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Thread: Check engine light help!

  1. #1

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    Check engine light help!

    Been searching for a while now and I can not figure out why my 1991 Mighty Max (4cylinder) continues to have Check Engine Light Code 42

    Forum states Code 42 Fuel Pump.

    Truck runs and idles fine. Replaced TPS, Fuel Pump, Fuel Regulator and O2 sensor. Can someone recommend what to check next?

    Any recommendations would be highly appreciated.

    Thanks

  2. #2

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    How frustrating! But you'll get to the bottom of it soon.

    1. Forgive me for even asking but are you 100% sure it's flashing code 42? Decoding the trouble codes can be confusing as hell and I've chased my tail a few times. Just a quick sanity check.
    2. Check out the Haynes Manual in the "Over 216 Manuals" thread in the Manuals forum. Chapter 6 is devoted entirely to emissions controls and self-diagnostics.
    I can help get your truck to pass California smog! PM me.
    California BAR Smog Inspector License #EO635469
    "Keep 'em on the road."

    See what I have for sale:
    http://stores.ebay.com/zims

  3. #3


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    How many Miles? is it the automatic light for changing the Timing belt that is reset by throwing the switch behind the dash? thats in the manual also...

  4. #4

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    Quote Originally Posted by LSR Mike View Post
    How many Miles? is it the automatic light for changing the Timing belt that is reset by throwing the switch behind the dash? thats in the manual also...

    Not sure what you meant by automatic light? Forgive me if i mis-understood you but there is not Automatic Light that is on my dash, it is definately the Check Engine Light that is on. Currently there is 100K on the odometer.


    Im 100% sure it is a code 42. I also just purchased the EGR Valve and EGR Temperature Sensor hopefully it will solve the issue.

  5. #5


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    It's an automatic Check engine light, popped at specific mileage points . The ECU turns on the Check engine light at 100,000 miles or whatever, you take it in for service, Mechanic changes your Timing belt and water pump(because it only a few bolts and a gasket at that point) then pops the cover on the right side of the dash, slides the little switch to the other side, Poof, no more check engine light. If the Timing belt breaks while you are driving, get ready to shell out big bucks.

  6. #6

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    Heres an update.


    I ordered a new Fuel Pump Relay. I removed the battery leads before replacing the old one. The car started up and just dies right away. Does even idle. I put the old one back in and starts up just fine but the check engine light still there.

    Possible new relay is bad? or is this symptoms of a bad ecu?

    Thoughts?

  7. #7

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    FIX:

    Pulled out the ECU and it is marked ECM 906, opened it up and found a hand etching marked MD163057, clearly this ECU has already been reworked. Two capacitors looks to have already been replaced and looks like a bit of soldering rework was completed. Capacitors looked to be in good condition and all connections and soldering points looked to be in order, but I decided to purchased a reman ECU from the local parts store and installed it along with the new Fuel Pump Relay that I had. Car started and died right away.

    Installed the old Fuel Pump Relay with the new ECU and car starts right up and check engine light is now gone. Car actually idled smoother and drove better.

    Want to thank all of you guys for your help and recommendations.

    Figured that the link below is a good find.
    http://www.mightyram50.net/vbulletin...7&d=1421459537

  8. #8

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    ^^^
    Thx !!! that's a good one, & noted !
    one size does not fit all = reworking a core & applying
    same to many platform variants.

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