Have an odd symptom
The hiace (2779cc non turbo) has always been a bit noisy but its increasingly clear that its due to combustion/exhaust noise. (being my first diesel I thought the noise was part and parcel of running one)
Today, when standing held rpm at 3000rpm and....almost silence - above or below this figure and a blowing exhaust sound reappears
Seems odd that its incredibly quite at this rpm only and would explain a washing machine noise I was worried about in an earlier post at 65mph (probably the cycling between quite and noisy)
Now I am resigned to pulling the floor (again) as I wonder if the exhaust manifold is cracked. (exhaust is good)
Only other thing I can think of is the egr (noted it has a flap in the section that joins the inlet manifold) - as it has a flap it must open and close - but can anyone explain how it works in practice - and is there any possible relationship between the egr system and this 3000rpm phenomenon.
It has happened before in third when cruising at probably this figure and at the time I thought the engine was starting and stopping - that is how dramatic the difference is
If anyone can offer words of wisdom it would be much appreciated
Thanks
Chris
- (#9212) chris turner, 20 Jun 03 17:53
Could be related OK. EGR is generally applies at lower revs and light throttle settings...
- (#9213) david miller, 21 Jun 03 1:24
Chris. David's comment spot on but, you might like to try isolating the EGR valve and there are some comments in Ace Answers. The diaphragm, which operates this valve, has a small hose leading to it. A ball bearing, or other obstruction, pushed into this hose will stop it from operating the EGR valve and you can then test the vehicle knowing that this valve is dormant. But, as David has pointed out, this valve should, usually, only operate at light throttle to re-circulate a small amount of exhaust gas through the inlet manifold
- (#9214) John Davis, 21 Jun 03 3:19
Thanks David and John
On further investigation the source of the 'blowing exhaust' is actually coming from the resonator.
This is large plastic chamber by the airfilter and is 'in line' betwen the outside air intake and filter.
It has 2 rubber 'flap valve' bungs underneath.
The noise is pressure coming out of the flap valves but the pressure becomes absent at 3000rpm when the vehicle is stationary
As the intake sucks I dont understand why the flap valves blow air out. (vortex, air pressure? could anyone explain?)
When the bungs are pulled out the noise is louder.
The noise from this resonator exceeds the noise of the engine (sounds like blowing exhaust)so if any mod could be made to reduce the noise it would remove any associations or jokes about tractor engines.
Wondered about a bit of pipe stuffed with exhaust wool rplacing bungs, or sticking sound deadening pads to the resonator - or maybe the first step would be to replace the bungs with new
Can anyone explain to me what the purpose of the resonator is - and how it works?
Having this understanding would allow me to decide what mods would be safe and not interfere with its operation
Do the townaces have them also?
Chris
- (#9215) chris turner, 21 Jun 03 16:43
resonators tune the sound of a duct. To give it it's full name it's a Helmholtz resonator, a sealed box tee'd off a straight duct.
Why blowing out? well, the intake sucks, yes. But in pulses related to the opening of the inlet valves. At times, these pulses can either add or cancel each other, creating more, or less flow or noise.
In petrol engines the technique is used on inlet and exhausts to improve scavenging. Mostly for noise reduction in diesels.
Are there any other parts of the inlet missing perhaps?
- (#9216) david miller, 22 Jun 03 8:22
Thanks for that David
I'll try some searches for the 'Helmholtz resonator'
>Are there any other parts of the inlet missing perhaps?< Nail on the head - looked again today and there is pressure pulsing down the side of the resonator (as well as the bungs beneath)- so maybe a loose hose or something above.
I'll pull the floor when I get an hour to investigate
Now you mention it, I have seen them on petrol cars I've had and often puzzled over what they where for.
Now a Haynes manual would never tell me that!
Thanks again David
Chris
- (#9217) Chris Turner, 22 Jun 03 16:39
Sealed the mating surface of the bungs (not flaps) with silicone sealant, lifted floor and sorted slight leaks to pipework joints and gave what I could an acoustic felt jacket. Much quieter now - in fact this new quietness made me realise how noisy the air intake is!(offside of van, level with doorhandle)
Now I did consider sponge behind the intake grill but I'll stop whilst ahead I think!
Thanks for help with this
Chris
- (#9293) chris turner, 24 Jun 03 17:19