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Juan Crespo
Juan Crespo, Tech Trainer
Category: Car
Satisfied Customers: 1526
Experience:  A.S.E. Master Technician, Advanced Level, Emissions - Asian, Domestic, & European
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I have a 1994 Mitsubishi Mighty Max 2.4L. My problem with my

Customer Question

Hello, I have a 1994 Mitsubishi Mighty Max 2.4L. My problem with my truck is that when the truck is first started cold it misses and it hesitates when accelerating, when it warms up it runs good. I did the head gasket because it leaked oil through the gasket. I replaced the coolant temp sensor with the thermostat. But still same problems. Swapped air flow sensor, fuel pump and regulator, fuel filter. Running fuel pressure was at 51psi. Took it to the smog and it passed in the 15mph and at the 25mph test.
Submitted: 1 year ago.
Category: Car
Expert:  Juan Crespo replied 1 year ago.

Hi there. Welcome to our site!

I’m a retired master technician and tech instructor with over 30 years experience. I also have access to a pretty good database on automotive service and repair. All of which enables me often times to offer you an educated guess on what the problem with your vehicle might be. However, if you’re thinking on working on the vehicle yourself, all my knowledge and resources won’t help you if you…

… don’t have tools or the skills to use them

… don’t know there will probably be some special tools and equipment needed for a proper diagnosis

… don’t realize it may take a few back and forth replies to solve the issue

… don’t understand that I will need you to provide specific information

Cold misfires mean the engine is not getting enough fuel. Since the problem clears up once the engine warms up, I would say the ECU is either not getting the proper signal from the coolant temperature sensor (could be caused by bad sensor or connector or wiring or air pocket in the cooling system) or the ECU itself is faulty (unable to interpret the signal it gets from the temp sensor or unable to increase injector-on time).

Do you know how to retrieve trouble codes from the ECU? If so, can you do that and share the results?

Customer: replied 1 year ago.
Hello the check engine I'd not on and never comes on. But I don't know how to retrieve trouble codes.
Expert:  Juan Crespo replied 1 year ago.

When you say it never comes on, does that mean it doesn't even come on whith ignition ON and engine OFF?

Customer: replied 1 year ago.
I mean the engine light it's not on to check codes... It will come on with the engine off. And the ignition on ..
Expert:  Juan Crespo replied 1 year ago.

OK. In that case, you'll need a cheap analog voltmeter (click here to see one under $10 at Walmart) to follow the instructions below:

Using Voltmeter

1. Turn ignition switch to OFF position. Locate Data Link Connector (DLC), next to fuse block (see attached graphic). Connect volt-meter positive lead to DLC self-diagnostic test mode terminal and negative lead to either DLC ground terminal.
2. Turn ignition switch to ON position. Disclosure of ECM memory will begin. If 2 or more systems are non-functional, they are indicated by order of increasing code number. Indication is made by 12-volt pulses of voltmeter pointer. A constant repetition of short 12-volt pulses indicates system is normal. If system is abnormal, voltmeter will pulse between zero and 12 volts.
3. Signals will appear on voltmeter as long and short 12-volt pulses. Long pulses represent tens; short pulses represent ones. For example, 4 long pulses and 3 short pulses indicate Code 43.

Let me know the results and we'll take it from there.

Best Regards.

Customer: replied 1 year ago.
There are no trouble codes stored. What else do you think I could try thanks
Expert:  Juan Crespo replied 1 year ago.

That only means the problem is bad but not enough to make the ECU to set a code. Next we need to measure voltage to and from the temp sensor to determine whether the problem originates at the ECU or the sensor itself. Starting with a cold engine, locate the ECU and its two connectors. Connect your voltmeter Red lead to the Yellow/Green (Y/G) wire that goes into a cavity towards the middle of the largest of the two connectors (see attached graphic). Connect your voltmeter's Black lead to either of the two Black wires (B) that go into two different cavities in the same connectors. Turn ignition ON engine OFF. Voltmeter should read either close to 5 or 12 volts. Start the engine and monitor the voltage. Whether it was originally 5 or 12V, it should start to drop as the engine gets warm until is about one quarter of its original voltage. If the voltage doesn't drop, we have a problem with the sensor or its connector or its wiring. If voltage does drop, we have a problem with the ECU - in that case we need a scan tool capable of reading injector-on time or a very fast voltmeter that can read frequency (Hz) or a lab scope to pinpoint whether the fault is internal or it's in the connections or wiring.

Please let me know what you find.

Best regards.

Customer: replied 1 year ago.
Hello I did not receive the diagram of the ECU. Thanks
Expert:  Juan Crespo replied 1 year ago.

My bad. Here it is.

Customer: replied 1 year ago.
Steal have the problem I don't know what to do with the this problem..thanks
Expert:  Juan Crespo replied 1 year ago.

What do you mean by "still have the problem"? Didn't you follow the diagnostic procedures I posted for you? Can you tell me what the results were?

Customer: replied 1 year ago.
Good morning I did the procedure you told me to do on temp sensor and looks everything it's working correctly..what it's next..thank you.
Expert:  Juan Crespo replied 1 year ago.

You're not being very specific with the results, but if by "looks everything is working correctly" you mean voltage at temp sensor is going from high to low as engine temperature increases, then we have a problem with the ECU - in that case we need a scan tool capable of reading injector-on time or a very fast voltmeter that can read frequency (Hz) or a lab scope to pinpoint whether the fault is internal or it's in the connections or wiring.

Best Regards.

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