'86 E150 fuel system issues (Redux)

Last Spring I posted about issues I was having with the fuel system on my '86 E150.  I thought I had solved the problem by replacing the rear tank fuel pump.  The few short test drives I took indicated the fuel selector valve, gauges and pumps were all working.  I knew the rear pump connector block wasn't in good shape and that it may have connectivity issues but I thought I had pried the connectors enough to make a good connection for now, and I would deal with replacing it later.  Well, later came.  On the first real trip in the van since I did this work (KC to Omaha and back), I ran the front tank to just outside of Omaha and then ran on the rear for a few miles and throughout town (maybe 25 miles).  Next day, I refilled the front to be safe and drove most of the way home on it.  Again, about 30 miles from home, I switched to the rear and all was still good.  But at the first stop off the exit ramp, when I went to pull away from the stop light, it died.  It then started doing what it did last Spring - run for a short distance on the main frame rail pump, but neither in tank pump seemed to be working (gauge was also not reading either tank).  I crawled under the rear, popped the connector, pried each connector with my pick, and put the connector back on.  It fired up and stayed running, but I switched back to the front tank to be safe for the next few miles home.  (I think the fuel selector valve gets hung up when the rear pump/gauge circuit loses connectivity and won't switch back to the front until the rear circuit is reestablished).

I crawled under it today and its clear that the rear pump (which has less than 100 miles on it), isn't working.  Because that electrical connecting block was bad, I dropped the tank, broke the connector apart and connected each wire to the posts of the sending unit with the bare connectors so I could easily test each circuit with everything connected.

The rear gauge and pump ground connectivity and resistance are good.  I get 10 V at the sending unit on the pump circuit, with engine running.  I pulled the sending unit and checked the connections on the pump itself.  Again, with engine running, I get 10 V on the +, and connectivity is good on the - side.  But the pump does not kick on.  I can, however, move the float up and down and the gauge responds accordingly.  Clearly, the FSV is working.

The resistance across the pump is about 2 ohms (what should it be?).  If I'm getting 10 V at the pump and the ground is good, and the pump doesn't turn on, the pump has to be bad, right?  Or am I missing something?
 
Since the previous pump didn't last 10K miles and this one didn't last 100, what could be going on?  Could a loose connection at the sending unit cause the pump to fail?  Could I be getting a voltage surge that is killing the rear pump?  just bad luck?  the second pump is a Delphi that cost $10 more than the Precision.

NOTE, I disconnected the fuel hoses at the sending unit when I did these tests. And when I pulled the sending unit, I sat the unit in a bucket with some gasoline to make sure I had fuel above the pump intake.

Thanks for any ideas you might have.  I'd really like to not have to drop this tank again...

That's a bummer.  

But let me ask some questions.  First, you said "The rear gauge and pump ground connectivity and resistance are good."  But how are you measuring the connectivity and resistance of the ground?  You can't just use the resistance scale on your meter as a connection can show as low resistance with low current, as with the meter's tiny current, and high resistance under load like with the pump.

It would be better to check the voltage across the connection with the pump running.  And check the voltage from the pump-side of the connection to a good ground with the pump running.  The latter tells you if your ground is good, and the former tells you if the connection is good.

Also you said "Again, with engine running, I get 10 V on the +, and connectivity is good on the - side.  But the pump does not kick on."  How was the engine running if the pump didn't kick on?  Anyway, if the pump doesn't come on but you have 2 ohms of resistance across it then that seems to say you have a wiring problem or the pump is frozen.

I think I would hit the pump with 12v directly from the battery and give it a known good ground.  That way you are bypassing all of the many connections as well as the resistance wiring in the harness.  Then if it doesn't work you know you have a bad pump.

Gary, I think the issue you raised with the ground also occurred to me late last night.  I've only so far tested the connectivity of the ground wire itself, but not necessarily that ground connection.  I connect an alligator clip to the ground wire eyelet where it bolts to the frame.  But whether I'm getting a good ground to the body at that spot is still an open question.  I also don't think I tested the ground wires under load (the ground wires from the pump and gauge connect to the frame at the same place)

As for how I tested the load on the + side of the pump with the engine running, the van will start and run on the front tank.  If I switch to the rear tank, it will run for a short time on the gas that is still in the lines so I can test the rear pump under load (if I do it quickly).  I have the + lead of my tester connected to the hot side of the pump and the - lead connected at the the ground eyelet.  Maybe I should connect the - lead to another ground point.

so, yeah, I will now test the pump by directly connecting to the battery.  If it spins up, then it seems the issue will be with that ground connection, which is going to be a real pain because the previous owner put a tow bar on the van which makes it really hard to even reach that ground point with the testing probe, let alone get a wrench on it.  I may have to cut the ground wires and find a new place to ground them.

Man, if I knew what I was doing I'd be dangerous.  

I hooked up the motor to a battery and it definitely does not spin up.  I also realized that when I checked resistance across the motor yesterday, I still had it wired up to the van so all I was measuring was the resistance of the ground back through the hot lead.  When I disconnected the assembly and measured the resistance across the pump, I got 80 ohms.  That's not good.  The new pump I picked up has 2 ohms across the pump, plus it spins when connected to a battery, as it should.  

I still wonder what could be causing the motor to burn out so quickly.  I never ran the tank dry; I put a new filter on with the new pump.

I think I will try to clean up or move the ground to a new location.  Anything else I should check/replace?  I have my suspicions about the FSV but is it the cause, or does it hang up because the pump fails?  The one on there now was replaced about 8K miles ago but its one of those brandless ones you can find on E-bay.

At least you are making progress.  

As for what is killing the pumps, I assume that the E-series is wired similarly to the F-series and that there's supposed to be an 8 - 9 ohm resistance wire in the circuit.  Do you know that it is there?  You could measure resistance from the battery to the pump.  Wouldn't have to pull the positive cable since the DVM won't be connected to ground, but it wouldn't hurt.

My wiring is slightly different than the F-150 but it is supposed to have that resistance wire.  I'll check the resistance (and try to find the wire).

Wait!  I messed up!  That resistance wire is for the Instrument Voltage Regulator, not the pumps!  The pumps appear to run on full battery voltage.