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Kenny Z.
Kenny Z., Ford Senior Master Tech
Category: Ford
Satisfied Customers: 5333
Experience:  Auto Trans, Drivability and Electrical Specialist
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We have an 2005 Ford Expedition 4wd, with the 5.4 engine.

Customer Question

Hi, We have an 2005 Ford Expedition 4wd, with the 5.4 engine. The problem it is having is when you start the car cold it runs perfect until it warms up then it starts missing and running real rough. But if you switch it to 4wd low it quits missing immediately and runs perfect but the second you switch it back to 2wd it immediately starts running rough again. I had heard that maybe it could be a vacuume leak. We did recently have the timing chain and cam phasers replaced. Any help would be apperciated.
Thanks, Mike
Submitted: 1 year ago.
Category: Ford
Expert:  Kenny Z. replied 1 year ago.

Hello Mike, my name is***** and thanks for your question.

When the vehicle is in 2wd there is full vacuum to the front hubs to keep them released. When switching to 4x4 or 4x4 low vacuum is removed to allow the hubs to engage. There should be no difference between 4x4 or 4x4 low as the vacuum routing is the same. I would be more inclined to suspect the misfire goes away in 4x4 low due to the powertrain control module default operating strategy is different then when in 2wd or 4x4 high due to engine load calculations. At his point I would ignore the 4x4 low issue and just concentrate on the misfire itself.

At this point you need to have the powertrain control module (PCM) tested for codes to see which cylinder is misfiring or if the PCM is going into load limiting strategy due to a fault from an input in the system.

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Expert:  Kenny Z. replied 1 year ago.

Hello again,

If you need further assistance please feel free to reply and we can continue. Otherwise please take a moment to rate my answer as you see fit. After rating, the thread is still available should you need further assistance.

Thanks,

Kenny Z

Customer: replied 1 year ago.
I installed a new battery and it is idling fine now in both 2wd and 4wd, The only problem it has now is when your are driving it and press gas to go up hills it fills bogged down with no power like its restricted. On an old school engine it would be like its starving for air. If it is idling and you punch the gas it stumbles and then is fine reving on up. Like on an old engine it would be like the bad accelerator pump. You can slowing press the gas while idling and it doesnt stumble and when driving and its fine if you are not trying to give it to much gas. I changed the fuel filter and the air filter, didnt help. No Check engine light either. Any ideas? Thanks, Mike
Expert:  Kenny Z. replied 1 year ago.

These engines are notorious for loaded engine misfires from the spark plugs breaking down under load. How many miles on the spark plugs?

Expert:  Kenny Z. replied 1 year ago.

Hello again,

If you need further assistance please feel free to reply and we can continue. Otherwise please take a moment to rate my answer as you see fit. After rating, the thread is still available should you need further assistance.

Thanks,

Kenny Z

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