I have a 2004 Cummins ISX 435ST set at 500hp with 820k miles in an Int. 9400i. I maintain the vehicle very well, oil every 15k, etc. This year I have lost approx. 1mpg and some power yet the engine runs well(other than noticable power loss). I had an overhead done 8 months ago. I have a PDI intake with the block-off plate for the EGR. That helped tremendously with low end. I had Cummins read the ECM code history and there are none other than oil temp., coolant temp, coolant level, etc. and none recent. I recently had my CAC welded when I found it to be leaking but that didn't solve the issue. Wouldn't I have codes if I had a turbo or fuel issue? I am looking for the fuel mileage/power issue as I am using 10% more fuel on the same route as I used to last year. The truck runs so good many have a hard time believing that the engine has 820k on it but it doesn't have 500hp available anymore, something has changed.
I would recheck the CAC as well as all the hoses and feed hose to the compressor again, maybe you are still low on boost. Do you have your engine SN you can provide? I can look and see if there is any OEM info. relating to the issue specific to your engine.
I was wondering if the variable geometry turbo can act up and still not throw a engine code? Seems like any issue that relates to my issue SHOULD throw a code?
I ran your S/N and dont see anything that stands out, I agree that the turbo would set a code, but only if it did not pass an initial test by the ECM, low boost would have to be monitored under load.
Going to post several entries here from the Fuel Mileage section of Cummins for your review.
Hope it helps......
New Turbo Options:
New Turbochargers for ISX CM870 and ISM CM875 Engines
The information in this document has no effect on present warranty coverage or repair practices, nor does it authorize TRP or Campaign actions.
This document announces new turbochargers with improved turbocharger shroud plate robustness.
This new turbocharger release introduces new part numbers that obsolete and supersede the present part numbers. The new part numbers are documented in the table below.
New ID21-1 Short TurbochargerOld ID21-1 Short Turbocharger New Turbocharger KitOld Turbocharger Kit
Interesting info. for low power....
When operating a vehicle on a chassis dynamometer or operating under fully loaded conditions, the User Fueling State (Engine Operating State) parameter must indicate Maximum Throttle or EGR Fueling Limit State when operating under peak torque conditions. If these states are active during maximum torque conditions (100 percent throttle operation and the engine is fully loaded and operating on the torque curve), this indicates that the air handling system is providing the desired boost pressure and no derates are presently active. If a performance complaint still exists, follow the engine performance troubleshooting tree to isolate the potential cause of the low power complaint.
If the User Fueling State (Engine Operating State) reads Air Fuel Control Derate for an extended period of time (greater than 10 seconds) during a hard acceleration or during normal operation, troubleshoot the turbocharger and air handling system. Air Fuel Control Derate indicates that there is not enough oxygen (boost pressure) entering the engine for complete combustion. The electronic control system then limits the amount of fuel being injected, to prevent excessive black smoke. Air Fuel Control Derate will be active for a few seconds during hard accelerations. It should not be active under steady state operating conditions. Failure modes that can cause excessive time operating in the Air Fuel Control Derate state include charge-air cooler leaks, charge-air cooler plumbing leaks, VGT turbochargers not meeting commanded position, a malfunctioning in-range intake manifold pressure sensor, a malfunctioning in-range ambient air pressure sensor, air intake restrictions, excessive exhaust restriction, worn or malfunctioning turbocharger, malfunctioning fuel injectors, and fuel system restrictions. To isolate the potential cause of the low power complaint, see the engine performance troubleshooting tree.
There are various power derates that can become active during extreme environmental operating conditions. Engines built in 2002 and later will log fault codes for these conditions, but it is possible for a derate to be active without a fault code. Confirm these User Fueling States (Engine Operating States) are not active under normal operating conditions:
Last one I can find, hope some of this helps.....
© 2008 Cummins Inc., Box 3005, Columbus, INNNN-NN-NNNNU.S.A. Printed from QuickServe® Online.
Page 1 of 3
Fuel Consumption Excessive
Fuel leak ............
Check the fuel lines, fuel connections, and fuel filters
for leaks. Check the fuel lines to the supply tanks.
Refer to the OEM service manual .
Go To Next Step
Hubometer or odometer is miscalibrated ............
Check the hubometer and odometer calibrations.
Calibrate or replace the hubometer or odometer, if
necessary. Calculate fuel consumption with new
Operator technique is not correct ............ Refer to Section 1, Operating Instructions .
Equipment and environmental factors are affecting
Consider ambient temperatures, wind, tire size, axle
alignment, routes, and use of aerodynamic aids
when evaluating fuel consumption.
Drivetrain is not correctly matched to the engine ............
Check for correct gearing and drivetrain
components. Refer to the OEM vehicle
Electronic fault codes active or high counts of
inactive fault codes
............ Refer to Section 1 .
Fuel grade is not correct for the application, or the
fuel quality is poor
Operate the engine from a tank of high-quality fuel.
Refer to Fuel Recommendations and Specifications
in Section V .
Lubricating oil level is above specification ............
Check the oil level. Verify the dipstick calibration and
oil pan capacity. Fill the system to the specified
level. Refer to Section 3 .
Air intake system restriction is above specification ............
Check the air intake system for restriction. Clean or
replace the air filter and inlet piping as necessary.
Refer to Section 3 .
All Rights Reserved. Last Modified: 15-Mar-2002
File:(NNN) NNN-NNNNt087-om Page 2 of 3
Exhaust system restriction is above specification ............ Check the exhaust system for restrictions. Refer to
the OEM service manual .
Overhead adjustments are not correct ............ Measure and adjust the overhead settings. Refer to
Section 7 .
Contact a Cummins Authorized Repair Facility
Well, i finally took it to Cummins in Phoenix. I must say that I was wrong about the troubleshooting process and accompanying costs. They charge a flat $115/hr and it can take upwards of 8 hours. Mine took three. They also start at the top of a flow chart regardless of what info you give them and go from there. Actually, they were very effecient. They just called to say its ready for pickup.
I had some minor issues worth a 1/10th or two and also had two major issues.
1. A manifold pressure sensor stuck in range and always showing 30 lbs. or so boost. It turns out that my intake had a lot of carbon buildup from the EGR gasses and was on/in the sensors, too. No fault code.ECM thought it had boost to work with when it really didn't.
2. I had two weak injectors that at low RPM put out enough spray that idle, etc. was fine and only produced a miss at around 1400 RPM and up. Wasn't really noticeable and speed. Again, no fault code. They say it probably would have started throwing a code soon.
I will keep you in mind for future questions and will let others know about you. Your info was right on but my issues required a technician with the proper software, as do so many nowadays.
Thanks again for your help.