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Checking fuel pump voltage

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Old 06-14-06, 12:07 AM
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Checking fuel pump voltage

I did some reading (and a little seaching even) and i was reading that i should make sure that my fuel pump was getting all the power it needed on my 89 TII. I checked my batt w/ the car off, 12.8 volts. So i went to check the fuel pump. I had the key on so it should be drawing power from the pump and i cant figure out which of the four holes to put the pos and neg on. I know it would make sense to just keep trying them all until i got a reading, and i did do that but i still couldnt get a reading

what am i doing wrong?
Old 06-14-06, 12:21 AM
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i cannor rember for shure but i think it is the blue wire. you can ground your neg lead to the car. you should have some one key the ignition on whyle you look at the meter.
Old 06-14-06, 05:59 AM
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The fuel pump only gets power when the engine is running or cranking. Plus it has a two-speed system that drops the voltage sent to the pump at low load. So the best thing to do is monitor the fuel pump voltage while driving.

What I did was to terminate the wires at one end of a length of speaker cable with male spade terminals, which slip into the back of the fuel pump plug (blue/green and black wires), run the wire to the passengers seat and twist the other end around the DMM probes. Then drove and watch the voltage. It should be ~9V at idle at cruise and >12V under load. Mine switched at 2-3psi boost.
Old 06-14-06, 06:25 AM
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Look for the two thickest wires.
If your DMM has auto polarity, it won't matter.
If you see a negative, you can reverse it for proper readings.
Or, hell, just ignore the "-" sign.

You really need to monitor the voltage when in boost / WOT.
Connect everything semi-permanently and go out for a drive.
It would help to have a friend to read the DMM for you for safety...


-Ted
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