2007 Ford Five Hundred - shudder/stutter/hesitation only at certain RPM & load

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May 29, 2020
I have a 2007 Ford Five Hundred/Mercury Montego, FWD and 6 speed Aisin. 147,000 on the clock.

I am experiencing a issue where I feel a light hesitation only when in a certain RPM range (1,000-1,300) and the engine is under load. For reference, this is around where I'd be driving in the 30-40 MPH range and I think I'm either in 4th or 5th gear. It's right around the load range in which you'd be expecting a downshift at about any moment.

If I floor it from a complete stop, it takes off quickly and shifts through out the gears perfectly with zero noticeable hesitation/shudder all the way to to 80 MPH.

I have NO check engine light and no pending DTC's.

Here's a list of what all I've replaced/serviced at this point:

- Plugs (OEM Motorcraft)
- Coils (OEM Motorcraft)
- Cleaned throttle body very thoroughly.
- Fuel filter (Wix)
- Fuel pump was replaced about 12 months ago with an OEM style Walbro. Didn't replace the basket and sending unit, just the pump and reinstalled.
- Dosed the fuel with Berryman's B12.
- Ran down the tank to nearly empty, refilled.
- Treated the intake with Berryman's B12.
- Cleaned MAF sensor with electronics cleaner and very light shop air.
- Checked air filter, blew out with shop air. It's relatively clean.
- Have checked for vacuum leaks, cannot hear or notice any.
- Flushed transmission with Valvoline MaxLife (TI-V rated), the old fluid was nasty and was flushed maybe 40,000 ago. I did not do a drain and fill. I disconnected cooler lines and let the transmission pump out the old fluid into a pan as I poured fresh in the fill tube.

Anyone have any ideas of what's going on? I hate to keep loading money in the parts cannon, but without a trouble code I'm kind of flying blind.. I've even datalogged the STFT and LTFT's and don't note any anomalies.

Right now I'm leaning towards the shudder being a product of the transmission or torque converter, perhaps - or perhaps a fuel injector is getting lazy. I haven't noticed any transmission slipping though, and I feel like it would really manifest itself when I floor it from a stop, but it doesn't.
Could be the DPFE Sensor
“DPFE” means “Differential Pressure Feedback of EGR”. It’s also referred to as "Delta Pressure Feedback of EGR", with ‘Delta’ meaning "difference" or "change". Regardless of the acronym’s definition, the DPFE Sensor reads changes in the pressure of the EGR system.

When a DPFE sensor begins to fail, it provides the PCM with bad/inaccurate data. This is because it is less sensitive and the PCM thinks less recirculated gas is being burned than is actually so. When this happens, the PCM adjusts the flow of the gas as a means of compensation and winds up opening the actuator too much. This results in too much EGR coming in and combing with the air which, in turn, leans out the fuel mixture. The result is the truck misfiring, stumbling, or hesitating. This system typically degrades over time and so is often hard to diagnose right away. It might start failing weeks ahead of the “check engine” light actually going on.

This information is borrowed from https://www.ford-trucks.com/how-tos...-are-the-symptoms-of-a-bad-dpfe-sensor-561275
Honestly for the speed and load range it sounds like the right conditions for torque converter shudder. Best cheapest option that I've had good luck with is a tube of shudder fix, but might only be a bandaid for a failing torque converter clutch. Otherwise the only way to correctly diagnose it is a scanner that can read transmission data and either find a tcc slippage pid or start comparing speed sensor pids when the converter is commanded locked.
I have a Ford Five Hundred, which was been a great car.

My recommendations.

First, check the Engine Mounts. Mine were shot, and it was causing the car to shift strangely. Once I replaced this bushing, the transmission actually lost a strange stumble and is much smoother.

I also replaced the lower front engine mount with a crow foot wrench.

Second, I replaced the transmission fluid with Redline D4 ATF (you can drain at the bottom, and then refill through the dip stick tube). This smoothed out shifts quite a bit.

Good luck.
You need to fire up FORScan, look at Mode 6 misfire data
Short/long term fuel trims
Is the MAF reporting evenly and cleanly

You've been more than thorough, but there's a little more info on the table to be interpreted

A smoke test is best for vacuum leaks, and the Duratec plastic upper plenum is known for them

If the fuel trims are out of line, could consider sending the injectors to a reputable flower tester & cleaner (we have one here on the site)

Or just pour in some Shudder Fix, I guess it can't hurt?
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