I hope that this hasn't been covered before but my 1995 XJ6 X300 3.2 auto has a slight whistle that is very much like the noise some turbos make as they spin up. Just a nice clean whistle that rises in frequency as the engine revs increase. However, it is quite quiet so you don't really hear it with the radio on or once the engine gets a bit louder.

The really odd thing as confirmed by my wife walking round the car you can't hear it outside the car. It's not there all the time but gentle application of the accelerator pedal will reliably induce it.

It is still there if

I turn off the fan for the vents.
The car is stationary
The radio is on or off (although it is way harder to hear with radio on)
I did wonder if it was related to the Tel - Mute kicking in on the radio despite not having a phone to trigger this, but I suspect that's for another day

Is there a fuel pump in the tank? Could it be that making the noise?

I'm sure someone knows the answer so I'd love to know how to eliminate it.

Mike

 

Mike:
The fuel pump can certainly make a whining noise. The fule pump runs for a few seconds after the key is switched to the "run" position. you might carefully listen then for the sound.

I thst is what it is, I wouyld turn the radio on until I wanted to endure the PITA to change the pump. It MIGHT be a sign of impending failure, or the pump might keep on for many mile like mine has.

 

I hadn't thought of listening when I first turned the ignition on. I'll try that.

 

Hi Mike,

Did you ask about the fuel pump in the tank because the noise seems to be coming from the rear of the car? The thing that may not make sense about the fuel pump whining is that the whine rises in frequency as the engine revs increase.

Ross - Can you tell us if the X300 fuel pump rpms vary with engine speed?

Mike - Your mention of the Tel-Mute kicking in on the radio reminded me that our '93 XJ40 developed a whine that rose and fell in frequency with engine speed, and it was caused by a failed suppressor capacitor allowing alternator noise to be picked up by the radio, which was audible as a faint whine any time the radio was on, even if the volume was turned all the way down. But since your noise happens when the radio is off, that's probably not your issue, unless your Tel-Mute issue isn't the only problem you have with the radio.

I'm sure you've thought about common sources of whines that vary with engine speed: alternator bearings/bushings, A/C compressor clutches, belt idler pulleys, air intake or vacuum leaks causing a whistle, maybe an obstructed air filter... Like you, I'd think those would be audible from outside the car, but I suppose they could be overwhelmed by engine noise.

Cheers,

Don

 

Thanks Don.

Of course the whistle (as opposed to a whine) has now stopped and I can't induce it but I'm sure it will be back.

Your list of whistles and whines are what I thought the culprits might be but I am 90% confident they aren't as you really cannot hear it in the engine bay and I believe you would even over the engine noise.

Of course I was being dim about the fuel pump, it presumably pumps at the same rate at all times returning unused fuel via the return line. Well that's probably good.

I could well believe that it was some electrical component causing this noise and these radios don't have the best reputation. Perhaps I should monitor if it still happens with Tel-Mute showing and when the radio is off and Tel-Mute is not showing.

Mike

 

No whistle without engine running and Tel-Mute irrelevant so we are tending to think it's an alternator induced whistle in the speakers. Can I live with it? Probably

 

Mike,

A few thoughts:

First, alternator whine can be a symptom of a failed diode, so it would be a good idea to have your alternator checked. But whine can also be caused by increased impedance in the alternator/battery circuit, and since corrosion on battery power and ground connections is a common issue on Jaguars, it would first be worth cleaning all the power connections between the battery and alternator, the engine ground strap, the battery terminals, and the negative battery cable ground point at the body.

The Alternator Suppressor Module is mounted in the LH side of the engine bay and is shown as Part 1 in the diagram below. The part number is LMB1820AA.






Here in the States, jaguarmerriamparts.com shows the module available for the astonishing "discounted" sum of $163.87, but I would be surprised if it contains anything more than an inexpensive capacitor/condensor. Maybe Ross can tell us. My guess is that it would probably be simple to replace its internals with less than $10.00 worth of parts from an electronics store.

Cheers,

Don

 

Thanks Don. I will check the battery to alternator connections as best I can! The positive battery strap seems to be prone to corrosion and I haven't looked for a few months.

 

Just what does the "suppressor" do?

.

 

Hi Al,

This is really a question for Ross, but since he seems to have been especially busy lately I'll give you a layman's answer (which really more than I'm qualified to give).

Lots of components in a car can generate Radio Frequency Interference (RFI), a type of Electro-Magnetic Radiation (EMR) that can be picked up and amplified by a radio-audio system. Sources of RFI include electric motors, generators (the voltage-producing component of an alternator), and electric arcs such as those produced by spark plugs, switches, relays, etc.

Capacitors (formerly called "condensers") are devices with several unique qualities. They can store an electric charge, the amount of charge depending on their capacity (measured in Farads, or more commonly in consumer electronics, microfarads and even smaller divisions). Another unique property of capacitors is that they block the passage of direct current (DC) but allow the passage of alternating current (AC). And, their impedance to the passage of AC decreases with frequency, so to high-frequency AC like RFI a capacitor is as conductive as a straight piece of wire. (Impedance can be thought of as the AC equivalent of DC resistance, just more complex).

So, a capacitor can be connected between the alternator and ground/earth, and because of its high impedance to DC, it poses no risk of shorting the 13-14V DC produced at the regulated output of the alternator. But to the radio-frequency AC noise created by the alternator, the capacitor's very low impedance represents a virtual short to ground, preventing most of the noise from corrupting the car's electrical circuits and minimizing the amount of noise picked up by the radio.

There are other issues such as ripple currents, eddy currents, etc., as well as other means of filtering and blocking noise (inductors, resistors, diodes), but this gives you the basic idea.

When Ross checks in he can explain it better and correct all the things I've gotten wrong.

Cheers,

Don

 

Well that made sense to me when in the past I have just put it down to magic.

So if the capacitor whose job it is to suppress the whine inducing high frequencies starts to break up then they can't short to earth.

Would the radio need to be on for the HF to be induced in the speaker circuit or can it be induced in the speaker wiring anyway?

Mike

 

Well, I had my doubts that sufficient energy could be induced into the speaker wires to produce sound from the speakers even when the audio system is turned off, but according to Crutchfield, a major seller of car audio products, it can:


The above is from this webpage:

Noise suppression guide


When you think of how car speaker wiring is bundled in harnesses along with power wires, ground wires, engine management wires, network wires and all the rest, it does seem logical that noise voltage can be induced in the speaker wires, but Crutchfield confirms that the amplitude of the noise voltage is sufficient to actually produce sound from the speakers....

We learn something new every day!

One other thing I should have mentioned about capacitors is that they do have a limited lifespan, depending on their type and operating conditions.

Cheers,

Don

 

Well reading their notes about engine noise makes me wonder if I do have a poor earth that is affecting the radio system as after a crackle while Tel-Mute is showing the aerial will go up or down.

Drat chasing earths is hard work.

 

Don, you have it exactly right about the purpose and function of the suppressor, and you described it much better than I could have!