by Tommy Samuels
You may have a problem similar to what I went through with my '99. Here are some tips that can help you along the way.
A multimeter -- you'll need this to be able to measure resistance and DC voltage.
Check the fuses with the meter. You want continuity.
Check (listen) for the main relay clicking in when you turn
on the switch. It's on the passenger side fenderwell and it's pretty loud. you
should hear it in the cockpit of the car. Then, move on to:
1. Pull the access panel in the package tray so you can get
to the fuel pump assembly.
2. Disconnect the electrial plug to the fuel pump and gas gage
3. The plug will have 4 wires. You're interested in a red wire
with a blue stripe and a black wire.
4. You want to measure voltage across these wires. You should
have 12VDC when you crank the engine over. It will stay at 12 VDC for 3-5 seconds
after you stop cranking the engine IF you leave the ignition switch in the ON
or RUN position
IF IT PASSES THIS TEST< THERE IS SOMETHING GOING ON WITH
THE FUEL PUMP> GO TO THE FUEL PUMP SECTION BELOW >>>>
5. Install a jumper between the Fuel pump and Ground pins on
the Diagnostic connector. This will pull in the fuel pump relay and you SHOULD
get 12VDC at the fuel pump connector with the ingnition switch ON. If it passes
this test, the fuel pump relay CONTACTS AND COIL are working. If it fails this
test , you probably have a BAD Fuel Pump RELAY. Remove the jumper from the FP
and Gnd terminals of the diagnostic connector.
6. Disconnect the plug from the fuel pump relay. There are
4 wires. Red with blue stripe goes to the fuel pump. Light green goes to the
6A. The other 2 should measure 12vdc with the switch ON.
6B. The light green wire should have continuity to ground when
trying to start the engine. This will stay on for 3 to 5 seconds after trying
to start the engine if you keep the switch ON (AS IN TEST 4). If you get an
ERROR on your meter doing this test, try test 6C
6C. Change the meter to measure VOLTAGE. measure voltage between the light green and the nearest ground while trying to start the engine. IF YOU GET 5VDC, YOU HAVE A PROBLEM WITH THE ECM.
Remove the fuel pump assembly from the tank
REMEMBER: gas is highly flammable. Remove the pump, drain ALL
the gas and let it sit out in the open for 20 or 30 minutes before doing the
If you have access to a 12 volt power supply you can test the
fuel pump by touching the 2 terminals on the left side of the 4 pin connector
with 12 volts. It SHOULD come on . If not don't give up yet!
Remove the short jumper wire from the 4 pin connector and the
fuel pump. Measure continuity from end to end on BOTH the Black and Blue wires.
Wiggle it around to be certain there aren't any breaks in the wire or loose
Test the pump by applying 12 vdc directly to the 2 pins on the fuel pump. If it runs, the pump is good. If it doesn't the pump is bad.
I just wanted to let you know that I recently replaced a faulty fuel pump in my '99 miata that was running, but not putting out enough pressure for the car to start. I thought it might be helpful to let the readers know that if the pump runs they should still try a fuel pressure tester to make sure the pump is doing what it's supposed to.
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28 May, 2009