I have a white 2004 F-250 XLT extended cab 4X4 with the 8’ bed, 5.4 engine. A few months ago when I start up a hill the ABS light on the dash comes on for 3 seconds and the speedometer dips 20-30 mph simultaneously. I don’t feel any braking take place or see any change in rpm. The inconvenience is when I have the speed control on and this happens it turns off. Recently it is happening more often and not only climbing a hill, seems to occur when there is slight acceleration and the rpm’s are between 1.5 and 2.0. My mechanic says the computer is not registering any error message. He changed out a sensor in the rear end with no success, he even asked some mechanic friends at the local ford dealer who also have no idea what could be causing this. Please help, I really like this truck. My other car is a 74 super beetle and as much as I like to drive the bug, the truck makes me feel big and important. Thanks for your time.
Manual transmission or automatic?
I assume the mechanic changed out a speed control sensor which is what I would have suspected first myself. The real trouble though may be a bad connection somewhere in the wiring to that sensor. By reconnecting all the connectors to the sensor it may clear up the trouble.
Another possible trouble area may be the alternator. It may be generating excessive noise at certain RPMs. To eliminate that possibility you could just remove the wire connection to rear of it and then take a test drive while the alternator is disabled. If the trouble doesn’t occur then the alternator may be the problem.
He said he checked all the connections, I will try the alternator disconnect and let you know what happens.
If I was working on this issue I would want to monitor the sensor signal before and during the occurance of the problem to verify things. A voltmeter may do the job or it may take a O-scope to check it.