Diesel Engine Troubleshooting

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Caterpillar EMS HEUI Trouble Codes

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Table 6-3 lists the most critical DTCs for this system. PID (parameter identifier) is a two- or three-digit SAE numerical code assigned to each component. For example, 91 refers to the throttle position sensor. FMI is a failure mode identifier used to describe the kind of failure detected, and flash refers to the number of blinks the code triggers on the “check engine” lamp. Some codes are merely informational and do not affect engine performance. Active codes, that is, those that turn on the diagnostic lamp and keep it on, mean that the problem requires immediate attention. The lamp will go out when the malfunction is repaired. Intermittent malfunctions, often caused by loose harness connectors or bad grounds, cause the lamp to blink and go out. These codes are then logged in computer memory, where they can be retrieved and erased with the appropriate scanner. Intermittent codes that are logged repeatedly need investigation.

HEUI trouble codes Caterpillar EMS HEUI Trouble Codes

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February 14th, 2011 at 7:40 am

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Caterpillar EMS Throttle Position Sensor

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The TPS is located under the accelerator pedal and generates a pulse-width signal that can read with a Fluke Model 97 or equivalent multimeter and a breakout box. The breakout consists of three 12-in. long No.10 AWG wires that bridge the harness connectors and three 6-in. long No. 12 AWG wires that make up to the meter.

1. Using Caterpillar PN 1U5804, crimp Deutch DT 04-3P-E008 male connectors to one end of each of the three long wires and DT 04-3P-E003 female connectors to the other ends. See Fig. 6-22.
2. Make up DT 04-3P-E003 female connectors to one end of each of three short wires. These connectors plug into the meter receptacle.
3. Solder the three short wires to the centers of the longer wires.

Set the meter to measure pulse-width percentage and, with the ignition switch “on,” depress the accelerator pedal. Pulse width varies with make and model, but should be in the neighborhood of 80–90% at wide-open throttle and drop to 10 or 20% with the pedal at rest. A spare TPS is good insurance.

breakout box Caterpillar EMS Throttle Position Sensor

Written by Ed

February 14th, 2011 at 7:38 am

Caterpillar EMS Hydraulic/electronic unit injector

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HEUI evolved from the EUI, and since mid-1994 has been used on Caterpillar, International T444E, DT466E, 1530E, certain Perkins models, and, most famously, on the Ford (International) Power Stroke. Unlike conventional camshaft-driven unit injectors, HEUIs are actuated by high-pressure crankcase oil. Since injection is no longer tied to camshaft motion, fuel can be injected at any crank angle. At higher-than-idle speeds, injector pressure is independent of engine rpm and can attain values of 30,000 psi.

Figure 6-18 illustrates the general layout of the Cat system that differs only in detail from Ford and other HEUI applications. Figure 6-19 shows the arrangement of the piping for the 3126B truck engine, which is the focus of this discussion. The high-pressure oil pump delivers crankcase oil to the injectors at cranking pressures of 500 psi that increase to as much as 3300 psi under speed and load. The computer-controlled injector actuation pressure control valve (IAPCV) regulates oil pressure by shunting pump output to the crankcase. Fuel pressure is regulated to 55 psi minimum.

HEUI schematic Caterpillar EMS Hydraulic/electronic unit injector

HEUI plumbing Caterpillar EMS Hydraulic/electronic unit injector

HEUI consists of five major components—a solenoid, poppet valve, mushroom shaped intensifier piston, barrel, and a seven-hole nozzle assembly (Fig. 6-20). Approximately 4A is required to energize the solenoid and 1.5A holds it open.

Upon command, the solenoid opens the poppet valve to admit high-pressure lube oil to the upper end of the intensifier piston (6 in Fig. 6-20). The oil forces the piston and plunger (7) down against fuel trapped in the injector body by a ball check valve. The fuel end of the plunger is smaller in diameter than the upper, or oil, end. The difference in cross-sectional area multiplies the hydraulic force acting on the fuel 7.5 times, to produce injection pressures of 3000–30,000 psi. Pressurized fuel lifts a second check valve, enters the cavity on the lower right of the drawing, and reacts against the needle shoulder to overcome spring tension. Nozzle-opening pressure (NOP) varies with the application. Some Cat injectors have an NOP of 4500 psi. Rebuilders of Power Stroke HEUIs look for 2750 +/_ 75 psi.

HEUI injector Caterpillar EMS Hydraulic/electronic unit injector

Note that both band width (the time the injector is open) and actuator-oil pressure determine the amount of fuel delivery.

HEUI injectors have undergone constant refinement. The most significant change is the split-shot PRIME (preinjection metering) version that first appeared on 1994 California Ford F series trucks and has since become almost universal.

These injectors work like other HEUIs, except that the plunger incorporates a radial groove that receives fuel through six bleed ports drilled in the face of the plunger. As the piston moves downward, the groove aligns with a spill port in the barrel, shunting pressure. The output-side check ball seats and injection stops. Further piston movement masks the port and injection resumes.

Written by Ed

February 14th, 2011 at 2:38 am

Caterpillar EMS High-pressure circuit

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Deactivating one EUI at a time will identify misfiring or dead cylinders. As mentioned previously, current values are high, and for your own safety, do not tamper with EUI wiring while the engine is running. Professional-quality scanners can safely deny power to the injectors so that the effect, if any, on engine performance can be gauged. When a weak cylinder is located, replace the injector and retest. If a new injector does not solve the problem, check valve lash to make certain that the valves are seating and, if necessary, make a cylinder compression. Caterpillar technicians use a boroscope, inserted through the injector mounting boss,to visually inspect cylinder internals.

Written by Ed

February 14th, 2011 at 2:32 am

Caterpillar EMS Low-pressure circuit

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Figure 6-17 illustrates the low pressure circuit for EUI-equipped engines. A gear-type transfer pump (9) delivers fuel from the tank (12) to the injectors (3). The pump incorporates a check valve (11) that permits fuel to flow around it during manual priming and a pressure-relief valve (10) to protect the system from over-pressurization.

Cat supplies dealer mechanics with a special tool, consisting of a pressure gauge, a sight glass, and the necessary fittings for makeup to mechanical and electronic low pressure systems.

UEI fuel system Caterpillar EMS Low pressure circuit

Check fuel pressure by removing the fuel pressure sensor at the base of the fuel filter. Install a pressure gauge and run the engine at rated rpm and load. Pressure should be 90 psi. If pressure is 75 psi or lower, check the fuel level in the tank, verify that the fuel cap vent is open, and that supply and return lines are in good condition. Pay particular attention to the return line, which can collapse if exposed to excessive heat. Replace the fuel filter. If necessary, replace the lift pump.

If fuel pressure is high, that is, 100 psi or greater, remove the fuel-regulating valve (10) and make sure the orifices near the tip of the unit are open. Flush out any debris and attempt to find the source of the contamination. Check for a clogged fuel return line. Verify that the transfer-pump relief valve functions.

Written by Ed

February 14th, 2011 at 2:31 am

Caterpillar EMS Electronic Unit Injector

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Both the 3100-3500 and C series engines employ EUIs that combine mechanical actuation with electronic control over fuel volume. Figure 6-15 illustrates an EUI in cross-section. A roller-tipped rocker arm, acting on in the injector plunger, provides the force necessary to generate the 28,000-psi injection pressure. The solenoid valve, shown on the left of the drawing, opens the spill/fill port to admit fuel into the injector barrel during the period of plunger retraction. A spring-loaded check valve, located near the injector tip and set to open at 5000 psi, remains closed during the fill process.

EUI cross section Caterpillar EMS Electronic Unit Injector

Injection can be initiated any time after the plunger starts its downward travel. But until the ECM signals the solenoid valve to close the spill/fill port, fuel merely cycles through the EUIs as a coolant and as a purge to remove any entrapped air.

Upon signal, the solenoid valve closes the port, trapping fuel in the injector barrel. Further downward movement of the plunger raises fuel pressure sufficiently to overcome spring tension acting on the check valve. The check valve opens and injection begins.

Injection continues until the ECM signals the solenoid to open the spill/fill port. Responding to the sudden loss of pressure at the injector tip, the check valve snaps shut. Injection ceases. The plunger continues its downward stroke, displacing fuel through the open spill/fill port and into the fuel-return gallery.

Although the software has primary responsibility for injector timing, plunger movement is affected by rocker-arm lash. The onset of pressure rise depends upon the clearance between the rocker arm and the plunger. A Caterpillar PN J 35637 height gauge is used to establish this critical variable (Fig. 6-16).

EUI position Caterpillar EMS Electronic Unit Injector

Written by Ed

February 14th, 2011 at 2:28 am

Caterpillar EMS

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Figure 6-12 illustrates the EMS used on Caterpillar 3116, 3176, 3406E, and 3500 engines. It is a relatively simple system, without the bells and whistles mandated by current emissions regulations. The ECM mounts on the engine, which reduces the electromagnetic radiation given off by the harness, simplifies packaging, and enables the computer to be cooled by fuel. A major engineering effort was required to isolate the electronics from the heat, vibration, solvents, steam, and water blasts that engines are exposed to.

3406E cat engine Caterpillar EMS

All sensors, with the exception of the oil pressure sensor, input data for efficient fuel allocation. Abnormally low or high sensor readings cause the ECM to set one or more trouble codes, which can be retrieved by connecting a scan tool to the SAE J1922 data link connector. The only computer-controlled actuators in this particular system are the electronic unit injectors (EUIs), cooling fan, and cruise control.

Written by Ed

February 14th, 2011 at 2:24 am

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Diesel Engine Actuators

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Sensors provide data to the ECM and actuators carry out the computer’s commands. The primary actuators are the electronic injectors, part and parcel of any EMS. Another almost universal type of actuator is the electronic governor. Figure 6-11 sketches the “drive-by-wire” governor used on the Deere 7L 6076 H. A switch on the electronic control module enables the operator to select any of three speed-control programs—true all-speed governing (as used in vehicles), min-max governing (for generator applications), and full-power boost. The latter option has a timer associated with it to prevent engine damage.

Other actuators control fuel pressure, turbo boost and, in some applications, exhaust back pressure.

throttle control Diesel Engine Actuators

Written by Ed

February 14th, 2011 at 2:19 am

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Diesel Engine Sensors

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Advanced c-r systems for motor vehicles include the following sensors:
• Temperature—ambient, coolant, intake air, fuel, and exhaust (upstream and/or downstream of turbo). Most of these sensors are negative temperature coefficient types, which lose internal resistance as temperature increases. Coolant and exhaust temperature sensor elements collect deposits that should be periodically removed.
• Pressure—atmospheric, fuel, turbo boost, crankcase, exhaust, and compressed air (for heavy trucks). Exhaust-gas pressure sensors monitor pressure drops across particulate traps.
• Position—rack, idle mode, variable-geometry turbocharging (VGT) control, turbo wastegate, back-pressure, and exhaust gas recirculation (EGR) valves. These sensors generally take the form of a switch or variable resistor.
• Mass air flow entering the manifold.
• Oxygen content in exhaust gas.
• Velocity—crankshaft rpm, road speed and, for some applications, turbo rpm. A coil responds to shifts in the magnetic field by generating a small signal voltage.

One-off EM systems, custom-built for existing installations, often retain the mechanical governor as a way to reduce costs. Production systems incorporate electronic governing, whose operation is controlled by the computer in concert with a magnetic engine-speed sensor. The ECM also uses speed-sensor data to calculate injector pulse width. Figure 6-9 illustrates sensor operation, which uses gear teeth as markers. Some speed sensors pick up the rpm signal from a single gear tooth, which has a distinctive shape and magnetic signature.

engine speed sensor Diesel Engine Sensors

In addition, a Hall-effect sensor, triggered by slit on the camshaft gear, generates a timing reference and, in some applications, reports engine speed. Failure of the camshaft position sensor shuts the engine down, often without warning. Bosch systems have a fail-safe feature that enables the computer to calculate timing from the crankshaft speed sensor when the primary reference is lost. The engine will continue to run, but starting may be more difficult. For some Cat models, either sensor can stand in for the other.

As mentioned earlier, accelerator position is reported as changes in the band width (duration of voltage) generated by the throttle position sensor (TPS). These sensors are not without problems, and Bosch again comes to the rescue by providing a second, backup throttle position sensor.

A mass air flow (MAF) sensor measures the volume of air entering the engine as a function of its cooling effect on a heated film or a platinum wire (Fig. 6-10). Supporting electronics measure how much current is needed to maintain the film at target temperature, which is about 75° F above ambient. As engine speed and air flow increase, correspondingly more current is needed. Current draw appears as an analog output voltage of between 0 and 5V. MAF sensors lose accuracy when contaminated and can be ruined by rough handling.

air mass sensor Diesel Engine Sensors

One would imagine that the computer, capable of several hundreds of thousands operations a second, would exert absolute control over the engine. But things get out of hand in ways the computer cannot predict. For example, fuel quality varies with each fill-up, injector nozzles wear unevenly, humid air exerts a greater cooling effect on MAF sensors than dry air. These and a hundred other variables affect combustion efficiency. The O2, or lambda, sensor closes the control loop by monitoring the level of oxygen in the exhaust gases.

Unlike other sensors, the platinum-coated zirconium-oxide O2 sensor generates its own voltage. Once it reaches operating temperature (approximately 700 C), the sensor develops nearly 0.7V in fuel-rich environments. As less fuel is burned and the oxygen content of the exhaust approaches that of the atmosphere, sensor voltage drops off to nearly zero. Signal voltage exhibits a sawtooth pattern. Normally, the computer uses this data, in conjunction with air-flow data, to deliver no more fuel than needed for combustion. Under load, the computer relaxes its standards a bit, richening the mixture for more torque. The O2 sensor then functions as a smoke limiter. The sensor also influences the amount of exhaust gas recirculated into the combustion chambers.

Inline engines have an O2 sensor threaded into the exhaust manifold at Y, where temperatures are high and exhaust gases are representative of all cylinders. V-type engines replicate the arrangement for each bank. An electrically heated fourwire (two wires to ground, one carrying signal voltage and the other battery voltage to the heater) O2 sensor will also be installed downstream of the catalytic converter. This sensor monitors converter efficiency and has no effect upon mixture strength. OBD-2 sensors are good for 100,000 miles, although response slows with age and contamination.

In event of malfunction, the EMS can disregard the O2 sensors and enter into open-loop operation. Working without the benefit of feedback, the computer adjusts fuel delivery to programmed values. Open-loop operation is, with good reason, called the “limp-home” mode.

Written by Ed

February 14th, 2011 at 2:17 am

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Bosch CAN bus

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A controller area network (CAN) employs a single line, or bus, to convey data to all components that make up the network. Individual components—computers, sensors, display panels, stepper motors, and other devices—respond only to those signals addressed to them. These components, or stations, still need power lines, but one signal line suffices for all. Multiplexing is not too different than old-fashioned telephone systems that rang every phone on the line. By counting the number of rings, you knew who should pick up the receiver.

To make production changes easier, message content, rather than the name of the intended receiving station, functions as the address. This enables new stations to be added without modifying the transmitters. An 11- or 29-bit word prefaced to each data packet identifies message content. Thus, engine-speed data will be received by all stations, but will be of interest only to the computer and the operator display panel.

Upon acceptance of a message, the receiving station scans it for errors and acknowledges receipt. Transmission speed ranges between 125 kb (1 kb = 1000 bits/ second) and 1Mb. Messages whose content changes frequently, such as the voltage drop that signals injector opening, have priority over routine traffic.

The CAN protocol has fairly wide use for automotive and truck applications, and will, experts say, become universal within the next decade.

Written by Ed

February 14th, 2011 at 2:09 am

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