RPM reduces then Alt goes low and rebounds
Thread Starter
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Junior Member
Joined: Jan 2005
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RPM reduces then Alt goes low and rebounds
1994 F150 4x4 111000 MILES
I replaced the Starter, it was bad;
I replaced the batt, it was old;
I replaced the Alt, it appeared that it was bad.
Symptoms: High speed 45 to 75 mph; slow down to stop, the RPM's are reducing and then the alt slips below the charge mark and then the rpm's rebound slightly and the alt moves to the charge mark. Once in awhile the engine will stall when coming to a stop. Sometimes the lights will dim but in general terms the rpm's reduce since I am slowing down and it appears that the charger dips low, and because of that then the rpms'swing back up again. Sort of like a rubber band effect. If I turn the lights, heater or AC and other acc off, it is not very noticeable.
I am thinking some rounding issues, but am open to many more suggestions. This problem has happened before and after the items above were replaced. Thx
I replaced the Starter, it was bad;
I replaced the batt, it was old;
I replaced the Alt, it appeared that it was bad.
Symptoms: High speed 45 to 75 mph; slow down to stop, the RPM's are reducing and then the alt slips below the charge mark and then the rpm's rebound slightly and the alt moves to the charge mark. Once in awhile the engine will stall when coming to a stop. Sometimes the lights will dim but in general terms the rpm's reduce since I am slowing down and it appears that the charger dips low, and because of that then the rpms'swing back up again. Sort of like a rubber band effect. If I turn the lights, heater or AC and other acc off, it is not very noticeable.
I am thinking some rounding issues, but am open to many more suggestions. This problem has happened before and after the items above were replaced. Thx
Senior Member
Joined: Jul 2004
Posts: 6,200
Likes: 39
From: Easton, Pa.
It's not the charging system doing it but to the extent the alternator stops outputting, this take a small load off the engine that affects the idle rpm.
You have some other fault causing the idle problem.
Dirty throttle body, small EGR leak or ???
Any codes?
You have some other fault causing the idle problem.
Dirty throttle body, small EGR leak or ???
Any codes?
Thread Starter
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Junior Member
Joined: Jan 2005
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I have not checked for codes lately. Although when I did there were no codes. I can check again, but I will investigate the EGR leak and dirty throttle body issue. The egr leak would be near the egr valve or elsewhere?