2000 Mercury Mountaineer 5.0L V8 AWD misfire code PO307, cyl 7 misfire

[Summajet]

I have a code PO307 misfire code on cylinder #7. It has 236,000 miles. I do hear lifter noise in that area. It has a skip and feels like it is stumbling a little.
I had a similar issue with my 03 yukon 5.3l on cylinder #2. That particular incident was a failed lifter and it had nodded the cam lobe. I know the Mntr. has a lot of miles and always has been a reliable dependable suv. Things I plan on checking,
1. Compression
2. spark plug wire
3. coil pack for cyl. #7

On the yukon i rebuilt that myself. It took many weekends to get it done, machine shop and ordering parts. Has anyone ever used a ATK motor from Advance Auto? I know they say 3 years and 36,000 mile warranty. I had read somewhere they are okay rebuilds but they use cheap seals and gaskets, leaks develop over time.
Any input would be appreciated.
Thanks,

 

[crunchie_frog]

My bet is on a bad plug wire. You might could swap 7 and 8, though am not sure if 7 is long enough to get to 8 or vice versa but they probably are.

 

[koda2000]

Chevy engines and Ford engines are not the same and do not suffer from the same problems. I'm not saying one is better than the other, but just because your Chevy had a cam wear issue doesn't mean your Ford will have then same problem.

Your issue is most likely a bad plug wire or spark plug. When's the last time they were replaced? My 2000 Mountaineer 5.0L has 270,000 miles on it and runs great. The spark plugs had just been replaced when I purchased it (w/175K) and I replaced the plugs and wires at about 250K when it developed misfires on multiple cylinders. Ford uses a waste-spark ignition system, this causes the spark plugs on one bank to wear a lot more than the on the other bank. I found 4 plugs that had a gap of maybe .060 while the other 4 were worn/gaped so large I couldn't measure them (maybe .090). It had Autolite double platinum spark plugs in it, which should work fine. I replaced them with new Autolite double platinum's and new Denso exact-fit plug wires.

I also recently had a misfire on my 2001 Explorer 5.0L at around 200k. I'd replaced the plugs when I purchased the Expl at around 180K and the previous owner had replaced the plug wires in the past w/Motorcraft plug wires, but did not route the new wires correctly. This caused one wire to wear on something sharp and short out. I replaced the plugs (which didn't need replacing) and again installed the Denso exact-fit wires. It's be perfect since.

Ford recommends spark plug change intervals of around 100K but I'd say 60K-70K would be a better change interval to be safe, with a minimum plug design of platinum. Motorcraft or Autolite recommended. If you want to spend the money, Motorcraft plug wires are probably the best choice, but as with most Motorcraft parts, they're expensive.

 

[MrQ]

Yeah, no. The stock 5 liter is a lot tougher to kill than that. Agree with the others, time to check spark plugs and wires.

 

[Summajet]

Evening, with more investigating this evening i noticed the exhaust manifold had a gray color. I noticed the sparkplug boot had cracked and was arcing on the manifold. I have never had a boot wire do this ever. I just replaced them may of 2019. They have a 2yr warranty from Autozone. Autozone does not sell them anymore. They sell denso and Autozone gold wires. I think you mention you had the densos.
Also how often should the O-2 sensors be repaced? Mine are original 225,000 plus miles.
I do need to replace the Valve Cover gaskets as they are leaking badly. It has some lifter noise in the 5 and 7 cylinder area.
Attached are pictures of the manifold and the boot wire.

 

[Mbrooks420]

I’d only use Motorcraft, or a very top quality wire set. These tend to be picky about it.

I’d lose no sleep over a little lifter tick on these

 

[RickOTR]

Go with Motorcraft wires and plugs, you'll that me later.

 

[crunchie_frog]

Evening, with more investigating this evening i noticed the exhaust manifold had a gray color. I noticed the sparkplug boot had cracked and was arcing on the manifold. I have never had a boot wire do this ever. I just replaced them may of 2019. They have a 2yr warranty from Autozone. Autozone does not sell them anymore. They sell denso and Autozone gold wires. I think you mention you had the densos.
Also how often should the O-2 sensors be repaced? Mine are original 225,000 plus miles.
I do need to replace the Valve Cover gaskets as they are leaking badly. It has some lifter noise in the 5 and 7 cylinder area.
Attached are pictures of the manifold and the boot wire.

My #7 has heat shielding on it, yours appears to not have this so you need to get wires with the same heat shielding as the OE wires. For me, the most important thing I have learned / observed with plug wires is following the EXACT routing and heat shielding of the original wires. I have an aftermarket set I got on RA for $8 that have nearly 100K miles on them. When I replaced the OE wires with the RA wires, I carefully removed the heat shielding from OE Motorcraft wires and took careful note of the routing and replaced them exactly the way they were. These wires run very near the exhaust manifold in multiple places and can easily close enough to burn the insulation off causing the high voltage spike to ground out before it gets to the plug.

 

[Summajet]

I did use motorcraft oem wires. I followed the same wire routing. I will look this weekend for some wire insulators at the junk yard. Last year I put alot of my time and parts into it.
Timing chain, water pump, new radiator hoses, tensioner, rear springs, new shocks front and rear, sprayed underside with undercoating, fuel pump, motorcraft wires and plugs, motorcraft cool packs, and other things. Other than needing to replace the rear main seal and definitely need replace valve covers it is a good truck. I had contemplated selling it and getting a 03 Ford f150 with 5.4 Triton. However I would not know how well the maintenance has been done and be starting all over again.
I have not replaced the 02 sensors and no issues that I know of with them.

 

[koda2000]

The Denso exact-fit wires wires have the same metal heat shielding as the OE wires. As said, the routing is also very important.

Autozone sells single replacement plug wires (at least they used to) if you just want to replace the one bad wire. Bring your wire in with you and get one that has the same ends and length you need.

 

[410Fortune]

USUALLY when you have a code for misfire it is not in the ignition.......it is an injector.
I said USUALLY. In order for the computer to recognize what cylinder is misfiring in the ignition it must go through several drive cycles and calculate exactly when the misfire is happening via the cam sensor...this is pretty rare.
Why? Because these ignitions are waste spark and two cylinders fire at the same time, also there is no feedback for the ignition to the computer for it to detect a misfire in the ignition USUALLY.

So with that said, if my 5.0 had a p0307 code I would suspect the FUEL INJECTOR,
ESPECIALLY if the code comes back right away after being cleared.........

 

[Summajet]

Once I replace the bad wire i will see if it comes back. I have a warranty left on th motorcraft wires from autozone. AutoZone does not sell motorcraft wires anymore. So they will credit me cost of original wire set under warranty. I can either order a motorcraft set from advance or rockauto or get denso from advance. Any other tell take signs of a bad injector, look at tailpipe or should smell gas coming from the exhaust?
Thanks

 

[koda2000]

Once I replace the bad wire i will see if it comes back. I have a warranty left on th motorcraft wires from autozone. AutoZone does not sell motorcraft wires anymore. So they will credit me cost of original wire set under warranty. I can either order a motorcraft set from advance or rockauto or get denso from advance. Any other tell take signs of a bad injector, look at tailpipe or should smell gas coming from the exhaust?
Thanks

Well, I don't think you can blame the shorted/burned plug boot on the wire. It should have a metal heat shield on it and it should have been routed in such a way as to not touch the exhaust manifold. If Autozone will give you a credit you're lucky. My AutoZone will usually take back anything if you ***** loud enough.

 

[Summajet]

I was not saying wire was defective. It does need heat shielding I agree.

 

[Summajet]

I received my motorcraft wires today. Replace the #7 wire and it runs fine now. I am going to replace the valve covers. Looks like the intake will have to come off to get access to the valve covers. Should i use the motorcraft valve cover gaskets or Fel-pro?
Thanks,

 

[410Fortune]

fel pro blue work well!

Glad you sorted out the misfire

 

[Summajet]

Yes, glad it is resolved. I ordered the fel-pro that is the revised version and is more heat tolerant . Debating on doing valve covers myself or pay shop $362.79. Lots of projects and no enough time
Lol