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Thread: Frequency valve not buzzing, no voltage

  1. #1
    Senior Member BladeBronson's Avatar
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    Frequency valve not buzzing, no voltage

    I’m stumped on what to do next. I’ve jumpered the RPM relay on the pins with brown and red/yellow wires. I’ve clicked the key twice to turn on the accessory power (and even started the engine - I’m not sure when the FV gets power) and there’s no buzz. I’ve disconnected the plug at the bulkhead and get no voltage reading. When the accessory is on and I inset the jumper, I hear a click from a relay in the electrical compartment, so I think somethings trying to work. I’ve removed the rear wall and can see the two wires as they go into the bulkhead connector, but am not sure where I can trace them to.

    Any thoughts on this?
    Christian Williams, Bay Area
    #3452 from 2000-2005
    #10644 since 2015

  2. #2
    Senior Member Bitsyncmaster's Avatar
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    Jumping the brown to double yellow/red wires on the RPM relay socket powers the lambda relay which then powers the FV and the lambda ECU. No key on is required. The click you hear must be the lambda relay. The power comes from fuse #7 but it your fuel pump was working than that fuse must be good. It may be your lambda relay (make sure you have the correct relay installed). That relay socket is the yellow one on most cars. The FV power wire does go through a bulkhead connector. So your not getting 12 volts at that connector with the jumper?
    Dave M vin 03572
    http://dm-eng.weebly.com/

  3. #3
    Senior Member BladeBronson's Avatar
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    That’s correct, no voltage at the bulkhead connector at all. I tried another lambda relay today with no difference. I’m trying to find my wiring diagram, but suspect that it could be the ECU.
    Christian Williams, Bay Area
    #3452 from 2000-2005
    #10644 since 2015

  4. #4
    Senior Member Bitsyncmaster's Avatar
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    Quote Originally Posted by BladeBronson View Post
    That’s correct, no voltage at the bulkhead connector at all. I tried another lambda relay today with no difference. I’m trying to find my wiring diagram, but suspect that it could be the ECU.
    The red/purple wire on the FV should get 12 volts no mater what the ECU is doing. You can use an ohm meter on the "lambda" relay center pin to the bulkhead. It could be your lambda relay is not getting the battery power so you can test that with a voltmeter.
    Dave M vin 03572
    http://dm-eng.weebly.com/

  5. #5
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    Make sure all the little ground wires on the intake manifold are there, one is for the frequency valve. Plug and unplug the frequency valve a couple of times. The connections corrode and can make a bad connection and by plugging and unplugging you might get it to buzz.
    David Teitelbaum

  6. #6
    Senior Member BladeBronson's Avatar
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    I dove deeper into this today. I haven’t had to troubleshoot this system before so I made a mistake in reporting no voltage. I was measuring voltage across the 2 pins of the bulkhead connector. When the RPM relay is jumped, I get voltage on each of the two pins when measuring from a pin to ground. There’s just no buzzing.
    Christian Williams, Bay Area
    #3452 from 2000-2005
    #10644 since 2015

  7. #7
    Senior Member Bitsyncmaster's Avatar
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    Quote Originally Posted by BladeBronson View Post
    I dove deeper into this today. I haven’t had to troubleshoot this system before so I made a mistake in reporting no voltage. I was measuring voltage across the 2 pins of the bulkhead connector. When the RPM relay is jumped, I get voltage on each of the two pins when measuring from a pin to ground. There’s just no buzzing.
    The lambda ECU when powered should be driving one side of the FV to ground at a 50% duty cycle. So you would read about half the DC voltage on that pin of the FV. If the lambda ECU is not working, you will read voltage on both FV pins since one is powered and the other one is open but will get voltage through the powered pin.
    Dave M vin 03572
    http://dm-eng.weebly.com/

  8. #8
    Senior Member BladeBronson's Avatar
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    Ah, very interesting. This is really pointing toward the ECU not working. A local owner has a spare that I might be able to test with. Thanks a bunch for your expertise on this, Dave.
    Christian Williams, Bay Area
    #3452 from 2000-2005
    #10644 since 2015

  9. #9
    Senior Member BladeBronson's Avatar
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    Another owner came over today and I did a little experiment on his car. First, I verified that by jumpering his RPM relay, his FV started buzzing loudly. I disconnected the FV at the bulkhead connector and measured each pin's voltage while the negative probe was grounded to the engine block. The bottom pin had 12 volts. The top pin had 0.2 volts (which is way less than the 50% that I was expecting). Anyway, his car is running just fine. I unplugged his ECU and the ground wire and connected my ECU to his car and repeated the tests. Everything was exactly the same, pointing to my ECU being good.

    So now I have to figure out why I would be getting ~11 volts on both pins (when measured with a multimeter with the positive probe on a pin at the bulkhead and the negative grounded to the engine block).
    Christian Williams, Bay Area
    #3452 from 2000-2005
    #10644 since 2015

  10. #10
    Senior Member Bitsyncmaster's Avatar
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    Quote Originally Posted by BladeBronson View Post
    Another owner came over today and I did a little experiment on his car. First, I verified that by jumpering his RPM relay, his FV started buzzing loudly. I disconnected the FV at the bulkhead connector and measured each pin's voltage while the negative probe was grounded to the engine block. The bottom pin had 12 volts. The top pin had 0.2 volts (which is way less than the 50% that I was expecting). Anyway, his car is running just fine. I unplugged his ECU and the ground wire and connected my ECU to his car and repeated the tests. Everything was exactly the same, pointing to my ECU being good.

    So now I have to figure out why I would be getting ~11 volts on both pins (when measured with a multimeter with the positive probe on a pin at the bulkhead and the negative grounded to the engine block).
    When the FV is disconnected, there is no pull up to 12 volts on the pin the ECU is switching from ground to open. To see the 50% DC voltage you need to keep the FV connected.
    Dave M vin 03572
    http://dm-eng.weebly.com/

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