3176 cat locked in limp mode?

Discussion in 'Heavy Duty Diesel Truck Mechanics Forum' started by sodbuster59, Apr 2, 2022.

  1. sodbuster59

    sodbuster59 Bobtail Member

    Oct 10, 2021
    we've been looking for a backup tractor to pull a hopper or side dump this fall and ran across a nice looking (inside and out) 91 FLD120 with wierd symptoms. It won't start without a shot of ether, but once it pops off seems to idle nice. Engine lite comes on right away, but as long as you don't lug it, it runs and drives fine, but putting it under a load is a no go.

    Mechanically it seems fine. Oil is good, fuel pressure in good, coolant is good. AC is not working tho.

    Ran a scan and it shows all 6 injectors as inactive. (how is it that it runs at all?)

    Jakes, tach, speedo and so on seem to work fine. Tried replacing timing sensor, no change. Installed Reman ECU, same results. ALL 6 injectors inactive.

    Any ideas what a guy should be looking for?

    3176 CAT1 pic.jpg
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  3. 201

    201 Road Train Member

    Apr 16, 2014
    high plains colorado
    Locked in limp mode, maybe a female cat will help,,:eek::D:p Sorry, old trucker, you know, I don't think the 3176 was Cats best motor, there's only 2 things with a diesel, fuel and air, and it's obviously getting fuel. Good luck, someone here will know.
    JoeyJunk and sodbuster59 Thank this.
  4. kranky1

    kranky1 Road Train Member

    Sep 16, 2015
    Ontario, Canada
    6 inactive injectors it wouldn’t run. Plugs and cable of whatever you’re scanning it with? Who knows, if it has wires there’s a good chance it’s ####ed. What code or codes is it throwing. That would be a good place to start. Sounds like the mechanical part of the injectors work, but the electronics seem to have an issue. 6 bad injectors isn’t likely. As far as wires go I think the only thing common between all six injectors is the ground bus in the ecu. Anything else is wire to cylinder, problems should be able to be isolated to one cylinder. But those wires all have to go through common plugs in the harness. There’s a limited number of things or places that can affect all six at once. There’s electrical shenanigans afoot someplace. The ether to start could be a bad oil pressure switch. Could need a whiff of diesel dristan before the ecu sees enough oil pressure to turn the fuel on.
    sodbuster59 Thanks this.
  5. bjytech

    bjytech Light Load Member

    Nov 9, 2013
    Had a C13 a while back with codes for all 6 injectors, and low power complaint, and had the keep the RPM's up under load. Ended up putting a new ECM on it, injector drivers inside the ECM had issues. other than that I would be looking at the injector harness.
  6. TA1199

    TA1199 Light Load Member

    Sep 12, 2015
    Staten Island, NY
    Check the wire harness. They get old, brittle and fall apart.
  7. little cat 500

    little cat 500 Road Train Member

    Jan 17, 2010
    Abbottstown PA
    Wire harness junk possible low fuel pressure as well
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