Poor 5.4L acceleration with A/C on
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Joined: Aug 2006
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Poor 5.4L acceleration with A/C on
I'm new to this forum and hope I can find some help. I have been working on cars for quite a few years but my 01 5.4L Expedition has me stumped. It has real poor acceleration at all times but only when the A/C is on. You have to mash the pedal to the floor to get it to move. Turn the A/C off, it runs great, excellent acceleration, no hesitation at all and good as you can get fuel economy for a 5.4L. I have a K&N air cleaner and replace 1 failed coil. My OTC scanner has no codes and no pending codes. Datastream shows o2's switching and fuel trim is good. I'm realy stumped. I pulled the upper intake thinking a port may be blocked with carbon, nope. The throttle body is as clean as a whistle, EGR and DPFE are working properly. Truck just turned 60k, is in excellent condition. I'm thinking about replacing the other 5 coils before I trade it in just because of frustration! Any help would be great. Thanks.
Post Fiend
Joined: Jun 2003
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Welcome dyurkosr!
I'm afraid I don't have a specific answer to your question, but perhaps one of other forum members can help.
Let me ask you this though: With the AC running (MAX AC will insure that) begin a moderate acceleration from a dead stop. When you are in the middle of second gear, turn the AC off. Do you feel a surge of power?
Try applying moderate pressure to the accelerator pedal and try switching the AC on and off. Does it make as big a difference as you are indicating? If so, the only thing I can think of is that the AC compressor is putting a greater than normal load on the motor.
I'm afraid I don't have a specific answer to your question, but perhaps one of other forum members can help.
Let me ask you this though: With the AC running (MAX AC will insure that) begin a moderate acceleration from a dead stop. When you are in the middle of second gear, turn the AC off. Do you feel a surge of power?
Try applying moderate pressure to the accelerator pedal and try switching the AC on and off. Does it make as big a difference as you are indicating? If so, the only thing I can think of is that the AC compressor is putting a greater than normal load on the motor.
Senior User
Joined: Nov 2003
Posts: 467
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From: Where the war is...
Same thing happens to mine, I have an 00 and about 67k miles on it, 5.4 I did the test hkiefus suggested and you can definitely feel the surge when you turn the AC off during acceleration. It just seems so weird that a compressor would load it down that much; didn't it used to be that the older cars had a vacuum switch that would cut off the compressor for a couple of seconds during acceleration, just seems our trucks would have the same kind of programming in the system. What do you all think?
Senior User
Joined: Feb 2004
Posts: 163
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From: Columbia, SC
Our 98 5.4 has the same symptom, it is really loaded down only with the ac on, it pulls a 5000 lb boat with the ac off easier then no trailer and driving with the ac on...how weird
I cannot believe a little ac compressor takes more energy then a 5000 lb boat
I cannot believe a little ac compressor takes more energy then a 5000 lb boat
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