Dilemma: power available should increase as density altitude decreases, right? Well as I've travelled in the past 2 weeks from 4-5000 feet elevation to sea level, my full throttle power seems to have decreased, and fuel consumption has increased. Granted it's gotten warmer as I go south, but the air density has still increased meaning more power should be available, but I'm not seeing an increase in boost pressure with lower elevations as I think I should, and have in the past. So here's the real question(s) I'm pondering:
1) Does ISM450 have inlet air temperature sensor? I see 2 sensors on top of my intake manifold. On my Silverleaf dash I get a appropriate reading for "Intake Manifold Temperature", but the "Inlet Air Temperature" reading is "0". Anyone else get a reading on the VMSPC for "Inlet Air Temperature"? If so, guessing I've got a bad sensor or wiring issue.
2) Other than a failing turbocharger or leaking CAC, any ideas on what to get looked at? Secondary fuel filter perhaps?
I want my HP and fuel economy back.
Woody.
Boost pressure would remain constant on altitude changes. Is your intake manifold temp. remaining 10 deg. above ambient? If much higher CAC leak. Turbo boost low, possible turbo issue. Also sensors could cause problems. Changing the fuel filter would be what I would do first, cheap and easy.
I know you said other than cac but that's usually the problem when our trucks act that way after filters and poor diesel have been ruled out.. Usually a cracked cac will make one smoke black in a pull along with very poor power.
I was getting a puff of black smoke on pullaways from a stop, but resonator install last month fixed that. No smoke during pulls. W.
Most of our trucks are newer than 01 and I have the software and laptop to plug up and point to the problem.. If your 01 has that capability I would go there after I left fuel issues.. Prevent throwing money at a unknown.
Craneman, yes the intake manifold temperature follows OAT. I guess these diesel turbos work a lot differently than turbos on airplanes then? On a turbo Lycoming for instance, the maximum available boost pressure (manifold pressure) decreases with higher altitudes (less air to pump). I may be overthinking this. Woody.
I think our turbos are able to compensate at 8,000 ft. I never see any difference going back and forth to the Sierras. Going from less than 1000 ft to over 8,000 ft.
There are two types of turbo installations. Waste gate turbos where the excess/waste pressure is vented overboard or down the exhaust pipe. At the altitude increases, the excess pressure diminishes until all the boost the turbo generates goes to the engine. This is called the "critical altitude." It's usually about 8000 feet in most installations. So, the diesel generates sea level horsepower up to 8000 feet. The waste gate may be external (on the outside of the turbo) or internal. With a non-wastegate turbo, the boost starts to drop as the altitude increases. This is the installation in our U300 Detroit.
Boost pressure loss may be the result of a wet or dirty air cleaner or a fuel filter starting to clog up as well as a leak somewhere.
Pierce
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FWIW, classic diesel turbosuperchargers are boost limited by the amount of fuel delivered, as Jumbo Goddard learned on the Bonneville Salt Flats with his twin turbo 8-Liter Bentley.
And
A normally aspirated engine will still develop 75% of its rated power at 7,000 feet.
PS The higher you go the faster the turbine spins. WWII aircraft were manifold pressure limited by turbine speed at altitude.
Yes, 75% HP at 7000 feet. This also means the radiator is only 75% as efficient along with the radiator fan. The addition of a turbo brings the HP up but also increases the heat the engine produces so puts more stress on cooling than at sea level. Also, EGTs may be higher, especially with mechanical engines as they may overfuel. Visible black smoke is a telltale.
To get really high altitudes, compound turbocharging has been done with one turbo feeding another. In WWII, bombers had two to four rows of radial cylinders. Besides the turbos, air coolers were installed between the cylinder banks originating the term "intercooler."
Pierce