Loss of power going uphill, Check engine light flashing. 2021 Miramar, Misfire

[tomlu_2000]

I hope someone finds this post when they have these symptoms or ANY owner of the 2020/2021 Ford Chassis with the newer 7.3L engine.

• 7.3L engine
• Illuminated MIL with DTCs P0300, P0316, P0301, P0302, P0303 and/or P0304 with a misfire or lack of power

Based on our latest experience, I would highly recommend that EVERY owner of this engine model purchase and replace your spark plug wires before this happens to you! Buy eight plug wires now if you haven't already done so. At least have them in the coach and on-hand because this will happen to you eventually.

Part Number Description Quantity
LC3Z-12286-C Package Contains 1 Piece, 8 Pieces Required Ignition Wire 8

$44 each on Amazon.

If you exhibit these symptoms, ABSOLUTLEY INSIST THAT THIS IS THE FIRST THING ANYONE TRIES. INSIST THAT THE PLUG WIRES ARE REPLACED BEFORE ANY OTHER TROUBLESHOOTING MEASURES ARE TAKEN!

INSIST! I did not and it cost me!

I know this situation really doesn't make a lot of sense, Please, JUST DO IT!

Scenario:

Week of 8/12/24
Leg four of our trip :From Dayton, OH to Erie, PA.

About 2:30 PM the engine light starts blinking as we go gently uphill. The blinking stops on flat or downhill terrain. The engine light stays off mainly, for quite a while. As we get closer to Akron, the situation worsens and the check engine light goes on solid. Blinking check engine light is now blinking almost all the time. I notice a lot less power now and an obvious misfire. We find a local Harvest Host to take us for the night. BTW: Harvest Host is an awesome program. I called a local RV repair shop and to my surprise, they called me back at 7PM! He got us scheduled in at 10AM the next morning; I was very surprised and pleased.

I won't name names here because the mechanic really knows his stuff and everything he said and did made perfect sense. Except he was wrong!; And I was right!

I walked in with a copy of this TSB up on my phone and went though it with the mechanic. :

https://static.nhtsa.gov/odi/tsbs/2020/MC-10183414-0001.pdf

He said it didn't make sense and went on troubleshooting. Replace the plugs and misfire was now only on cylinder 3. Moved plug wires around still cylinder 3 misfire. Compression is perfect on all cylinders. Visual on cylinder 3 is perfect. Finally at 2:30 PM one of the techs decides to swap the left-side and right side plug wires. Viola, the problem moved to the other side. So, he replaces the plug wires and we are out of there around 4:30 PM. Coach runs perfectly.

Lesson Learned:

INSIST theses plug wires get replaced BEFORE ANY OTHER TROUBLESHOOTING steps are taken! INSIST!

Save $$$ - Buy them today and throw them in the coach for when the time comes!

Not doing so cost us $1,500 instead of $400 and a day and a half that we will never get back. We sat out front of the repair shop, on a bench, from 9:30 AM to 4:30 PM, with our poor dog, waiting for parts to arrive and unnecessary troubleshooting to take place.

I hope this post saves someone time and money and prevents another interrupted vacation or adventure.

Thanks for reading!

-Tom



2020 F-53 Motorhome Chassis

• 7.3L engine
• Illuminated MIL with DTCs P0300, P0316, P0301, P0302, P0303 and/or P0304 with a misfire or lack of power

 

[16ACE27]

Thanks for the refresher Tom. But that information about bad plug wires on the 7.3 has been out on this and many other forums since a couple of months after the engines were released into the wild. Your mechanic should have known that from the instant you drove in unless he rarely sees a 7.3 liter and has no subscription service to AllData or similar mechanics information service.

 

[Lt Keefer]

You should post the name of the mechanic so we can all avoid him and his shop. He ripped you off and should be reported to the proper authorities.