P2138, won’t rev above 3000 rpms, lots of smoke

Discussion in 'Mazdaspeed 3/6 Engine' started by jsilva, Apr 12, 2020.

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  1. Ssinstaller

    Ssinstaller Gold Member

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    P2138 is only caused by the throttle pedal or bad wiring between it and the pcm.

    20200426_141323.jpg

    Test the pedal and it's wiring to find your issue.
     
    Ssinstaller, via a mobile device, Apr 26, 2020
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  2. jsilva

    jsilva Silver Member

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    Thanks! I had been focussing on the fact that it happened right from the first start after I had done work which had the intake manifold off (and therefore the throttle body) and assumed it was something I did.

    It‘d be nice if I didn’t have to take things apart again :) Do you have any advice for testing?
     
    jsilva, via an iPhone, Apr 26, 2020
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  3. Ssinstaller

    Ssinstaller Gold Member

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    20200426_202118.jpg 20200426_202338.jpg 20200426_202152.jpg 20200426_202221.jpg 20200426_202241.jpg
     
    Ssinstaller, via a mobile device, Apr 26, 2020
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  4. jsilva

    jsilva Silver Member

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    That’s really great Ssinstaller, thanks so much! I look forward to investigating.
     
    jsilva, via an iPhone, Apr 26, 2020
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  5. jsilva

    jsilva Silver Member

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    I had a look today and realised I’m not totally sure which connectors are being referred to in the service manual.

    50143933-E761-4F64-B002-63F762016349.jpeg

    I’m assuming the one I circled is the connector with 3A to 3AA. But can I safely assume the other connector with 2A through 2AD is adjacent to the right (in the photo)?

    That is seriously cramped! :) I’m not sure yet how I’m going to be able to get my hands in there and also see what I’m doing at the same time.
     
    jsilva, via an iPhone, Apr 28, 2020
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  6. jsilva

    jsilva Silver Member

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    Today I took out the front seat hoping to get more room, and indeed it gave me more room but the hump in the floor was killing my back. I was thinking I’d take out the PCM so it’s not quite as difficult.

    However I’m unsure how to test the terminals. There is no space to wedge the test lead in to make contact with anything.

    Am I supposed to make a hole in the wire housing? Seems pretty silly to require doing that just to test. Or am I missing something?
     
    jsilva, via an iPhone, Apr 30, 2020
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  7. Ssinstaller

    Ssinstaller Gold Member

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    These would be the easiest.


    Or you can get some normal 1mm pin test leads that will fit in the back of the connectors.
     
    Ssinstaller, via a mobile device, Apr 30, 2020
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  8. jsilva

    jsilva Silver Member

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    Thanks Ssinstaller. I went ahead and got a decent kit which includes a variety of test leads. A couple of years ago I got a nice set of leads for my Amprobe multimeter but I’ve only ever done home electronics troubleshooting (vintage amps, instruments) and didn’t even know about piercing leads or 1mm tips! :)
     
    jsilva, via an iPhone, May 1, 2020
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  9. jsilva

    jsilva Silver Member

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    I tested the connectors today.

    - 3D had smooth voltage as the APP was pressed, and in the voltage range according to the service manual.

    - 2A had 1.3V (or so) and didn’t change with the APP. So obviously an issue there.

    - I tested for an open circuit as the instructions say and everything was ok.

    - I didn’t test for a short circuit. Partially because my back was really hurting by that point. Was that a mistake?

    Since the error was in the first step (but the APP is clearly working), and there was no open circuit which means there is continuity from every APP pin to the PCM, and since this problem happened when I was fiddling around the throttle body, I’m guessing it’s the throttle body?

    But what’s the likeliness two throttle bodies would stop working at the same time? I know it’s possible but I feel like I’m still missing something. Maybe it’s because I didn’t test for a short circuit?
     
    jsilva, via an iPhone, May 7, 2020
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  10. Ssinstaller

    Ssinstaller Gold Member

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    The wiring you're testing is for the actual gas pedal. If you have a circuit not showing the voltage as expected in the manual, that would mean your gas pedal is bad, not the throttlebody.

    There are no shared wires between the APP and the throttlebody.

    I would test for a short before replacing the pedal assembly.
     
    Last edited: May 7, 2020
    Ssinstaller, via a mobile device, May 7, 2020
    #30
  11. jsilva

    jsilva Silver Member

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    The service manual says that if there is failure in the first step—if the two terminals don’t change voltage smoothly in response to the APP—that replacing the throttle body is the remedy. Replacing the accelerator is in the second step—if the voltages aren’t in range as the chart shows.

    Since on mine the voltage doesn’t change on 2A in response to the APP I’ll never make it to the second step. So it’ll be either the wiring harness or the throttle body. (And it’d only be the wiring harness if I test again and there is a short.)

    Or am I misreading?
     
    Last edited: May 7, 2020
    jsilva, via an iPhone, May 7, 2020
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  12. Ssinstaller

    Ssinstaller Gold Member

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    20200507_221328.jpg 20200507_221040.jpg

    This test is written pretty poorly.
    But, I think step two is saying if the terminals 2a and 3d are behaving as expected and the throttle blade is not, then you need to test the TB and replace if it's found to be bad.

    The voltage readings on pins 2a and 3d are 100% generated by the pedal, they should follow the voltages shown in the manual even if there was no throttlebody present. Also the throttlebody isn't listed as a possible cause for you MIL.

    I just checked the pcm diagram to be sure, and there are no direct connections between the APP and the throttlebody.

    I'd finish the wiring test and if you don't find any shorts replace the pedal.
     
    Last edited: May 7, 2020
    Ssinstaller, via a mobile device, May 7, 2020
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  13. jsilva

    jsilva Silver Member

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    I follow what you’re saying Ssinstaller. Either way I saw an accelerator on eBay for cheap enough from a high volume and highly rated seller and so I went ahead and bought it. I’ll still do the remaining electrical tests... such a pain!

    For testing for shorts, can I just use the cigarette lighter as a ‘power supply’? I’m not sure where else to use. Also, do I need the connectors out of the PCM for those tests as well?
     
    jsilva, via an iPhone, May 7, 2020
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  14. Ssinstaller

    Ssinstaller Gold Member

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    Power supply would be pin 2k at the pcm or pin A at the pedal.

    Easiest way to test. Pull connectors from pedal and pcm.

    At the pedal you should have:
    No continuity between any pins.
    No voltage on any pins.
    No continuity from A, C,D,E,F to chassy ground.
     
    Ssinstaller, via a mobile device, May 8, 2020
    #34
  15. jsilva

    jsilva Silver Member

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    Thanks! I’ll give it a go tomorrow and see what I turn up.
     
    jsilva, via an iPhone, May 8, 2020
    #35
  16. jsilva

    jsilva Silver Member

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    Ok ... I finally got on to this.

    The only thing I noticed, which may not be of significance, is that there was no continuity between APP pin B (or E) to chassis ground. I don’t know there should be, but in the manual it omits those pins when testing for a short circuit to ground.

    Since none of the tests specified failed I went ahead and replaced the accelerator pedal, and it made no difference.
     
    jsilva, via an iPhone, May 20, 2020
    #36
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  17. jsilva

    jsilva Silver Member

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    Based on Ssinstaller’s wiring diagram, would it be worthwhile to test for continuity between 3P, 3M, 3Q, and 3J on the PCM and the corresponding wires on the throttle body?
     
    jsilva, via an iPhone, May 20, 2020
    #37
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  18. Ssinstaller

    Ssinstaller Gold Member

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    That pin is the sensor ground it is connected to pin 2H at the pcm, it may be isolated from the body ground.
     
    Ssinstaller, via a mobile device, May 20, 2020
    #38
  19. jsilva

    jsilva Silver Member

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    So should I check for continuity from APP pin B to PCM 2H?
     
    jsilva, via an iPhone, May 20, 2020
    #39
  20. jsilva

    jsilva Silver Member

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    Duh, I forgot I already checked the continuity between APP B to PCM 2H and it’s fine.
     
    jsilva, via an iPhone, May 20, 2020
    #40
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