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Thread: 90 Ram 50 running issues.

  1. #1

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    90 Ram 50 running issues.

    So I have had this truck since may. It started giving me problems in the morning driving to work. missing, cutting out, and sometimes would quit. The way home from work it would run fine. Then it started running so horrible that I couldn't drive it. No check engine light even. Put new plugs, cap, rotor, fuel filter, and air filter. Ran good for a day then back to running bad. U could mess with the maf and it would run a little better and you could get it to start by partial plugging it. So put a new one on. then wouldn't run at all. Now it wasn't getting fuel pressure. Put a new fuel pump in and now it has pressure but also a check engine light and still wont run. No power and the diagnostic port either. I was checking where I was getting power and cycled the key and the light was off, fired right up and ran fine, turned if off and it wouldn't start again. Anyone have these problems? Thanks in advance

  2. #2

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    1990 Mitsubishi Mighty Max
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    Has the ECM ever been rebuilt? When mine went out on my '90 about 5 years ago, it was running perfectly till it cut out as I slowed for a stop light. It cranked but wouldn't catch so I had to push it out of traffic. After sitting for about 15 minutes, it did start and I was able to limp it home at about 25 mph tops with some bucking. Drove about 8 miles and it died in my driveway! Swapped the ECM from what was then my project '91 and it ran fine. I had the ECM rebuilt for about $200 by an outfit in FL and re-installed it and it's been running great ever since.
    1990 MM 4x4 3.0
    1991 MM 4x4 3.0 Diamonte
    1994 MM 2wd (work in progress)

  3. #3

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    That's what I was hoping it wasn't. Do you have a website of phone number for the company in fl? Thanks bud

  4. #4

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    I used Foreign Auto Computer Repair in Zephyrhills, FL on the recommendation of a Mitsubishi shop who has used them for years. I was very happy with their turn around time as well. Good luck!
    1990 MM 4x4 3.0
    1991 MM 4x4 3.0 Diamonte
    1994 MM 2wd (work in progress)

  5. #5

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    thank you!

  6. #6

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    The soldering and traces are notoriously horrible on the early FI ECUs and a flaky ECU produces symptoms like the ones you're experiencing. I had a '92 with similar erratic cutout problems. I bought a "remanufactured" spare and took it and the original ECU to someone I know in the circuit board repair business and he basically shotgunned both boards with patches to repair all of the visible and micro-cracks he saw.

    Also get a wiring diagram and triple check all of the grounds in the engine bay and under the dash. My old truck had two grounding straps that were so corroded they were useless. Clean and cover the ground connections with dielectric grease.

  7. #7

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    There is also some type of oil in the capacitors, I believe, that eventually leaks onto the board causing erratic problems. People often detect a "fishy" smell when these leaks occur. Please post your results when you take your next step, it's always educational.
    1990 MM 4x4 3.0
    1991 MM 4x4 3.0 Diamonte
    1994 MM 2wd (work in progress)

  8. #8

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    Quote Originally Posted by lush90 View Post
    There is also some type of oil in the capacitors, I believe, that eventually leaks onto the board causing erratic problems. People often detect a "fishy" smell when these leaks occur. Please post your results when you take your next step, it's always educational.
    Yes, the 1990s were the "bad capacitor plague" era for a lot of PCBs. Look for bulging tops on the caps or any kind of discolored ooze coming out of them. Either means the caps are toast and need to be replaced. Luckily they're inexpensive to replace and anyone with a good soldering station can replace them for you. Can you pull the ECU and pop the cover off and take a look at the board and see if anything is obviously wrong with it?

  9. #9

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    I checked the grounds and all were good. did pull the ecu and it did look like some burnt flaky stuff in spots. I'll check more on the capacitor. But no power to the diagnostic port seemed problematic to the ecu.

  10. #10

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    Even if the solder joints look OK to the naked eye, there can be tiny cracks that you can only see under a powerful magnifying glass in good light. My ECUs looked OK to me, the caps weren't bulging and were clean, but when I took them to the board repair guy, he showed me under the glass that nearly every joint was failing.

    This was around the time manufacturers were switching to lead-free solder so the manufacturing technology hadn't caught up to the regulations I'm guessing.

  11. #11



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    Vibrations and poor solder cause "cold solder joints" that make intermittant connections to components. They are not always visible, so a total resolder is the only way to fix these boards. Cap replacements are also called for as the heat and vibrations beat them to death. Remember, these trucks were never meant to last 20+ years, so the repairs are going to be a total rehab.
    Pennyman1
    The best Dodge that Dodge never made
    Living the D-50 lifestyle since 1980

  12. #12

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