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Fluctuating Idle With Electrical Load

1K views 5 replies 3 participants last post by  jackjtr 
#1 ·
I noticed this last night and thought I would share.

I had just gotten home from an hour long drive. Engine was running at operating temperature. I had the headlights and fog lights turned on.

I've had a "surging" or fluctuating idle for a while now. It will go between 400rpm and 500rpm every second. Usually, it will fluctuate enough to kill the engine. Last night, it was idling completely smoothly right at 500rpm.

I normally turn the engine off before I turn the lights off, but I turned the lights off first. Immediately, the idle started fluctuating and the engine tried to die like it usually does. Turned the lights back on, and the "normal" idle resumed.

I would logically expect the opposite to happen, where an increased electrical load would cause idle problems, but in this case, it solved them.

What do you guys think? OVP relay?
 
#3 ·
the surging idle is duty cycle adjustments and normal, depending on many things including electrical load. Never underestimate the power of a well brushed regulator, buy 2 and keep one as a spare. While you are at it clean all the ground points at the Brake pump, PS pump, starter and don't forget the big thing: The ignition coil converts plenty of power and can wear out. SO a well sorted electrical system plays well with the duty cycle and these are electrical and rather primitive computers. The alternator draw is substantial with radio and fog lights and head lamps. Throw in AC and wipers and you are in a big negative situation. Funny recall, state of the art PC I had was a 386 DX 16 with 40 mb HD. Windows 3.11 just came out with it and took up 38MB lol, a lot like the current demand on these 80 amp alternators.....
 
#4 ·
The voltage regulator has about 1000 miles on it.

I'm currently not running an O2 sensor, but I have a frequency valve and all of that, so I'm looking into some sort of "manual" O2 sensor input if that's possible. Maybe with a potentiometer....

I really have to get my hands on an exhaust analyzer and set the mixture properly. I played around with it a bit today, but I want it to be precise.

Funny that you mentioned ground points. I had a no start situation after my top end work, and it ended up being the ground strap coming off of the coil to the power steering pump. Who would have thought?

Windows 3.11 was released 4 years before I was alive... earliest I can remember is the "Flying Through Space" screensaver from Windows 98. The Haunted House screensaver was pretty entertaining too.


Sent from my iPhone using Tapatalk
 
#5 ·
Keep in mind that no 02 sensor is going to cause a fluctuation in idle, or at least a significant hunt for idle as the air mixture and various other signals to the ECM Idle Relay, Idle Air valve and Temp Sensor will be distorted. So that is a gentleman's way of knowing that the system is dependent upon signals and sequencing of signals. No signals received may mean inefficient fuel, surging and something else not working properly. HD may be someone who knows exactly, but the O2 is a necessary evil for the entire mix.
 
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