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Thread: running really rich

  1. #1

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    running really rich

    so about 2 weeks ago i picked up another mitsu,its a 90 with the 2.4 and 5 speed,210k on the odo when it stopped working,about a year ago the guy got the motor swapped out with a lower mileage motor,he said its got about 55-60k on it now,and has receipts from the swap,motor came out of a 91,im having problems with the motor running funne when its at set speeds and idle,it idles rough and spits and sputters when youre cruising at a set speed,but accelerating it has no problems,when you get on it a little it blows a little black smoke,and im getting horrible gas milage,like 8mpg or so and i have no clue of what it can be,help!!!

  2. #2



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    If it has a carburetor check the idle mix screw and turn it in a turn or two. The float could be sunk or the needle and seat has somthing stuck in it. Or the main jet came loose. The choke is not working correctly.
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  3. #3


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    2.4's in 91 are Fuel Injected. Sound like it's in open loop mode. Possibilities, MAF, 02 sensor (check first), Timing, (most likely wasn't set properly, gotta ground that ECU Pin).

  4. #4



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    Quote Originally Posted by LSR Mike View Post
    2.4's in 91 are Fuel Injected. Sound like it's in open loop mode. Possibilities, MAF, 02 sensor (check first), Timing, (most likely wasn't set properly, gotta ground that ECU Pin).
    Does any body know what year the change over happened? If someone could add it in the Wiki History it would be greatly appreciated.
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  5. #5

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    the o2 sensor is new,thats what i thught the problem was,if i unplug the maf while its running it idles up and kills,doesnt that mean its still good? timing is as close as i can get it,all the marks are dead on on the belt,ive tried to set the distributor,skip a tooth one way and it revs slowly and backfires out the intake,skip a tooth the other way and it wont start,itll just backfire out the exhaust and blow a lot of black smoke

  6. #6



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    Which MAF and ECU was used, I know the 90 has a different ECU/MAF as the MAF is different and has a little different pinout. So maybe one of those is not the correct part?

    Camoit, carb'd went up to 89, FI was 90-up. I'll edit the WIKI
    Josh
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  7. #7


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    Download this manual

    http://www.onsiteconcrete.net/d-50/F...-1983-1993.zip

    Read how to set up the Timing, your doing most of the stuff right, but you have to ground the Timing adjust Pin of the ECU to keep the ECU from varying the timing (like a vacuum advance). The manual may also give you some insight to the problem. Plus, if you're going to have the truck, you gotta have a book!

  8. #8

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    I'll download it when I get home,but the 90 maf ECM and o2 were used,as the o2 changed too

  9. #9



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    Quote Originally Posted by DroppedMitsu View Post
    Camoit, carb'd went up to 89, FI was 90-up. I'll edit the WIKI
    Right on.. Looks like the the first Fuel Injection & ECU experts have started to find the thread.

    I knew it was in there some where when the conversion started.
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  10. #10

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    Well,it may not be the 90 ECM,the guy didn't say it was changed but I tried a 91 computer just for the hell of it and it does the exact same thing,Wednesday I'm going to a buddys house to try his ECM,his is a 90 too

  11. #11



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    I do know that there is a 1 year California only, ECM after dealing with Crandall and his V6. IDK if it ran into the 4 cylinders, but it is in the V6 engines.
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  12. #12


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    There is a California and a federal version of all the ECU's It's controlled by a jumper on the PC board.

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