Vibrating needle on boost gauge at idle

steveo · Apr 26, 2017

So, I noticed tonight that at idle on my 300tdi defender, the boost gauge needle vibrates (for want of a better word) from just under zero to just over.

I'm sure it hasn't done this before. The gauge measures both boost and vacuum (hence it reading under zero) but obviously as its plumbed into the boost pipe, it only measures boost.

How could it be measuring under zero? If I rev at standstill, it then measures boost, which I'm also sure it hasn't done before. Any thoughts, wise ones?

notenoughtime · Apr 26, 2017

It should show vacuum at idle as turbo isn't producing boost and the Pistons are sucking the air from the intake hence the vacuum

steveo · Apr 26, 2017

notenoughtime said:
It should show vacuum at idle as turbo isn't producing boost and the Pistons are sucking the air from the intake hence the vacuum

But its connected via a t piece in the boost pipe to the injection pump - surely this would never have a vacuum?

notenoughtime · Apr 26, 2017

Inlet will have vacuum when there is no throttle/boost

Kwakerman · Apr 26, 2017

steveo said:
So, I noticed tonight that at idle on my 300tdi defender, the boost gauge needle vibrates (for want of a better word) from just under zero to just over.

I'm sure it hasn't done this before. The gauge measures both boost and vacuum (hence it reading under zero) but obviously as its plumbed into the boost pipe, it only measures boost.

How could it be measuring under zero? If I rev at standstill, it then measures boost, which I'm also sure it hasn't done before. Any thoughts, wise ones?

Descent gauges will often use some form of dampening system (it could be fluid damped). If its vibrating (when it wasn't previously) then it could be a physical fault with the gauge or the whole gauge is being vibrated. Try disconnecting the pipe at the pump end, if the gauge still vibrates then you know it isn't being caused by actual pressure/vacuum variations in the pipe.

bankz5152 · Apr 26, 2017

Ive got a Stack gauge plumbed into the inlet it has never read below zero but it does vibrate a tiny bit at idle, i wouldnt be too concerned tbh.

steveo · Apr 27, 2017

Cheers guys - my concern is that this is new, and there is no vibration of the gauge housing (its not fixed in the dash).

Can someone rev theirs up at idle and see if the gauge moves? I'm sure one didn't before.....

bankz5152 · Apr 27, 2017

If I rev it hard and rev up and down eventually the boost gauge will move up a little

Kwakerman · Apr 27, 2017

bankz5152 said:
If I rev it hard and rev up and down eventually the boost gauge will move up a little

Snap mines the same, I've got a VDO gauge and it doesn't flicker (in a mud pod on top of dash)

Vibrating needle on boost gauge at idle

steveo

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notenoughtime

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steveo

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notenoughtime

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Kwakerman

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bankz5152

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steveo

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bankz5152

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Kwakerman

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