2018 Ford edge significant fuel efficiency loss after Flex plate repair and maintenance

Need help troubleshooting why my vehicle has lost fuel efficiency!
I drive a 2018 Ford Edge for work. We received a ‘dealer customer service’ report stating that there could be an issue with the Flex Plate. The vehicle was already outside the mileage window for Ford to help with any of the cost, however the dealership did an inspection and told us it was in fact cracked and recommended replacement along with tune up and other ‘scheduled maintenance’ due to the mileage (127K at the time).
Due to costs we went to a local auto mechanic vs dealership for the repair.
They replaced the Flex plate (drive plate), replaced spark plugs, Transmission service and transfer case service.
As soon as I received the vehicle after repair - the battery was dead and needed jumped (battery has since been replaced). Then noticed the steering wheel was off lightly and the fuel efficiency had dropped drastically (normal 28-33 mpg down to 23-25 max mpg) When I called to discuss they offered to fix the steering wheel and do an alignment for free and checked that the correct spark plugs were used, but even after that it has not gotten better at all. My understanding is I should get better gas mileage after tune up not worse. I gave it a couple of weeks and a few tanks of gas to see if it got any better.
NOPE. So we opted to go ahead an have the Fuel system service performed to see if that helps as they still have not given any other indication on what could be causing this.
Well nothing has gotten better and I am now on tank 3 since the final service.
Only other services completed during this time was an oil change.

Does anyone have any insight on what could be causing this drop in efficiency? It is costing the company a lot more right now. Could any of the above services have caused damages? Any suggestions on what to try next?

Thanks for your time

Just a thought…
if you normally use synthetic oil and they put in conventional oil it is possible to lose a little in gas mileage. with synthetic oil there is less friction in the engine.

28-33 mpg in an Edge? That’s high, were you measuring it by the fillup gallons, or depending on the readout? Our older MKX never got over 25, averaged under 20. Fuelly reports an average of 21 mpg for the 2018, almost all 25 mpg and under.

Our company always uses full synthetic on our oil changes, but it a good thing to double check. Unfortunately the fuel efficiency went down even before the oil change, just has never gotten better.

Thanks for the suggestion.

I have watched this super close being the only one who has ever driven this particular vehicle. The engine has recorded the mileage at 29 mpg over the life of the vehicle. I do watch it per tank of gas as well and depending on where I have driven being a lot of freeway/interstate I would actually get upwards of 33 and no lower than 28 when I have highway or in town. (screen readout that also tells you fuel efficiency on dash)
I have been loosing about 100 miles per tank of gas than what I was filling up prior.
It is such a strange situation and maybe It was a fluke that it did so well up to now.

Thanks for your thoughts.

If you are using the vehicles gas mileage gauge, then I would stop using that. it can be off. maybe from the battery going dead. An easy way to calculate gas mileage is to remember the odometer reading or to reset the mileage counter when filling up a gas tank. When doing so next time, obtain the mileage accrued between the two gas fill-ups. Then divide the mileage figure by the amount of gas filled the second time to obtain the gas mileage.

also, double check the tire pressure. maybe they lowered it a little to match the factory tire pressure. and you normally keep it at a higher pressure to squeeze out a little better gas mileage.

With all the work that was done, one or more vacuum hoses could be disconnected or incorrectly routed.


also, double check the tire pressure. maybe they lowered it a little to match the factory tire pressure. and you normally keep it at a higher pressure to squeeze out a little better gas mileage.

Good point and I will check that. The mileage calculation is also something I have been doing with each receipt since our company keeps track of mileage on our fuel account.
I appreciate your help

Great thought. I will look into that next.

The flex plate is located at the interface between the engine and transmission, near the transmission’s torque converter. If the torque converter somehow was affected by the flex plate repair, it might not go into lockup mode when it should. Lockup mode is used to improve mpg. The drivetrain computer commands lockup mode at speeds higher than about 30 mph. It can’t remain in lockup mode all the time bc the engine would stall whenever you stopped, so lockup mode is turned on and off as you drive. There’s a wire from the computer to the transmission which commands to the torque converter for doing that, and maybe that wire wasn’t re-connected.

Other things that can decrease mpg, inaccurate coolant temp sensor; problematic coolant thermostat; problematic fuel trim values. All are fairly easy for a shop to test using their scan tool.

That is great information. I will have it checked out with your recommendations and see where it goes from there.
Much appreciated.

If the math is correct, I’d suspect the other services. If the battery was dead though the computer may have lost its memory fir the historical fuel ratio setting. After some driving, the history may recalculate. Or they screwed something else up like wires, o2 etc. to change the flex plate, the trans has to be separated so lots of other work involved and wires to be plugged back like fourth gear or lock up converter that could affect mileage. A diagnostic computer can tell.

The Flexplate (flywheel if you prefer) bolts to the end of the crankshaft flange (opposite the harmonic balancer/vibration damper, the Torque converter bolts directly to the Flexplate (the converter has 4 studs welded to it that pass though the flexplate with nuts used to join the 2 parts together (it’s a Ford thing and maybe others also), no reason to do anything to the converter except push it back in a little to keep it from falling out until ready to install the trany again…

No wires going to the torque converter, the wire you speak of is in the vehicles transmission wiring harness that goes to the trany case plug (pan in this case), the trans valve body has a TCC solenoid that directs fluid flow to the converter clutch in a way that makes it lock up, then reverses or stops that flow to disengage the TCC, the TCC solenoid and the rest of the shift solenoids are all mounted to the valve body and the black plastic cover has the plug that pokes through the side cover pan (for the vehicles transmission wiring harness) and also has all the wiring and or circuitry going to the solenoids, and I think the TCC is in the middle of the row… And before you ask, I don’t have a clue as to what that loose plug goes to at this time and don’t care as it is behind the pan and nothing internal is needed to be messed with to replace a flexplate…

My thought on the fuel mileage decrease is that with the battery going dead the system has not yet relearned your driving habits… You should slowly see the mileage go back up…

But then again I have been wrong before, so that is all I got, NyQuil making it real hard to read what I wrote… :rofl: :face_with_thermometer: :man_facepalming:


Of course you are correct, not a simple thing to attach a wire to something that rotates … lol … I clarified the functionality above.

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