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1990 Mazda Miata will crank but not start. Just replaced battery, spark plugs, and air filter. I used some starting fluid in the air intake and the engine started so I believe its a fuel problem. I tried using the diagnostic terminal to start the fuel pump but there was no buzz. I removed the access cover to get to the fuel pump and I disconnected a wire lead. I used my volt meter on (DCV 20 setting) two of the four prongs and recieved a reading of around 7 volts. I know the pump requires 12v. The voltage at the battery and the diagnostic terminal both read 12.5v and 12.4v respectively. What could cause my pump to be receiving reduced power? and is there any way i can check to see if the fuel pump itself would function if it received the correct voltage?

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  • crzyyak
    crzyyak Oct 26, 2013

    I replaced the fuel pump and shes running again. A little concerned because the engine is much louder than it was before

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You may want to check your relays for a fuel pump relay, because if you are getting some power but not all, it may be due to a bad Relay. It would be tough to distinguish which wire would be the power for the fuel pump unless you remove it to go off of, to see which terminals powers the pump (+/-) and which ones are for the sending unit. A wiring diagram of the car would be nice to have to show you, It's almost safe to assume that in the plug the "thicker" wires are going to be your power, while the thinner ones are for your sending unit (guage). Check Relays FIRST, then assume that it's the pump, because very rarely do the wires go bad, unless you were in an accident or off roading with it.

Posted on Oct 12, 2013

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  • crzyyak
    crzyyak Oct 12, 2013

    ok will check it tomorrow, been having trouble finding the relay. thankyou.

  • crzyyak
    crzyyak Oct 12, 2013

    I got impatient and went out to take a look at it. I found the relay and I know exactly where its at and i can see the bolt holding it in place unfortunately i cant get a good angel for my socket wrench. Who ever worked in this area before me got a little tape and zip tie happy so most the wiring is tied together in big thick bands wrapped with black tape so its hard to see the wiring colors and zip tied to everything. Since i know the air bag wiring is somewhere in those wires i need to proceed carefully and figure out how to get that bolt out

  • crzyyak
    crzyyak Oct 12, 2013

    Angle*

  • crzyyak
    crzyyak Oct 12, 2013

    Still can't get to the relay. Reran the volt meter test at the fp and got a reading of 12.5v. i was just to slow connecting the meter after turning the key

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Not sure what you are using as a ground when checking voltage. If you check at the connector you should have 12 volts at the blue wire with the red stripe (red prong on volt meter) and you can check putting the ground/black prong on your volt meter on either one of the black wires on the connector. When turning the key just to the on position you\'re only going to get full power for about 2 seconds unless you\'re turning the engine over. If you\'re not getting full voltage try putting the black prong (leaving the red one from meter on the terminal that has the blue wire with the red stripe) using a good ground on the body of the vehicle (the black prong from meter). Now if you\'re getting the voltage you need then you need to trace the black wire(s) to where they are grounded out on the vehicle and clean/tighten and repair the ground as well as making sure you are getting zero continuity from where the ground is on the body to the connector at the fuel pump. A bad ground will cause weak power. These are also the 2 wires you need to apply direct power (on the pump side of the connector) in order to check the pump as you asked. Since there are 2 black wires at the connector, if you have direct power to the blue and red wire and put your ground on one of the black wires and it doesn\'t run, than try using the other black wire (or where it would be on the terminal of the connector...pump side) at the connector because that would mean you are testing the wrong ground wire for the pump itself. If your ground is good down there and it turns on when applying direct power than it could be a number of things but the 2 most common would be the fuel pump relay or the air flow meter/sensor. Start with check power and ground and direct powerfirst. If the pump is working when putting direct power and your grounds are good then further testing needs to be done of course. I\'ll be happy to help you with further testing if needed like checking the relay and/or air flow meter. You will need an ohm meter for further testing. I hope I was detailed enough for you to understand the testing needed at this point and I hope I was able to help

Posted on Oct 12, 2013

  • 1 more comment 
  • crzyyak
    crzyyak Oct 12, 2013

    I will check this out tomorrow as well thankyou

  • crzyyak
    crzyyak Oct 12, 2013

    unfortunately I do not have a wiring diagram

  • crzyyak
    crzyyak Oct 12, 2013

    good call on the volt meter. i retried it today and got 12.5 v when i first turn the key. tried running the ohm test not sure how. Don't think i did it right because i didn',t get a reading from any of the connections i tried

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