Fuel Injection System - Digital Cadillac Eldorado IX

COMPONENT TESTING

Note. Specific component testing information not available. Refer to any tests performed during TROUBLE SHOOTING .

DESCRIPTION

The Digital Fuel Injection (DFI) system is a speed density fuel system which accurately controls air/fuel mixture providing maximum engine performance and minimizes emissions.

The system consists of 11 major systems and sub-assemblies: Fuel Delivery, Air Induction, Data Sensors, Electronic Control Module (ECM), Electronic Spark Timing (EST), Idle Speed Control (ISC), Emission Controls, Closed Loop Fuel Control, System Diagnostics, Cruise Control and Torque Converter Clutch (TCC).

The ECM, an on-board computer, monitors engine operations and environmental conditions. The ECM controls amount of fuel metered through injector valves based upon engine demand and exhaust emissions. Fuel is supplied to engine through 2 electronically pulsed (timed) injector valves located in throttle body.

Note. Primary sub-systems which affect fuel system operation will be covered in this section: fuel delivery, air induction, Idle Speed Control (ISC), data sensors and Electronic Control Module (ECM). See DFI CONTROL SYSTEM article in COMPUTER CONTROLS section for more information.

FUEL DELIVERY

An electric in-tank fuel pump, supplies pressurized fuel to the throttle body. The ECM actuates the fuel pump through a fuel pump relay when ignition is turned on. If engine is not started within 2 seconds, the ECM will deactivate fuel pump until engine is started.

As a back-up system to fuel pump relay, the fuel pump can also be activated by an oil pressure switch. The oil pressure switch is normally open until oil pressure reaches approximately 4 psi (.28 kg/cm 2 ). If fuel pump relay fails, the oil pressure switch closes when oil pressure is obtained, operating the fuel pump. Inoperative fuel pump relay may result in extended cranking times.

The fuel pressure regulator, an integral component of the throttle body, provides proper pressurized fuel up to 20 psi (1.40 kg/cm 2 ). A diaphragm-operated relief valve regulates fuel pressure. Relief valve is exposed to atmospheric pressure, maintaining constant pressure between 9 and 12 psi (.6-.8 kg/cm 2 ) across fuel injectors. Unused fuel is returned to fuel tank through fuel return line.

During normal engine operation, 2 fuel injectors are actuated alternately by the ECM. The injectors direct metered atomized fuel into throttle bores above throttle valves. Both injectors are actuated simultaneously during cranking.

AIR INDUCTION

The air induction system consists of throttle body and intake manifold. Air entering the throttle body is distributed to each cylinder through intake manifold.

Throttle body contains a special distribution skirt below each injector valve to improve fuel distribution. Airflow rate is controlled by throttle valves connected to accelerator linkage. Idle speed is determined by throttle valve positioning.

Throttle valve positioning is controlled by the Idle Speed Control (ISC) solenoid which is activated by the ECM.

DATA SENSORS

Each sensor furnishes an electronic signal to ECM which modifies injector pulse due to engine operating conditions. The following sensors are used

Manifold Air Temperature Sensor (MAT)

Mounted in the intake manifold, directly in front of throttle body, the MAT sensor measures intake air temperature. The sensor resistance changes due to air temperature.

The ECM uses these resistance changes to determine intake air density and then adjusts injector pulse accordingly.

Coolant Temperature Sensor (CTS)

The CTS is mounted in engine coolant stream of intake manifold. This sensor is a thermistor which changes resistance based on coolant temperature.

Sensor provides coolant temperature information to ECM for fuel enrichment, ignition timing, EGR operation, canister purge control, air management, idle speed control, and closed loop fuel control.

Sensor resistance will be high with cold coolant temperatures and low with hot coolant temperatures.

Manifold Absolute Pressure Sensor (MAP)

The MAP sensor monitors intake manifold pressure changes due to engine load and speed variations. MAP sensor also calculates barometric pressure under certain conditions, allowing ECM to use sensor readings to provide barometric pressure input. MAP sensor is mounted on rear of intake manifold.

Increase of intake manifold pressure requires additional fuel. The increase of manifold pressure produces a higher voltage at MAP sensor. This information is sent to the ECM so injector pulse width is increased. Decrease in manifold pressure results in decreased pulse width.

Throttle Position Sensor (TPS)

The TPS, mounted on the throttle body, is connected directly to throttle shaft. Alteration of throttle angle changes output voltage of TPS to the ECM. These output voltages are used to determine fuel delivery.

Vehicle Speed Sensor (VSS)

The VSS creates an output signal which indicates vehicle speed to the ECM. VSS produces a weak signal which is amplified by a buffer amplifier on DeVille and Fleetwood models. Buffer amplifier is not used on remaining models.

Speed sensor is mounted on transaxle. Buffer amplifier is located behind glove box. The ECM uses VSS signals to operate fuel economy data panel, integral cruise control, idle speed control system and fuel delivery modification under load conditions.

Engine Speed Sensor

Engine speed signals are delivered from the 7-terminal HEI module contained in the distributor to the ECM. The ECM calculates time between pulses to determine engine speed and ignition spark advance.

Oxygen Sensor

Mounted in the exhaust manifold, the oxygen (O2) sensor monitors the amount of oxygen in the exhaust stream. The sensor generates a weak voltage which varies with exhaust gas oxygen content.

Increased oxygen content creates a lean mixture, resulting in a low output voltage. Decreased oxygen content creates a richer mixture, resulting in a higher output voltage. ECM monitors these voltages to determine correct air/fuel ratio.

Power Steering Pressure Switch (PSPS)

The PSPS is a normally closed switch which opens when power steering pressure is indicated. Normal voltage is supplied to the ECM through the PSPS. Under pressure, the switch opens and voltage loss is noted at the ECM. ECM uses this signal to extend ISC plunger and stabilizes idle speed.

Park/Neutral Switch (P/N)

The Park/Neutral switch sends a signal to the ECM when placed in Park or Neutral. The ECM uses this signal to stabilize idle speed.

ELECTRONIC CONTROL MODULE (ECM)

The ECM monitors information from various sensors, and controls the systems affecting vehicle performance. Sensor inputs are supplied to the ECM and processed to maintain proper pulse width, correct idle speed and proper spark advance. The ECM also performs a system diagnostic function.

IDLE SPEED CONTROL (ISC)

The ISC, mounted to the throttle body, is an electrically driven actuator which changes throttle angle according to ECM demands. An internal switch by-passes this function when throttle is opened enough to allow TPS to move from idle position.

ADJUSTMENTS

Note. For adjustments of ISC Motor and Throttle Position Sensor, see the V8 TUNE-UP article in this section.

PRELIMINARY CHECKS

The following systems and components must be in good operating condition prior to trouble shooting fuel system.

1. Ensure no hard codes are stored in the memory.
2. All support systems and wiring.
3. Battery condition and specific gravity.
4. Ignition system condition.
5. Engine compression pressure.
6. Fuel supply pressure and flow.
7. Electrical connections and terminals.
8. Vacuum lines, fuel hoses and pipe connections.
9. Exhaust system.
10. Ensure "Engine Control Light" is operable.

FUEL SYSTEM DIAGNOSIS

1. Fuel pressure should be checked. Connect Fuel Pressure Gauge (J-25400-300) to fuel line service fitting. Measure fuel pressure while cranking engine.
2. If pressure is not between 9-12 psi (.6-.8 kg/cm 2 ), see appropriate A-4 FUEL SYSTEM DIAGNOSIS CHART in COMPUTER CONTROLS section. If pressure is between 9-12 psi (.6-.8 kg/cm 2 ), see appropriate A-5 INJECTOR DIAGNOSIS CHART in COMPUTERIZED ENGINE CONTROL section.

FLOODING, ROUGH IDLE

1. If appropriate A-5 INJECTOR DIAGNOSIS CHART indicated fuel injectors continue to spray fuel with electrical connection removed, replace injector(s) as required.
2. After using appropriate diagnostic chart, remove injector(s). Inspect large and small "O" rings for cuts, distortion or other damage. Check that steel back-up washer is located beneath large (upper) "O" ring. Use new "O" rings during installation. (Scheme 108)
3. Inspect fuel injector fuel filters for cleanliness and damage. Clean or replace as necessary. DO NOT immerse injectors, filters or rubber parts in carburetor cleaner.

HARD START

1. Check fuel pressure. If pressure bleeds off immediately, check for fuel lines or injector leaks with ignition on and engine stopped. Cap fuel return line at throttle body.
2. Turn ignition on, then off while noting pressure drop. If pressure drops rapidly, check for faulty fuel pump check valve or fuel leaks in the tank. If pressure holds with ignition on and return line capped, inspect fuel pressure regulator for leakage.
3. Check ignition timing. Check HEI voltage output, ignition system components and spark plug condition. Check spark plug wire resistance. Replace spark plug wire if resistance exceeds 50,000 ohms.
4. Check for sticking or binding TPS or throttle linkage. Check for leaking intake manifold or throttle body gaskets. Check for restricted exhaust system.
5. Check for restrictions at MAP sensor vacuum ports. Check for vacuum trapped in MAP sensor. Check coolant sensor and MAT sensor accuracy. Check for damaged engine components.

STALL AFTER START

1. Inspect vacuum hoses and electrical connections. Ensure hot air tube is connected to air cleaner. Check air cleaner thermostatic valve operation.
2. Check PCV and EGR valve operation. Check Electronic Spark Timing (EST) if engine will run with EST disabled. Check fuel pressure. Fuel pressure should be a steady 9-12 psi (.6-.8 kg/cm 2 ) in all speed ranges.
3. If fuel pressure is not within specification, see appropriate A-4 FUEL SYSTEM DIAGNOSIS CHART in COMPUTERIZED ENGINE CONTROL section. Check for overcharged A/C system or inoperative cooling fan.
4. Check for plugged or restricted fuel lines. Check for defective ignition system. Check for restricted exhaust system.

HESITATION, SAG, STUMBLE

1. Inspect vacuum hoses and electrical connections. Check air cleaner thermostatic valve operation.
2. Check fuel pressure. Fuel pressure should be a steady 9-12 psi (.6-.8 kg/cm 2 ) in all speed ranges. If fuel pressure is not within specification, see appropriate A-4 FUEL SYSTEM DIAGNOSIS CHART in COMPUTERIZED ENGINE CONTROL section.
3. Check for defective spark plugs. Check PROM for correct application. Check for sticking or binding TPS. Check EGR valve operation.
4. Check fuel injectors for fuel leakage. Separate injector connectors and remove injectors. Reconnect injector connectors. Crank engine while observing injectors.
5. Fuel should flow from both injectors. If fuel does not exist at both injectors, see appropriate A-5 INJECTOR DIAGNOSIS CHART in COMPUTERIZED ENGINE CONTROL section.
6. Check HEI ground for good contact. Check canister purge system operation. Check for restricted exhaust system.

SURGES AND/OR CHUGGLE

1. Verify transmission operation in all ranges. Check air cleaner thermostatic valve for proper operation.
2. Check for open or short in the following circuits: HEI by-pass number 424, EST number 423 and Viscous Converter Clutch (VCC) numbers 420 and 422.
3. Check EGR valve operation. Check ignition system. Check fuel pressure. Fuel pressure should be a steady 9-12 psi (.6-.8 kg/cm 2 ) in all speed ranges. If fuel pressure is not within specification, see appropriate A-4 FUEL SYSTEM DIAGNOSIS CHART in COMPUTERIZED ENGINE CONTROL section. NOTE: The following procedure will require a vehicle of same make, model and year to be used for comparison.
4. Check for exhaust restrictions. Use Pressure Gauge Tap (J-35314) with a 0-15 psi (0-1.1 kg/cm 2 ) range. Block drive wheels. Apply parking and service brakes.
5. Place vehicle in Drive and load the engine at a steady 1600 RPM. If there is a 1.0 psi (0.1 kg/cm 2 ) or greater backpressure difference, exhaust system is restricted. Check for vacuum leaks.

LACK OF POWER OR SLUGGISH

1. Inspect air cleaner condition. Check air cleaner thermostatic valve operation. Ensure throttle valve fully opens. Check ignition timing. Check for faulty spark plugs or ignition system.
2. Check for restricted fuel filter. Check fuel pressure. Fuel pressure should be a steady 9-12 psi (.6-.8 kg/cm 2 ) in all speed ranges. If fuel pressure is not within specification, see appropriate A-4 FUEL SYSTEM DIAGNOSIS CHART in COMPUTERIZED ENGINE CONTROL section.
3. Check EGR valve operation. Inspect for restricted MAP vacuum fitting. NOTE: The following procedure will require a vehicle of the same make, model and year to be used for comparison.
4. Check for exhaust restrictions. Use Pressure Gauge Tap (J-35314) with a 0-15 psi (0-1.1 kg/cm 2 ) range. Block drive wheels. Apply parking and service brakes.
5. Place vehicle in Drive and load the engine at a steady 1600 RPM. If there is a 1.0 psi (0.1 kg/cm 2 ) or greater backpressure difference, exhaust system is restricted.
6. Check for vacuum leaks at intake manifold and throttle body. Ensure transmission operates properly.

DETONATION, SPARK KNOCK

1. Check for overheating conditions. Check ignition timing. Check EGR valve operation. Inspect MAP sensor for restrictions in MAP hose or throttle body MAP port.
2. Check PROM for correct application. Check fuel pressure. Fuel pressure should be a steady 9-12 psi (.6-.8 kg/cm 2 ) in all speed ranges. If fuel pressure is not within specification, see appropriate A-4 FUEL SYSTEM DIAGNOSIS CHART in COMPUTERIZED ENGINE CONTROL section.
3. Check transmission for proper operation. Check for loose intake manifold bolts. Check for correct spark plugs. If condition still exists, vehicle may require use of high octane gasoline.

CUTS OUT, MISSES

1. Check for injector intermittent operation. See appropriate A-5 INJECTOR DIAGNOSIS CHART in COMPUTERIZED ENGINE CONTROL section.
2. Check cylinder compression. Check ignition system. Check ignition timing and idle speed. Check EST operation.
3. Check fuel pressure. Fuel pressure should be a steady 9-12 psi (.6-.8 kg/cm 2 ) in all speed ranges. If fuel pressure is not within specification, see appropriate A-4 FUEL SYSTEM DIAGNOSIS CHART in COMPUTERIZED ENGINE CONTROL section.
4. Check for contaminated fuel. Check for defective internal engine components.

BACKFIRE

1. Inspect for loose wiring grounds at engine block. Check ignition system for faulty components. Check ignition timing.
2. Inspect distributor for worn components. Ensure AIR system is pumping air into the exhaust manifolds at all times.
3. Check intake manifold bolts for tightness. Check for damaged internal engine components.

POOR FUEL ECONOMY

1. Check air cleaner thermostatic valve operation. Inspect air cleaner condition. Check ignition timing and ignition system operation.
2. Check for improperly applied VCC. Check for restricted exhaust system. Check for proper accuracy of data panel.

ROUGH, UNSTABLE OR INCORRECT IDLE, STALLING

1. Inspect vacuum hoses and electrical connections. Observe ISC operation in output cycling. Watch for ISC sticking or binding while manipulating the 4 terminal ISC connector.
2. Check for binding throttle linkage or cruise control cable. Check ignition system and ignition timing.
3. Check fuel pressure. Fuel pressure should be a steady 9-12 psi (.6-.8 kg/cm 2 ) in all speed ranges. If fuel pressure is not within specification, see appropriate A-4 FUEL SYSTEM DIAGNOSIS CHART in COMPUTERIZED ENGINE CONTROL section.
4. Check for leaking or intermittent injector operation. See appropriate A-5 INJECTOR DIAGNOSIS CHART in COMPUTERIZED ENGINE CONTROL section.
5. Check EGR and PCV valve operation. Check air cleaner thermostatic valve operation. Check fuel evaporative system.
6. Check for loose ECM grounds. Check for rapid cycling of A/C clutch. Check P/N switch circuit. See appropriate PARK /NEUTRAL SWITCH CIRCUIT chart in COMPUTERIZED ENGINE CONTROL section.
7. Check for air leak at throttle body mounting and intake manifold. Check for worn ignition distributor or internal engine components.

DIESELING

Check for leaking injectors. See appropriate A-5 INJECTOR DIAGNOSIS CHART in COMPUTERIZED ENGINE CONTROL section.

EXCESSIVE EXHAUST EMISSIONS (ODORS)

1. Check air cleaner thermostatic valve operation. Check PCV and EGR valve operation. Check for vacuum leaks. Ensure engine is operating at normal operating temperature.
2. Check ignition timing, ignition advance, idle speed and spark plug condition. Check for fuel in crankcase. If fuel exists, check PROM for proper application.
3. Check fuel pressure. Fuel pressure should be a steady 9-12 psi (.6-.8 kg/cm 2 ) in all speed ranges. If fuel pressure is not within specification, see appropriate A-4 FUEL SYSTEM DIAGNOSIS CHART in COMPUTERIZED ENGINE CONTROL section.
4. Check for leaking injectors. See appropriate A-5 INJECTOR DIAGNOSIS CHART in COMPUTERIZED ENGINE CONTROL section. Check for air at exhaust manifold ports at all times. Check catalytic converter for lead contamination.

INTERMITTENT ENGINE STALL, NO CODES

1. Check fuel pressure. Fuel pressure should be a steady 9-12 psi (.6-.8 kg/cm 2 ) in all speed ranges. If fuel pressure is not within specification, see appropriate A-4 FUEL SYSTEM DIAGNOSIS CHART in COMPUTERIZED ENGINE CONTROL section.
2. Inspect ISC throttle switch operation. Enter diagnostics. See appropriate GENERAL MOTORS DFI CONTROL SYSTEM THEORY & OPERATION article in COMPUTERIZED ENGINE CONTROL section.
3. Operate throttle from open to closed position. Note switch status light during operation. If light operation is intermittent, check ISC switch and throttle linkage for proper operation.
4. Check TPS operation. False TPS reading may create a stall due to improper acceleration enrichment or if false high throttle angle during coast down is indicated.
5. Check for intermittent operation of coolant, MAT or MAP sensors. Ensure hose to MAP sensor is not restricted. Check EGR valve operation.
6. Check for intermittent injector operation. See appropriate A-5 INJECTOR DIAGNOSIS CHART in COMPUTERIZED ENGINE CONTROL section. Check for voltage loss at the time of stall. If voltage loss exists, inspect charging system, battery and wiring.
7. Check for improperly applied VCC. Inspect ignition switch circuits for intermittent open circuit.
8. On stalls existing during low fuel level or deceleration, inspect fuel sending unit and fuel pump strainer.
9. If stall exists during normal closed throttle while coasting to a stop, check TPS setting and ISC-to-throttle linkage gap which will not allow throttle switch to close.
10. Stall may exist when power steering pressure is applied or when shifting transmission into gear. Check proper switch condition. Check for proper ISC-to-throttle linkage gap.
11. If stall exists during A/C operation, check A/C clutch indicator light operation or for high A/C head pressure.
12. On stalls occurring during engine starts with hot ambient air temperatures, check the evaporative emission control canister and solenoid.
13. If stall exists during cold or warm weather, check air cleaner thermostatic valve operation.

Removal

1. Remove air cleaner. Disconnect TPS, ISC motor and injector electrical connections. Remove throttle return springs, cruise control, throttle cable and downshift cable.
2. Disconnect and mark vacuum hoses and lines from throttle body. Using a back-up wrench, remove fuel inlet line and return lines. Remove throttle body retaining bolts. Remove throttle body and gasket.

Installation

Install throttle body using new gasket. Tighten bolts to specification. See TORQUE SPECIFICATIONS table at end of article. Replace fuel line "O" rings. Tighten fuel lines to specification. Reverse removal procedure for remaining components. If ISC or TPS were changed, see appropriate TUNE-UP article in this section for adjustment procedures.

1. Remove air cleaner. Disconnect TPS electrical connector. Remove TPS retaining screws. Remove lock washers and retainers.
2. Remove TPS from throttle body, noting location of TPS pick-up lever in relation to throttle shaft lever tang for installation reference.

1. With throttle valve in closed idle position, install TPS sensor on throttle body assembly. Ensure lever is located above tang on throttle actuator lever. Install retainers and new TPS screws and lock washers.
2. Tighten screws so TPS will move but is not loose. Reconnect electrical connector. Adjust TPS. See the V8 TUNE-UP article in this section.

Removal & Installation

Remove air cleaner. Disconnect electrical connector. Remove retaining screws and ISC. Reverse removal procedures for installation. Adjust ISC. See the V8 TUNE-UP article in this section.

Note. The ISC motor is factory calibrated and should not be disassembled. Replace as complete assembly only. DO NOT soak ISC motor in carburetor cleaner.

Scheme 108

1. Remove air cleaner. Disconnect electrical connector from injectors. Remove fuel metering cover-to-throttle body retaining screws. Remove fuel metering cover and pressure regulator. CAUTION: DO NOT remove fuel pressure regulator screws from fuel metering cover. Fuel pressure regulator and fuel metering cover are serviced as an assembly only.
2. Leave fuel meter cover gasket in place to prevent damage to casting during injector removal. Using a screwdriver or Injector Remover (J-26868), remove injector from fuel meter body. (Scheme 109)
3. Remove large "O" ring and steel back-up washer from injector. Remove small "O" ring in fuel meter body injector cavity. (Scheme 108)

Scheme 109

1. Lubricate "O" rings with ATF. Install small "O" ring on nozzle end of each injector. Install "O" ring upward against injector fuel filter. Install steel back-up washer in recess of fuel meter body.
2. Install large "O" ring directly above back-up washer. Press "O" ring downward into cavity recess. The "O" ring must be even with top of fuel meter body surface. CAUTION: DO NOT install steel washer and "O" ring after injector is installed into cavity. This will not allow proper seating of "O" ring, resulting in fuel leak.
3. Install injector using a pushing and twisting motion to center nozzle "O" ring in bottom of injector cavity. Align raised lug on injector base with notch of fuel meter body. Push downward on injector, ensuring it fully seats in cavity.
4. Injector is correctly installed when lug is seated in notch and electrical terminals are parallel to throttle shaft. Install new dust seal on fuel meter body. (Scheme 109)
5. Install fuel return gasket and fuel meter cover gasket on fuel meter cover. Install fuel meter cover. Install short retaining screws next to fuel injectors.
6. Tighten retaining screws to specification. See «TORQUE SPECIFICATIONS»(/cadillac/eldorado/ix-1986-1991/remont/testing-diagnostics/#fuel-injection-system-digital__torque-specifications) table at end of article. Install injector electrical connector. Install air cleaner.

1. Remove fuel metering cover and injectors. See «FUEL METERING COVER & INJECTORS»(/cadillac/eldorado/ix-1986-1991/remont/testing-diagnostics/#fuel-injection-system-digital) in this article. Remove fuel inlet and outlet line fitting nuts and gaskets from fuel metering body.
2. Remove fuel metering body-to-throttle body retaining screws. Separate fuel metering body from throttle body.

Install new gasket on throttle body. Ensure cutout portion of gasket aligns with throttle body openings. Reverse removal procedures. Tighten screws and fuel fittings to specification. See TORQUE SPECIFICATIONS table at end of article.

TORQUE SPECIFICATIONS

TORQUE SPECIFICATIONS

1988 DeVille & Fleetwood Wiring Diagram. Scheme 110

1988 Eldorado & Seville Wiring Diagram. Scheme 111

See also:
• TROUBLE SHOOTING
• TORQUE SPECIFICATIONS