No start condition

Tiny
DARKMATT
  • MEMBER
  • 1990 MITSUBISHI MIGHTY MAX
  • 3.0L
  • V6
  • 4WD
  • MANUAL
  • 120,000 MILES
Vehicle sat for three years. Put new battery in and good fuel it started right up. Drove it home about ten miles ran great. Started it a few days later and it ran for ten minutes then shut off. Eventually got it started again ran then shut off hasn't started since. Has no spark. Swapped coil assembly with my Montero and Montero runs fine. Swapped MFI relay and Montero runs fine. Tested output from distributor and crank position sensor voltage oscillates like I would expect. Checked ECU ground circuit checks good. Opened ECU no burn spots. Question is, what input to the ECU causes an output to the coil other than the crank position sensor in the distributor? Does a bad airflow sensor cause the ECU to not output a spark?
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Sunday, December 30th, 2018 AT 11:09 AM

6 Replies

Tiny
JACOBANDNICKOLAS
  • EXPERT
Hi and thanks for using 2CarPros.

I have a feeling the problem is related to the main engine control relay. See picture 1 Failure of the engine control relay could interrupt power supply to the fuel pump, injectors and ECU, resulting in start failure.

Here are the directions for diagnostic of the relay:

CAUTION: Use caution when connecting jumper wires to the relay. If the polarity is incorrectly connected, the relay will be damaged.

Fig. 1 Relay Test
Pic 2

COMPONENT TEST
1. Supply 12 vdc to relay terminals 8 (-) and 10 (+). Using a voltmeter, check for voltage between terminals 4 (+) and 8 (-) and between terminals 5 (+) and 8 (-). Refer to Fig. 1.

Voltage
12 vdc

Fig. 2 Relay Test
Pic 3

2. Supply 12 vdc to relay terminals 6 (-) and 9 (+). Using an ohmmeter, check for continuity between terminals 2 and 3. Refer to Fig. 2.

Continuity
Should exist when voltage is supplied.
Should NOT exist when voltage is NOT supplied.

Fig. 3 Relay Test
Pic 4

3. Supply 12 vdc to relay terminals 7 (-) and 3 (+). Using a voltmeter, check for voltage between terminals 2 (+) and supply battery ground terminal. Refer to Fig. 3.

Voltage
12 vdc when terminal 7 is connected.
0 vdc when terminal 7 is NOT connected.

HARNESS TEST
1. Disconnect the negative battery cable and the ECU connector.
2. Reconnect the negative battery cable and turn the key to the ON position.
3. Using a volt meter, check the voltage between ECU harness terminal 110 and ground.

Voltage
System voltage.

4. Turn the key to the OFF position.
5. Disconnect the control relay connector.
6. Using an volt meter, check the voltage between relay harness terminal 10 and ground.

Voltage
System voltage.

7. Using a ohm meter, check for continuity between relay harness terminal 8 and ECU harness connector terminals 63 and 66.

Continuity
Should exist.

8. Using a ohm meter, check for continuity between relay harness terminal 4 and ECU harness connector terminals 102 and 107.

Continuity
Should exist.

If any of the previous tests produce unsatisfactory results, the harness will need to be repaired or replaced. Once repairs have been completed, road test the vehicle to confirm that the repair has corrected the problem.
If the same problem reoccurs, it is possible that there is an intermittent failure of the component or the ECU. Check for looseness at all harness junctions and test for an intermittent failure.

I don't know if you need these, but here are links that show how to test wiring, use a test light, and how to use a multi meter:

https://www.2carpros.com/articles/how-to-check-wiring

https://www.2carpros.com/articles/how-to-use-a-voltmeter

https://www.2carpros.com/articles/how-to-use-a-test-light-circuit-tester

Here is a link that shows in general how a relay is tested:

https://www.2carpros.com/articles/how-to-check-an-electrical-relay-and-wiring-control-circuit

Let me know if this helps or if you have other questions.

Take care,
Joe
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Sunday, December 30th, 2018 AT 11:32 PM
Tiny
DARKMATT
  • MEMBER
Thanks for the information, however I have verified the engine MFI relay works. I removed it and installed it in my 1990 Montero and the Montero runs fine with the mighty maxes MFI relay. I have tested the coil, distributor, air flow sensor and the transistor that the ECM controls for spark all items work when installed in the Montero. The only thing I can't test that way is the ECM the computer from the mighty max is different than the Montero. So, can the engine computer fail from sitting for years? Do they lose the program? Where should I send it for testing? I don't imagine it could be anything else.
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Tuesday, January 1st, 2019 AT 11:53 AM
Tiny
JACOBANDNICKOLAS
  • EXPERT
Hi and welcome back:

Honestly, it does sound like you have eliminated all other possibilities. When sitting, corrosion can be a problem and poor connections can be an issue. Also, pins can move in the connector which can cause problems.

As far as the programming, it shouldn't have lost it. Also, if moisture was an issue, the ECM may have failed. Here are the ECM diagnostics. Try this and let me know what you find.

ELECTRONIC CONTROL UNIT (ECU)
When checking or correcting engine component malfunctions, check basic engine components prior to troubleshooting the Electronic Control Unit. See: Computers and Control Systems > Reading and Clearing Diagnostic Trouble Codes > Reading Diagnostic Trouble Codes

To test the Electronic Control Unit (ECU), located to the right of the glove box, proceed as follows:

NOTE: Diagnostic memory is erased if the battery or the ECU connector is disconnected. Do not disconnect the battery before the trouble codes are completely read. If a sensor connector is disconnected with the ignition switch turned on, the diagnosis code is memorized. In this case, disconnect the battery negative terminal for 15 seconds or more, and all diagnostic memory will be erased.

1. Using the procedures contained in ON-BOARD DIAGNOSTICS extract all malfunction codes. Diagnosis memory is erased if the battery or the ECU connector is disconnected. Do not disconnect the battery before the trouble codes are completely read. See: Computers and Control Systems > Reading and Clearing Diagnostic Trouble Codes > Reading Diagnostic Trouble Codes

CAUTION: When battery voltage is low, trouble codes cannot be read. Be sure to check the battery for voltage and other conditions before starting the test.

Self-Diagnosis Connector Location

2. Does the ECU output a steady 12 vdc at the diagnostic check connector?
A. If not, and the ECU is suspected to be faulty, check the POWER AND GROUND CIRCUITS test to confirm that the ECU is being supplied with power and ground.
B. If so replacement of the ECU is required.

NOTE: Before replacing a ECU that is found to be faulty, insure that no other condition exists that will damage the new unit. This can be best done by testing the inputs and outputs to the ECU for over voltage/inappropriate power readings or grounds. Use the image in CHASSIS ELECTRICAL DIAGRAMS and the individual component testing procedures to identify the correct readings for each pin. Check all pins (at the harness with the ECU removed) that supply a signal to the ECU, for their correct readings and check all other pins to insure that there are no uncalled for voltage readings or grounds present.

ECU Probing Technique

To test pins using a multi-meter do not remove the connector from the ECU, instead insert a straight pin or needle from the back side of the connector to access each pin.
NOTE: Before replacing an ECU that is found to be faulty, insure that no other condition exists that will damage the new unit. This can be best done by testing the inputs and outputs to the ECU for over voltage/inappropriate power readings or grounds. Use the ECU Terminal Identification image and the individual component testing procedures to Identify the correct readings for each pin. Check all pins (at the harness with the ECU removed) that supply a signal to the ECU, for their correct readings and check all other pins to insure that there are no uncalled for voltage readings or grounds present.

3. Compare all the remaining codes to the following list and perform the required inspections called for in each of the categories that are affected by a code.

Check power supply for:
1. Faulty battery.
2. Faulty fusible link.
3. Faulty fuse.
4. Check for faulty body ground.

Check fuel supply for:
1. Damaged fuel line.
2. Clogged or damaged fuel filter.
3. Faulty fuel pump.

Check ignition system for:
1. Faulty spark plugs.
2. Faulty ignition wiring.
3. Faulty distributor.
4. Faulty ignition coil.

Check emission control system for:
1. Faulty PCV system.
2. Faulty EGR system.
3. Vacuum leak.
4. Ignition timing and idle speed.
All categories:
ECU system faults are often caused by poor harness contact, therefore check that all of the connectors in all of the affected systems are secure and have continuity.

4. After completing all of the system inspections required in step 3 Perform all of the inspections and component tests (refer to COMPONENT TESTS) that are listed for each code that has appeared.

5. If faults were found in step 4, make repairs/replacements as required and clear the fault code from the ECU. Performance test the vehicle against the customer complaint and retest the ECU for fault codes.
6. If the same codes appear retest the repaired/replaced component, If it performs as specified, proceed to step 6.
7. If different fault codes appear, proceed to step 3, and attempt to resolve the new codes.
If NO fault codes were found in step 4, proceed to step 6.

8. If after performing all the required inspections though step 4, NO components were found to be faulty or at step 5 after repairs NO components were found to be faulty, replacement of the ECU is required.

After check and correction of malfunction is completed, disconnect battery ground cable or ECU connector for 10 seconds or more to erase trouble codes. The memory is not erased if power supply is restored within 10 seconds.

Let me know what you find.

Joe
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Tuesday, January 1st, 2019 AT 5:07 PM
Tiny
JACOBANDNICKOLAS
  • EXPERT
Hi and welcome back:

Honestly, it does sound like you have eliminated all other possibilities. When sitting, corrosion can be a problem and poor connections can be an issue. Also, pins can move in the connector which can cause problems.

As far as the programming, it shouldn't have lost it. Also, if moisture was an issue, the ECM may have failed. Here are the ECM diagnostics. Try this and let me know what you find.

ELECTRONIC CONTROL UNIT (ECU)
When checking or correcting engine component malfunctions, check basic engine components prior to troubleshooting the Electronic Control Unit. See: Computers and Control Systems > Reading and Clearing Diagnostic Trouble Codes > Reading Diagnostic Trouble Codes

To test the Electronic Control Unit (ECU), located to the right of the glove box, proceed as follows:

NOTE: Diagnostic memory is erased if the battery or the ECU connector is disconnected. Do not disconnect the battery before the trouble codes are completely read. If a sensor connector is disconnected with the ignition switch turned on, the diagnosis code is memorized. In this case, disconnect the battery negative terminal for 15 seconds or more, and all diagnostic memory will be erased.

1. Using the procedures contained in ON-BOARD DIAGNOSTICS extract all malfunction codes. Diagnosis memory is erased if the battery or the ECU connector is disconnected. Do not disconnect the battery before the trouble codes are completely read. See: Computers and Control Systems > Reading and Clearing Diagnostic Trouble Codes > Reading Diagnostic Trouble Codes

CAUTION: When battery voltage is low, trouble codes cannot be read. Be sure to check the battery for voltage and other conditions before starting the test.

Self-Diagnosis Connector Location

2. Does the ECU output a steady 12 vdc at the diagnostic check connector?
A. If not, and the ECU is suspected to be faulty, check the POWER AND GROUND CIRCUITS test to confirm that the ECU is being supplied with power and ground.
B. If so replacement of the ECU is required.

NOTE: Before replacing a ECU that is found to be faulty, insure that no other condition exists that will damage the new unit. This can be best done by testing the inputs and outputs to the ECU for over voltage/inappropriate power readings or grounds. Use the image in CHASSIS ELECTRICAL DIAGRAMS and the individual component testing procedures to identify the correct readings for each pin. Check all pins (at the harness with the ECU removed) that supply a signal to the ECU, for their correct readings and check all other pins to insure that there are no uncalled for voltage readings or grounds present.

ECU Probing Technique

To test pins using a multi-meter do not remove the connector from the ECU, instead insert a straight pin or needle from the back side of the connector to access each pin.
NOTE: Before replacing an ECU that is found to be faulty, insure that no other condition exists that will damage the new unit. This can be best done by testing the inputs and outputs to the ECU for over voltage/inappropriate power readings or grounds. Use the ECU Terminal Identification image and the individual component testing procedures to Identify the correct readings for each pin. Check all pins (at the harness with the ECU removed) that supply a signal to the ECU, for their correct readings and check all other pins to insure that there are no uncalled for voltage readings or grounds present.

3. Compare all the remaining codes to the following list and perform the required inspections called for in each of the categories that are affected by a code.

Check power supply for:
1. Faulty battery.
2. Faulty fusible link.
3. Faulty fuse.
4. Check for faulty body ground.

Check fuel supply for:
1. Damaged fuel line.
2. Clogged or damaged fuel filter.
3. Faulty fuel pump.

Check ignition system for:
1. Faulty spark plugs.
2. Faulty ignition wiring.
3. Faulty distributor.
4. Faulty ignition coil.

Check emission control system for:
1. Faulty PCV system.
2. Faulty EGR system.
3. Vacuum leak.
4. Ignition timing and idle speed.
All categories:
ECU system faults are often caused by poor harness contact, therefore check that all of the connectors in all of the affected systems are secure and have continuity.

4. After completing all of the system inspections required in step 3 Perform all of the inspections and component tests (refer to COMPONENT TESTS) that are listed for each code that has appeared.

5. If faults were found in step 4, make repairs/replacements as required and clear the fault code from the ECU. Performance test the vehicle against the customer complaint and retest the ECU for fault codes.
6. If the same codes appear retest the repaired/replaced component, If it performs as specified, proceed to step 6.
7. If different fault codes appear, proceed to step 3, and attempt to resolve the new codes.
If NO fault codes were found in step 4, proceed to step 6.

8. If after performing all the required inspections though step 4, NO components were found to be faulty or at step 5 after repairs NO components were found to be faulty, replacement of the ECU is required.

After check and correction of malfunction is completed, disconnect battery ground cable or ECU connector for ten seconds or more to erase trouble codes. The memory is not erased if power supply is restored within ten seconds.

Let me know what you find.

Joe
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Tuesday, January 1st, 2019 AT 5:07 PM
Tiny
DARKMATT
  • MEMBER
Update. I found that the ECM from the mighty max and the Montero are virtually identical. Same circuit card numbers and components. The only difference I found was the ignition timing circuit has a different hand drawn number on it otherwise the components are the same. I took the Montero computer out of its case and installed it into the case of the mighty max, both are 1990 V6 federal with manual transmissions. I installed it into the mighty max and voila it runs. I didn't want to leave it in and potentially ruin my Montero's ECM so I switched it back, Montero runs fine. So now I need to have the ignition circuit in the computer repaired. I read somewhere that the capacitors can be a problem but they don't look like they are swelled or damaged or leaking. Does anyone know of a reputable repair shop that can test and repair a 1990 mighty max v6 ECM?
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Monday, February 18th, 2019 AT 12:29 PM
Tiny
JACOBANDNICKOLAS
  • EXPERT
Welcome back:
I'm glad you got it figured out. Honestly, I have no idea who repairs them. Are you able to purchase a remanufactured or new one?

Joe
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Monday, February 18th, 2019 AT 5:29 PM

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