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Thread: 93 Mm v6 4x4 has just given up on life

  1. #1

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    93 Mm v6 4x4 has just given up on life

    So I know there are plenty of these "truck won't start" threads but most of the ones I can find pertain to the 4 cylinders. Also I can't find any specific guides or lists on steps to fix issues so any help would be appreciated. First of all got a 93 Mm from a friend for free and I have checked for fuel: got it. Checked for air: obviously got it. Checked for spark: got it. Swapped whole distributor, cap, and rotor with the ignitor from a working 6G72 still same issue. Don't have the tool to check for fuel pressure but when I pulled the fuel pressure line off there was pressure in the line. I also took the fuel pressure regulator out and cleaned it. Nothing. Fuel pressure relay does click when turning ignition on and I took the ECU out and verified that there are no busted caps, bad connections, or leaking fluids the inside of the thing looks brand new. My next step is looking at timing. But is there something I'm missing? Something obvious to check? I will owe you several beers just for opinions... O and the truck has just shy of 80k on it.

  2. #2

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    Hi Chrio, welcome to mightyram. First up - get someone to do an error code check on it. Just because the innards of the ECU 'look' ok, doesn't make it so. And it will nail down the fault 95% of the time. 80k is past it's timing belt service interval - any stickers showing it has been replaced around the 60k mark?

  3. #3

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    Also post up some picks of your Alaskan 4x4!

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    Sounds like you came across a lucky low mileage truck. As mentioned I would verify your ecu is working properly. You could also swap in a 91-93 3000gt/stealth sohc ecu to verify it's running properly. On a side note my MM was having a hard time starting. Would have to crank, stop, crank for days then hopefully start. Crawled under the truck and noticed someone had attempted to do some electrical work to my fuel tank. Needless to say that work extended into the tank too. I have finally fixed it and it performs like a pro.

  5. #5

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    Quote Originally Posted by geezer101 View Post
    Hi Chrio, welcome to mightyram. First up - get someone to do an error code check on it. Just because the innards of the ECU 'look' ok, doesn't make it so. And it will nail down the fault 95% of the time. 80k is past it's timing belt service interval - any stickers showing it has been replaced around the 60k mark?
    I tried to check it for codes but all I had was a digital multimeter that only went down to 200 ohms... But the check engine light doesn't stay on if you leave the key in it. I tried using the multimeter on volts so I could actually get a reading and it goes like 2v, 1v, 4v, 1v, 11v, 3v, 2v, 10.5v and repeat.

  6. #6

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    Quote Originally Posted by Chargerx3 View Post
    Sounds like you came across a lucky low mileage truck. As mentioned I would verify your ecu is working properly. You could also swap in a 91-93 3000gt/stealth sohc ecu to verify it's running properly. On a side note my MM was having a hard time starting. Would have to crank, stop, crank for days then hopefully start. Crawled under the truck and noticed someone had attempted to do some electrical work to my fuel tank. Needless to say that work extended into the tank too. I have finally fixed it and it performs like a pro.
    I tried using a ECU from a auto 94 montero that ran when it was left sitting thereand got a check engine light and the truck still wouldn't start. I didn't know about the ECU from the stealth/3000gt though thank you!

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    I don't know about the 94 monteros. I think there was an ecu generation change in 94 if they are anything like the 3000gt's. I currently am running a 92 sohc stealth ecu for a while now. Runs great.

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    Quote Originally Posted by GoodApollo View Post
    Also post up some picks of your Alaskan 4x4!
    Only good picture i have at the moment! will post more when i can get the thing moving!
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  9. #9

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    Quote Originally Posted by Chargerx3 View Post
    I don't know about the 94 monteros. I think there was an ecu generation change in 94 if they are anything like the 3000gt's. I currently am running a 92 sohc stealth ecu for a while now. Runs great.
    Now i just have to find a stealth or 3000gt ha ha they are not very common up here in Alaska

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    Quote Originally Posted by Chargerx3 View Post
    I don't know about the 94 monteros. I think there was an ecu generation change in 94 if they are anything like the 3000gt's. I currently am running a 92 sohc stealth ecu for a while now. Runs great.
    Are there any other Mitsubishi's i could borrow a ecu from to test?

  11. #11

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    I think 90-93 montero and raider v6 too.

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    Quote Originally Posted by Chargerx3 View Post
    I think 90-93 montero and raider v6 too.
    I'll see if i can find any donors. what codes are common for it to throw when the ecu is bad?

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    Depends on what circuit the electrolyte flows to. You likely won't ever get a cel.

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    Alright I got the ECU out and apart and i cant see anything to drastic. here are some pics though. what do you guys think?Click image for larger version. 

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  15. #15

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    Can't see anything but check closely to the bottom of those 3 large capacitors. Anything wet is a bad sign.

  16. #16

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    Quote Originally Posted by Chargerx3 View Post
    Can't see anything but check closely to the bottom of those 3 large capacitors. Anything wet is a bad sign.
    Ok got the capacitors off and one of them had a drop of something on the board (circled blue). and is the stuff circled in red in the pictures just sealant??
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  17. #17

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    if the caps have left stains on the PCB - they're toast. As for the mystery substance in your red ringed image, I got nada on that.

  18. #18

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    I think the stuff in the red circle is just where some of the anti-condensation coating pooled up. It's nothing to worry about.

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    Looks good. The film layer you are seeing is the conformal coating. Its there to protect your electronics from oxidation. Are you installing your own capacitors? If so, I hope you noted which way they were oriented. Don't install them backwards.

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    Quote Originally Posted by Chargerx3 View Post
    Looks good. The film layer you are seeing is the conformal coating. Its there to protect your electronics from oxidation. Are you installing your own capacitors? If so, I hope you noted which way they were oriented. Don't install them backwards.
    Ok new capacitors soldered on. not the same size but the same ratings on all of them and they are not crappy rubycons. also stripped the old peeling coating and got some epoxy to paint on to coat it. why do you need to coat the PCB? why couldn't you just seal the metal case the board comes in?
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  21. #21

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    Maybe coat it with clear nail polish? If a track on a PCB oxidises there's a good chance it will burn off the board.

  22. #22



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    It is also to insulate the traces on the board
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  23. #23

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    Quote Originally Posted by Chyrio View Post
    I tried to check it for codes but all I had was a digital multimeter that only went down to 200 ohms... But the check engine light doesn't stay on if you leave the key in it. I tried using the multimeter on volts so I could actually get a reading and it goes like 2v, 1v, 4v, 1v, 11v, 3v, 2v, 10.5v and repeat.
    you nee to use old style analog meter, not digital. voltage changes to quickly to read on digital. on analog meter you can count as the needle swings back and forth, long and sort pulses. it will repeat the codes continually one after another as many as are in the system. and In order. such a 1 long 3-short, 2 long 4-short and if nothing else it will repeat the same thing.

  24. #24

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    Alright put the ecu with the brand new capacitors in and tried it and nothing. Same issue.... Another note i moved it into the garage so now it's warm and i also charged up the battery. Still no check engine lights but i am going to go buy a analog meter like BUGS4G suggested soon and double check. What's the next thing to check? I'm thinking injectors. And start tearing the engine down looking for issues. And other ideas gentleman?

  25. #25

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    Most of the diagnostic tests don't run until the engine has been running for a little bit. You generally won't find any fault codes that'll help with a no-start condition, especially on older cars and trucks.

    I'm chasing a similar issue on a friend's 94 Stealth TT. It's got fuel and spark, it cranks strong, the electronics all check out, the computer works in my Stealth....but his car just won't run. I'm absolutely dumbfounded.

    About the only thing I can suggest is to check your timing marks and do a compression test. I'm interested to see what you find out. Maybe it'll help me with my friend's car.

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