Vacuum erratic when electric fans turn on

[forestb]

A while back ago while I was adjusting my mixture screws on my quadrajet using a vacuum gauge I noticed that whenever my electric fan turned on I noticed that the vacuum would drop slightly and become less stable. Meaning that the needle would jump up and down. Is that normal? It doesn’t seem like it should be doing that. My only thought is that my fans are somehow effecting the power going to my distributor.

[The Rocknrod]

Do you know where your alternator sensing wire is attached? Is it a 3 wire?

[forestb]

No I don’t. I don’t even know what that is. It is a single wire internally regulated single wire alternator.

[forestb]

It sounds like as though that is not the way my vacuum should react when my fans turn on. I am sorry if I seemed harsh when responding to the previous response. I appreciate any help I can get.

[Getter-Done]

Does this happen with the air cleaner on or off the Carb?

If you have the air cleaner off, the extra air flow could cause a Difference,



Do you have 12 volts running to the distributor?

[forestb]

The air cleaner is on. I will check what the volts are at the distributor

[Wrenchbender Ret]

The extra load on the alt. is slowing down the engine enough to efect the vacuum. Try increasing the idle speed a little.
George

[forestb]

So I am getting 12 volts at the distributor with the fan off. It drops to 11 when the fan turns on.

[Getter-Done]

Is the cab grounded to the frame?
And also,
Does the Front radiator support (Have a Great) ground to the frame?

[Wrenchbender Ret]

Do you have a relay in the fan circuit. If not it is preferred to have one.

[forestb]

Originally Posted by Getter-Done

Is the cab grounded to the frame?
And also,
Does the Front radiator support (Have a Great) ground to the frame?

The cab is grounded to the frame. But other than the bolts the radiator support is not. The radiator is aluminum and so is the shroud that the fan is bolted to and the fan is plastic. What is the best way to ground it?

[forestb]

Originally Posted by Wrenchbender Ret

Do you have a relay in the fan circuit. If not it is preferred to have one.

I don’t recall. I will have to take a look.

[forestb]

I looked though my old receipts and the harness that came with the fan does indeed have a relay.

[forestb]

I think that my thermostat for the fan completes the ground. I am wondering if grounding the radiator support will interfere with that.

[cadillac_al]

The fan must draw some juice if it drops voltage to 11 volts. The alternator isn't keeping up.

[forestb]

Originally Posted by cadillac_al

The fan must draw some juice if it drops voltage to 11 volts. The alternator isn't keeping up.

What do you think the solution for this is? More powerful alternator? New alternator? Smaller pulley? Better grounds?

[forestb]

Also do you think that this could cause a random stutter during acceleration?

[kwmech]

Engine running it should read 13.5 volts up to 14.5. Key on engine off 12.5

[The Rocknrod]

I would ensure there were grounds to everything including the alternator to motor and motor to battery, If you radiator support has anything ground to it then by all means that needs a clean ground, including frame, body etc, etc. You can't have power if you don't have grounds.
As far as your alternator please read this article on alternators - http://www.madelectrical.com/electri...hreewire.shtml
They work!

[forestb]

Originally Posted by kwmech

Engine running it should read 13.5 volts up to 14.5. Key on engine off 12.5

Where are you talking about when you say "it"? Where should I be checking it?

[forestb]

I have a frame to engine ground and on that same bolt a engine to frame ground. I also have a engine to frame and a cab to frame ground but no core support to frame ground. I also have a alternator to valve cover bolt ground.

[forestb]

Originally Posted by The Rocknrod

I would ensure there were grounds to everything including the alternator to motor and motor to battery, If you radiator support has anything ground to it then by all means that needs a clean ground, including frame, body etc, etc. You can't have power if you don't have grounds.
As far as your alternator please read this article on alternators - http://www.madelectrical.com/electri...hreewire.shtml
They work!

I will take a look at the article. I think my alternator has a socket for me to use three wires and also just the one wire.

[The Rocknrod]

Originally Posted by forestb

I will take a look at the article. I think my alternator has a socket for me to use three wires and also just the one wire.

When I purchased mine from powermaster I made sure they sent me a 3 wire, sensing type alternator. Since my brackets are powder-coated I also ran a ground from the alt body (in the back) to the engine block, which is also grounded to the battery.
I'd call the manufacturer or look up the part number to make sure if it were me.

[forestb]

Originally Posted by The Rocknrod

When I purchased mine from powermaster I made sure they sent me a 3 wire, sensing type alternator. Since my brackets are powder-coated I also ran a ground from the alt body (in the back) to the engine block, which is also grounded to the battery.
I'd call the manufacturer or look up the part number to make sure if it were me.

How do I go about reconnecting a 3 wire after I have already installed a single wire? Where do those three wires need to go? I just looked at the web sight I guess I have to figure out what type of alternator I have first.

[The Rocknrod]

Originally Posted by forestb

How do I go about reconnecting a 3 wire after I have already installed a single wire? Where do those three wires need to go? I just looked at the web sight I guess I have to figure out what type of alternator I have first.

The link I posted explains it all and why. I'm assuming you have an aftermarket wire harness?