Interesting no start issue

  • FrozenZ
    FrozenZ
    Senior Member
    • 584
    #1

    Interesting no start issue

    So:

    Car was having hard hot starts for about a month (but ran idled and fine after) and then decided not to start. 84NA2T running 87T ECU, auto transmission. No idle controls, no o2 sensor, but ran like a top for 2 years like that. Battery is brand new.

    Car will fire once if you leave it for 10 minutes or so, otherwise it just cranks. It isn't sputtering or backfiring or anything.

    In troubleshooting I have put on a new CAS, cap and rotor. I have spark, tested with a spark tester on the #1 wire.

    Fuel pressure is 37PSI after the filter before the rail. Fuel pump primes when key is turned. Not smelling gas in the engine bay so I don't *think* it's flooding.

    Injectors have +12VDC when ignition is ON. What I don't know is if the injectors are firing and I am not sure how to test that - tried the screwdriver trick and I don't *think* they were firing but I am not sure. If the EFI relay was toast would I be getting 12VDC there at all?

    ECU is only throwing the fuel temp sensor code.

    Tried unplugging MAF and CHTS. Neither made any difference.

    Not sure what to try next. Help?
  • FrozenZ
    FrozenZ
    Senior Member
    • 584
    #2
    Update:

    Replaced EFI relay because why the fuck not. No difference.
    Ran fuel pump directly off the battery. No difference.
  • FrozenZ
    FrozenZ
    Senior Member
    • 584
    #3
    Well fuck me. Bad ECU, or at least bad injector drivers. Put in the car's original minty fresh 84NA ECU and it started right up. Now I need a turbo auto ECU :P
  • wbnethery3
    wbnethery3
    Senior Member
    • 437
    #4
    Originally posted by FrozenZ
    Car was having hard hot starts .................................................. .................................. Bad ECU
    ^Come in after work and see a time capsule of a guy talking to himself^

    Seriously though, thanks for sharing what you did… this is why FORUM>>>>fb ---- all day, every day…
    '86 NA - original owner (1986-93) and final owner (2005-present)

    My build thread: http://z31performance.com/showthread…-Got-mine-back

  • FrozenZ
    FrozenZ
    Senior Member
    • 584
    #5
    It's never the ECU (except when it's the ECU).

    Have since discovered that a MT ECU will run an auto car just fine if you have no idle controls.

    Cautionary tale for future troubleshooters: it really is very rarely the ECU. I swapped ECUs only *after* dumping codes, testing fuel pressure, testing spark, and doing things to fix the codes the ECU was throwing.
  • Mike87
    Mike87
    Junior Member
    • 26
    #6
    Oh man i just posted a thread with an identical issue. I think my issue is the ecu too