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uksteve · 02-23-2018, 08:54 AM

Would having air in isb system affect turbo boost
Isb 275

BFlinn181 · 02-23-2018, 10:21 AM

You better have air in the engine, it depends on it for combustion and boost. If air is leaking out after the turbo has built up pressure, it would affect boost.

An ISB has a variable vane turbo and an integrated exhaust brake. Perhaps your exhaust brake is stuck partially on or your turbo isn't operating properly, but it's more than an 'air' problem.

uksteve · 02-23-2018, 11:52 AM

Sorry I meant air in the fuel system

dennis45 · 02-23-2018, 12:21 PM

Quote:

Originally Posted by uksteve

Sorry I meant air in the fuel system

Indirectly air in the fuel system will cause turbo boost to drop because of engine misfire or not firing at all.
In simple terms,
The turbocharger is driven by hot exhaust gas. The more fuel, the higher the exhaust temperature, the higher the temperature, the more boost pressure.

If you have air in the fuel system most likely the engine would not run. Period.

http://www.explainthatstuff.com/how-...gers-work.html

BFlinn181 · 02-23-2018, 01:27 PM

Quote:

Originally Posted by uksteve

Sorry I meant air in the fuel system

If air gets introduced because you did a filter change, ran out of fuel, or had a break in a fuel line, most likely the engine won't start or require more cranking than your batteries and starter can produce.

A small amount of air, as when changing the filter, can often be cranked past or engine will start. Within minutes that air will be pushed out and fuel will flow normally. It shouldn't continue to cause problems after the air clears the fuel system.

uksteve · 02-23-2018, 01:56 PM

I had a leak at the inlet to the lift pump
So I’m hoping that’s what was causing a slight loss of turbo power
Haven’t had time to take the rig out yet
So hopefully that was the problem

BFlinn181 · 02-23-2018, 02:30 PM

Quote:

Originally Posted by uksteve

I had a leak at the inlet to the lift pump
So I’m hoping that’s what was causing a slight loss of turbo power
Haven’t had time to take the rig out yet
So hopefully that was the problem

That leak was causing the engine to have a poor air/fuel mixture, which could result in misfiring or incomplete burning of fuel. That's a loss of power, not 'turbo power.' The turbo just increases the amount of air introduced into each cylinder and increases the pressure in the cylinder to allow more complete combustion of the fuel/air mixture. The incomplete burning and engine missing might show up on a boost gauge if that's what you noticed.

3rd stage · 02-24-2018, 08:02 AM

Quote:

Originally Posted by uksteve

I had a leak at the inlet to the lift pump
So I’m hoping that’s what was causing a slight loss of turbo power
Haven’t had time to take the rig out yet
So hopefully that was the problem

Exactly the problem I found on our 8.3C. The inlet fitting to the mechanical lift pump was leaking, causing more cranking than I thought was proper in order to start. After fixing, the coach ran soooo much better, with more power, and smoother too!