleigh, NC
Just pulled the plug. It appears that it was only screwed in about half way. I'm thinking the threads are crossed. It's the #7 so it's pretty tight. can it e repaired without pulling the head?
 

wrldky

Well-known member
Apr 21, 2004
410
7
Raleigh, NC
I was nervous about re-taping it so I took it to a shop and had it done ($200) Seemed to drive fine at first but then threw the same code. When accelerating the check engine light would flash and then stop when the car stopped. Any ideas? I will change to coil pack but can I get a confirmation that it will only throw one code and not codes in pairs. Thanks!
 

squirt

Well-known member
Nov 13, 2008
824
13
Los Angeles
Yes, it's been known to happen. You can have a coil that fails on a single cylinder. Before buying a new one/pair, I'd swap them and see if the misfire follows. If not, you've probably got a mechanical issue. For me, with identical symptoms, it was a wiped cam lobe on cyl 8.
 

jprover2

Well-known member
Apr 8, 2017
146
10
Birmingham,Al
Don't just limit your thinking to ignition for misfire codes. Fuel injectors that are clogged or not functioning can also cause the conditions needed to throw a DTC related to misfire. :ack:
 

best4x4

Well-known member
Mar 1, 2015
595
72
Beaumont, TX
Like I said when I had issues it was P0300 & P0307 only no other cylinders. Replaced the coils and no more issues. I would not waste my time moving the coils around only to find it misfiring again. Then you'll have to tear it all down again. Replace the coils (very cheap) and be done with it IMHO.
 

wrldky

Well-known member
Apr 21, 2004
410
7
Raleigh, NC
Changed to wires, coils and fuel injectors last night. Put it all together and it fired up. It was revving high so i turned it off because I noticed the throttle cables were not adjusted correctly. Adjusted them and then could not get the truck to turn over. Checked everything. Was stumped. Woke up in the middle of the night and went to the garage to put a voltage tester on the battery. Was reading 9 volts. Had it tested and it is bad. Hopefully a new battery will do the trick. Stay tuned.