totally stumped! fuel pump not working

[smallclone]

so i was driving and the car stalled. i have the dmc-h new fuel pump system.

i took a paperclip and jumped the rpm relay. nothing.

i checked inertia switch, its down.

checked fuse 7, its fine.

i checked voltage from the fuel pump harness and getting 12.5 volts.

i hooked up the pump with the module still connected straight to the battery and the pump will run.

I disconnected the three fuel senders wires since it ran without them when just connected to the battery and tried again and still the pump wont run with the rpm relay jumped even though the pump is getting 12.5 volts.

im totally stumped at this point.

any new takes on this would be appreciated.

[Bitsyncmaster]

You need to verify you have grounds on the pump. Just checking the pump voltage to a frame ground does not verify the pump grounds are connected. Now if you measure on the pump connector from it's ground to the 12 volt wire on the pump power wire then a non-working pump would indicate the pump has failed.

[smallclone]

You need to verify you have grounds on the pump. Just checking the pump voltage to a frame ground does not verify the pump grounds are connected. Now if you measure on the pump connector from it's ground to the 12 volt wire on the pump power wire then a non-working pump would indicate the pump has failed.

i checked voltage straight from the harness.

I tested the pump hooked into the battery and the pump worked.

[David T]

The car can stop for reasons other than a non-runniing fuel pump. For instance you could be out of gas because your fuel gauge is not working or is inaccurate. On the OEM fuel pump set up a bad pick-up hose can kink or collapse or it has a leak and is sucking air. Usually happens when you have less than 1/2 tank of gas. The first step is usually trying to figure out if you have BOTH spark AND gas. An easy way to start is to squirt some Ether (just a little, don't overdue it!) into the mixture unit and see if you can get it to fire at all. If you get it to run even a little you know you have ignition so you try to figure out why you don't have fuel. If you get nothing you should pull a spark plug and see if you get any spark while cranking. If you don't see a nice blue spark you know you have to figure out what is causing that. A bad connection, a bad impulse coil, whatever. A bad impulse coil often presents as the car will start up and run but after around 20 minutes or so it dies. Won't restart till it cools off and then the cycle repeats. Another possibility is a bad alternator. If the alternator fails and you are running on the battery, the motor will run till the battery voltage gets too low to make sparks. You would notice that though because when you try to restart, the motor will crank very sluggishly. Main point is don't fixate on the fuel pump, the motor can stop for other reasons too.

[mr_maxime]

i checked inertia switch, its down.

are you sure the switch actually works? you may want to bypass it.

[Ron]

i checked voltage straight from the harness.

I tested the pump hooked into the battery and the pump worked.

Sounds like you may be using a volt meter. It may read 12V+ but they don't supply a load heavy enough to test the feed...Voltage OK, but a poor connection might not be handling the current required.

I'd suggest an ice pick probe/light to test circuits, but, it working when connected to the battery directly suggest the same thing...

Maybe use the harness ground with battery (+), and then, harness feed with battery (-) to get another clue???

[smallclone]

Sounds like you may be using a volt meter. It may read 12V+ but they don't supply a load heavy enough to test the feed...Voltage OK, but a poor connection might not be handling the current required.

I'd suggest an ice pick probe/light to test circuits, but, it working when connected to the battery directly suggest the same thing...

Maybe use the harness ground with battery (+), and then, harness feed with battery (-) to get another clue???

so using a pick probe i found a few things. First off with the RPM relay socket jumped, the two wire fuel pump harness with only glow on the ground side.

the pick will glow at the inertia switch on the pos+ and ground- side

Fuse 7 does not glow at all

Fuse 1 will glow but only if the key is not in run pos.

[Ron]

Trying to be careful here:

so using a pick probe i found a few things. First off with the RPM relay socket jumped, the two wire fuel pump harness with only glow on the ground side.

If you connected the probe's wire to the battery (+) and the probe tip to the pump harness ground, and it lights, the pump's ground is OK.
If you connected the probe's wire to the battery (-) and the probe tip to the pump harness feed, and it does not light, the pump is not getting its feed.

the pick will glow at the inertia switch on the pos+ and ground- side

This tells you that the inertia switch is probably fed and grounded OK, but not if the switch is OK or in the proper position...

Fuse 7 does not glow at all

Fuse 7 should be hot at all times. It feeds the RPM relay, Distributor, Vac Solenoid, Ignition and Idle ECUs...
If you remove Fuse #7 then connect the probe's wire to the battery (-) and the probe's tip to the the receptacle's feed side, the probe should light regardless of Key position. (Both wires are Brown). Confirm/chase Fuse #7's feed wire, if not.
[Same if you leave the fuse installed and probe either side of the fuse (via the little holes on top), assuming a good fuse and connection.]

If you remove Fuse #7 and connect the probe's wire to battery (+) and the probe's tip to the receptacle's output terminal, the components connected to it should ground the probe and make it light. If not, chase that Brown wire looking for a break or bad connection etc.

(If you remove the fuse and connect the probe in place of the fuse, it may blow the probe's bulb...like a fuse rated too low.)

Fuse 1 will glow but only if the key is not in run pos.

Fuse #1 should be hot when the key is on, only. It feeds the Lambda's Relay & ECU, FV, CPR,...and Fuel Pump.
If you remove Fuse #1 then connect the probe's wire to the battery (-) and the probe's tip to the the receptacle's feed side, the probe should light regardless of Key position. (It has a White wire). Confirm/chase the feed wire back to the Aux 1 Relay if not. Check the Relay's output too.

If you remove Fuse #1 and connect the probe's wire to battery (+) and the probe's tip to the receptacle's output terminal, the components connected to it should ground the probe and make it light. If not, chase the Green Wire, looking for a break or bad connection on the way to the RPM relay -- The RPM relay passes this power to supply the pump...


Sounding like: Fuse #7 feed, Inertia Switch, or something very odd with Fuse #1/Aux Relay 1 output.
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