300zx tt rebuild won't start

Discussion in 'Technical' started by Blue300, Apr 21, 2019.

  1. Blue300

    Blue300 New Member

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    Hi.
    Having problems with my 300zx tt not starting after a full engine rebuild, auto to manual conversion, high flowed turbos, bigger injectors, wiring specialties engine harness, dw300 fuel pump etc.

    Engine cranks over no problems but won't fire, good voltage in coil pack connectors, fuel pump fuse and relay but there is no voltage going to the fuel pump connection or FPCM, it also seems as there is no voltage going to the ecu after checking pin 16 where the harness plugs in to the ecu with a multimeter.

    It seems strange as other parts of the wiring harness such as the coil pack connectors and the abs control module are getting perfect battery voltage, also the fuel pump relay but where the plugs connect with the fuel pump it is completly dead.

    Im not sure if the car alarm is somehow stopping the fuel pump and ecu from working as some sort of immobilizer function. I would greatly appreciate any help as the car is basically finished and this is driving me nutts,

    Thanks.
     
  2. Martin Williams

    Martin Williams Well-Known Member

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    You said you had good voltage to Fuel pump relay , is the relay operating? is it fully plugged in? You could bypass Fuel pump relay and listen for the pump to run.
     
  3. Blue300

    Blue300 New Member

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    Relay works no problems, its clicking and haw very low resistance. The pump worked when i connected it directly through the battery but still didn't start because the injectors weren't operating as no power is going to the ecu
     
  4. DazzaZ32

    DazzaZ32 Active Member

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    And you have checked all the wiring in the engine bay to make sure you haven't crushed something putting the engine back in?
    Are all the earths connected?
     
  5. Blue300

    Blue300 New Member

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    All the other wiring in the engine bay appears fine, nothing is spliced or cracked. The earths have been connected as to where they were before the engine cane out
     
  6. IB

    IB ?????

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    Make sure you have your fuel lines the right way(the two hoses can easily be swapped). If you get them backwards you won't get any fuel in the rail.
     
  7. Blue300

    Blue300 New Member

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    Im starting to think it may be a problem with the ground wires. The connectors that have a good voltage are being tested with the multimeter ground directly on the negative battery terminal.
    When the multimeter ground cable is contacting the body ground, the voltage drops and when it contacts the engine ground there is no more than 4 volts maximum.
    Other engine wiring harness connectors that are getting no voltage are further away from where ive attached the body ground.
    So im thinking there's no way the fuel pump or ecu can get power as there is no ground cable thats working properly anywhere near them
     
  8. Cliff

    Cliff Member

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    Have you checked the ground that goes on the transmission bell housing? It can be a pain to get to and easily missed when putting an engine back in (ask me how I know... lol)
     
  9. Blue300

    Blue300 New Member

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    I didnt think of that but it makes perfect sense that it would be a good earth point, i will try tomorrow.
    I re attached one of the earth cables from the fuel rail to the cylinder head, directly underneath the hose that connects the air regulator to the balance tube.

    Doing that has increased the voltage to 12 volts from the engine earth points, for the connectors in the engine bay but now the coil pack connectors are dead but the ecu has power and the fuel pump connector is showing 0.03 volts compared to it having no voltage at all.

    Another problem i think it might be is i haven't yet re connected the gauge cluster (after having to pull the dashboard apart to fix the heater core). So im thinking that is causing problems with the ecu connecting with the fuel pump interrupting the voltage
     
  10. Cliff

    Cliff Member

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    Its likely that trying to start the car with any of the grounds not perfectly connected that your PTU has been fried (again, ask me how I know.. :().

    I would check to make sure you have:

    2 grounds on the back left hand side of the plenum
    1 ground on the back right hand side of the plenum
    1 ground from the fuel rail connected to the lower plenum
    1 ground connected to the transmission bell housing

    Also, it's fairly straightforward to diagnose the PTU with a multimeter and this diagram:

    Screenshot_20180627-162432_Chrome.jpg


    Only after all the above steps have been performed would I buy a new PTU (they're expensive...)
     

    Attached Files:

  11. Blue300

    Blue300 New Member

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    Ok thanks for the info. Im wondering if maybe I've fried the ecu also as the red diagnosis light is staying on
     
  12. Blue300

    Blue300 New Member

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    Wow this car is really surprising me now. So before i pulled the engine out when it was still driveable, the clock, wipers, mirrors, and climate control never used to work. I changed over fuses and relays but still nothing but the engine was running ok back then.

    I've now plugged in all the mirrors, wipers, clock and climate control connectors just to see if that would change anything and they are now all working perfectly. But still no power voltage going to the efi harness or fuel pump.

    I have no idea of what is going on with the electrical side of this car
     
  13. Cliff

    Cliff Member

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    Well it has to be one or more electrical connections somewhere so dont give up hope, slow progress is still progress.

    Try looking around the brake booster for a couple connections/connectors. On mine (LHD) there are a couple connections that are not part of the efi harness and I think go to the fusebox under the hood. One small one goes to the clutch master cylinder but there is a larger connection on the firewall. I unplugged these during my first engine pull not realizing the weren't actually connected to the engine.

    Curious if you tested your ptu yet. I dont think it would affect your fuel pump but it still may be toasty if anyone tried to crank a Z without all grounds connected. Worth a try I figure. Good luck!
     
  14. Blue300

    Blue300 New Member

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    Finally after almost two weeks of headaches and tearing my hair out. I thought prehaps i'll unplug the auto transmission module to see if that does anything but before i could get a chance to do so, i noticed there was a connector that wasn't plugged into anything.
    When i installed the efi harness i thought that connector was for the auto transmission and now that its manual it didn't need it, but the auto module was still connected to another plug, this got me scratching my head and after looking around for a couple of minutes i found a plug from the main harness.
    I connected them up, turned the ignition on and finally heard the buzzing noise. After doing this process several times, the smell of fuel came squirting out of the filter. All of the harness connectors are reading around the same voltage as the battery.
    The car still didn't start though as the cas may need to be adjusted or whatever it is im sure it wont be too much of headache compared to the last couple of weeks,

    Thanks to everyone for their help.
     
    Cliff likes this.

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