Is my ECU bad?

Discussion in 'Engine & Performance' started by svdsinner, May 30, 2017.

Sponsored By: Moe's Performance
  1. svdsinner

    svdsinner Junior Member

    Age:
    46
    Posts:
    17
    Likes Received:
    0
    Joined:
    Oct 19, 2016
    Ram Year:
    1998
    Engine:
    5.9L V8
    '98 2500, 5.8L gas.

    My truck went suddenly from running to cranking without firing.

    The ECU isn't sending signals either to activate the fuel pump relay, or activating the spark plugs. The ignition coil and the relay have both tested as good.

    From what I've seen, the ECU waits until it gets signals from the crank position sensor and the cam shaft sensor before turning on the fuel pump and the ignition coil. I replaced the crank position sensor since I heard this is a common cause. No improvement.

    I think the issue has to be either the ECU or the camshaft sensor, neither seem like high probabilities to me. Am I missing any other likely culprits?

    I've got plenty of electrical test equipment, so I can take oscilloscope reading on things if it will help.

    How can I confirm the ECU as either good or bad?

    If it is the ECU, is it easily replaceable?



    Sent from my SM-G950U using Tapatalk
     
  2. dudeman2009

    dudeman2009 Senior Member

    Age:
    22
    Posts:
    1,459
    Likes Received:
    166
    Joined:
    Feb 9, 2016
    Location:
    Lansing, Michigan
    Ram Year:
    2001 1500 Sport with enough electrical modifications to make my brain hurt
    Engine:
    Magnum 360
    The fuel pump should prime as soon and the truck is turned to run. Check the ASD relay in the underhood fuse block. Sometimes those go bad and cause this issue.
     
  3. svdsinner

    svdsinner Junior Member

    Age:
    46
    Posts:
    17
    Likes Received:
    0
    Joined:
    Oct 19, 2016
    Ram Year:
    1998
    Engine:
    5.9L V8
    What's the logic relationship between the relays? Firstly, is the ASD relay supposed to energize when the key moves to On? (Or does it energize/de-energize on some other event?) If it does, the fuel pump relay turns on, and if not it won't? (Or do the two relays output work in series? IOW, if the ASD is bad, will the Fuel Pump relay always be de-energized?)

    Sent from my SM-G950U using Tapatalk
     
  4. dudeman2009

    dudeman2009 Senior Member

    Age:
    22
    Posts:
    1,459
    Likes Received:
    166
    Joined:
    Feb 9, 2016
    Location:
    Lansing, Michigan
    Ram Year:
    2001 1500 Sport with enough electrical modifications to make my brain hurt
    Engine:
    Magnum 360
    The ASD relay and fuel pump relay should be energized at key on by the PCM separately. They do not come into contact in anyway outside of both being wired into separate circuit of the PCM. The ASD relay is energized by the PCM when it senses a signal from the crank sensor while cranking, in the run mode the relay shuts off after 1.8 seconds if no input is detected from the crank sensor. The fuel pump relay is energized at key on at all times during cranking, however it shuts off after 3 seconds if the engine is not running.
     
  5. Brandon pixley

    Brandon pixley Junior Member

    Age:
    40
    Posts:
    1
    Likes Received:
    0
    Joined:
    Dec 1, 2017
    Ram Year:
    1999
    Engine:
    5.9
    I have a 99 Dodge that will start run for about 10 minutes die but will start right back up and act like it's out of time I have replace the crankshaft sensor and the camshaft sensor is the computer bad
     
  6. SportRam00

    SportRam00 Member

    Posts:
    56
    Likes Received:
    13
    Joined:
    Apr 1, 2016
    Location:
    Joppa, MD
    Ram Year:
    2000
    Engine:
    Magnum 360
    With key on/engine off, do you see you something that says NO BUS in the odometer read out? No start plus that NO BUS would be a tell tale sign of an ECU issue.

    Also, have you tried to reseat the plugs on the ECU itself? When mine was bad, I would reseat and press on the plug closest to the engine and the truck would start.
     

Share This Page