RX-7 Fueling/MAP sensor problem?

Discussion in 'OT Driven' started by z284pwr, Sep 1, 2006.

  1. z284pwr

    z284pwr OT Supporter

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    Since I know there are a few RX-7 owners here I figured I would ask. This appears to be a rare or never happened type thing as the guy was in contact with a pretty big RX-7 shop in Flordia I believe he said and the main tuner had no ideas, but anyway....

    Its a '93 RX-7. Last time it ran it was running stock
    twins non-sequential on a Power-FC. Anyways, it got T-boned and is
    being rebuilt. He put on a single turbo and a fuel kit I guess its
    called with 1600cc primaries I think he said through a resistor I
    guess they need.

    He has also tried a different computer so it doesn't appear to be
    that.

    So I went and checked it out. The Power-FC has the MAP sensor
    highlighted and with key-on its showing 1.1? bar, at 4.88 volts? So
    in other words the car thinks its at full boost all the time. He
    has changed tried a different MAP sensor with no change. I dunno
    what wire it is since I couldn't find any pin-outs but by grounding
    the green/yellow wire the volts would drop down to approximately 2.8
    volts, however, this was only when I used a volt meter between the
    two, if I used wires it straight grounded it to 0 volts.

    The other issue is fuel. It has pressure at the rail but the
    injectors don't appear to be opening. With starting fluid the
    engine does start and die so it has spark. This I have no idea on
    what to look at? He tried stock injectors as well and had the same
    problem.

    I'm going with wiring problems on both cases? The car has been
    rebuilt and came back to him as a rolling chassis which was running
    before which is why I'm gonna go with that. Some of the harness has
    been cut and put back together, I soldered what appeared to be all
    the really bad connections and all the grounds appeared to be on the
    engine as well so I'm not sure.

    If any has any ideas on these issues it would be appreciated and the
    guy with the car would really appreciate it as it hasn't run for a
    year and a half.

    Thanks
     
  2. Dysfnctnl85

    Dysfnctnl85 IT/Apple/Rotary/(D)SLR Crew

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    It definitely sounds like there are some wiring issues with the car...I hate hunting down those gremlins. If there appears to be anything wrong with the stock harness wrt insulation or any exposed wires, I would tend to blame them before anything else.
     
  3. z284pwr

    z284pwr OT Supporter

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    It's definitely some wiring issues.
    For a little update, today I verified that the injectors were okay to the ECU, SO, I wired the ECU side of the injectors up, and wired the other side of the injectors straight to battery and it fired right up, right as can be, but still fired right up...

    SO, definitely 2 wiring issues, the injectors don't have 12v and the MAP sensor is all sorts of screwed up.
    I would assume the easiest way to fix the injectors is just rewiring the 12v wires to the EGI Main fuse by the driver's side fender.

    I have no ideas on the MAP sensor yet however.
    I'm thinking that a wire has melted through somewhere so the MAP sensor always gets voltage, however, this one is confusing, if I use a volt meter on the MAP wire the voltage drops slightly as if the meter is putting a resistance on it or something? When we had the engine running, even with the volt meter on, the MAP reading would change with engine but once I pulled the volt meter off, the MAP reading would peg back at 4.8 volts causing it to run extremely rich obviously?
     
  4. deusexaethera

    deusexaethera OT Supporter

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    Make sure the battery is properly grounded to the chassis. If it's not, everything in the electrical system will go haywire in random fashion as the voltages in individual components change and electricity flows into places it's not supposed to go.
     
  5. Tom93R1

    Tom93R1 Member

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    Could be a grounding problem in your harness, my friend had problems with the MAP reading on the PFC being lit up and it turned out to be one of the grounds on the wiring harness, I think one that connectos to a fuse box but I dont remember for certain.

    Honestly it sounds like things are bad enough that I would just replace your wiring harness. It is a $700 purchase and alot of work but if it is as bad as things sound you could end up saving yourself from a broken apex seal and several thousands in rebuilding costs.

    To clarify for you, the 1600cc injectors would be the secondaries. The 93+ RX7 uses high impenence injectors and the Bosch 1600cc injectors are low impedence, so you add a resistor inline so you dont burn up the injector drivers in the ECU.
     

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