Basic Testing - 6-cyl Toyota Supra A70

PRELIMINARY INSPECTION & ADJUSTMENTS

Note. The following diagnostic steps are here to prevent overlooking a simple problem. This is also the place to start diagnosis for a "NO-START" condition.

The first step in diagnosing any driveability problem is to verify that the problem exists. This may be accomplished by test driving the vehicle under the conditions during which the problem reportedly occurs.

Prior to entering self-diagnostics, a careful and complete inspection of several systems is required. Most driveability or "no-start" problems are not related to computerized engine control systems, but are in fact simple mechanical, electrical, fuel or vacuum related faults. Most engine control problems are the result of mechanical breakdowns, poor electrical connections or damaged or misrouted vacuum hoses.

Before considering the computer system as a possible cause of problems, ignition high tension wires, fuel supply, electrical connections and vacuum hoses should be checked. Failure to do so may result in improper diagnosis or lost diagnostic time.

VISUAL INSPECTION

Perform a visual inspection of all electrical wiring. Look for chafed, stretched, cut or pinched wiring. Inspect electrical connectors and connections for tight fit and corrosion. Repair as necessary. Inspect all vacuum hoses for proper routing, cuts or pinched areas. If necessary, see VACUUM DIAGRAMS section to verify routing and connections. Repair as necessary. Inspect air induction system for possible vacuum leaks.

COMPRESSION

Engine mechanical condition can be checked using a compression gauge, vacuum gauge, or an oscilloscope capable of performing a relative compression test. See oscilloscope instruction manual for availability and description of relative compression feature. For procedures and specifications, see D - EFI ADJUSTMENTS article in this section.

EXHAUST SYSTEM BACKPRESSURE

The exhaust system can be checked with a vacuum gauge or a pressure gauge. Remove O2 sensor or air injection check valve, if equipped. Connect a 1-10 psi gauge and run engine at 2500 RPM. If exhaust system backpressure is over 1.75-2 psi, exhaust system or catalytic converter is plugged.

If a vacuum gauge is used, connect it to intake manifold vacuum. Observe vacuum gauge. Open throttle part way and hold steady. If vacuum gauge slowly drops after stabilizing, exhaust system should be checked for a restriction.

FUEL PRESSURE

Basic diagnosis of fuel system should begin with determining fuel system pressure.

Scheme 1

1. Turn ignition on, with engine off. On all models, place jumper wire across "+B" and "FP" terminals of engine check connector in engine compartment. (Scheme 1) See «ENGINE CHECK CONNECTOR LOCATION»(/toyota/supra/a70-1986-1993/remont/testing-diagnostics/#basic-testing-6-cyl) table. ENGINE CHECK CONNECTOR LOCATION Model (1) Location Cressida Left shock tower Land Cruiser On firewall, under wiper motor Supra Front of left shock tower (1) Label on inside of engine check connector cover has check connector pin identification. All "FP" and "B" pins will be in same location.
2. On all models, listen for fuel pump running sound. Feel for pressure in fuel line between filter and fuel rail. Turn ignition off. Remove jumper wire. If fuel pump sound was present and fuel hose showed pressure, go to FUEL SYSTEM PRESSURE TEST.
3. If no pressure or fuel pump sound was present on all models, connect a jumper wire from battery source to "FP" terminal of engine check connector. NOTE: All models use in-tank fuel pump. Fuel pump contains internal relief valve and check valve.
4. If fuel pump ran after battery source was connected to "FP" terminal in step 3), check EFI main relay and related wiring. Also check "EFI" and "IGN" ("AM2" on MR2) fuses. See FUEL PUMP CONTROL CIRCUIT in this article. For more information on wiring, see WIRING DIAGRAMS in this section.

FUEL SYSTEM PRESSURE TEST

Note. Before testing fuel pressure, check all fuel delivery and return lines for leaks.

1. Ensure battery is fully charged. Turn ignition off. Place container or shop towel under cold start injector. Slowly loosen cold start injector union bolt to relieve fuel pressure. Remove union bolt and 2 gaskets.
2. Install fuel pressure gauge to the cold start injector delivery pipe. (Scheme 2) Wipe off excess gas. (Scheme 2)
3. On all models, install jumper wire between engine check connector "FP" and "B" pins. (Scheme 1) See ENGINE CHECK CONNECTOR LOCATION table.
4. On all models, turn ignition on, with engine off. Measure fuel pressure. Fuel pressure should be same as unregulated pressure. See appropriate FUEL PUMP PERFORMANCE table.
5. If fuel pressure is high, replace the fuel pressure regulator. If fuel pressure is low, check the following: Fuel hoses and connections. Fuel pump. Fuel filter. Fuel pressure regulator.
6. Remove jumper wire installed in step 3). Start engine and run for 2 minutes. Disconnect vacuum sensing hose from fuel pressure regulator and plug hose end. Fuel pressure regulator is mounted on fuel rail. NOTE: Land Cruiser, and Supra Turbo it is necessary to allow engine to idle for 2 minutes to stabilize fuel pressure. These models are equipped with a fuel pressure-up system which temporarily increases fuel pressure after a hot start.
7. Measure unregulated fuel pressure at idle speed. See appropriate FUEL PUMP PERFORMANCE table.
8. With engine still idling, reconnect fuel pressure regulator sensing hose. Measure regulated pressure at idle.
9. If regulated pressure was not as specified, check vacuum sensing hose and fuel pressure regulator. On models so equipped, check fuel pressure-up system. See I - EFI SYS/COMP TESTS.
10. Stop engine. Note fuel pressure. Leave fuel pressure gauge attached to engine for at least 5 minutes.
11. Residual fuel pressure after 5 minutes should be at least 21 psi (1.5 kg/cm 2 ). If pressure is not as specified check for leaking injectors, fuel pressure regulator or bad check valve in fuel pump.
12. Relieve fuel system pressure. Remove fuel pressure gauge. Install cold start injector. Run engine and check for fuel leaks.

Note. For more information on checking fuel injectors and other fuel sub-systems, see I - EFI SYS/COMP TESTS article in this section.

Scheme 2

FUEL PUMP PERFORMANCE

EFI MAIN RELAY

1. The "EFI" fuse supplies constant battery voltage to the EFI main relay. On all models, EFI main relay supplies battery voltage to "+B" pin of engine check connector. If fuel pump will not turn on when the "+B" and "FP" pins are jumpered, check EFI main relay. (Scheme 3)
2. Also check circuit that turns on EFI main relay. Depending on model, relay may either be turned on directly by ignition switch or by "M-REL" terminal of ECU. For more information on wiring, see WIRING DIAGRAMS in this section.
3. On all models, EFI main relay provides battery voltage to "+B" terminal of circuit opening relay.

CIRCUIT OPENING RELAY

1. Circuit opening relay controls fuel pump circuit. ECU receives an input signal at "STA" terminal when engine is cranking. This same starter signal is also applied to terminal "STA" of circuit opening relay.
2. Starter signal energizes circuit opening relay during cranking, which in turn activates the fuel pump. On all except Supra (7M-GTE), when airflow meter senses airflow to engine, fuel pump switch in airflow meter provides the relay ground. On Supra (7M-GTE), circuit opening relay is grounded by ECU through "FC" terminal.

Fuel Pump Relay & Fuel Pump Resistor (Cressida & Supra)

On these models a separate fuel pump relay and resistor are used between the circuit opening relay and the fuel pump.

Note. For more information on testing relays and fuel system components, see I - EFI SYS/COMP TESTS article.

Scheme 3

DIAGNOSTIC CODES

Note. ECU is programmed to detect ignition problems. Checking for trouble codes can speed up your diagnosis. If ECU detects a problem a diagnostic code will be set in memory. For information on system self-diagnostic capabilities and how to retrieve codes, see TESTS W/CODES article in this section.

Code 12 (No RPM Signal)

ECU will store trouble code No. 12 in memory if it does not receive signal from either "NE" pick-up coil (RPM) or "G" pick-up coil (crank position) within 2 seconds of engine cranking.

Code 13 (No RPM Signal)

ECU will store trouble code No. 13 in memory if it does not receive signal "NE" pick-up coil (RPM) when engine speed is above 1000 RPM.

Code 14 (Ignition Signal Problem)

ECU will store trouble code No. 14 in memory if it does not receive "IGF" (ignition detection) signal 6-8 times in succession.

Scheme 4

1. On models with integral ignition coil, disconnect spark plug wires. Remove spark plugs. Install spark plugs to each spark plug wire. Ground spark plugs. Spark plug tester can also be used. (Scheme 4)
2. On models with an external ignition coil, disconnect high-tension (coil) wire from distributor. Hold wire about 1/2" away from ground. CAUTION: To prevent gasoline from being injected, do not crank engine for more than 2 seconds.
3. On all models, crank engine and check for spark. If spark does not occur, check ignition coil, ignitor and distributor connections.
4. If connections are good, check resistance of high-tension wires. If resistance is not 25,000 ohms maximum Per Wire, replace wires. If wires are okay, go to next step.
5. Check power supply to ignition coil and ignitor. Place ignition switch in "ON" position. Check for voltage at ignition coil positive terminal. If voltage is not present, check wiring between ignition switch, coil, and ignitor. If voltage is present, go to step next step.
6. Check ignition coil resistance. See IGNITION COIL RESISTANCE TESTS in this article. If ignition coil resistance is not as specified, replace coil. If coil resistance is within specification, go to next step.
7. Check pick-up coil resistance. See PICK-UP COIL RESISTANCE TEST in this article. If resistance is within specification, go to next step. If pick-up coil resistance is not as specified, replace pick-up coil or distributor.
8. Check air gap between reluctor and pick-up coil. See PICK-UP COIL AIR GAP CHECK in this article. If air gap is incorrect, replace distributor assembly.
9. If air gap is correct, check ignition "IGT" signal from ECU. See appropriate trouble code No. 14 chart in G-TESTS W/CODES article. If "IGT" signal is okay, replace ignitor.

Primary Coil Resistance

1. Disconnect ignition coil so it is isolated from remainder of system. Using ohmmeter, measure resistance between coil positive (+) and negative (-) terminals. (Scheme 5)- (Scheme 8).
2. If primary resistance is not within specification, replace ignition coil. See «IGNITION COIL RESISTANCE»(/toyota/supra/a70-1986-1993/remont/testing-diagnostics/#basic-testing-6-cyl) table. If resistance is within specification, proceed to SECONDARY COIL RESISTANCE.

Secondary Coil Resistance

1. Disconnect ignition coil so it is isolated from remainder of system. Using an ohmmeter, measure resistance between coil positive (+) terminal and coil tower. See «IGNITION COIL RESISTANCE»(/toyota/supra/a70-1986-1993/remont/testing-diagnostics/#basic-testing-6-cyl) table. (Scheme 5)- (Scheme 8).
2. If resistance is not within specification, replace ignition coil. If resistance is within specification, proceed to PICK-UP COIL RESISTANCE TEST.

IGNITION COIL RESISTANCE

Scheme 5

Scheme 6

Scheme 7

Scheme 8

Land Cruiser

Measure pick-up coil resistance between terminals "G" and "G(-)", and between "NE" and "G(-)". (Scheme 9)or (Scheme 10). If resistance is not within 140-180 ohms, replace distributor. If resistance is within specification, proceed to PICK-UP COIL AIR GAP CHECK.

Cressida & Supra (Non-Turbo)

Measure resistance of pick-up coil between terminals "G1" and "G(-)", "G2" and "G(-)", and between "NE" and "G(-)". (Scheme 9)or (Scheme 10). If resistance is not within 140-180 ohms, replace distributor. If resistance is within specification, proceed to PICK-UP COIL AIR GAP CHECK.

Scheme 9

Scheme 10

Pick-Up Coil Air Gap Check

Using a flat, non-magnetic feeler gauge, check air gap between signal rotor and pick-up coil projection. (Scheme 11)or (Scheme 12). Air gap should be.008-.016" (.20-.40 mm). If air gap is not within specification, replace distributor.

Scheme 11

Scheme 12

Note. ECU is programmed to detect ignition problems. Checking for trouble codes can speed up your diagnosis. If ECU detects a problem, a diagnostic code will be set in memory. For information on system self-diagnostic capabilities and how to retrieve codes, see TESTS W/CODES article in this section.

ECU will store trouble code No. 12 in memory if it does not receive signal from either "NE" pick-up coil (RPM) or "G" pick-up coil (crank position) within 2 seconds of engine cranking.

ECU will store trouble code No. 13 in memory if it does not receive signal from "NE" pick-up coil (RPM) when engine speed is above 1000 RPM.

ECU will store trouble code No. 14 in memory if it does not receive "IGF" (ignition detection) signal 6-8 times in succession.

SPARK TEST

1. Remove duct between air cleaner and intake plenum air connector. Disconnect cruise control, accelerator, and throttle cables (automatic transmission only).
2. Remove 6 hoses from idle speed control pipe. Remove 2 bolts and idle speed control pipe from intake plenum air connector. Remove oxygen sensor wire from clamp. Disconnect hose from PCV pipe. Remove 2 bolts and disconnect PCV pipe with hoses from cylinder head covers and throttle body.
3. Disconnect hose from intake plenum air connector. Remove 2 bolts, loosen clamps, and remove intake plenum air connector. Remove oil filler cap. Remove 5 nuts from "TOYOTA TURBO" labeled ignition coil pack cover, and lift off cover.
4. Remove nut and disconnect No. 1 and No. 2 wires from ignition coil and clamp. Move ignition coil pack with bracket out of the way and remove all spark plug wires from spark plugs.
5. Remove all spark plugs. Install oil filter cap. Install spark plug wires onto the original 6 spark plugs or use several high output spark testers along with spark plugs. (Scheme 4)
6. If spark plug testers are available, install one on each wire of separate coil packs along with one spark plug to other spark plug lead per coil pack.
7. If spark testers are not available, install all 6 spark plug wires to the 6 removed spark plugs. Ground each spark plug and/or spark tester securely. CAUTION: Ignition coil primary or ignitor circuit damage can result if each spark plug and/or spark plug tester is not securely grounded.
8. Disconnect solenoid resistor block and cold start injector connector. Cold start injector is on bottom of air intake chamber. Solenoid resistor block is on top of right side shock tower (4-wire connector).
9. Crank engine and check for consistent Blue spark across plug gaps. (Scheme 4) If all spark plugs and/or spark testers do not fire, check ignition feed to coil pack and ignitor circuits. See IGNITION FEED CIRCUIT TEST under IGNITION COIL in this article.
10. Verify that camshaft sensor signals are received by ECU. See IGNITOR TEST in this article. Also, verify camshaft sensor moves when engine is cranked.
11. If only one or 2 spark plugs and/or spark plug testers show an inconsistent spark across the gap, test that particular coil pack for ignition coil primary resistance as well as spark plug wire resistance. See IGNITION COIL RESISTANCE. Ignition high-tension wire resistance should be 25,000 ohms maximum per wire.

Ignition System Connection Checks

1. With ignition switch in the "OFF" position, check connections of all 3 ignition coil primary circuits. Check for loose connections or corrosion. Tighten and/or clean connections as required.
2. Check connection on primary feed wire to coil and ignitor. If loose or corroded connections exist, correct them and repeat SPARK TEST.
3. If no spark output is observed or no problems were located and resolved in this test, proceed to IGNITION FEED CIRCUIT TEST under IGNITION COIL in this article.

Ignition Feed Circuit Test

1. Disconnect ignition feed 2-pin connectors from coil packs. Turn ignition switch to the "ON" position. Measure voltage between terminal No. 1 (battery feed) and ground. (Scheme 13)
2. There should be 12 volts present with ignition on. If reading indicates a problem, repair open circuit between ignition switch and battery feed to coil pack. If no battery feed problems are detected, go to PRIMARY COIL RESISTANCE.

Scheme 13

Using an ohmmeter, measure resistance between positive and negative terminals of ignition coils. (Scheme 14) Replace ignition coil if resistance is not to specification. See IGNITION COIL RESISTANCE table. If no problems are detected, proceed to IGNITION COIL GROUND TEST.

Note. It is not possible to check ignition coil secondary resistance.

Scheme 14

Ignition Coil Ground Test

Turn ignition off. Disconnect ignition coil connectors. Using an ohmmeter, ensure there is no continuity between ignition coil terminals and ground. If there is continuity, replace ignition coil. If no problems are detected, proceed to IGNITION OPERATIONAL CHECK.

IGNITION COIL RESISTANCE

Feed To Ignitor Test

Turn ignition off. Unplug ignition module 6-pin connector. Ignition module 6-pin module connector is located next to alternator. Turn ignition switch to the "ON" position. Check for 12 volts between terminal No. 3 and ground. (Scheme 15) Reconnect 6-pin connector. If feed voltage is not present, repair open in wiring harness and retest system. If feed circuit is okay, proceed to PICK-UP COIL RESISTANCE.

Scheme 15

Pick-Up Coil Resistance

To test resistance of the 3 pick-up coils, disconnect camshaft position sensor 4-wire connector. Measure resistance from terminal "G(-)" to terminals "G1", "G2" and "NE". (Scheme 16) Resistance of each pick-up coil should be 140-180 ohms. If resistance is not as specified, replace camshaft position sensor assembly. If pick-up coil resistance is within specification, proceed to PICK-UP COIL AIR GAP CHECK.

Scheme 16

Using flat, non-magnetic feeler gauge, check air gap between signal rotor and pick-up coil projection. (Scheme 17) Air gap should be within.008-.016" (.20-.40 mm). If air gap is incorrect, replace camshaft position sensor assembly. If air gap clearance is within specification, proceed to IGNITOR TEST.

Scheme 17

Ignitor Power Transistor Check

1. Turn ignition off. Unplug ignition module 4-pin connector. Disconnect each ignition coil pack 2-pin connector.
2. Turn ignition switch to "ON" position. Connect ohmmeter between terminal No. 2 of third ignition coil and ground. Using a 3-volt dry cell battery, apply 3 volts to terminal No. 2 of 4-pin connector. With 3 volts applied, check that ohmmeter indicates momentary continuity. (Scheme 19)
3. Connect ohmmeter between terminal No. 2 of first ignition coil and ground. Apply 3 volts to terminal No. 4 of 4-pin connector. With 3 volts still applied to terminal No. 4, also apply 3 volts to terminal No. 2. Check that ohmmeter indicates momentary continuity. (Scheme 19)
4. Connect ohmmeter between terminal No. 2 of second ignition coil and ground. Apply 3 volts to terminal No. 3 of 4-pin connector. With 3 volts still applied to No. 3, also apply 3 volts to terminal No. 2. Ensure ohmmeter indicates momentary continuity. (Scheme 19)

Scheme 18

Scheme 19

Note. For adjustment procedures, see appropriate D-ADJUSTMENTS FUEL INJECTION article.

IGNITION TIMING

IGNITION TIMING

IDLE SPEED & MIXTURE

6-CYLINDER IDLE SPEED SPECIFICATIONS

SUMMARY

If no faults were found while performing F-BASIC TESTING, proceed to G-TESTS W/CODES, if available. If no codes are present, or vehicle does not have a self-diagnostic system, proceed to H-TESTS W/O CODES for diagnosis by symptom (i.e. ROUGH IDLE, NO START, etc.).

See also:
• ENGINE CHECK CONNECTOR LOCATION