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Whirring when motor is cold - Bighorn 3.2L petrol

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Whirring when motor is cold - Bighorn 3.2L petrol

Postby DesmondD » Fri Nov 17, 2017 7:26 am

For the past couple of months I've noticed a whirring noise from my 1993 3.2L petrol Bighorn. My garage has been unable to identify it. Here are the details:
1. The pitch of whirring varies with engine revs - this is so obvious when pulsing gas pedal that anybody could hear it
2. The whirring disappears once engine reaches running temperature
3. It's not the AC idler pulley as garage changed that as it had a noisy bearing
4. It's not the alternator as garage changed that because brushes box got burned up by oil getting in somehow and burning (2nd time in 4 years but that's a different story)
5. It's unlikely to be a belt noise as it doesn't change when I spray water on the belts (a friend suggested I try this out)
6. If it's an exhaust manifold crack, then it must only be sucking air in as a CO monitor shows no CO accumulation under the closed hood
7. This may be unrelated but, after starting, the exhaust sound varies from sputtery to normal every 5 seconds or so - could this be related to (6) above with air being sucked in and then fooling the O2 sensor?
8. This may also be unrelated but, when cold, the engine sometimes misses on accelerating for the first 500 metres or so (misleading O2 reading being sent to engine computer because of 7 above?)
9. Can it be a timing belt, or timing belt tensioner, issue? - both were replaced 6 months ago - and would this quieten down when the engine warms up?
All suggestions will be very much appreciated.
DesmondD
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Re: Whirring when motor is cold - Bighorn 3.2L petrol

Postby geeves » Fri Nov 17, 2017 12:14 pm

First thing I would do is remove the fan belts and try again. Then if its quiet look at power steer alternator air con water pump. If not maybe the idler on the cam belt. How long before the belt is due to be replaced. Belts that are too tight can also cause whines
Sanding your knuckles before starting work can help. That way you cant skin them
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Re: Whirring when motor is cold - Bighorn 3.2L petrol

Postby DesmondD » Tue Nov 21, 2017 7:46 am

Thanks for this advice. Cam belt (that I called timing belt in my originl post) was replaced 10 months (5000 km)ago. But what's really strange is the whirring noise has suddenly subsided signifcantly all on its own, and is now only there when one one gives it a bit of gas but you have to know to listen for it. I suppose the belts stretch a bit with time and that might ease off any over-tensioning?? Could the whirring conceivably be from the fuel pump? My sound directionality isn't much good but it does seem to come from the front and the fuel pump is in the tank, right?
DesmondD
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Re: Whirring when motor is cold - Bighorn 3.2L petrol

Postby geeves » Tue Nov 21, 2017 9:14 am

You havnt changed the air filter lately?
Sanding your knuckles before starting work can help. That way you cant skin them
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Re: Whirring when motor is cold - Bighorn 3.2L petrol

Postby DesmondD » Tue Nov 21, 2017 6:37 pm

No, not at all. I get the vehicle serviced regularly and I must confess I've never even wondered what my garage does about the air filter - I tend to only get involved with mechanical issues when my garage doesn't seem to be able to help (and then I long for the 1957 Morris 1000 that I started out with in the 1960s on which I could do, and did do, just about everything). I'll look at the air filter tomorrow and see if it looks clean, or if tightening the top or anything can induce any whistling/whirring sounds.
DesmondD
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Vehicle: 1993 Bighorn LWB 3.2L petrol auto

Re: Whirring when motor is cold - Bighorn 3.2L petrol

Postby geeves » Wed Nov 22, 2017 4:48 am

It is sounding like an air leak but only cold is a puzzle.
Sanding your knuckles before starting work can help. That way you cant skin them
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Re: Whirring when motor is cold - Bighorn 3.2L petrol

Postby DesmondD » Wed Nov 22, 2017 7:55 pm

I checked the air filter and all clips on the cover were secure, and the filter itself looked absolutely new, all clean and white. After putting it back I started the motor and could detect no particular sound from the filter. But in any case the whirring/whining has now all but disappeared.
I'm also wondering if a belt was previously much too tight, but after the alternator replacement (that I alluded to in my initial posting) it was only a little too tight and has now stretched a bit??
And could it have been the water pump?? Could the whirring sound have been disappearing after the thermostat opened when the impeller may have had less work to do in flowing rather than stationary liquid?? But that also wouldn't explain why the sound has now disappeared - unless the thermostat has now miraculously stayed open - but the motor still warms up in the usual amount of time, so that's not likely.
DesmondD
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Re: Whirring when motor is cold - Bighorn 3.2L petrol

Postby geeves » Thu Nov 23, 2017 5:07 am

its hard to diagnose something that isnt there any more
Sanding your knuckles before starting work can help. That way you cant skin them
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Re: Whirring when motor is cold - Bighorn 3.2L petrol

Postby DesmondD » Thu Nov 23, 2017 7:01 am

I ageee completely, and it also saves a bit of money when problems fix themselves. But actually, I guess if it was anything serious, my orignal worry, it would have got worse and not better. So all's well that ends well. And thanks for the discussion. It still helps us who don't know so much..
DesmondD
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Vehicle: 1993 Bighorn LWB 3.2L petrol auto


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