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Thread: Running lean..... in warm weather?

  1. #1

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    Running lean..... in warm weather?

    My father recently passed down his 93 mighty max to me since I'm recently out of prison and starting over. Well it needed a mass airflow sensor, after replacing it ran great. In the winter weather. Now that it's warmed up some outside in the great state of TN, in warm weather, and after it has reached normal operating temperature it runs lean. This is by the way a 93 mighty max 2.4

    Anybody have any idea of what is causing this? I'm stumped. Between my dad and myself we have 60+ years of mechanic experience and neither one of us can figure it out. I found your site and joined in hopes someone, anyone can help me out.
    Last edited by DroppedMitsu; 03-09-2016 at 10:44 AM.

  2. #2

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    Quote Originally Posted by mightymax37110 View Post
    My father recently passed down his 93 mighty max to me since I'm recently out of prison and starting over. Well it needed a mass airflow sensor, after replacing it ran great. In the winter weather. Now that it's warmed up some outside in the great state of TN, in warm weather, and after it has reached normal operating temperature it runs lean is is by the way a 93 mighty max 2.4

    Anybody have any idea of what is causing this? I'm stumped. Between my dad and myself we have 60+ years of mechanic experience and neither one of us can figure it out. I found your site and joined in hopes someone, anyone can help me out.
    Sorry guys. Was supposed to say lean not rich.

  3. #3

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    I'm gonna guess throttle position sensor.
    The greatest gift you have to give to the world is that of your own self~transformation.

  4. #4

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    Quote Originally Posted by royster View Post
    I'm gonna guess throttle position sensor.
    TPS? In cold weather it runs fine. I don't understand how that could be the TPS.
    I also left off, if it starts doing it while driving, I can push the clutch in,a completely turn off the ignition, let it coast for about 5 - 10 seconds, turn ignition back to on position and let out of the clutch, it runs good again for a few minutes

  5. #5



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    It sounds like bad caps in the ECM - there are threads on here on what to look for and how to change them out.
    Pennyman1
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  6. #6

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    Hmmm, what is your ignition coil like? I think this is one of those 'snowball' things. I'll throw my hypothesis at this - coil is tired, starting to break down. Engine senses a change and attempts to tune it out. An electronic ignition coil is good for about 10-15 years before it starts to drop output.

  7. #7

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    It's the original coil, but the analog multimeter kept popping for ecu.mass airflow. Internal air temp switch. Keep in mind it's a brand new (remanned) cardone maf

  8. #8

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    Does anyone have the links to the threads about replacing caps in the ECU?

  9. #9



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    Fixed thread title and post for you. I got nothing on the issue right now, I'll think on it and let you know
    Josh
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  10. #10

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    Quote Originally Posted by DroppedMitsu View Post
    Fixed thread title and post for you. I got nothing on the issue right now, I'll think on it and let you know
    Thank you

  11. #11

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    Tps checked fine. Now it is doing it in any outside air temp as soon as it gets to normal operating temp. Coolant temp sensor, coolant temp switch, and temp sending unit are all functional. Has to be in the ECU correct? Would taking the thermostat out and running it without one stop this issue?

  12. #12



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    Definitely sounds like the ECU, some capacitors probably started leaking or something else funny happened.
    Josh
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  13. #13

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    Last edited by BradMph; 03-12-2016 at 10:20 AM.

  14. #14



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    We have a manual on these ECU and how to repair them.

    http://www.mightyram50.net/vbulletin...ECMs-and-ECU-s

  15. #15

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    I'm looking at that ECU board and it is a mess. Like it's been exposed to salt water...

  16. #16

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    Replaced ecu with working ecu, still same issue. But come to find out it isn't leaning out, when it bogs it's actually losing fire. So would that be the little black box on the engine or the coil itself?

  17. #17

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    Hmm, coil issue? If it was the ignitor module the engine would be dead (well, I think - unless it is loading up and getting hot, then misfiring)

  18. #18

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    I've narrowed it down to the fuel pump. 99% sure it's surging when it gets hot

  19. #19

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    Ok. Well after putting a fuel pressure test gauge on it and running it for an hour it ran great. barked 3rd gear on dry pavement, then I removed the test gauge, and here we go again. What am I missing? Anybody? Somebody?

  20. #20

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    What was the fuel pressure like with the gauge on? Might be a pressure regulator issue(?) It doesn't explain why it ran great with the test gauge hooked up...

  21. #21

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    It was staying steady at 38 psi at idle. slowly press the throttle and it would raise to about 45 - 50 psi. Blip the throttle quick and the pressure would drop but not lower than 28 psi. As soon as i removed the gauge and took off down the road it went to starving for fuel again.

  22. #22



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    there is something wrong there - an electric pump shouldn't fluctuate that much on pressure. I would try the regulator first, then the pump.
    Pennyman1
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  23. #23

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    I still think it has something to do with something else. today when it was over 70 degrees out it would starve for fuel, after it reached normal operating temp. But tonight it is fairly chilly outside and it runs fine. When it runs fine the temp gauge stays below normal. When it does it, it stays just above normal operating temp.

  24. #24

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    Try something stupid - leave the fuel cap off. My brother had a Mitsubishi Scorpion that would bug out in hot weather - it would run like crap like it was...starving of fuel (it was a carb'd 4G52 engine). I figured out that the fuel tank would build vacuum for some unknown reason. Opening the cap released the vacuum and next minute it would run perfectly.

  25. #25

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    Already checked evap. Seems to.be functioning correctly. Although I didnt check the.gas cap. I swear if that's all it is I'm gonna be mad lol

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