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Dec 13, 06
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Fuel Injection Testing

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This page is to provide some BASIC test procedures for common problems, test procedures referenced from the 1991 B2600i factory manual.

Component List

The B2600i Fuel Injection system contains the following parts:

Throttle Body
Engine Control Unit
Injectors
Pressure Regulator
Pressure regulator control solenoid
Pulsation damper
Airflow Sensor
Oxygen Sensor

Low and high pressure fuel filters
Distributor
Check and Cut valve
Two-Way check valve
Throttle Position Sensor
Coolant Temp Sensor
Intake Air Temp Sensor

Before performing any tests or maintenance on the fuel system release fuel pressure by starting engine and disconnecting the opening relay located in the driver side kick panel until the engine stalls then perform required test or repair.

Throttle Body

Type: Single Barrel Horizontal Draft
Diameter: 55 mm (2.2 in.)

Cleaning: Only use throttle body cleaner, other solvents will strip the coating on the aluminum and cause drivability problems later.
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Engine Control Unit (ECU)

Located in passenger side kick panel.
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Injectors


Type: High Impedance
Drive: Voltage
Resistance: 12-16 Ohms at 20 deg C (68 deg F)
Volume: 74-89 cc /15 sec. (356cc per min.)
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Pressure Regulator

Pressure regulator is mounted on the end of the fuel rail and has an orange vacuum line connected to it.

To test pressure regulator release fuel pressure then install pressure gauge between main fuel line and fuel filter. Start engine and run at idle, pressure should be between 28-37 psi.

To perform leak down test install pressure gauge like above. Use a hose plier clamp to pinch off the fuel return line on the pressure regulator. Locate the 2-pin yellow test connector near the fuel filter and install a jumper wire accross the 2 pins. Make sure the opening relay is connected and turn the ignition switch to the on position for 10 seconds to run fuel pump. Turn the key to the off position and remove jumper wire from test connector, watch fuel pressure for 5 minutes. If pressure is below 21 psi replace the fuel pressure regulator.

Note: If faulty may cause a "rolling" or "hunting" idle may also cause hard start when engine is warm.
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Pressure Regulator Control Solenoid (PRC)

The PRC is mounted to the charcoal canister on the passenger side of the engine compartment and has an orange vacuum line connected to it.

Start testing by verifying the solenoid is getting vacuum, this can be done by starting the truck and removing the orange vacuum line from the solenoid, place thumb over the port and feel for vacuum. If no vacuum is felt repair the vacuum leak this may fix a rough idle or hard start problem.

Locate the Blue with Black stripe terminal wire and ground it with a jumper wire (solenoid connector still on). Hold thumb over part and verify no vacuum is felt. If you are sure the jumper wire made contact then check the solenoid.

To test solenoid, disconnect the connector and blow through the orange vacuum line, air should flow from the opposite port. Disconnect the solenoid and connect to 12 volts and again blow through the port for the orange vacuum line. Check that air comes out of the valve filter which is the cylindrical piece on the opposite side of the connector. If solenoid fails either check replace it.

Note: A bad PRC will cause similar or same problems as a bad pressure regulator.
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Pulsation Dampener

The purpose of the pulsation dampener is to help steady idle and improve driver comfort it is located on the side of the intake manifold between runners for cylinders 3 and 4. To test locate the dampener then start the truck, place your finger on the skrew of the pulsation dampener head. If pulsation is not felt replace the dampener.

Note: A faulty pulsation dampener will NOT cause a major drivability problem.
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Airflow Sensor

Located on the driver side of the engine compartment, located inline with the intake ducting between the air filter and resonance chamber.

Testing is done with engine running and again with ignition on:

Blue with Yellow stripe wire should measure 12v.
Green with Orange should measure 0v.
Green with Black should measure 1-2v key on, .9-5v engine running.
Green with Yellow and Black with Orange stripe wires should both read about 0v
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Oxygen Sensor

Oxygen sensor must reach 600 deg F before it will start to function, warm up engine before testing. Disconnect the sensor and connect sensor wire to red voltmeter probe, touch the black probe to ground. Rev engine at 4,500 rpm until meter reads about .7v (or 700 mV). Snap throttle open several times and check that the meter reads between .5-1v while enigne is accelerating and between 0-.4v when decelerating. If not as specified replace O2 sensor once the sensor has reached operating temperature voltage should change quickly when throttle is snapped, if the readings are sluggish replace the sensor.
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Filters

Low Pressure: In tank made of nylon mesh may clog intermittently if tank contains rust.
High Pressure: Mounted on passenger side firewall, paper element, fuel line connects to top and bottom.
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Coolant Temp Sensor

Oxygen sensor must reach 600 deg F before it will start to function, warm up engine before testing. Disconnect the sensor and connect sensor wire to red voltmeter probe, touch the black probe to ground. Rev engine at 4,500 rpm until meter reads about .7v (or 700 mV). Snap throttle open several times and check that the meter reads between .5-1v while engine is accelerating and between 0-.4v when decelerating. If not as specified replace O2 sensor once the sensor has reached operating temperature voltage should change quickly when throttle is snapped, if the readings are sluggish replace the sensor.
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Intake Air Temp Sensor

The Intake Air Tempurature Sensor, commonly called the IAT is mounted in the Dynamic Chamber. The sensor works by creating a resistance which gets lower as temperature increases. To test the sensor simply measure it's resistance and the given temperatures below and see if you're values match.
Temperature Resistance
77 deg F29.7 - 36.3 K Ohms
185 Deg F3.3 - 3.7 K Ohms

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