Theft light blinks and engine misses
Senior Member
Joined: Jul 2004
Posts: 6,200
Likes: 39
From: Easton, Pa.
Some one mentioned alternator whine.
It may or may not be the antenna ground but if a 'rectifier' stack is going bad in the alternator it may cause excess wine in the AM radio.
I had the antenna issue and AM was picking up the PCM and it's micro processor signals that sound quite strange.
.
An advanced way to test for an 'alternator' issue at the battery is to use a voltmeter set on the AC scale and look for lower AC voltge response on the meter.
Normally there should be very small to no AC showing in the millivolt range.
With the meter in the AC mode it should not respond to the 14 volts DC only the AC riding on the DC. The meter seperates the two and displays only the AC part.
The radio will be sensitive to the AC on it's 14 volt feed if the amplitude is high enough and vary in frequency as the alternator changes rpm..
This is not a signal that is picked up by the antenna.
.
For after market radios mounted external such as Ham or CB, alternator whine may be an issue.
The way out of this is to make your own filter with a large threaded link from the hardware store acting as a 'core', 20 feet +/- # 10 wire from the auto store wound on this core, a 3000mfd + Capactor at 25 volts or more from Radio Shack to ground at it's output end grounded to the chassis, and a project box to house it all in plus connectors and inline fuse from the battery to the filter to the unit being powered.
This filter will handle 30 amps or more of current most store unit won't depending on the fuse size providing current being drawn outsid the limit of the filter wire.
Good luck.
It may or may not be the antenna ground but if a 'rectifier' stack is going bad in the alternator it may cause excess wine in the AM radio.
I had the antenna issue and AM was picking up the PCM and it's micro processor signals that sound quite strange.
.
An advanced way to test for an 'alternator' issue at the battery is to use a voltmeter set on the AC scale and look for lower AC voltge response on the meter.
Normally there should be very small to no AC showing in the millivolt range.
With the meter in the AC mode it should not respond to the 14 volts DC only the AC riding on the DC. The meter seperates the two and displays only the AC part.
The radio will be sensitive to the AC on it's 14 volt feed if the amplitude is high enough and vary in frequency as the alternator changes rpm..
This is not a signal that is picked up by the antenna.
.
For after market radios mounted external such as Ham or CB, alternator whine may be an issue.
The way out of this is to make your own filter with a large threaded link from the hardware store acting as a 'core', 20 feet +/- # 10 wire from the auto store wound on this core, a 3000mfd + Capactor at 25 volts or more from Radio Shack to ground at it's output end grounded to the chassis, and a project box to house it all in plus connectors and inline fuse from the battery to the filter to the unit being powered.
This filter will handle 30 amps or more of current most store unit won't depending on the fuse size providing current being drawn outsid the limit of the filter wire.
Good luck.
Last edited by Bluegrass; Nov 30, 2012 at 10:49 PM.
Senior Member
Joined: Aug 2005
Posts: 149
Likes: 0
From: Tomball
05 F 150 5.4 with 155K miles. I have had the same issue since the truck was new. I have changed plugs and coils over the years, but the problem persists, and the loss of power seems to be getting worse. I notice the red light/loss of power most often when disengaging the throttle. I will occasionally be driving along at 55 mph and will let off the gas. Maybe 1-2 seconds after raising my foot and I am coasting, the nose of the truck will drop and the light comes on. This lasts for maybe 5-10 seconds. I can get back in the throttle with the light on and the truck accelerates, but not as smoothly or quickly as it would normally.