5.9 ISB Turbo Question

BlueLine · 12-30-2010, 08:23 PM

Cummins 5.9 ISB Turbo in a 1999 Winne Adventurer,Freightliner Chassis. A while back I was complaining of the lack of accurate instrumentation which has now been addressed by following the advice of several responses, including FreighLiner to consider a VMSpc. "I NOW HAVE INFORMATION". I never had Turbo information before and what I'm getting now is a little confusing to me. My Turbo Pressures range anywhere from a .1 at startup idle and anywhere upward to 25.9 PSI at cruise, and sometime 0.0 at cruise at low torque and horsepower demands. The pressures fluctuate continually during the drive depending on terrain or the need to accelerate for passing. Also the readings seem to be a little retarded in reporting after the demand. The engine seems to be performing OK and I get anywhere between 12.2 and 13.7 MPG while towing a 3500# load. No white or black smoke. A RV'r during this past week told me that all diesels should indicate between 5 psi at idle and up to 26 psi but never 0 psi. I guess the NEVER "0" is my main concern. Am I seeing a problem or a pending problem? My percentage of load, Developed HP and Torque is what I try to control to improve mileage, but this turbo thing has me wondering. Can someone enlighten me in laymen terms?

94-Newmar · 12-31-2010, 03:30 AM

Quote:

Originally Posted by BlueLine

Cummins 5.9 ISB Turbo... A RV'r during this past week told me that all diesels should indicate between 5 psi at idle and up to 26 psi but never 0 psi. I guess the NEVER "0" is my main concern. Am I seeing a problem or a pending problem? Can someone enlighten me in laymen terms?

I cannot comment on the lag time you're seeing with the monitor, but I can tell you that seeing 0 boost at times is perfectly normal UNLESS you have a newer Sequential/VGT type turbo, which on a 99, you do not have. My 8.3 with a mechanical gauge will read 0 at 60 mph on flat ground, at idle and while decelerating.

Lug_Nut · 12-31-2010, 05:07 AM

Zero is absolutely a normal reading at low idle. If you are on a higher than normal idle using the cruise control you might see 1+ psi.

J Walker · 12-31-2010, 07:45 AM

I have a 2000 ISB and my VMSpc indicates an occasional 0 psi turbo boost when power is zero. Your description of seeing 0 psi boost when in cruise control at low power sounds like you are getting less boost at times. I would not be surprised if all of our engines operate slightly differently. Your engine appears to be working well judging from your MPG. A VMSpc log is a great record and it allows you to monitor changes in your engine and to compare with others. If you send me a private message with your email address I will send you one or two of my logs. Maybe we will both learn something.

stuhly · 12-31-2010, 10:01 AM

0 psi at idle is normal for 550 to 700 rpm idle. The lag time for the reading is most likely because it takes a few seconds for the turbo to spool up to speed after you get on it.

RustyJC · 12-31-2010, 10:29 AM

Your boost figures look normal for a 1999 ISB.

Rusty

BlueLine · 12-31-2010, 06:41 PM

Phew!!! You all made my day, I just knew with the word Turbo attached I was looking at some big bucks if things were'nt normal. We just got back from Christmas at Myrtle Beach State Park and everything was what I thought to be a Perfect trip, Thanks for your information and making it so. BTW Picked up a great deal on New front seats at Campers World. And also picked up a STS TPMS....Life is good.

Mopar1973Man · 01-06-2011, 08:04 AM

I'm slightly different from you... I'm still 5.9L ISB...

But I'm typical cruise 55 MPH boost is about 2-3 PSI with a HX35 Holset turbo.

But if you want to inspect the turbo here is how to do it...
Turbo Inspection

sknight · 01-06-2011, 09:33 AM

Think of it this way. Boost it tied directly to your right foot. The more you feed it the more boost you'll have. During idle you'll have nothing, you lay into it the boost goes up. Actually diesels produce "Vacuum" just like a gas engine, there's just no throttle blade to contain it but a good mechanical vacuum gauge will actually show right at 1-2"hg idling depending on the setup.

The delay you see is most likely just turbo lag. It takes a few moments to get the impeller spooled up to speed.

Mopar1973Man · 01-06-2011, 09:56 AM

Just like said above...

Quote:

Boost it tied directly to your right foot.

More boost means more fuel being used which in turn means lower MPG's... Boost gauge is a good thing to watch to aid in controlling your MPG number.

CyberVet65 · 01-06-2011, 07:40 PM

For us older guys a boost gauge is much like the old vacuum gauge that we used to put on our 4 barrel carburator street machines. The higher the number equals less mpg!
Chet