Fuel Pump Woes... no power??

[bfloyd]

Heading out to a concert yesterday afternoon and made it about 25 miles before the car died on the interstate. Merging from one interstate to another the engine starting sputtering going up the crossover ramp, loosing power as I went. Engine completely shut off by the time I hit the entrance ramp and we coasted to a stop along the shoulder.

Tried cranking and cranking, and it seemed like it wasn't getting fuel. The tank was full. I have in my car the new DMCH combo fuel pump / fuel sender unit that was installed in the summer of 2015. Noticed on the dash that all of the gauges worked EXCEPT the fuel gauge. It read zero. I'm assuming that since the gauge didn't read anything that would indicate no power going to the pump / fuel sender. I checked the fuse and it was fine. I checked the inertia switch and it was fine. The only thing I haven't done is physically check the electrical connections at the pump. Kinda hard to do on the side of the road with trucks whizzing by at 80 mph. Will take the trunk apart this weekend to verify the connection and put an electrical tester on the connectors to see if I've got power.

This "new pump" has roughly 11k miles on it since installed in 2015. Any other suggestions as to what I can look for?

[iflights]

I'm not an expert, but these are what I would do.
Check the connections and voltage at the pump.
Inertia switch plug is troublesome as well, you could jump center pin to end pin (black wire) to take switch out of the electrical loop.
Jump the RPM relay in an attempt to isolate it to the relay or pump if not seeing voltage at pump.

[David T]

Verify power and ground to the pump. You will have to jump (bypass) the RPM relay. If you have power & ground to the pump and it isn't running you found the problem. Can also be the RPM relay so you have to check it too. Check that your inertia switch has a white splotch of paint on it and it is NOT attached to a bracket hanging off the Lambda counter but is on the side of the footwell. Other possibility is a bad connection in the wiring harness plug up by the windscreen reservoir.

[mr_maxime]

Also, are you sure the inertia switch is functional? Mine didn't work and was bypassed. Then that bypass got burnt up.

[bfloyd]

My inertia switch IS located on a bracket on the side of the lambda counter, but it does not have a white splotch of paint on it as far as I know. The inertia switch IS functional as I had to test it while doing the DMCH Fuel Pump recall wiring modifications. I'll start digging into it on Saturday morning.

[David T]

Look up Safety Campaign No. RA-0003. Service Bulletin SC-06-7/82. You need to get it done, the original inertia switch has a high failure rate and must be removed, relocated and replaced. Since you don't have this recall done you now must make sure ALL applicable recalls have been completed. BTW, the white splotch of paint tells you that you have the replacement inertia switch. If you don't have a switch with that splotch of paint you have an original.

[bfloyd]

Have determined that its probably not the pump but the electrical power to the pump.

Jumped the RPM relay, key in the "run" position, and measured 0.001 volts at the two pin power connector at the pump.

Read another thread about jumping the inertia switch to take it out of the loop, but my inertia switch seems to be an early model. There is no connector at the bottom of the switch. The wires just come off the harness and go directly into the bottom of the switch.

[Bitsyncmaster]

Have determined that its probably not the pump but the electrical power to the pump.

Jumped the RPM relay, key in the "run" position, and measured 0.001 volts at the two pin power connector at the pump.

Read another thread about jumping the inertia switch to take it out of the loop, but my inertia switch seems to be an early model. There is no connector at the bottom of the switch. The wires just come off the harness and go directly into the bottom of the switch.

You don't need the key on when jumping the RPM relay. You can use the black wire on the fuel sender as a ground for your meter and test if the white/purple wire gets power. If so than your problem is in the ground side (inertia switch).

[DMCMW Dave]

Have determined that its probably not the pump but the electrical power to the pump.

Jumped the RPM relay, key in the "run" position, and measured 0.001 volts at the two pin power connector at the pump.

Read another thread about jumping the inertia switch to take it out of the loop, but my inertia switch seems to be an early model. There is no connector at the bottom of the switch. The wires just come off the harness and go directly into the bottom of the switch.

That is actually a plug. Unplug it and put in a jumper wire.

DSCN2198.jpg

[bfloyd]

So, went out to the garage tonight to poke around with a tester.

On the fuel pump wiring diagram fuse #7 should be HOT all the time. Found a good ground and pulled #7. The fuse itself is good. Took the test probe and found that one side of the fuse terminals is hot with 12.79 volts. That's good. Put the fuse back in and moved on to the RPM relay connector.

According to the pump circuit wiring diagram the power from Fuse #7 goes directly to pin #30 on the RPM relay connector. Verifying my ground was still good, I took the probe to pin #30 and got nothing. I dont get it?

Does a wire just randomly break driving down the road at 80mph?

Got more digging to do.