MBE 4000 – Section 17.2 Low Horsepower Interview

Section 17.2
Low Horsepower Interview

To determine if low horsepower is causing a power concern, use the driver questionnaire, the troubleshooting tree, and the low power troubleshooting chart.‪

Section 17.2.1
Driver Questionnaire

This section should serve as a guideline for the technician.‪

For an example of the driver questionnaire see Figure "Driver Questionnaire" .‪

Figure 1. Driver Questionnaire

Section 17.2.1.1
Driver Questionnaire

Ask the driver to answer the following questions before attempting to repair an intermittent problem, or a problem with symptoms but no diagnostic codes. Use this and the response as a guideline.Refer to "17.2.1.2 Questionnaire Response Guideline" , “Questionnaire Response Guideline.”‪

1. How often does the problem occur? Can you and the driver take the vehicle and demonstrate the problem in less than 30 minutes?
2. Has the vehicle been to other shops for the same problem? If so, what was done there?
3. Did the radio, dash gages, or lights momentarily turn OFF when the problem occurred?
4. Does the problem occur only at specific operating conditions? If so, at what load? Is it light, medium, or heavy?
5. Does the problem occur at a specific engine operating temperature? If so, at what engine temperature?
6. Does the problem occur at a specific engine operating altitude? If so, at what altitude?
7. Does the problem occur only when above or below specific outside temperatures? If so, what temperature range?
8. Does the problem occur during other conditions e.g. during or after rain, spray washing, snow?
9. Did the problem occur at a specific vehicle speed? If so, at what vehicle speed?
10. Does the problem occur at specific engine RPM? If so, at what engine RPM?

Section 17.2.1.2
Questionnaire Response Guideline

The following are typical responses to the driver questionnaire:‪

PERSONAL INJURY ‪
To avoid injury from loss of vehicle/vessel control, the operator of a MBE electronic controlled engine must not use or read any diagnostic tool while the vehicle/vessel is moving.‪

1. If the problem is repeatable, take the vehicle for a drive with Detroit Diesel Diagnostic Link (DDDL) connected and note the conditions when the problem occurs. Be prepared to take snapshot data using DDDL. Ensure you operate the vehicle after correcting the problem and duplicate the operating conditions before releasing the unit, in order to verify the problem is corrected.
2. If the vehicle has been to other shops for the same problem, call the other shops and find out what has been done. Avoid replacing the same components again unless absolutely sure they are the problem! It is unlikely a component will fail again following a recent replacement.
3. If other vehicle devices are affected, this indicates there may be something wrong with the ignition wiring.
4. Operate the engine under similar load and temperature conditions. Check the fuel system for restrictions, fuel filter, and fuel tanks for foreign objects blocking the fuel supply. Also, check the air system. Utilize the DDDL snapshot feature.
5. Operate the engine at this temperature while attempting to duplicate the problem. Use the DDDL snapshot feature.
6. It may not be possible to duplicate the fault or problem unless you can operate the unit in a similar environment. You may want to talk to the Customer Support Center, or a dealer in that area. They may have helpful experience.
7. If possible, troubleshoot the problem in a similar temperature range.
8. If the problem seems to occur during or after the engine is subjected to rain/spray washing, thoroughly inspect the connectors for moisture entry.
9. If the problem occurs at a specific vehicle speed, check the parameters affecting vehicle speed to verify they are programmed close to the vehicle speed where the problem occurs. Check vehicle speed and watch DDDL (snapshot) for changes to see if the pulse wheel (VSS signal) is loose.
10. If the problem occurs at a specific engine rpm, unplug the oil, coolant, and air temperature sensors, and note any changes to the problem. Gather this data and contact the DDC Customer Support Center at 313-592-5800.

Section 17.2.2
Troubleshooting Tree

Following is the troubleshooting tree for low horsepower:‪

Figure 2. Troubleshooting Tree

Section 17.2.3
Low Power Troubleshooting Chart

There are three basic checks that should be performed:‪

• Check for active/historic codes. Refer to MBE DDEC Application/Installation Manual (7SA825) Appendix A (fault codes). All causes need to be checked once the fault is identified. Record faults on the Application For Adjustment (AFA) claim, if there is to be a claim.
• Check the VCU/PLD parameters, progressive shift settings, and torque limiting values. Are they correct? Is proper rating applied? If vehicle is new, is it spec'd correctly?
• Check that the dyno-measured power is within DDC specifications as listed in Table "Minimum Acceptable Wheel HP Model 460" for minimum acceptable wheel HP data. Record data on AFA claim.

Note: Service information letter instructions published following the date of this document take precedence.

Possible causes of low power and symptoms are listed in Table "Low Power Troubleshooting Chart" .‪

Possible Causes‪	Symptoms‪
	Loss of Power‪	Misfires‪	Poor‪ Acceleration‪	Erratic Idle‪	Engine Dies‪	Black Smoke‪	Excessive Oil‪ Consumption‪
Fuel Filter Restriction refer to "17.1 Factors That Affect Wheel Horsepower" ‪	X‪	X‪	X‪	—‪	X‪	—‪	—‪
Air in the Fuel refer to "17.3 Aerated Fuel" ‪	X‪	X‪	X‪	X‪	—‪	—‪	—‪
Faulty Injector(s) refer to "17.1 Factors That Affect Wheel Horsepower" ‪	X‪	X‪	X‪	X‪	X‪	X‪	—‪
Faulty Turbocharger refer to "17.1 Factors That Affect Wheel Horsepower" ‪	X‪	—‪	X‪	—‪	—‪	X‪	—‪
EGR Valve refer to "17.1 Factors That Affect Wheel Horsepower" ‪	X‪	—‪	X‪	X‪	—‪	X‪	—‪
EPV or Air Supply Lines refer to "17.1 Factors That Affect Wheel Horsepower" ‪	X‪	—‪	X‪	X‪	—‪	X‪	—‪
Charge Air Cooler Leak refer to "17.5 Restricted or Cracked Charge Air Cooler or Leaking Intake Manifold" ‪	X‪	—‪	X‪	—‪	—‪	X‪	—‪
Intake or Exhaust Manifold Leak refer to "17.5 Restricted or Cracked Charge Air Cooler or Leaking Intake Manifold" and section "17.6 Faulty Exhaust System" ‪	X‪	—‪	X‪	—‪	—‪	X‪	—‪
Quality/Grade of Fuelrefer to "17.1 Factors That Affect Wheel Horsepower" ‪	X‪	X‪	X‪	X‪	—‪	X‪	—‪
Restricted Air Intake refer to "17.1 Factors That Affect Wheel Horsepower" ‪	X‪	—‪	X‪	—‪	—‪	X‪	—‪
Crankcase Overfilled refer to "17.1 Factors That Affect Wheel Horsepower" ‪	X‪	—‪	X‪	—‪	—‪	—‪	X‪
Faulty Fan Operation, Always On refer to "17.1 Factors That Affect Wheel Horsepower" ‪	X‪	—‪	X‪	—‪	—‪	—‪	—‪
Debris in Fuel Tank - Air Vent Plugged refer to "17.1 Factors That Affect Wheel Horsepower" ‪	X‪	X‪	X‪	X‪	X‪	—‪	—‪