Whirr noise and vibration at highway speeds

[BIGSLVRXJ]

Hey everyone been trying to figure this problem out but having absolutely no luck. I now have A/C but this was happening before hand so it's not that. When going at highway speed I will have a slight surging vibration and like a whirrrrrrrr noise. I just replaced a perfectly good fuel pump with a new one thinking that was it, it wasn't. I've been reading up on the ballast resistor would that likely be it? If so what are the correct voltages. It sounds like across the terminals like .4 or something? Anyone else have suggestions? Oh 1990 4.0 AW4.
Thanks a lot,
Collin

 

[8Mud]

The resistance in the ballast resistor will change, when it gets hot. Most, I´ve measured, were (about) 3 volts less than battery voltage on one end, cold, with the ignition on and not running. Some people have gotten other voltage differences, some a little higher and some a little lower.
If the surge is at around 2000 RPMs, it´s possible it´s the O2 sensor. Mine did that, later the idle started hunting.
I once drove around for awhile with a fuel pressure dial tied to my winshield wiper. But a standard fuel pressure test, would have probably sufficed.
Might want to have a look at yout distributor shaft and check the cap real good. The shaft will move up and down some, but much if any side play, is a cause for concern, only a matter of time, before the rotor strikes a lug in the cap. A questionable distributor, will sure enough make a Brrr sound.

 

[BIGSLVRXJ]

The resistance in the ballast resistor will change, when it gets hot. Most, I´ve measured, were (about) 3 volts less than battery voltage on one end, cold, with the ignition on and not running. Some people have gotten other voltage differences, some a little higher and some a little lower.
If the surge is at around 2000 RPMs, it´s possible it´s the O2 sensor. Mine did that, later the idle started hunting.
I once drove around for awhile with a fuel pressure dial tied to my winshield wiper. But a standard fuel pressure test, would have probably sufficed.
Might want to have a look at yout distributor shaft and check the cap real good. The shaft will move up and down some, but much if any side play, is a cause for concern, only a matter of time, before the rotor strikes a lug in the cap. A questionable distributor, will sure enough make a Brrr sound.

Well, I've just heard the ballast resistor controls the vibes and noise the fuel pump makes and I have noise and vibrations coming from back there. I just replaced my 02 sensor last winter but I suppose it could be fouled, is there a way to test that? The other thing I wondered is how do I check for distributor play? I just replaced my cap and rotor also but I've never checked the shaft. Thanks a lot for the suggestions 8Mud.

 

[8Mud]

Well, I've just heard the ballast resistor controls the vibes and noise the fuel pump makes and I have noise and vibrations coming from back there. I just replaced my 02 sensor last winter but I suppose it could be fouled, is there a way to test that? The other thing I wondered is how do I check for distributor play? I just replaced my cap and rotor also but I've never checked the shaft. Thanks a lot for the suggestions 8Mud.

Try wiggling the shaft from side to side, when the shaft wiggles about the same distance as the clearance from the rotor end and the cap lugs, your getting close to catastrophy. Rotor wiggling around in there, can´t be a good thing. It will move up and down a bit (never seeme to hurt much) and the gears do get worn and make a brrr sound.
The only time I can really hear my fuel pump, is when I turn the key to the run position and let it sit for a few seconds, before I start. I do it from habit, it seems to make the starts faster. It will run for a few seconds, then shut off (or get really quiet).
Í´m not a ballast resisitor expert, but have looked at mine a little, did an ohm test, but don´t remember the results off hand, a guess would say it´s pretty close to one ohm, with the wires diconnected and the resisitor cold. I have a jumper wire with a couple of spade connector tied around the wires, right next to the resistor and another near tied next to the connector for the thermo switch for the aux fan (nothing to do with this thread, but they are next to each other kind of).
Do remember checking voltage on a couple of occasions, seem to remember it being near 9-10 volts on the pump end of the resisitor.
Had one ballast resistor that got splashed with water and the back blew off, kind of like putting a hot glass in cold water. But it still worked, replaced it anyway, they are cheap, if you buy the generic ones.
Had an 87, that never had a ballast resistor, never noticed any pump noise, but maybe I was just used to it.
The ballast resistor was put in there to lower the voltage, when the motor was running and the resistor is bypassed during start and pump gets gets full battery voltage (or whatever is left over, after the starter gets it´s share).
Guess a ballast resistor could short across the windings and the pump could get too much voltage while while the motor was running, causing noise. A simple volt test should tell.
Lets get creative, get somebody to crawl around in the back and hold his ear to different spots and see where it´s loudest. I do that all the time with my son. Could be a CAT, a muffler, or something else.
I had a rusted piece of something in a muffler, that made kind of a Brrr, I kind of liked it, made my XJ sound kind of like a Ferrari.
If you just replaced the rotor, make sure it´s down all the way, they go on the shaft hard sometimes. I usually put a VERY lite, coat of grease on the shaft. I´ve had the shaft get a coat of rust on it and the rotor went on hard, a very lite buffing with a 3 M pad and then blowing the rust dust out of the distributor cured that.

 

[BIGSLVRXJ]

Okay try and update ya a little here. I replaced the rotor and cap about a year and a half ago, I can't remember if thats when the noise started or not, but I will check the shaft tomorrow. I had the muffler replaced yesterday and the cat is fine also. I originally thought it might be exhaust noise, but its not, I can tell for sure. So for the ballast resistor do I measure voltage across the terminals or with one plugged in and one to ground? Really appreciate the suggestions, thanks.

 

[Matthew Currie]

You haven't made it entirely clear whether the whirring noise is dependent on engine speed or not. The first thing you need to do, if you haven't already, is to put the tranny in neutral, and see what changes when you let off the gas.

If it's engine speed related, one more possibility might be the fan clutch, or an idler pulley.

 

[8Mud]

Okay try and update ya a little here. I replaced the rotor and cap about a year and a half ago, I can't remember if thats when the noise started or not, but I will check the shaft tomorrow. I had the muffler replaced yesterday and the cat is fine also. I originally thought it might be exhaust noise, but its not, I can tell for sure. So for the ballast resistor do I measure voltage across the terminals or with one plugged in and one to ground? Really appreciate the suggestions, thanks.

Start the motor, hold a volt meter probe on one end of the resistor to chassis ground, note the volts, hold it on the other end, note the volts, with everything connected. Might want to check the voltage at the battery, just to compare. Should be fewer volts on one end of the resisitor than the other. I´d like to give you a diffinative number, but it changes with the load, as the resistor heats, the resistance changes and the output voltage changes some. A better word for the resistor, might be a compensating resistor instead of a ballast resistor, the resistance changes with the load (amp draw).
Good question from Matthew, is it speed dependant, RPM dependant, does it change around corners.
Could it be harmonics from the exhaust (even new) or a piece of metal that rattles at a certain wind speed?
Had a howl that drove me nuts, finally decided it was wind speed dependant. Looked at everything possible, hours and hours, turned out to be an end cap on my roof rack.
Sound travels in strange ways, had a roar, that sounded like it was coming from the tranny hump. Turned out to be a front hub.

 

[BIGSLVRXJ]

You haven't made it entirely clear whether the whirring noise is dependent on engine speed or not. The first thing you need to do, if you haven't already, is to put the tranny in neutral, and see what changes when you let off the gas.

If it's engine speed related, one more possibility might be the fan clutch, or an idler pulley.

It's really kind of hard to tell. It seems that it is intermittent on the freeway, so I guess its intermittent at higher rpms(above say, 2000) Are you saying put the tranny in neutral and let off the gas while I'm going 55? I just replaced the idler pulley about 4 months ago but the fan clutch would be a possibility I suppose, how do you tell if its about shot?

 

[BIGSLVRXJ]

Start the motor, hold a volt meter probe on one end of the resistor to chassis ground, note the volts, hold it on the other end, note the volts, with everything connected. Might want to check the voltage at the battery, just to compare. Should be fewer volts on one end of the resisitor than the other. I´d like to give you a diffinative number, but it changes with the load, as the resistor heats, the resistance changes and the output voltage changes some. A better word for the resistor, might be a compensating resistor instead of a ballast resistor, the resistance changes with the load (amp draw).
Good question from Matthew, is it speed dependant, RPM dependant, does it change around corners.
Could it be harmonics from the exhaust (even new) or a piece of metal that rattles at a certain wind speed?
Had a howl that drove me nuts, finally decided it was wind speed dependant. Looked at everything possible, hours and hours, turned out to be an end cap on my roof rack.
Sound travels in strange ways, had a roar, that sounded like it was coming from the tranny hump. Turned out to be a front hub.

Well as I said its not as much just noise it almost sends like a wave of vibration through the frame and there is the whirr noise I was talking about. The turning thing brings up an interesting point though because, I have been getting a grinding from the ps pump when turning even at low speeds. Could the pump be making that much noise and vibration at higher speeds?

 

[8Mud]

Could be anything, but changing parts and hoping to get lucky, gets real expernsive real quick.
Try Matthews suggestion, see what happens, try it again while driving next to a wall (doubt your gonna be able to do that at freeway speeds) and have somebody listen out the window. I´ve localized many sounds like that.
Harmonics, often get worse, then better, at different RPM´s, what may be worse at highway speeds, may be there at lower speeds, but just not as noticeable.

 

[BIGSLVRXJ]

Yeah I kind of figured there would be a lot of things that it could be. I guess I'll just wait till whatever it is gets louder and hopefully that will help me pinpoint it. Thanks for all the help guys.