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24 Valve Diagnosis and service Tips
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Source: Chrysler Master Tech Issue #2 Reference Book dated February 1998

It should come as no surprise that when an engine is redesigned, especially one that replaces a mechanical control system with electronic modules, diagnosis and service of customer complaints with that engine will also see some changes.

DIAGNOSIS

One advantage of electronic control of engine systems is enhanced diagnostic ability through tools such as the DRB III scan tool.

Diagnostic trouble codes, or DTCS, can be read with the DRB III on diesel-powered vehicles in much the same way they are on other vehicles. Make sure that you choose the module you want to read trouble codes from, such as the ECM or PCM (Fig. 35).

Fig 35 - typical display to choose controller

DTCs that are accompanied by an illuminated malfunction indicator lamp, or MIL, are usually emission-related, while a check gauges lamp will be associated with DTCs that indicate problems in other areas.

You can also use the DRB III to monitor sensor readings with the sensor display (Fig. 36) and check the operation of electronically controlled switches and solenoids with the actuator tests.

Figure 36- typical DRB III display.

The DRB III can also be used for system tests while the engine is running.

You can use the DRB III pressure tester to check for restrictions on the inlet side of the transfer pump. Typical readings on the inlet side of the transfer pwnp should be no more than six inches of mercury.

Another tool that is used for diagnosis of the diesel fuel system is a combination pressure/vacuum gauge, special tool number 6828 (Fig. 37).

Fig 37 - pressure/vacuum gauge

To check the pressure side of the transfer pump, you'll need to obtain special fittings to adapt the gauge to the inlet side of the fuel filter. These fittings are equipped with a spring-loaded shut-off valve (one-way check valve) and are commercially available from a tube fitting supplier. Use Parker Access valve, male connector - part nwnber AVU 1 -2 - or equivalent.

On the inlet side of the fuel filter, up to 16 psi is normal with the key on and engine off. During engine cranking, the pressure reading should be about 7 psi, while a minimum of 10 psi with the engine running is typical in a system that is operating normally.

LOW POWER COMPLAINTS

Many times, the diagnostic trouble code description alone will be the only thing you need to solve the problem. On low-power complaints, for example, MAP sensor malfunction DTCs and fuel-related codes, such as a transfer pump circuit failure, may be present.

Other possible causes of low power complaints include the fuel temperature too high, coolant temperature too high or low, or incorrect turbocharger waste gate settings, all of which may set a DTC.

Conditions such as air in the low-pressure fuel system, low pressure in the transfer pump or low oil pressure probably won't set a code and require further diagnosis.

A clogged fuel filter can be a cause of poor performance. A pressure drop accross the filter test ports of 5 psi or greater indicates a clogged filter. Other symptoms of a clogged fuel filter can be white smoke or misfiring at high speeds and light loads, and loss of 'power at meduim to high speeds.

The repair for a clogged fuel fileter is -you guessed it - changing the Filter element cartridge.

Be sure to check for any intake air restrictions (Fig. 38) that could be adding to a low-power condition. Also check for loose clamps on the air ducting from the turbocharger to the intercooler and from the intercooler to the intake manifold.

Figure 38 -Make sure there are no restrictions to the air intake system that could cause a low power complaint

HARD STARTS

Hard start complaints may be caused by a problem with the transfer pump.

Insufficient voltage at the fuel injection pump can also cause hard starts. Check for voltage that is less than 7 volts.

SERVICE

The new Cummins engine also brings with it some service procedures that are different than they have been in the past. One of these procedures is purging air from the low-pressure side of the fuel system after a fuel filter change or if the vehicle runs out of fuel.

First loosen the banjo bolt at the low-pressure fuel supply line on the side of the fuel injection pump (Fig. 39). Next, momentarily engage the starter but do not allow the engine to start.

Figure 39 - To purge. air from tiie low-pressure side of the fuel systetm, first loosen the banjo bolt on the side of the fuel injection pump.

Then release the key to the RUN position, but do not turn it back to OFF. The tranfer pump will continue to run and purge air from the fuel system for about 25 seconds.

Repeat the process until all air has been eliminated from the system. Then tighten the banjo bolt at the supply line to the fuel injection pump. Once you are satisfied that all the air has been purged from the system, attempt to start the engine.

Once it starts, be sure to check for any fuel leaks while the engine is running.

To purge air from the high-pressure side of the fuel system, first loosen any two of the fuel line connections at the cylinder head for cylinders one, three and four (Fig. 40). Then crank the engine until fuel without any air bubbles squirts from the loosened fuel lines.

Figure 40 -To purge air from the high-pressure side of the feel system, first loosen two fuel line connections at the cylinder head.

Tighten the fuel line fittings to 40 N-m, or 28 to 30 foot- pounds. Proper torque here is critical. Then start the engine and raise the engine speed to between 1,200 and 1,500 rpm. The engine may run a little rough and be quite noisy until the remaining air has been purged from the other high- pressure lines.

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Last Update June 2, 1999