Suburban whine

[efc]

HI,
Got an interesting problem.Worked on a 6 month old suburban with 2 batteries to operate all the functions for the FD that this belongs to.Have whine when the vehicle is running and goes up and down just like alternator whine,so I temp. setup the power to both batteries direct with and without an EMI filter. No luck. Suspected that the alternator was the problem and I could not get rid of it. Customer called back and said that the alternatorwas bad, only supplying 90 amps instead of the needed 140.HOWEVER the noise is still there even with the new alternator. Any thoughts?

[Bill_G]

Anything special hooked up, or just plain vanilla radio, antenna, mic installs? The noise could be creeping in on an accy tht is connected to the radio. Could be a ground loop between the mount and the batt neg.

[efc]

No, nothing special,a-plus,gnd, switched ign. that is it.Now they do have other radios in the
console an 800 and a UHF.

[AEC]

Does the vehicle have an isolator connected to the alternator by chance?

If there is one, was it wired properly to separate the batteires from each other while not loading the alternator?

Two batteries tells me there should be an isolator...

Possibly the fusible link(negative) to the vehicle's body is missing as well?

Since you stated both the original and replacement alternator were/are whining regardless, I doubt this would be caused by a faulty regulator circuit in either of the two.

Faulty ground paths, as well as corroded/poor battery connections can cause alternator whining, the trouble is finding it before larger problems arise.

Getting back to the isolator suggestion....Check to ensure all nuts,screws are down tight, and the cables on all connections in the charging circuit are not frayed or making contact anywhere in the engine compartrment.

[Jim202]

May I suggest that you provide the radio or radios that are having this problem. Some radio models are
more prone to this issue than others. There may be a simpler way to solve the problem than jacking up
the vehicle and sliding under a different model.

Jim

HI,
Got an interesting problem.Worked on a 6 month old suburban with 2 batteries to operate all the functions for the FD that this belongs to.Have whine when the vehicle is running and goes up and down just like alternator whine,so I temp. setup the power to both batteries direct with and without an EMI filter. No luck. Suspected that the alternator was the problem and I could not get rid of it. Customer called back and said that the alternatorwas bad, only supplying 90 amps instead of the needed 140.HOWEVER the noise is still there even with the new alternator. Any thoughts?

[efc]

hI

Sorry, the radio is a CDM 1250, pretty good unit. Now the isolater, I will have to check that out.I did
temporarly run the power leads through the open passenger window right to each battery. First one battery
then moved wires to the other battery, to try to use the battery as a "filter".

[Wowbagger]

A couple of checks:

Are you sure it is alternator and not fuel pump? You could try disconnecting the alternator, then starting the vehicle. If the whine persists check the fuel pump.

If you disconnect one battery from the alternator and run the radios off that battery, does the whine continue?

Have you checked the engine grounds? A bad ground could introduce noise.

[efc]

Wowbagger,

Thanks those are some good idea, esp. the fuel pump......never thought of that one. The grounds I thought of after the fact. Maybe
too quick to point the finger at alternator.

Thanks

[Bill_G]

Let us know if it turns out to be the fuel pump. I always thought they were non-variable. I wouldn't expect a whine that goes up and down with the engine to come from a motor with a constant speed, but maybe I don't understand how the fuel pump works. I still think there is a ground loop, but we'll find out.

[efc]

Yea, I will let all of you know, and yea I thought the same about the fuel pump, but with the new vehicles, who knows.

Thanks

[SlimBob]

Let us know if it turns out to be the fuel pump. I always thought they were non-variable. I wouldn't expect a whine that goes up and down with the engine to come from a motor with a constant speed, but maybe I don't understand how the fuel pump works. I still think there is a ground loop, but we'll find out.

Well, the motor will slow down (lug) due to pressure backing up, leading to a lowered tone and a higher current draw.

[Bill_G]

Well, the motor will slow down (lug) due to pressure backing up, leading to a lowered tone and a higher current draw.

That's what I thought - that it pressurizes the fuel rail, but stays at a relatively constant speed that does not change much with engine rotation. However, I am open to the concept that the tank and fuel pump are loosely coupled to the vehicle chassis and are either inducing high speed noise through the wire harness, or tossing noise directly on the power line which couples to other devices through the power distribution block. We've all seen strange things happen in vehicle power systems.

[AEC]

Since the fuel pump is usually submerged in fuel, and sealed in a steel 'coffin' of sorts, there is a possibility of EMF being induced in the wiring.

And since these wires are not very large, and never run inside any shielded braiding, I can see how it can occur, but most fuel pumps are of the 'wobble' design and have no rotating mass I am aware of(since I never took one apart).

I have a pump from my Buick I may have to disassemble now, just to find out how they are built :-O

Aside from a rubber gasket around the plug/socket, three leads to the pump, and a couple from the level sensor are all that are around.

Maybe it's not the pump itself, but the induced EMF on the level sensor leads.

[efc]

Thanks, I will let you know