Transmission slipping/misfire solved, P0300 2007 Ford Explorer 4.6L 3-valve

[fireinsyde]

I'm posting this solution to "pay it forward" for all the posts I've utilized in the past.

2007 Ford Explorer XLT with 4.6 L 3-valve engine, with 6R60 6-speed transmission.

Radiator was leaking a year ago, so I changed the radiator. Disconnecting the transmission lines to change the radiator meant that I had to top off the transmission fluid level when the job was done (a chore in and of itself in these trucks.) I did that.

Around that time, the truck began to "slip" or "lug" or "stutter" on the highway while in 5th or 6th gears only, and when accelerating between 50MPH and 70MPH. The problem was worse when climbing a hill, and went away completely if you either hit the gas hard to downshift the transmission, or when you shut off the OD, and caused the RPMs to rise that way.

No OBD codes were ever triggered.

After a lot of research, it seemed very similar to a "torque converter lockup shudder", and other transmission problems which are caused by incorrect fluid levels. These transmissions are VERY sensitive to improper levels, and can lead to slippage with as little as 1/2 quart underfilled or overfilled.

I spent a very long time alternating between a filler hose and a vacuum gun trying to get the transmission fluid to a perfect level (I used the correct motorcraft Mercon SP). What was DRIVING ME CRAZY was that each adjustment of transmission fluid in half-quart increments would change the nature of the slipping problem. It would improve slightly, or even by half, and then with another adjustment of fluid, would then get worse again. The fact that fluid adjustments led to changes in the slippage problem had me convinced beyond all doubt that the problem was the transmission. This coupled with the fact that I had drained the cooler lines to begin with.

The problem was not the transmission. It was spark plug misfire. After months of this, the truck FINALLY threw a P0300 code, and only after I revved it to 6,500RPM while passing on the highway.

Research showed that transmission slippage, torque converter shudder, and spark plug misfire all give a very similar feeling, and are mistaken for each other all the time.

I changed all 8 coils and plugs, and the problem is gone.

As for the confusing fact that the transmission level actually improved or worsened the problem...all I can figure is that the lower or higher fluid level affected the slippage in the converter, thereby putting greater or lesser load on the engine as I adjusted the fluid level, and it changed the conditions of the misfiring.

And it is the world's most incredible coincidence that the problem started right around the time I disconnected the transmission lines.

It was a tricky one. The moral of the story: if your transmission is slipping or lugging, consider changing your plugs and coils.

Good luck.

 

[07EddyB]

That's a pretty common thing - blaming the transmission for bad coils. I have a somewhat similar story - I had very similar problems but could not get a misfire code from the engine. I decided around that point to change the transmission fluid and filter anyway since the Ex had 100K on it. After several runs and draining some fluid I got the level right. I haven't had problems since. So - it really was the transmission then right?
No.
The difference is that now my transmission is more willing to downshift then it was before thus my engine isn't lugging as much as it was so the coils are happier. I know I should throw a set of coils at it but I just don't want to throw that money at it now. I figure not all of them are bad and I can play the waiting game to see what eventually fails.

Oh - and welcome to the board. You have done what may be an internet first - posted a solution on your first post as opposed to a question. It's at least very rare. Thx.

 

[explorer1007]

I guess I have similar problem as yours. My car would stutter when climbing a highway ramp but it goes away when I step on the gas pedal to push it. I thought my transmission was going so I changed the fluid 2 weeks ago. The fluid was a bit low but wasnt a problem. The stutter is still there.

I'm about to change all plugs and coils, was it easy for you? Any broken plugs? Mine were changed about 85k back in 2012 and now it is 165k. The plugs from 2012 shouldn't break right?

BTW, my coils are originals. I bet they are about to go bad.

 

[boominXplorer]

In my experience these plugs for the 3v v8 are only good for about 60k. #3 coil is common to have water in it from the cowl clip in a 4th gen.

A lot of people spend a bunch replacing the coils when they don't need it, the issue is in the boot ($7 vs $70). If you have a solid miss all the time, yes you likely have a bad coil. If it's intermittent or under high load / low rpm then it's likely moisture in the boot. You also need to check the terminal at the bottom of the coil for rust if extreme moisture is present.

If the plugs have been changed before you likely have a revised set and hopefully the last person put anti seize on the tips. Only use Motorcraft plugs.

 

[Explorer_PL]

Welcome and thank you Fireinsyde -

Yes, this is what typically happens with the 4.6/6r60 combo.
I can attest to it after owning my 06 for close to 12 years and after 266k miles.

Many times I was certain it's time for a new tranny only to finally get the 300 error and after replacing coils or plugs all was back to normal.
Those 6R's are very reliable when properly maintained. Mine stil shifts same way as 12 years ago.

 

[fireinsyde]

I guess I have similar problem as yours. My car would stutter when climbing a highway ramp but it goes away when I step on the gas pedal to push it. I thought my transmission was going so I changed the fluid 2 weeks ago. The fluid was a bit low but wasnt a problem. The stutter is still there.

I'm about to change all plugs and coils, was it easy for you? Any broken plugs? Mine were changed about 85k back in 2012 and now it is 165k. The plugs from 2012 shouldn't break right?

BTW, my coils are originals. I bet they are about to go bad.

I got 7 plugs out whole, and the last one broke. I used the method of soaking them with PB Blaster penetrating catalyst, and it works great. Soak them (literally fill the spark plug cavity half full of PB Blaster,) then crack them each 1/8 or 1/4 turn, or however far they will move, and then soak them some more! Let it sit for several minutes. And go back and forth between any plug that will budge with minimal force. It's a game of backing them out 1/4 turn at a time, until they hang up again.

And of course, once the whole job is finished, change the oil.

Most likely one of them will snap, but you can get the Lisle extractor tool set on eBay for $40 ahead of time ($90 at NAPA), and have it ready. It works great.

Many suggest getting the engine hot before doing this whole procedure.

To save money, I bought MSD Street Fire coils from Summit Racing. MSD is a top-of-the-heap name in ignitions, so I trust them completely. $168 for all 8 coils. Take note, they have different sets for 3-valve and 2-valve engines.