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xfi will not start as well as classic

Discussion in 'FAST Support Forum' started by kidglok, May 7, 2013.

  1. kidglok

    kidglok Member

    Joined:
    Apr 2, 2012
    trying to figure out why i cant get my xfi 2.0 to start as well as my friends classic, we discovered his other car with xfi wont start as easy either. Mine has to crank and crank and crank before she will fire, his classic will make 2 revs then fire right up. Ive copied all the tables, iac cranking fuel, even scaled the injectors from his 72's to match the same pulswidth i would need with the 83's. I even have gone as far as to adjust the battery offset voltage to match. Still no dice.

    we logged my car xfi 2.0 with caspers direct harness, his ttop with xfi (1.34) and caspers adapter, and finally his 87 gn(x) with classic fast and precision harness and noticed some weird things.

    this is during cold start


    first attachment: as you can see with the classic everything is fine, rpm readings and injector dutycyle are in line with what we would expect


    second attachment: ttop with xfi and caspers adapter- rpms read 12750 and dutycycle is maxed out for the moment


    third: my car- 2.0 with direct harness, notice the rpms jump to 1500 and the dutycycle is maxed at 100%. (as a side note mine would not record an a/f richer then the leanest (15.94) xfi can read untill 3 seconds after the initial crank.

    Could this be why we cannot get any xfi to start as well as the classic?? something has to be going on in the background here...
     

    Attached Files:

  2. kidglok

    kidglok Member

    Joined:
    Apr 2, 2012
    Ttt anyone?
     
  3. pbp1

    pbp1 Member

    Joined:
    May 19, 2009
    The RPM spikes you are seeing are noise. This has to be addressed as they are causing false fueling commands (the 12500 is actually triggering your fuel cut i am sure. With these adapter harnesses, the grounds can be iffy at best because you are relying on 25+ year old factory wiring from the adapter out. I would suggest taking the 3 main grounds (Power return, Analog return, and Digital return) out of the adapter and directly to the battery. It's been a while since I installed one with a Caspers adapter so I can not remember how the main powers and grounds were handled but they absolutely have to go right to the battery, not to a body ground, not to the frame, not to a common ground stud that has a big wire going right to the battery, directly to the Battery negative terminal!!!!! This should eliminate the noise and will probably fix the cranking issue. Even if it doesnt, you will be able to properly deal with your cranking fuel issue with the noise gone. You cant really compare BPW between the Classic, XFI, and XFI 2.0 because they all deal with the injector opening time differently. If you want to duplicate the fuel, you have to look at the opening time and battery corr. % as those are added to the base pulsewidth.
     
  4. kidglok

    kidglok Member

    Joined:
    Apr 2, 2012

    Thanks for the response. I notice when looking at the pinout chart there is 6 return grounds
    A12- main power return ground
    B7- main power return ground
    B8- digital auxiliary inputs return ground
    B24- analog inputs return ground
    B25- main power return ground
    C11- analog auxiliary inputs return ground

    Which 3 of those are used?
     
  5. norbs

    norbs Active Member

    Joined:
    Jun 12, 2011
    Location:
    toronto
    All the grounds on the XFI are common to each other on the board, doesn't really matter!
     
  6. kidglok

    kidglok Member

    Joined:
    Apr 2, 2012
    So I only have to run one of those back to the battery?
     
  7. kidglok

    kidglok Member

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    Apr 2, 2012
    And what's a digital auxiliary input? The sensors go to analog inputs../
     
  8. norbs

    norbs Active Member

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    Jun 12, 2011
    Location:
    toronto
    Technically, Yes, but since the case is internally grounded, this creates another ground loop.
     
  9. kidglok

    kidglok Member

    Joined:
    Apr 2, 2012

    Soo your suggesting I run pin __ back to the battery?
     
  10. norbs

    norbs Active Member

    Joined:
    Jun 12, 2011
    Location:
    toronto
    No, it reality you should run a few wires back to the battery 3 or 4 of the heavy pins should be sufficient with 14 awg wire. I thought you had an adapter harness? Then ignore my suggestion, but the adapter harness does make ground loops if you ground it to the dash.
     
    Last edited by a moderator: May 11, 2013
  11. TurboNova

    TurboNova Active Member

    Joined:
    Jan 30, 2009
    Location:
    Lake Havasu City AZ.. but mostly travel tuning
    A12
    B7
    B8
    B24
    B25
    D1

    all go directly to battery ground.

    Do not connect C11 to the battery directly.
     
  12. pbp1

    pbp1 Member

    Joined:
    May 19, 2009
    The power grounds are the only ones that are common so that leaves you with the power grounds tied together in one wire. The digital ground and analog ground are not connected to power grounds. C11 is not an external ground. it is for returning signals to the ECU. you should follow the main wiring schematic and tie the power returns together and keep the digital and analog returns seperate. That makes a total of 3 ground or return wires that need to go directly to the battery.
     
  13. norbs

    norbs Active Member

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    Jun 12, 2011
    Location:
    toronto
    Interesting ..........ohmmeter shows as follows PINS common in ECU header with continuity. Please explain this? Please post an internal schematic of the ecu grounding if possible.

    A1,A2, A12,A13,B7,B8,B24,B25,C5,C11,D1,D3,D5,D6,D8,D10,D12,D15
     
    Last edited by a moderator: May 13, 2013
  14. kidglok

    kidglok Member

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    Apr 2, 2012
    English norbs for us non electricians!
     
  15. norbs

    norbs Active Member

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    Jun 12, 2011
    Location:
    toronto
    Means they are all connected together in the ecu, unless the meter is picking up wrong readings through some of internal components, screwing up the readings.
     
  16. kidglok

    kidglok Member

    Joined:
    Apr 2, 2012
    so a12 b7 b25 and d1 tied together back to the battery, b8 and b24 seperately, and c11 has the sensors ground on it.

    b25 shows as a main power return on the schematic but doesnt go anywhere?
     

    Attached Files:

    Last edited by a moderator: May 12, 2013
  17. pbp1

    pbp1 Member

    Joined:
    May 19, 2009
    I am only referring to what needs to happen to the grounds outside of the ECU. Just because there is some continouty between these pins does not mean that they are designed to be grounded through each other.
     
  18. pbp1

    pbp1 Member

    Joined:
    May 19, 2009
    A12, B7, and D1 are the main power returns and they get spliced together along with the ground for the relay. That is one wire that needs to go directly to the battery.
    B8 is the Digital ground, it also needs to go directly to the battery.
    B24 is the Analog ground, it also needs to go directly to the battery.

    B25 is internally connected to B7 so it doesnt need to be grounded.
    D3, D5, D6, D8, D10, D12, and D15 are the same deal, they are all tied to D1 so they do not need to be grounded.

    This is all right on the main schematic. No need to re-engineer this or make it more complicated than necessary, just do it like the wiring diagram.
     
  19. kidglok

    kidglok Member

    Joined:
    Apr 2, 2012
    update

    grounded what was recommended directly to the battery, and still the same thing. Im running out of ideas :confused:
     
  20. norbs

    norbs Active Member

    Joined:
    Jun 12, 2011
    Location:
    toronto
    I am also seeing noise, when cranking, the spike is 1500 RPM though. I have taken ALL the grounds back to the battery with individual wires, except pin C11, as that grounds my analog sensors.
     

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