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Tim's Auto Repair
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Chevrolet Blazer 4x4 (Mid Size): I have a 1992 s10 blazer 4.3L

Resolved Question:

I have a 1992 s10 blazer 4.3L I have replaced the fuel pump, cpi unit, and fuel relays it seemed to be running fine then it just quit while I was driving and it is not getting any fuel. has power to the pump? What could be causing this?
Submitted: 5 years ago.
Category: Chevy
Expert:  Tim's Auto Repair replied 5 years ago.


do you have a spark on the plug wires??

does the fuel pump come on for 2 seconds when you first turn the key on?


Customer: replied 5 years ago.
Yes there is spark and the pump kicks on when you turn the key.
Expert:  Tim's Auto Repair replied 5 years ago.


i think you have one of two pssible problems here

the problem is that the computer doesnt know that the engine is turning,thus,to activate the injectors....

1-the ignition module,,even though you do have a spark,it may not be sending a signal to the computerthat the engine is turning..

2-the pick-up coil inside the distributer..these will just quit working sometimes,,if it is the pick-up coil,you may concider just replacing the complete distributer with a new rebuilt unit,sense it will need to be pulled and took apart to replace the pick-up


Customer: replied 5 years ago.
I dont think it is either one of these if you hit it with either it will start then die so it has spark
Expert:  Tim's Auto Repair replied 5 years ago.

i understand it has a spark.......yes,,it is one of these......the injectors dont have a pulse.and the fuel pump doesnt run when the starter is turning..this is why it wont start and run..,,the computer doesnt know the engine is turning,thus not activating the pump or the injectors


Customer: replied 5 years ago.
Relist: Inaccurate answer.
Expert:  Tim's Auto Repair replied 5 years ago.


i have seen this many,many times

let me give you a few test....when the ignition module does this,,there is no good test for it,,you local parts store can test it for spark...but not for referance,,you may want to replace it first..


1992 Chevy Truck S10/T10 Blazer 4WD V6-262 4.3L VIN W CPI
Ignition Control Module Description and Operation, Components: Distributor Reference Signal

The distributor reference signal provides the ECM with both engine RPM and crankshaft position information. This enables the ECM to operate the fuel pump relay and energize the fuel injector.

When the engine is cranking or running the ECM receives Distributor Ignition (DI) reference pulses from the ignition module. If the wire becomes open or grounded the engine will not run, as the ECM will not operate the injector.

1992 Chevy Truck S10/T10 Blazer 4WD V6-262 4.3L VIN W CPI
Pick-Up Coil Testing and Inspection, Component Tests and General Diagnostics
graphicFig. 4 Pickup coil test connections

Note Make sure the ignition switch is "OFF".

1. Remove distributor cap.
2. Disconnect pickup coil connector from IC module.
3. Connect ohmmeter as shown in step 1, and flex pickup coil leads while observing meter. Meter should indicate infinite resistance at all times. If not, pickup coil is defective.
4. Connect ohmmeter as shown in step 2, and flex pickup coil leads while observing meter. Meter reading should remain constant between 500 and 1500 ohms. If not, replace pickup coil.

Note To replace the coil, remove the distributor.


1992 Chevy Truck S10/T10 Blazer 4WD V6-262 4.3L VIN W CPI
Fuel Delivery and Air Induction Description and Operation, Components: General System Description

Fuel Control Description for CPI (Central Port Injection)

The fuel control system is controlled by an Electronic Control Module (ECM) located in the passenger compartment. The basic function of the fuel control system is to control fuel delivery to the engine. Fuel is delivered to the engine by a Central Port Injection (CPI) unit. The main control sensor is the Oxygen (O2) sensor, which is located in the exhaust manifold. The O2 sensor tells the ECM the amount of oxygen in the exhaust gas, and the ECM changes the air/fuel ratio to the engine by controlling the fuel injector. A 14.7:1 air/fuel ratio is required for efficient catalytic converter operation. Because the constant measuring and adjusting of the air/fuel ratio, the fuel injection system is called a "Closed Loop" system. Several other important engine operation parameters include: engine speed, manifold pressure, engine coolant temperature, and throttle position. These parameters determine the "mode" of engine operation.

Fuel Control Operation Components

The fuel control system consists of the following components:
- Central Port Injection (CPI)
- Fuel pump
- Fuel pump relay
- Fuel tank
- Accelerator control components
- Fuel lines
- Fuel filter
- Evaporative emission control system


The fuel control system has an electric fuel pump. located in the fuel tank on the gage sending unit. It pumps fuel to the CPI unit through an in-line fuel filter and fuel supply line. The pump provides fuel at a pressure above the regulated pressure needed by CPI injector. A pressure regulator in the CPI unit keeps fuel available to the injector at a constant pressure. Fuel in excess of injector needs is returned to the fuel tank by a separate line. The ECM controls the injector that is located in the Central Port Injection (CPI) assembly. The CPI delivers fuel in response to the pulse width mandated signal from the ECM in one of several modes. In order to properly control the fuel supply, the fuel pump is operated by the ECM through the fuel pump relay and oil pressure switch.

Modes of Operation

The ECM monitors voltages from several sensors to determine how much fuel to give the engine. The fuel is delivered under one of several conditions called "modes." All the modes are controlled by the ECM.

Starting Mode

When the key is first turned "ON", the ECM turns on the fuel pump relay for two seconds, and the fuel pump builds up pressure to the CPI unit. The ECM checks the Coolant Temperature Sensor (CTS), Intake Air Temperature (IAT) sensor, Throttle Position Sensor (TPS), and Manifold Absolute Pressure (MAP) sensor, then determines the proper air/fuel ratio for starting. This ranges from 1.5:1 at -36°C (-33°F) to 14.7:1 at 94°C (201°F) running temperature. The ECM controls the amount of fuel delivered in the starting mode by changing how long the injector is turned "ON" and "OFF." This is done by "pulsing" the injector for very short time.

Clear Flood Mode

If the engine floods, clear it by pushing the accelerator pedal down all the way. The ECM when pulses the injector at 16.5:1 air/fuel ratio, and holds this injector rate as long as the throttle stays wide open, and the engine is below 600 rpm. If the throttle position becomes less than 65%, the ECM returns to the starting mode.

Run Mode

The Run Mode is the mode under which the engine operates most of the time. In this mode, the engine operates in one of two conditions: "Open Loop" and "Closed Loop."

Open Loop/Closed Loop

When the engine is first started, and it is above 400 rpm, the system goes into "Open Loop" operation. In "Open Loop," the ECM ignores the signal from the O2 sensor, and calculates the air/fuel ratio based on inputs from the Coolant Temperature Sensor (CTS) and Manifold Absolute Pressure (MAP) sensor. The system initiates in "Open Loop" while the ignition is turned to the "ON" position and battery voltage is applied to the Oxygen sensor's built-in heater element. Approximately 30 seconds after voltage is applied to the heater, the sensor reaches a temperature above 500°C, then "Closed Loop" operation is achieved. Throughout various vehicle operational conditions, the heater element ensures the sensor consistently operates in that temperature range. Heated sensors contain an internal, electrically powered heater. As such, they are not as dependent on engine heat to achieve minimum operation temperature. The heated sensor becomes active faster during engine warm up than an unheated sensor. This may or may not be desirable, depending on the design of the particular emission control system. The heated sensor remains active during long idles on engines with cool exhaust while the unheated sensor may cool below its minimum operating point and stop satisfactory function. This allows the air/fuel ratio to stay close to 14.7:1.

Acceleration Mode

When the ECM senses rapid changes in throttle position and manifold pressure, the system enters the Acceleration Mode and provides the extra fuel needed for smooth acceleration.

Deceleration Mode

When deceleration occurs, the fuel remaining in the intake manifold can cause excessive emissions and backfiring. When the ECM observes a fast reduction in throttle opening and a sharp decrease in manifold pressure, it causes the system to enter the Deceleration Mode, reducing the amount of fuel delivered to the engine. When deceleration is very fast, the ECM cuts off fuel completely for short periods.

Highway Fuel Mode (Semi-"Closed Loop")

This mode comes into operation at highway speeds and it's purpose is to improve fuel economy. For the ECM to operate in this mode, it first must sense the correct engine temperature, spark timing, canister purge activity and constant engine speed. During semi-"Closed Loop" operation, there will be very little block learn and integrator movement and the oxygen sensor values will read below 100 millivolts.

Decel En-leanment

On deceleration, the ECM senses a high MAP vacuum (low voltage or kPa) and leans the fuel spray for emission reasons, but it should be noted that the ECM can trigger this condition (Decel En-leanment) while the vehicle is not moving.

Decel En-leanment Operation

This mode of operation can be mis-diagnosed as a lean condition. The ECM will run the system lean on decel, or if the MAP sensor senses a low voltage (high engine vacuum), with the vehicle standing still, it will lean out the fuel delivery. If it is noted while testing an ECM system and the transmission is in park, that the O2 reading is low (usually below 100 mV) and the block learn and integrator are both around 128 counts, lower the engine speed to 1000 rpm. If the oxygen sensor and block learn numbers respond normally at this rpm, it is possible that the system was fooled into the Decel En-leanment mode of operation. If the oxygen sensor and block numbers do not respond at the lower rpm readings, there are other problems with the vehicle.

Battery Voltage Correction Mode

When battery voltage is low, the ECM can compensate for a weak spark delivered to the distributor by:
- Increasing injector on time
- Increasing the idle rpm
- Increasing ignition dwell time

Fuel Cut-Off Mode

No fuel is delivered by the injector when the ignition is "OFF." This prevents dieseling. Also, fuel is not delivered if no reference pulses are seen from the distributor, which means the engine is not running. Fuel cut-off also occurs at high engine rpm, to protect internal engine components from damage.


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