2.8l Pfi "a" Charts Pontiac 6000 I

MODEL IDENTIFICATION

Repair procedures in this article are sometimes identified by a specific body code. The following table lists GM division, model name, and body types that apply to the body codes.

MODEL IDENTIFICATION

DESCRIPTION

The computerized engine control system monitors as many as 19 engine/vehicle functions. (Scheme 787) This system controls engine operation and lowers exhaust emissions while maintaining fuel economy and driveability. The Electronic Control Module (ECM) is the "brain" of the CCC system.

The computerized engine control system is primarily an emission control system, designed to maintain a 14.7:1 air/fuel ratio under all operating conditions. When the ideal air/fuel ratio is maintained, the 3-way catalytic converter can control Oxides of Nitrogen (NOx), Hydrocarbon (HC) and Carbon Monoxide (CO) emissions.

ECM Conditions Sensed & Systems Controlled. Scheme 787

SPECIAL DIAGNOSTIC TOOLS

Note. Special "Scan" testers plugged into the ALDL may be used to read trouble codes and check voltages in the system on the serial data line (terminal "E" on EFI and terminal "M" on EFI with P-4 systems). These testers can save a great deal of time. For additional information see SCAN TESTER USAGE and SCAN TESTER - TEST DATA PARAMETERS table in this article.

The computerized engine control system is most easily diagnosed using a "Scan" tester, however, other tools may aid in diagnosing problems if a "Scan" tester is unavailable. These are: tachometer, test light, ohmmeter, digital voltmeter with 10-megohm impedance (minimum), vacuum pump, vacuum gauge, fuel injector test lights and 6 jumper wires 6" long (one wire with female connectors at both ends, one wire with male connector at both ends and 4 wires with male and female connectors at opposite ends). A test light, rather than a voltmeter, must be used when indicated by a diagnostic chart.

SCAN TESTER USAGE

Note. Prior to connection of scan tester to vehicle, diagnostic system should be checked to determine if system is operating properly and if information received by scan tester will be accurate. This is done by performing appropriate DIAGNOSTIC CIRCUIT CHECK for that system. If vehicle does not pass diagnostic circuit check, information received by scan tester may be invalid.

CCC Scan tester is a specialized tester which, when plugged into ALDL, can be used to diagnose on-board computer control stems by providing instant access to circuit voltage information without need to crawl under dash or hood to back-probe sensors and connectors.

Scan testers cut down diagnostic time dramatically by furnishing input data (voltage signals) which can be compared to specification parameters. See SCAN TESTER - TEST DATA PARAMETERS table. They also furnish information on output device (solenoids and motors) status. Status parameters, however, are only an indication that output signals have been sent to devices by the ECM. It does not indicate if devices have responded properly to that signal. This will need to be verified at output device using a voltmeter or test light.

Note. Code 12 should always exist when ALDL is grounded with key on and engine not running but may not be indicated by all makes of scan tester.

If trouble codes are not present, this is not an indication that there is not a problem. CCC related problems are about 20 percent codes and 80 percent driveability. Sensors that are out of specification WILL NOT set a trouble code but WILL cause driveability problems. Use of a scan tester is easiest method of checking sensor specifications and other data parameters. Tester is also useful in finding intermittent wiring problems by wiggling wiring harnesses and connections (key on, engine off) while observing data parameters. See the SCAN TESTER - TEST DATA PARAMETERS table below.

Note. Information obtained by scan tester is only as accurate as the tester itself. If erroneous voltage signals are suspected, it will be necessary to verify tester information using a digital voltmeter and wiring schematic. If non- existent codes are evidenced, turn ignition off, remove tester, turn ignition on. Ground ALDL "DIAGNOSTIC TERMINAL". If same codes are not flashed by "SERVICE ENGINE SOON" light that were indicated by scan tester, tester cannot be used on vehicle as information obtained by it may not be accurate.

SCAN TESTER - TEST DATA PARAMETERS

Note. Information in the following tables is typical readings taken on vehicle with engine idling, upper radiator hose hot, closed throttle, transmission in Park or Neutral, "closed loop" status achieved and all accessories off (except as noted in tables). Data parameters are updated every 1 1/4 seconds. On systems using P-4 computers, parameter updates are virtually instantaneous. Not all devices & systems are used on all models.

PORT FUEL INJECTION

Note. This ECM voltage chart can be used with a digital voltmeter to help save time in diagnosis. Voltages on the car being tested my vary slightly from these due to battery or alternator charging level.

DIAGNOSTIC CIRCUIT CHECK

The diagnostic circuit check is an organized approach for identifying a problem caused by the fuel injection system. Driver comments normally fall into one of the following areas: steady "SERVICE ENGINE SOON" light, driveability problem and engine "CRANKS BUT WON'T RUN".

DIAGNOSTIC CIRCUIT CHECK PROCEDURES

1. Steady "SERVICE ENGINE SOON" light with the ignition on and engine not running confirms battery voltage to the ECM.
2. Code 12 should flash 3 times, followed by any other trouble codes stored in memory.
3. Record all stored trouble codes (except Code 12).
4. With the engine running and the diagnostic terminal grounded, the ECM will respond to the oxygen sensor signal voltage and use the "SERVICE ENGINE SOON" light to display this information as follows: Closed loop confirms the O2 sensor signal is being used by the ECM to control fuel delivery, and the system is working normally. Signal voltage will vary from below .35 to above .55 volts. Open loop indicates that oxygen sensor voltage is unusable to the ECM. Signal voltage is a constant value between .35 and .55 volts. System will flash open loop from 30 seconds to 2 minutes after engine starts or until sensor reaches normal operating temperature. If system fails to go to closed loop, see Code 13. "SERVICE ENGINE SOON" light out indicates lean exhaust. Oxygen sensor signal voltage will be less than .35 volts and steady. "SERVICE ENGINE SOON" light on steady indicates rich exhaust. O2 sensor signal voltage will be greater than .55 volts and steady.
5. Road test of the vehicle using field service mode must be done at steady speeds. In this mode, the following conditions may be observed and are considered normal: light on too long under acceleration, light off too long under deceleration, light on too long with idle below 1200 RPM.
6. Clearing codes. Ignition should be off. Remove continuous battery fuse for 30 seconds. Fuse and holder are located near battery.

Flow Chart, Diagnostic Circuit Check. Scheme 788

Flow Chart, Diagnostic Circuit Check. Scheme 789

"SCAN" DIAGNOSTIC CIRCUIT CHECK

The "SCAN" Diagnostic Circuit Check is an organized approach for identifying fuel injection problems using an Assembly Line Communication Link (ALCL). This communication link can provide diagnostic information for display on any "SCAN" device or tool designed for this purpose.

1. If the "SCAN" tool is not operating, check on another vehicle. If okay, the cigar lighter socket should be checked for 12 volts and a good ground. If the "SCAN" tool reads "no data" or "no ALCL", with the ignition "ON", check the serial data wire for an open or short to ground between ALCL terminal "E" and the ECM. Also check for an open diagnostic test terminal from ALCL terminal "B" and ECM. With ignition on, the serial data line should have a varying 2-5 volts and the diagnostic line about 5 volts.

Flow Chart, "Scan" Diagnostic Circuit Check. Scheme 790

Flow Chart, "Scan" Diagnostic Circuit Check. Scheme 791

Schematic, "Scan" Diagnostic Circuit Check. Scheme 792

CHART A1 - NO "SES" LIGHT

"SERVICE ENGINE SOON" light should be on steady when ignition is "ON" and engine is not running. Battery voltage is supplied directly to the bulb. The ECM turns the light on by grounding circuit 419 at the ECM.

If both continuous battery supply voltages are lost at terminals B1 and C16 or the ignition feed to terminal A6 is not present, the check engine light will not come on.

Note. The following step numbers refer to the numbers on the Diagnostic Flow Charts.

1. Solenoids are turned on or off by the ECM, using internal electronic switches called "Drivers". Each driver is part of a group of 4 called "Quad-Drivers". Failure of any driver can damage any other driver in the set. Use an ohmmeter to check resistance of solenoids or relays listed in chart.

Flow Chart A1, No "Service Engine Soon" Light. Scheme 793

Flow Chart A1, No "Service Engine Soon" Light. Scheme 794

Schematic A1, No "Service Engine Soon" Light. Scheme 795

CHART A2 - NO CODE 12 "SES" LIGHT ON STEADY

Steady "SERVICE ENGINE SOON" light should be on with ignition "ON" and engine not running. Battery voltage is supplied directly to the bulb. With the diagnostic terminal grounded the light should flash a Code 12 followed by any other trouble codes stored in memory. A steady light indicates a short to ground in the light control circuit 419, or an open in circuit 451.

Note. The following step numbers refer to the numbers on the Diagnostic Flow Charts.

1. If the light goes off when the ECM connector is disconnected, then circuit 419 is not grounded. Also check the connector terminals for proper contact at this time.
2. This step checks for an open diagnostic circuit 451.
3. This step checks for a faulty ECM or PROM. If Code 51 is stored when PROM is removed, replace PROM.
4. Solenoids are turned on and off by the ECM, using internal electronic switches called "Drivers". Each driver is part of a group of 4, called "Quad-Drivers". Failure of 1 driver can damage any other driver in the set.

Chart A2, Won't Flash Code 12 "SES" Light on Steady. Scheme 796

Chart A2, Won't Flash Code 12 "SES" Light on Steady. Scheme 797

CHARTS A3A & A3B - ENGINE CRANKS, BUT WON'T RUN

Battery condition and engine cranking speed are okay, and there is adequate fuel in the tank. If engine starts but immediately stalls, SEE TROUBLE SHOOTING charts in the CEC TESTS W/O CODES article in this section.

Note. The following step numbers refer to the numbers on the Diagnostic Flow Charts.

1. "SERVICE ENGINE SOON" light on shows ignition and battery supply to the ECM.
2. Fuel pump fuse should be checked at this time and if blown, repair fuel pump circuit before proceeding. Secondary voltage is checked using tool (ST-125). No spark indicates a basic HEI problem.
3. This test checks if ECM is receiving reference signal and is controlling the injectors. If the test light blinks while cranking, the ECM should be considered okay. Be sure to check both sides of engine and that the test light makes good contact between connector and terminals during test. Use test light (J-34730-2) or equivalent.
4. This test checks fuel pressure using Pressure Gauge J-34730-1). Wrap shop towel around fuel pressure tap to absorb fuel leakage when installing gauge.
5. The following can cause a "No Start" condition: An EGR valve sticking open, fouled spark plugs, TPS binding in the wide open position, defective cold start circuit or water in fuel, or a defective MAF Sensor. If all okay, SEE TROUBLE SHOOTING procedures in the CEC TESTS W/O CODES article in this section.

Flow Chart A3A, Engine Cranks But Won't Run. Scheme 798

Flow Chart A3A, Engine Cranks But Won't Run. Scheme 799

Schematic A3A, Engine Cranks But Won't Run. Scheme 800

A3B - ENGINE CRANKS, BUT WON'T RUN (CONT.)

Note. The following step numbers refer to the numbers on the Diagnostic Flow Charts.

1. 6) This test checks for 12 volt supply to injectors.
2. 7) This test determines if the distributor module is not generating the reference pulse or if the wiring or ECM are at fault. By touching circuit 430 with a test light, a reference signal is being generated. If the test light (J-34730-2) blinks a the injector, then the ECM and wiring are okay.
3. 8) If the ECM is seeing high TPS voltage it may be in the clear flood mode. Disconnecting the TPS will allow the ECM to use a default value and turn the injectors on. If the TPS ground wire and connections are okay, the TPS should be replaced.
4. 9) Each time the test light touches circuit 430, the ECM should turn the fuel pump on for 2 seconds.
5. 10) All checks made to this point would indicate that the ECM is at fault. However, there is a possibility of circuit 467 or 468 being shorted to a voltage source either in the engine harness or in the injector harness. To test for this condition, disconnect the ECM connectors and injectors. Turn ignition "ON". Probe circuits 467 and 468 with a test light connected to ground. There should be no light. If light is present, repair short. If okay, check harness for terminals shorted together. Check each injector resistance. Resistance should be more than 10 ohms. If all checks okay, check ECM ground circuits before replacing the ECM.

Chart A3B, Cranks, But Won't Run (Cont.). Scheme 801

Note. EFI system under pressure. To avoid spillage, refer to field service procedures for testing or making repairs requiring disassembly of fuel lines or fittings.

Chart A3B, Cranks, But Won't Run (Cont.). Scheme 802

CHART A7A - FUEL SYSTEM DIAGNOSIS

The ECM turns the in-tank fuel pump on for 2 seconds when the ignition switch is turned "ON". It will turn it on again during cranking and will keep it on as long as the engine is running or cranking and the ECM is receiving HEI distributor reference pulses. If there are no reference pulses, the ECM will shut the fuel pump off within 2 seconds after the key is turned "ON" or engine stopped. The fuel pump will deliver fuel to the fuel rail and injectors, then to the pressure regulator, where the system pressure is controlled to 34-47 psi with the ignition on, engine stopped or during WOT. Excess fuel is returned to the fuel tank.

Note. The following step numbers refer to the numbers on the Diagnostic Flow Charts.

1. Use pressure gauge (J-34730-1). Wrap a shop towel around fuel pressure tap to absorb any fuel spillage when installing gauge. Ignition "ON" pump pressure should be 40.5-47 psi. This pressure is controlled by spring pressure within the regulator assembly.
2. When the engine is idling, the manifold pressure is low (high vacuum) and is applied to the fuel regulator diaphragm, this will offset the spring and result in a lower fuel pressure. The idle pressure will vary slightly depending on barometric pressure, however, the pressure idling is less indicating pressure regulator control.
3. Pressure that continues to fall is caused by one of the following: In-tank fuel pump check valve not holding, pump coupling hose leaking, pressure regulator valve leaking or an injector that is sticking open.
4. An injector sticking open can best be determined by checking for a fouled or saturated spark plug(s). If a leaking injector can not be determined by a fouled or saturated spark plug the following procedure should be used. Remove plenum, cold start valve and remove fuel rail bolts. Reconnect cold start valve. Connect a hose to valve nozzle and insert into a gasoline container. Lift fuel rail out just enough to leave injector nozzles in the ports. CAUTION: Be sure injectors are not allowed to spray on engine and that injector retaining clips are intact. This should be carefully followed to prevent fuel spray on engine which would cause a fire hazard. Pressurize the fuel system. Lift each side of rail up and observe for injectors leaking.

Flow Chart A7A, Fuel System Diagnosis. Scheme 803

Flow Chart A7A, Fuel System Diagnosis. Scheme 804

CHART A7B - FUEL SYSTEM DIAGNOSIS

Note. The following step numbers refer to the numbers on the Diagnostic Flow Charts.

1. Pressure, but less than 40.5 psi. falls into two areas: Regulated pressure, but less than 40.5 psi. Amount of fuel to injectors okay but pressure is too low. System will be lean running and may set Code 44. Can also be hard starting cold and poor overall performance. Restricted flow causing pressure drop. Normally, a vehicle with a fuel pressure of less than 24 psi. at idle will not be driveable. If the pressure drop occurs only while driving, the engine will surge and then stop as pressure drops rapidly.
2. Restricting the fuel return line allows the fuel pump to develop its maximum pressure. When battery voltage is applied to the ALCL pump test terminal "G", pressure should be approximately 60 psi.
3. This test determines if the high fuel pressure is due to a restricted fuel return line or a pressure regulator problem.

Flow Chart A7B, Fuel System Diagnosis. Scheme 805

Flow Chart A7B, Fuel System Diagnosis. Scheme 806

CHART A9 - COLD START VALVE

The cold start valve is used to provide additional fuel during the crank mode to improve cold starts. This circuit is activated only in the crank mode. The system is controlled by a thermal time switch which provides a ground path for the valve during cranking when coolant temperature is below 95°F (35°C).

Note. The following step numbers refer to the numbers on the Diagnostic Flow Charts.

1. Disconnecting the distributor 4-way connector will disable the other injectors. The amount of pressure drop depends on the temperature of the engine.
2. This test will determine the continuity through the thermal switch to ground.

Flow Chart A9, Cold Start Valve. Scheme 807

Flow Chart A9, Cold Start Valve (1 Of 2). Scheme 808

Flow Chart A9, Cold Start Valve (2 Of 2). Scheme 809

Schematic A9, Cold Start Valve. Scheme 810

Component Locations (A Body). Scheme 811

Component Locations (F Body). Scheme 812

Component Locations (P Body). Scheme 813

ECM Terminal Identification (Except Fiero). Scheme 814

ECM Terminal Identification (Fiero). Scheme 815

FWD PFI CCC Wiring Diagram. Scheme 816

RWD PFI CCC Wiring Diagram. Scheme 817

Fiero PFI CCC Wiring Diagram. Scheme 818