I finialy got gauges installed. I think I have a boost leak but I'm not sure as I don't know what I'm looking at. So I will give the details and some one can explain how and when the boost is made and what the the numbers should be.

At idel gauge reads 0

From take off from dead stop , not stomping on it just taking off normal and going through the gears the gauge will get to 20 and then when it shifts into Hi gear it goes to almost 0

Going down the highway at 60mph the gauge reads 8

The boost will increase as the rpms do however when I get to a steady speed the pressure drops.

So my questions are:

When does the boost create the pressure?

Does the pressure hold steady?

Should I see any pressure at an idel?

If I do have a boost leak where do I start looking for it?

 

The boost occurs when the exhaust expanding as it burns flows out of the engine ans into the turbo. The expansion from heat causes this. In some cases, like on some Chebbies with a Duramax, I have seen boost at an idle, but most diesels do not put out boost at an idle. When you give it some fuel, by pressing the accelerator pedal, more fuel goes into the engine and the resulting burn of that fuel expands more than at an idle, hence your acceleration/ability to pull the vehicle weight. The additional expansion causes the turbo to spin faster, which is what builds boost pressure. Once you decrease the load on the engine the boost will drop to a level dictated by the turbo design and the amount of burning fuel expansion coming through the exhaust.
Once you are up to speed, say 60mph, yes, there is a lot of flow through the exhaust and intake, and the turbo is spinning faster than when you are idling, but there is not necessarily any boost pressure because you are not putting more fuel in than the engine needs, and the flow/expansion is under control. When you have a moderate load on the engine, the fuel being put into the engine causes only a little additional expansion, driving the turbo less, and causing less boost to build up.
All the numbers you have stated are normal.

If you were to have a boost leak, the likely location is always the rubber boots that connect the various metal parts. In many case you will hear the air escaping as a whine or "scream", due to the vibration of the rubber as the air pushes past it. The easiest way to track something like this down is to put the engine under load while looking under the hood for the problem. Much easier with an automatic than a manual transmission.


Chris

 

Thanks Chris, that helps a lot and makes sense.

 

This may help also> http://dodgeram.org/tech/dsl/FAQ/turbo_faq.htm

 

Boost is just higher air pressure in the intake system between the turbo and the intake valves caused by the turbo spinning and pushing air. The boost gauge tells how much air pressure is in the system--from zero to about 30 psi. Any engine works better if it doesn't have to suck air into the cylinders. The boost makes it easier for the piston to travel downward because it doesn't have to suck air. Gas engines work more efficiently with turbo boost too. And a blower is the same principle, but it's just operated by a belt off the crankshaft pulley instead of by exhaust gasses.

 

With the numbers you tell us, I'd say there is no boost leak. They are on target for a stock turbo.