Hesitation when accelerating

Tiny
TOOT8676
  • MEMBER
  • 2008 FORD EXPEDITION
  • 5.4L
  • V8
  • 2WD
  • AUTOMATIC
  • 187,000 MILES
Vehicle randomly decelerates when accelerating, rough idle, bad fuel mileage, almost the way it feels when running out of gas. I have replaced MAF and CAM sensor, throttle body, and a new PCM, fuel filter. Ford had a recall on this year's 5.4L engine that was not done on my vehicle, so when changed the PCM. After replacing PCM, it still continues to stall/hesitate when accelerating. We have checked fuel pressure and it was right. 90% of the time only does it after going high speed, when I have to stop (coming off interstate) it stalls or hesitates. But before the PCM was replaced it was anytime the vehicle stopped or idled for a few minutes. Never threw any codes until last week, then replaced the PCM. Everything is clear and scanner showing that everything is working properly. It is not.
Tuesday, July 3rd, 2018 AT 9:56 AM

3 Replies

Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 51,500 POSTS
Can I ask how the engine stalls? Is it gradual or does the car shake like you are stopping a manual transmission car without pushing in the clutch pedal?

Here is a guide that can help:

https://www.2carpros.com/articles/stall-at-idle

Let me know, Cheers, Ken
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Thursday, July 5th, 2018 AT 12:08 PM
Tiny
TOOT8676
  • MEMBER
  • 2 POSTS
I guess it is more of a bog, the way it feels and acts when running out of gas, or how a clogged catalytic converter would do (they have been checked). The 5.4L does not have a EGR valve, and all the vacuum lines do not appear to have any leaks.
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Thursday, July 5th, 2018 AT 12:39 PM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 51,500 POSTS
I have seen engine coolant temperature sensors do this they can get super heating and short out then cool slightly and start working again. This issue does not stay long enough to trigger a code but causes engine problems. Here is a guide to help you see what you are in for when changing the sensor out:

https://www.2carpros.com/articles/coolant-temperature-sensor-cts-replacement

Check out the diagrams (below). Please let us know what happens.

Cheers, Ken
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Friday, July 6th, 2018 AT 9:42 AM

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