High pitched whine above 2500rpm - any ideas?

[Snoozie]

Hi I bought a bongo in April from a garage and noticed a high-pitched 'singing' whine whenever I press the accelerator a bit more than I would usually when driving - e.g. if going up a steep hill. It happens between 2500 rpm and 3000rpm, and only when the vehicle is moving. I have a diesel 4WD bongo (1996).

I took it for an independent checkover at a bongo specialist garage soon after I bought it because it was delivered with no oil in it which made me a bit wary of the seller (or at least the mechanics he uses to service and MOT vehicles before they are sold). The guys who checked it said they had never heard that noise before and thought it could be the turbo but would have to investigate further. I have since taken my bongo back to the original garage because the middle section of the exhaust was blowing which they have replaced under warranty, and I asked them to look into the whine. They also don't know what it is, but said it wasn't the turbo. They suggested perhaps it was air escaping somewhere, although they have apparently checked all hoses etc.

Just wondered if anyone else has experienced this sort of noise (though I appreciate that it's a bit hard to describe a noise!) or has any ideas what it might be?

[winchman]

You could video the noise and put it on youtube so we can have a listen, I woukd think its the boost on the turbo, it could be a slight leak on one of the pipes, is it still as powerfull?

[Snoozie]

It's hard to say if it is still as powerful as I noticed the whine very soon after getting the vehicle. I felt that it was losing a bit of power, but I thought that the fact that the exhaust was blowing might cause that a bit.

I thought it could be a slight leak on the turbo pipe, although the general mechanic at the sales garage that I took it to had a quick look before I booked it in to go to the garage proper. He got under the passenger seat while I revved up the engine and said that the pipe was taut. But I suppose that it could be a really tiny pin hole. At least if it is that I guess that it's nothing to worry about and the garage should be able to find it if they are prepared to take another look.

Can I ask ...does the fact that it doesn't make the noise when stationary and revving, but only when moving, point to the turbo pipe?

Video/ record it and put it on you tube ? ....err I don't have the technology ! Not even got a camera on my phone! I have a dictaphone which (I think) must store stuff as sound files, but I am showing my techie ignorance now!

I can try to find out how I get get the noise available to the forum, but am off for an escape to Wales very soon so will have a go when I get back - and bump this thread if no-one objects.

Just saw a post on the board about some bongo fury members meeting in Wales very near to where I will be. Perhaps if I find them I can give a few members a demo and someone might have the facility to record the sound

[winchman]

From memory the Turbo will be generating its maximum pressure at this speed whilst at idle it just coasts around not generating much.
Best to get the other local Bongo owners to have a look.
These sort of things can often be difficult to find but simply solved.
If you drive it and try and get it to make the noise, try again with all the electrical stuff turned on as this will load the alternator, if the noise is different it could point to that, I still think its a turbo pipe, but I may just be blinkered, so get a few opinions, are thee no Bongo specialists near you?

[dave_aber]

If it sounds anything like a slipping belt, then it is either a) a slipping belt or b) a warped exhaust manifold.

Warped manifolds are quite common. First thing to check is the No.1 exhaust manifold stud at the front end of the head. It may have sooty marks around it and the surrounding area. The end of the stud itself and the associated nut may be missing, as these snap under the strain.

If it is, then it really needs to have the manifold removed and skimmed, and all the studs replaced.

Not a massive job, and a decent machine shop should be able to tackle it for £150 or so.

There is a fact sheet detailing how to fix it, which my local place completely ignored when they fixed mine!

[Velocette]

This is a massive long shot but | have had it on my motorbike. Check around the air intake and in the filter box for a leaf or a bit of stray PVC tape that is acting as a reed at certain revs/vacuum. It isn't very likely to be the answer but would be lovely if it were.

[winchman]

This is a massive long shot but | have had it on my motorbike. Check around the air intake and in the filter box for a leaf or a bit of stray PVC tape that is acting as a reed at certain revs/vacuum. It isn't very likely to be the answer but would be lovely if it were.

Now thats a good point we had the famous plastic bag stuck in an air intake at work, that caused all kinds of problems

[Simon Jones]

Have you eliminated gearbox / front / rear diff noises? Try dropping it down to 3rd gear with the hold button so that the revs are between 2500 & 3000, but the transmission & road speed is lower.

[Northern Bongolow]

i would go with dave on this one,as the garage have looked for the obvious and not located anything.
no1 stud or number 8 stud gone.
http://www.igmaynard.co.uk/bongo/forum/ ... ud#p418217

[Snoozie]

Thanks so much to everyone so far for all your helpful suggestions. I really appreciate your thoughts.

I will note down everyone's suggestions and look at what people have said to look for, and also take your ideas to the garage when I get back from Wales. Because the noise started as soon as I got the vehicle and I informed the garage of the problem well within the 3 month warranty period I think they should sort it out under warranty. I'm sure they will appreciate a few pointers as they didn't find the problem themselves.

I have booked into to Deb's N.Wales meet so there might be someone there who may also be able to confirm any ideas you guys have as they will have a chance to have a listen to it.

[Northern Bongolow]

if your planning a wales hike before you fix the noise, rule out wrong tyres fitted, if in doubt make a note of each one and post it on here, the guys will help, its important that the size and wear is within the limits on a 4wdrive.

[David Edwards]

Is the missus in the car when it happens....sorry couldnt resist.