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sprinkles08, ASE Certified Technician
Category: Mitsubishi
Satisfied Customers: 21589
Experience:  ASE Master and Advanced level certified. Factory trained with 15 years dealership experience
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1999 montero, ECU is not sending coil trigger signal on 3/6

Customer Question

1999 montero, ECU is not sending coil trigger signal on 3/6 coil pack.
JA: Are you fixing your Montero yourself? What have you tried so far?
Customer: Yes, I replaced plugs, wires, and 3/6 coil.
JA: Have you checked all the fuses? Do you have a wiring diagram?
Customer: no wiring diagram, the problem is intermittent. usually runs good when it sits overnight. may loose 3/6 coil pack after 30-40 minutes of driving.
JA: Anything else you want the mechanic to know before I connect you?
Customer: I probed gate signal on coil transistors, Q10 and Q12 had no gate signal when 3/6 coil not firing.
Submitted: 9 days ago.
Category: Mitsubishi
Customer: replied 9 days ago.
Actually it was Q10 and Q13 that did not have gate trigger signal when 3/6 coil was not firing.
Customer: replied 9 days ago.
I also did not see the trigger signal on IC12 or IC8 for the Q10 and Q13 gate lines. I guessed at which line from the MH7202F chip were the Q10 and Q13 gate signal and did not see a pulse signal when 3/6 coil was not firing, but then did see a pulse signal when the 3/6 coil started firing again.
Customer: replied 9 days ago.
Is there some condition that will cause the MH7202F processor to stop sending the 3/6 gate signal? The other 4 cylinders never loose spark and always had the gate signal present on their coil transistors.
Expert:  sprinkles08 replied 8 days ago.

Hello and welcome to JustAnswer!

If you're losing coil drivers it could be due to a failure in the engine controller, a shorted driver circuit between the controller and coil, or there may be a cam timing related issue.

What fault codes are setting?

Customer: replied 8 days ago.
The code from autozone was p0300, random cylinder misfire.Says propaple causes are:
Ignition system fault
Fuel system faulty
Vacuum leak
Engine mechanical condition
Expert:  sprinkles08 replied 8 days ago.

There isn't a coil driver code setting? Without unplugging anything you did check for spark and found two cylinders had none?

Customer: replied 8 days ago.
That was the only code autozone read. Yes, i checked the spark by pulling the wire plug out of the coil slightly and the 3,6 coil is not firing. Noid light showed no pulse signal at input connector to coil. I probed the signals in the ecu when engine was running and the coil transistors q10 and q13 had no gate pulse signal. I traced the gate lines back to pin 8 on ic12 for the q10 gate, and pin 6 on ic8 for the q13 gate. I believe i was able to trace the lines to the mh7202f processor and it seems the processor in not sending the gate signal out.
Expert:  sprinkles08 replied 8 days ago.

What should be done is monitor cam/crank sync with a scan tool to ensure it isn't perceiving the engien is out of time, but if it runs otherwise ok then that probably isn't the issue. If ok then the coil driver circuit should be tested for a short to power or ground. If ok then the ECM can be condemned.

Customer: replied 8 days ago.
Ok, i dont have a scan tool but when the coil is firing it runs great. Would the short to power or ground be inside the ecu or between the ecu and the coil? Is there a condition that the ecu would sense that would cause it to stop sending the gate signal only to the 3,6 coil? Is there a way i can get part numbers for the ic chips in the ecu and possibly a schematic of the ecu board?
Expert:  sprinkles08 replied 8 days ago.

It can be shorted internally or externally. All you're concerned with is testing the circuit and if the wiring isn't shorted then the ECM is replaced. There are no internal parts nor service information available because it isn't a field serviceable item.

Customer: replied 8 days ago.
Ok, if i get another ecm does it need to be repeogramed at the dealer?
Expert:  sprinkles08 replied 8 days ago.

If you have a transponder key then it would need to be programmed once installed before the engine will start.

Customer: replied 8 days ago.
Is there a reason that the ecu would purposefully only shut down the 3,6 coil firing system and leave the other 4 cylinders firing?
Expert:  sprinkles08 replied 8 days ago.

Yes, incorrect cam timing as I mentioned previously.

Customer: replied 6 days ago.
I was mistaken about the ecu. The trigger signal was getting to the power transistor module but there was no pulse at the coil input connector. I replaced the power transistor module and seems to be running fine. Thanks.
Expert:  sprinkles08 replied 6 days ago.

I'm glad you got it repaired.

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