Electric fan changes air fuel ratio, huh?

[Gregs672000]

HI electrical experts, got one for ya... yesterday I watched my air/fuel ratio change from 14.1 or so at idle to 13.5 or so when the electric fan switched on and for as long as it ran, with corresponding engine idle smoothness changes. Back to normal when the fan shuts off. Volts drop from 14.4 to 14.1 on my meter with the fan on (GM 1 wire 65amp alt). Since the engine changes, it must be pulling power that influences the ignition system (?). Newer non stock wiring throughout, and remember I run a mega jolt system, but it has a dedicated ground and I've cleaned all of them throughout the car (maybe not the fan switch though?). Haven't looked closely yet to see where I'm pulling power for the mega jolt controller, but how could that influence the coil pack output as it seems to? Any ideas?

[jhayden]

Greg,

While we wait for the experts to respond, you are running fan power through a separate relay, aren't you? Also, how many amps draw is your fan rated for?

Jon

[redroadster]

Lets clarify ...Im not sure exactly what your saying it looses power when it does this?
The engine ( in a 311? With a mega jolt ign ) lugs slightly when the radiator fan ? Kicks on and drops .3 volts
At idle ?
The alt gets hard to turn with elect. Load
You're going to have more voltage with lite load
Amps = elect. current flow
Volts = measurement of elect power
A redundant ground test to the fan would be worth doing
Plus a amp draw test of the fan as well as alt. & batt.
It may be discharging amp wise ( its still 14 v ?)
A high amp draw like a fan usually needs a capacitor for the startup or it can zap other accessories
Mega jolt have a I C. in it ? probably , got to watch mil amp draw on that

[Datrock]

Could it be as simple as when the load from the fan kicks on, the voltage drop is not igniting the one wire alt to energize so you have a voltage drop from the fan's amperage load. Possibly the alternator is taking a load from the fan but not getting the needed amperage back into the system. Is your one wire GM alt wired directly to the battery or thru the harness? It would be good to hear from other GM alt users to see if they may also have idle drop when the internal VR ignites to start charging.

[Gregs672000]

Thanks all, I have a few other things on my mind at the moment so I'm not digging in too far yet, but 1) not sure on a relay for the fan (probably not) 2) alt is self exciting and active per all meters, showing 14.4 volts at idle then drops to 14.1 with the fan on. If it weren't for the fact that the engine itself changes I'd assume that the air fuel meter is reading wrong or somehow influenced by the voltage drop, but the engine does change. Maybe I can post a video at some point...

[jhayden]

Greg,
The consensus is that a good quality relay is a really good idea on any high amp draw electrical device. Since most fans pull a minimum of 15A, they qualify. I run them on both our cars, and it keeps the high current loads confined to the engine bays rather than running through the firewall. When the fans kick in, the load is on the battery, and the switch load is negligible, thus helping to prevent any drop in current to sensitive equipment.
Jon

[redroadster]

How hot is it in tacoma ?
magnetism goes down as the temp rises. Like the fan blowing on to it at idle .
How is fuel ratio being determined ?

[Daryl Smith]

Could be as simple as the extra load on the engine, pulls the rpm down a bit into a different ignition setting.
Have you tried putting a timing light on it to see a change in timing?
If you are still getting 14 volts, I doubt it is affecting the actual spark, just more load on the engine, requiring slightly more horsepower from the engine....How that interacts with the ignition I can understand with rpm/vacuum, but, what the interaction with the carb...? maybe someone else has some insight?

[JT68]

I bet the O2 is correct. Its prob just due to load and rpm difference. If it was closed loop, within milliseconds the ecu would make the correction, but with carbs you are simply at a less efficient (more rich) operating point. Seriously doubt the wideband cares about minor voltage changes-anyone designing instrumentation knows to use regulated current sources making them immune to large changes in supply voltage. EEdesign101.

[garth]

I bet the O2 is correct. Its prob just due to load and rpm difference. If it was closed loop, within milliseconds the ecu would make the correction, but with carbs you are simply at a less efficient (more rich) operating point. Seriously doubt the wideband cares about minor voltage changes-anyone designing instrumentation knows to use regulated current sources making them immune to large changes in supply voltage. EEdesign101.

I'll double down on JT's explanation. I have a A/F ratio meter on my car and it is insensitive to voltage change between 11.5 and 15.5 Volts. I was curious about it's performance so warmed it up and ran at a constant 3000 rpm resulting in a steady A/F ratio = 13.9 at a ambient temperature of 18C. I use this as a crude benchmark reference for engine tune. At 3500rpm changing the nominal 12V supply by turning on headlamps and and fan had no impact on A/F reading. My cheap $20 gauge and sensor appears to be reliable and accurate. I plan to re-measure A/F at 28-30C if we experience a summer here.

[Gregs672000]

Thanks All! I had not considered the extra load on the engine with the draw of the fan at idle. I'll run it at higher rpm and see if it drops then. This discussion may have solved a question I have had for years... I could often get the engine to idle at a steady mid 14's at one stop, then at the next stop it would read mid-low 13's. I thought it was fuel/carb issue, but maybe it's just that the fan was running! Doh! Ha!

[23yrRebuild]

Hi Greg,
FWIW, I use a Hayden electric fan with adjustable thermostat & relay. My GM 1-wre alternator feeds directly to the battery. I have stock SU's, so fuel ratio is not effected by electrical load. My cigarette lighter voltmeter does indicate a voltage does drop when the fan comes on, but the fan switching on does not seem to effect my idle, or lug my alternator due to electrical loading.
Mike

[fj20spl311]

Try disconnecting the alternator and running your test. If it doesn't change the AFR then we'll all know that the load causes the changes.