engine speed vs electrical output (c900)

- J
- John B
  
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posted
20 years ago

Sun, Apr 4, 2004 6:21 PM

Hi,

Recently I noticed an electrical phenomenon in my c900: a correlation between engine speed and electrical output. For example, the headlights dimming when the AC is switched on. Also, the cabin heating/cooling fan running more slowly when the engine is at idle, and speeding up when engine is revved. The car always starts with no problem, and the battery reads slightly over 12v at rest. Could this indicate an impending alternator problem, or is it pretty much normal?

Thanks,

John

1992 900s n/a

- G
- Grunff
  
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posted
20 years ago

Sun, Apr 4, 2004 6:50 PM

The voltage will vary between ~11V and ~14.5V depending on the load. Perfectly normal.

- L
- Lance Morgan
  
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posted
20 years ago

Mon, Apr 5, 2004 5:53 PM

Does your battery icon/alt dash warning light come on when you turn the key to the run position, prior to starting? The dash bulb is good? and not lit while driving

With engine off, and no surface charge (turn on headlights for 15 sec or take reading +4 hr after engine shut down), good batt should read

12.6V or more. 12.4 is approx 75% charge, etc. 12.2V is 50%, drops quickly w/just a tenth or two.

Batt/alt V output should be approx 13.8V - 14.2V with engine running (usual voltage range: it can be outside that at times but that should be short-lived). Shouldn't be much difference between batt and alt (ideally close to 0V diff, certainly no more than 0.7V)

Or can have your batt and alt load tested, w/latter including amperage output at given RPMs

If dash light is out, and new one comes on when driving, more suggestions can be provided

With A/C on, your ECU should receive appropriate signal from switches/sensors to bump up idle RPM slightly

Lance