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Thread: More 4.7 drama. Cranks but no start

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    Default More 4.7 drama. Cranks but no start

    P0688
    - Weak battery
    - Low voltage while cranking
    - Faulty Engine Control Module (ECM) relay
    - Blown ECM fuse - Faulty ECM
    - ECM harness is open or shorted
    - ECM circuit poor electrical connection
    - You're fucked

    I've checked all the fuses, swaped relays, has a good battery, stood on my head...Just cranks.

    11.27 @ 118.23
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    Duner's Avatar
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    Pull the plugs from the PCM and see if any of the connections are crummy.
    This will also reset it.
    Plug them back in.
    See if it does anything with that.
    Duner
    4.7 Turbocharged CC in white - 12's
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    1999 Dodge Dakota R/T RC Turbo: 10.51 @ 130.13 MPH

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    Clean as a whistle, I'll plug em back in.

    Edit...No change.
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    Bad PCM?

    How to check?
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    My ''03 did the same thing ! Found out bad pcm ! Now i just have to figure out how to get rid 03 r/t in sacramento ,ca Bought 07 ford ranger v-6 motor !

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    I found a place that sells pcms for 250, you fill out a form with vin, mileage etc..
    Truck has been acting funky for awhile, wonder if this was the problem, pcm was dying.
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    I found a place that sells pcms for 250, you fill out a form with vin, mileage etc..
    Truck has been acting funky for awhile, wonder if this was the problem, pcm was dying.

    What is the name of the place.

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    They are all over, I'm going with a place on eBay, 16,000 feedback, all good.
    Last edited by Adobedude; 09-04-2016 at 03:52 PM.
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    Guess they don't make a carb swap for the 4.7!

    Could've hit the U-Pull in Albuquerque, I'm sure there are plenty of Rams/Dakotas with blown 4.7s in there that you could've got a PCM from. I would assume if this was your problem and you swapped one in from a wrecking yard, it would at least start and die. Then you could get the VIN and mileage flashed into it locally.

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    I'm just trying to get rid of it...It's been nothing but issues lately.
    I need to get it into my garage so I can at least work on it in the fucking shade. We're trading it in, the wife wants a Jeep Wrangler.

    I just pulled the passenger side power window regulator off, it's going in the tin can so I can roll down the window while strapped in the seat, it's hot as fuck out there. I really miss the rear window slider, that went away with the roll bar.
    Last edited by Adobedude; 09-04-2016 at 07:44 PM.
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    I've just ignored the truck since September, today, new battery, old one was 7 years old....Cranked and barely sputtered. Hit the intake with a shot of starter fluid...started and ran for a couple seconds. Did it a couple times

    Fuel pump?

    When I turn on the ignition, it's dead quiet.
    11.27 @ 118.23
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    BIGROB's Avatar
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    Could be.
    You should hear the pump run for 2 seconds.
    Swap the pump fuel and AC relay, they are the same relay. Easy way rule out a bad relay.

    Project Maverick. I feel the need, the need for speed

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    Osee's Avatar
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    Quote Originally Posted by BIGROB View Post
    Could be.
    You should hear the pump run for 2 seconds.
    Swap the pump fuel and AC relay, they are the same relay. Easy way rule out a bad relay.
    I never hear mine running? Unless you need you be underneath it?


    Mods - TB Spacer, Short Throw Dipstick, Performance Auto Zone Intake "0.30 over bore", R/T Cam, Performance Chip, Radiator Delete

    Rev limiter? that's what valve springs are for!

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    I've played musical relays....No change.

    The loss of power I've had over the past year (I don't drive it much) could point to a failing fuel pump, or a bad PCM. IF the PCM is bad, FP won't run.

    I'm gonna spend the 250 for a new PCM before I pull the bed to change the Pump. The way the truck died was...I'M DEAD, no indication of a fuel pump failing. I mean it just fucking quit.
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    Well shit...I thought I could hear mine, maybe not.
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  16. #16
    Osee's Avatar
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    Quote Originally Posted by Adobedude View Post
    I've played musical relays....No change.

    The loss of power I've had over the past year (I don't drive it much) could point to a failing fuel pump, or a bad PCM. IF the PCM is bad, FP won't run.

    I'm gonna spend the 250 for a new PCM before I pull the bed to change the Pump. The way the truck died was...I'M DEAD, no indication of a fuel pump failing. I mean it just fucking quit.
    My dads old 4.7 dak did this, just left him stranded in the middle of nowhere Manitoba


    Mods - TB Spacer, Short Throw Dipstick, Performance Auto Zone Intake "0.30 over bore", R/T Cam, Performance Chip, Radiator Delete

    Rev limiter? that's what valve springs are for!

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    Quote Originally Posted by Osee View Post
    My dads old 4.7 dak did this, just left him stranded in the middle of nowhere Manitoba
    Well thankfully, mine left me stranded in my driveway.
    What was it?
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  18. #18
    BIGROB's Avatar
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    On ever Dodge I ever owned I could hear the fuel pump in the cab with the doors closed.
    Maybe it's just my big dumbo ears.

    With a rag and a small screwdriver you can press the schrader valve on the fuel rail and see if it quirts from residual fuel pressure.

    If you do need a PCM I can recommend Solo Auto Electronics in Miami. I've gotten three different PCMs from them. Nelson over there is very helpful.
    Last edited by BIGROB; 11-14-2016 at 07:47 PM.

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  19. #19
    Osee's Avatar
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    Quote Originally Posted by Adobedude View Post
    Well thankfully, mine left me stranded in my driveway.
    What was it?
    Fuel pump, had like 180,000kms I think


    Mods - TB Spacer, Short Throw Dipstick, Performance Auto Zone Intake "0.30 over bore", R/T Cam, Performance Chip, Radiator Delete

    Rev limiter? that's what valve springs are for!

  20. #20

    Friggin' R/T's Avatar
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    You getting fuel pressure at the rails? Check the little schrader valve

    And you should be able to hear the fuel pump prime when you turn the key to the ON position.

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    Fuel pump is dead, but a bad PCM can do that too.
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  22. #22
    BIGROB's Avatar
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    Quote Originally Posted by Adobedude View Post
    Fuel pump is dead, but a bad PCM can do that too.
    Time for a PCM (Put Carburetor Manifold) change

    Project Maverick. I feel the need, the need for speed

  23. #23

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    I don't know if this will be of any use with a 4.7

    http://troubleshootmyvehicle.com/chr...t-a-no-start-2

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    It will run with starter fluid....It's not getting fuel.
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  25. #25

    Friggin' R/T's Avatar
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    Does the fuel pump not run at all? can you jump the relay to see if the PCM is making it not run or if it's actually dead?

    2002 Flame Red RC R/T
    272 RWHP 315 ft/lb TQ
    218/226 Comp Cam, Stage 1 Ported EQ Heads, PRW 1.6 Roller Rockers, PIE Custom Tune, Full spintech exhaust with 3" side exit, 52mm Holley, Ported Kegger, Viper E-Fan, Powerdemon Trans, Hotchkis Springs, Leafs and Sway Bars, R/T 20's, Gen 3 viper seats, Custom "Rejected" State Inspection Sticker
    Plenty More to come

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