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Normal turbo PSI variation for 2004 ISL 400

April 23, 2020, 08:58:17 am

Normal turbo PSI variation for 2004 ISL 400

What's the max or normal PSI  for the turbo on hard acceleration. We get a max of 22 psi.

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Re: Normal turbo PSI variation for 2004 ISL 400

Reply #1 – April 23, 2020, 09:39:45 am

In my 2002 ISL engine the wastegate on the turbo doesn't even begin to open until 20 psi.  I have seen over 30 psi of boost.  (I don't know what year they went to the variable geometry turbo (VGT), so check to see what turbo you have)  I would look to see if the wastegate is stuck open.  When you look at the turbo you will see a vacuum/pressure line going to an actuator on the turbo, follow the linkage down to where it links up to the lever on turbo itself.  The lever should be pointing up at a 90 degree angle when closed which it should be if the engine isn't running.  If it isn't then you have a stuck wastegate valve.  Disconnect the linkage and spray pb blaster or some other type of lubricant see if you can move the lever; however if it is stuck you will more than likely need to replace the turbo.  If the wastegate isn't stuck open then you may have blown seals in turbo and your turbo pressure is going down the oil drain tube, but you would think you would be burning oil and have a lot of blowby.  If it is your seals you will also need a new turbo.  To check this take off the air intake boot  and exhaust boot on turbo and look for oil.  Also put finger on turbo shaft and see if there is any kind of wiggle both up and down and back and forth.  If there is any more than the tiniest bit of movement or there is a lot of oil in turbo than the turbo is bad.  To test the actuator and see if it is bad you can put 20 to 25 psi of regulated air to the actuator and see if actuator moves.  If it doesn't you have a bad actuator and can replace just the actuator.  While you are at it check the vacuum/pressure line and make sure it doesn't have any leaks.

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Re: Normal turbo PSI variation for 2004 ISL 400

Reply #2 – April 23, 2020, 09:57:22 am

Call Cummins with your engine serial number to verify max boost.

If lower, yes, it could be a turbo issue, OR, at least as likely, a leak between turbo and engine with the CAC (Charge Air Cooler) being a likely culprit.

But, start with the facts on your engine before initiating a snipe hunt.

BTW, has max boost gone down or is this 22 PSI the boost you have seen historically?

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Re: Normal turbo PSI variation for 2004 ISL 400

Reply #3 – April 23, 2020, 10:06:02 am

I have owned the coach for 10 months and that's all I have ever seen as max boost

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Re: Normal turbo PSI variation for 2004 ISL 400

Reply #4 – April 23, 2020, 10:09:39 am

Actually, I see two levels of "what to do" here:

1. Determine from Cummins correct max boost for your engine serial number.

2. If, say, the answer is 24 PSI, YOU have to determine how much money to throw at increasing the other 2 PSI.

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Re: Normal turbo PSI variation for 2004 ISL 400

Reply #5 – April 23, 2020, 10:19:42 am

How does it run ?  Does it use more oil than expected?
Good chance that the turbo is fine and the slightly low reading is out of range gauge, small inlet leak, etc.
 The turbo inspection allows about 012 lateral move ment at the nut. 
99% of turbo systems will oil fog The inlet track a slight amount.
Lube the control lever.  Disconnected, you should be able to hear it seat as you lever it. If the closing feel and sound is a soft thud instead of a metal clink. You may have some oil goo on the seat.

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Re: Normal turbo PSI variation for 2004 ISL 400

Reply #6 – April 23, 2020, 11:29:34 am

All good answers. The turbo boost on our was bad when I bought it and it turned out to be some small holes in CAC caused by the bolts holding fuel cooler loose and the cooler was moving a lot. Those bolts punched 3 holes in  the rad. I took it off and sealed them and all has been well for over 7 or more years now. I see up to 32 lbs boost but that is because of Banks Stinger on engine.
John

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Re: Normal turbo PSI variation for 2004 ISL 400

Reply #7 – April 23, 2020, 11:33:50 am

Agree with Protech,have rebuilt hundreds of big turbos and 99% of the failures were clogged oil passages,the rest were the valve train destroying the impeller.

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Re: Normal turbo PSI variation for 2004 ISL 400

Reply #8 – April 23, 2020, 12:00:12 pm

Without a wastegate, the max boost will drop at anything above sea level and with elevated ambient temps, the boost will also be less, even at sea level. With a wastegate, the boost will stay around the max until the critical altitude is reached. At that point, the boost will be less the higher you go. This is usually around 7,500 feet. But in hot weather, the density altitude may reach the critical altitude of 7500 feet at 5000 feet ASL.

So, as an example, say the pressure altitude is 7500 feet and the outside air temperature is 90 degrees. The density altitude will be 11,000 feet and may be even higher if the humidity (dew point close to ambient temp) is more than normal. Your wastegate turbo will be well above it's critical altitude plus the intercooler (CAC), radiator, radiator fan will not be as efficient cooling the incoming air and the air passing through the radiator will be less because of fan efficiency loss and the radiator will not see the air density it would at lower elevations so will not cool as well. EGTs may be higher too.

So, you need a controlled temperature and elevation environment to really see if you are loosing boost pressure. The wastegate can be checked for operation and the intercooler for clamps/leaks/cracks. Check the air cleaner restriction gauge to make sure the reading is not higher than Cummins recommends.

Pressure altitude to density altitude chart: Pressure Altitude Conversion To Density Altitude Table

Excellent automotive density altitude calculator with good explanation here: Automotive Density Altitude Calculator

About the last post from John44. If you don't allow the oil temperature to cool before shutting down, you will get clogged oil passages. So fast idle (1000 rpm) the engine for several minutes before shutting down after a pull. Oil temps don't go down as fast as coolant temps. Synthetic oil won't coke during heat sink.  If pieces of the valve train do damage the impeller, you are SOL anyway.

Pierce

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