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2003 Tacoma 3RZ Flooding ECU Issue

Discussion in 'Technical Chat' started by Be ez, Nov 22, 2017.

  1. Nov 22, 2017 at 1:06 PM
    #1
    Be ez

    Be ez [OP] New Member

    Joined:
    Apr 4, 2017
    Member:
    #215387
    Messages:
    3
    Hi Everyone,

    I recently picked up a troubled 2003 Prerunner which led the previous owner on a goose chase. I believe I've identified the issue but wanted to get some opinions before I drop coin getting an ECU.

    A little background on the truck, the PO purchased the truck running good however after having it sit for the winter it developed a misfire and began blowing white smoke out the exhaust. His "mechanic" identified it as a cracked cylinder or blown head gasket (couldn't remember) but they decided to source a used motor and swap it. With the new motor in using all original sensors and ecu he had the same misfire and white smoke so he gave up and sold it to me.

    When I got it home and started it I first noticed fuel spraying out of the downpipe flange, white smoke and the obvious misfire. Worried about it catching fire I pulled apart the exhaust and fixed the leaks so I could keep it running while I figured it out. Right away it became obvious the white smoke was excessive fuel and P0304 narrowed it down to cylinder 4. I changed all the plugs and swapped around the coil packs and found that the misfire remained in cylinder 4. Next I decided to check injector resistance; while resistance was good I found constant voltage at injector 4 even when not running. After checking for shorts in the harness I'm fairly confident the ECU is supplying constant voltage to the injector causing these issues. Finally I started the truck with the 4th injector unplugged and while obviously the misfire remained, the white smoke and fuel smell were gone.

    My questions are:
    1) Has anyone experience anything like this?
    2) Are there any outside factors that would cause an ECU to do this or is it certainly an inside fault?
    3)Is there a diagram available for the ECU's internal layout?
    4) Can I leave the 4th injector unplugged for the mean time to get around?
    5) Could I piggyback the 4th injector plug off the 3rd as a temporary fix to get some fuel into the 4th cylinder?
     
  2. Nov 26, 2017 at 8:27 PM
    #2
    MGMTacos

    MGMTacos Member

    Joined:
    Nov 17, 2017
    Member:
    #236270
    Messages:
    6
    Sounds logical to me if the white smoke and fuel smell disappear when you pull the injector plug, and since a head gasket issue is more than likely ruled out.
    (1) Iv'e experienced similar issue with different vehicles.
    (2) Moisture could be a factor, sometimes things just go bad out of the blue for no apparent reason.
    (3) Try dealer. I searched google to no avail.
    (4) I personally wouldn't, but it isn't as bad as an over fueling injector
    (5) No, it'll run just as rough as if it was unplugged.

    However. Usually constant voltage is supplied to the injectors and the ECM grounds each injector. If you have confirmed the ground wire is not chaffed on the frame anywhere. I would call the nice folks at your local toyota dealership and try to get a wiring diagram for the ECM terminals. Then check the ground terminal on the ecm with a multi meter to confirm the issue.

    Hope this helps
     
  3. Nov 27, 2017 at 9:30 PM
    #3
    Be ez

    Be ez [OP] New Member

    Joined:
    Apr 4, 2017
    Member:
    #215387
    Messages:
    3
    Unplugged the harness from the ecu and lost ground at the plug so I can rule out a short circuit in the loom. Checked the pin at the ecu confirmed a short at the 4th injector pin. However I noticed that it's also throwing a code now for the A/F sensor (P0135) which got me thinking a little more. I've heard of bad grounds throwing the P0135 code so maybe the issue is ground related. I'll test the A/F sensor and check all the grounds but if not it must need an ECU.
     
  4. Nov 27, 2017 at 10:31 PM
    #4
    MGMTacos

    MGMTacos Member

    Joined:
    Nov 17, 2017
    Member:
    #236270
    Messages:
    6
    Id say the code is just a result of the over fueling or a lean condition from one injector being unplugged.
    My money would be on the ECU.
    Another way to test if you haven't already.
    Take the electrical connector off the cylinder 4 injector and put both leads of the meter in the plug. Have someone crank the motor and watch for fluctuating voltage at the plug. If the voltage is constant and doesn't fluctuate this would also confirm the problem with the ecu. I think the same relay that operates the EFI operates the fuel pump, but i'm not for certain. I'd probably just pull the other injector plugs so the engine won't start. You don't want the engine to start or have fuel dumping into the cylinders when cranking it over.
     

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