Boost?

I thought I might have a problem with my turbo not working quite properly so I fitted a boost guage last week.

It only ever seems to get 0.75 bar of boost at 4k RPM - I thought this should be more like 1 bar. You can see the boost drop a little when it reaches "full" and the waste gate opens. I'm aware the guage might not be 100% accurate but is there an easy way I can test the waste gate isn't opening too early? I assume they are spring tensioned. Maybe it's opening too early before full boost? I don't get much smoke so it's not overfuelling.

As you have a boost gauge fitted it might be useful to lubricate and adjust the wastegate control rod .. you'll be able to see what an adjustment makes more easily than people just adjusting and 'feeling' it under power ..

Only do small changes, 1/4 or 1/2 a turn at a time ... and worth recording the changes at every point so you can return to standard if necessary..

rojbarker said:

I thought I might have a problem with my turbo not working quite properly so I fitted a boost guage last week.

It only ever seems to get 0.75 bar of boost at 4k RPM - I thought this should be more like 1 bar. You can see the boost drop a little when it reaches "full" and the waste gate opens. I'm aware the guage might not be 100% accurate but is there an easy way I can test the waste gate isn't opening too early? I assume they are spring tensioned. Maybe it's opening too early before full boost? I don't get much smoke so it's not overfuelling.

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I've not done this work myself, but I believe measuring the boost accurately is dependant on where you connect the boost gauge.

Incidently it should be 1 bar from about 1800 to 4000rpm on full throttle. You are testing it on full throttle aren't you?

I did read some where else the reading won't be exactly 1 bar unless you tap into the manifold itself. I've used the pipe that feeds the fuel pump so thought this would give me the best indication. I ran it up to full throttle under load and it still barely gets past 0.75.

I will try cleaning up the wastegate linkage - is adjusting it pretty straightforward?

rojbarker said:

I thought I might have a problem with my turbo not working quite properly so I fitted a boost guage last week.

It only ever seems to get 0.75 bar of boost at 4k RPM .

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If its a 200Tdi they only boost to around 0.7Bar, 300Tdi is a bit more, forget how much offhand.

The reading at the pump boost diaphram should be the same as the manifold pressure, after all its what the pump uses to control the injection fuelling.

landy.man said:

The reading at the pump boost diaphram should be the same as the manifold pressure.

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How do you work that out then? Wont the losses between the turbo and the fip diaphragm be different to the losses between the turbo and the manifold?

What we really need to know is where the specified 0.7 bar is measured and then measure in the same place

So 0.7 is right....bugger, I was hoping I'd found the reason why mine feels so sluggish these days! Thanks lads, back to the drawing board I recks.......

Just a quicky - wots .7 & 1.0 bar in ****ies? Is 14****ies= 1 bar?

The Mad Hat Man said:

Just a quicky - wots .7 & 1.0 bar in ****ies? Is 14****ies= 1 bar?

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0.7 bar = 10.152 641 661 pound/square inch
1 bar = 14.503 773 801 pound/square inch

At least that is what a conversion website I found said

200 tdi = 0.7 bar
300 tdi - 1.0 bar

if you look at the intercooler, inlet manifold and turbo/hoses as a sealed unit it will al be at the same pressure when the waste gate opens

taking a boost gauge reading off the injector pump feed will give an accurate boost pressure reading, at least it did on both of my 300tdi's

you can turn up the boost on the 200 to 1bar but unless you add more fuel you wont see much improvement

That's where I'm taking it from, the pipe from the turbo to the lift pump diapraghm. I guessed that that was the most pragmatic approach!
Surely if the boost is running higher, it will compensate by adding more fuel (to a degree?)

I guess if you up the boost it will have a greater effect on the pump diafram but the factory setting on 0.7bar boost should operate the pump to its full extent (setting) so I still dont think you will see much difference
but the only way to find out is shorten the wastegate rod and try it. but do it a little bit at a time and check with your gauge after each adjustment

there are some very good "how to's" in the various forums how to increase fueling by adjusting the injector pump which can give loads more power

ccrdave said:

if you look at the intercooler, inlet manifold and turbo/hoses as a sealed unit it will al be at the same pressure when the waste gate opens

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but its not a sealed unit, the inlet manifold leads to 4 inlet valves....

Richard Martin said:

but its not a sealed unit, the inlet manifold leads to 4 inlet valves....

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Ok so if you are saying the loop is open then how does pressure build?

more air than required = pressure build (just to play devil's advocate!)

Think I read somewhere the "proper" place to measure is the small pipe at the turbo (the one to the actuator I think) but the best place is at the manifold but I can't remember the reasoning.

I.m.o, if you've tweaked the pump as is usual, you'll probably gain a little by upping the boost a bit, if the standard is .75bar I wouldn't want to go higher than a .bar (14.7psi). You'll find the engine gets hot quicker under load though so if you're rad's a bit tired I'd sort that first.... just my opinion though.

Richard Martin said:

How do you work that out then? Wont the losses between the turbo and the fip diaphragm be different to the losses between the turbo and the manifold?

What we really need to know is where the specified 0.7 bar is measured and then measure in the same place

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Are you not thinking of flow rate losses? these will be dependent on pipe diameter. However the pressure will be the same in them all, since after all they are physically connected together. So long as the pipes are big enough to allow sufficient flow to move the diaphrams then all is well.

When the fuel injection pumps are tested, the pressure applied to the boost diaghram is considered to be equal to the boosted inlet pressure.