When I turn my cooling fan on, the lights dim, the pump slows down, and most importantly, the engine rpms DROP!

Im running an msd 6al and A1000 fuel pump, thats it. No electric water pump, no stereo, and only the single stock fan. The alternator is new.

I see 13.4 volts at the pump, and 13.1 when I turn the fan on. My battery is pretty old, could it be that?

 

sounds like it is getting worn out.
The factory one for that year is about a 95A version, so i'm not sure you really need a higher amperage alt, maybe just a new one.

It's not the battery.

How's your wiring from alternator to battery? And battery to fan?

 

Its a pretty new alternator. About three years old and only maybe 300 miles. I did buy it in Germany, and probably bought a cheapie. I think its made by sun---- something.

Wiring from alt to battery is some pretty thick wire I made up, but peiced it together with a large galvanized cable clamp. It was something I did a while ago and never thought about it. I do remember checking resistance on it and didnt get any.

Battery to fan is factory except for a relay I put in.

I can't understand why my rpms drop from a loss of .3 volts.

 

how are you measuring the 13.4 and 13.1V multimeter?
If you turn absolutely everything off, what is the voltage?
13.x on the battery is low, I would hope for 14.4V. You might have a dicey alt.
Is this serp drive? Normal pulley size on it, and on crank/waterpump?

 

A cheap multimeter yea. Everything off, what do you mean? Fuel pump off?

Serp drive, normal pulleys all the way around.

I'll check voltage right at the alternator and the battery next time I fire it up. Couple days, doing some supercharger repulleying.

 

ok, no not the fuel pump
head lights off, fan off, big stereo off, etc.
Should be showing 14.4 V.

How about your batt to ground wire? Engine block to ground?
If those are fine (clean connections, check for breaks etc), then i'd be replacing the alt.

 

Oh yea thats with everything off, no stereo installed. 13.4 at the fuel pump. I'll get a reading at the battery, might be different. I've done it before but dont remember, dont think it was in the 14's.

Grounds are perfect.

I'll look up what alternator it is, check volts at alternator.

I'm going to need as many volts to my pump as I can get when I switch to E85 is this is pretty important. Thanks sonix. I'll get back in a couple days.

 

Got 14.3 at the battery today. Read 14.0 with the fan on. The power for the relay is straight to the battery, power for the MSD is right off the alternator.

The rpms dropped 200 when i switched the fan on. After the fan was on for a bit, I turned it off and the motor only raised maybe 50 rpms, then 50 again when I switched the fan back on.

I'm so confused here why my rpms would drop. Either losing spark power or its putting a lot of strain on the alternator maybe?

 

Your sig states a carb, correct? In this case there isn't any idle speed control. Increasing the load on the engine will drop the idle RPM. The idle will also vary some with manifold and air inlet temperature. Then again with minor changes in the closing of the throttle blades.

A mech distributor can also change timing a bit with changes in temperature and idle.

RBob.

 

How does turning the fan on tie into that?

 

It takes power to spin the fan, so turning on the fan increases the load on the electrical system, which puts an increased load on the alternator, which then takes more energy to turn, and puts an increased load on the engine.

 

200 rpms though? I was surprised to see that my voltage only dropped .3 with the fan on.

I feel like I should be tuning my carb now with the fan and headlights on.

Its only a stock fan, but did they have two speeds from the factory? Or is it just on and off? Is it supposed to be resisted at all? The thing does pump out some air. Cleans the garage floor off.

 

At idle your engine isn't putting out much power. The increased load from the fan is a very large percentage of the surplus power available.

Factory fans are one speed.

 

Ok, I won't worry about it then and just tune accordingly if it drops too low on any given day. Thanks for the help.

 

A better alternative is to use a throttle kicker so you never have to worry about it.

 

Whats that? I have a guess.....my hood is dzus'ed on and not fun to take off by myself.

Ever see those manual ***** in the cabin for idle? One of those would be very nice. But I cant seem to use the right words to find a setup.

 

It's a solenoid that'll open the throttle very slightly to raise the idle speed. Holley makes an expensive universal one, but they were factory equipment on all sorts of vehicles, especially ones that came with A/C.

 

A **** sounds cheap and maintenance free, and light. Ever seen or heard of anyone rigging one of those up? I also dont have a throttle stop on yet, maybe I could integrate it into that.

 

You've already got a feature in the interior for manually controlling the speed of the engine.

 

Well I like to set my idle as low as I can because my supercharger sounds like a jet plane at certain idle speeds, the lower I get it the better, but on various days of humidity and temperature its a pita to change the idle.

I did find a "hand" throttle but its a lever, I dont think thats very safe in a 700+ hp car.