For test, why not unplug inertia switch, and use a short piece of wire to jumper the connector pins together.

 

We tried that yesterday. Nothing from pump.

I will try that again today when I do the testing on the wires.

 

Allow me to ask a few simple questions.

When you use a multimeter, for voltage you are in parallel with the circuit. For amperage there are two methods depending on the meter, a clamp-on senses the current flow thru the conductor by the sensor detecting the electro-magnetic field.
A standard ampmeter has to be in series with the conductor does it not?

The voltage not being a constant 12volts but starting at 6 and climbing is indicative of a problem is it not?

Sounds like a high resistance ground issue exists somewhere in the circuit or the wiring carrying the voltage is severely degraded somewhere, like a damaged insulation, some broken strands of wire or poor connection somewhere in the circuit. It's been a long time since I did much active troubleshooting but those are the areas I would be checking.

A single strand of wire will allow the voltage to be present but will not carry the current needed to do the work.

Voltage is the potential to do the work EMF (electro motive force). Amperage is the current or energy expended in doing the work. You may have to trace the entire length of wire to find the actual problem as it could be anywhere along the path.

 

Despite what my wife will tell ya, Im not an idiot. I have a BS from a big ten university. However, EE was not my thing. I did what I could to get a B- in my one required EE class and never looked back

Thus, I dont know the answer to these for sure. I am slowly getting proper test procedures from Savannah, which is why I am about to do a 3rd round of multimetering when I get home today.

But yes, Im pretty sure you are right about amperage. I dont know what a climbing voltage means. Suppose I could look that up right now...

As I mentioned remembering, I did put the headliner back on in between the time it started and then didnt. It looks likely I will have to take it down and check the wires behind that.

I did check the fuel pump ground (E400) on the rearmost drivers side post, and it looked fine.

 

Just to clarify (this is for inertia switch wires)...

Key off
- Neg Battery post to the engine side wire: volts climb
- Neg Battery post to washer bottle side wire: 8v

Key ON (pos II, fuel pump prime period)
- Neg Battery post to the engine side wire: 12.2v
- Neg Battery post to washer bottle side wire: 5.2v

Key ON more than ~5 sec (pump relay clicks off)
- Neg Battery post to the engine side wire: volts climb
- Neg Battery post to washer bottle side wire: 5.2v


What this means I do not know

 

I don't see why you would have a different reading on each side of the inertia switch, it should be closed internally, like a light switch turned on. That's why we asked about jumping it out. What kind of volts do you get back at the pump? Have you tried putting (+) 12 volts to the wire at the inertia switch? Have you take pump wire connector off to check for corrosion?

 

Not sure if this answers your question, but these readings are taken at the connector pins with the inertia button disconnected.

I will check volts at pump with/without an inertia jumper.

Pump connector pins have some blue-green. There is also goo which I assume is dielectric grease in there.

 

The blue green is a worry, would want clean all that out if possible. When you say volts are building up, in a direct current circuit, that can be done with a capacitor. If you have enough blue green goop, it won't conduct substantial current, but could have enough to make meter rise. A capacitor is basically two metal plates separated by goo with insulating properties, or just air.

 

Not implying you are an idiot. I have worked with some degreed EE's would could not read schematics or troubleshoot worth a damn. I was an Aviation Electrician long ago during the war. Learned a lot in the Navy working on aircraft and test equipment. But Savannah is a whole lot more competent than I till am. I am just trying to help in some small way with what little recall still exist in my worn down nueron paths.

With key off, I would expect zero voltage at the inertia switch. That is basically a leakage voltage or something of that nature. For a test, I would be tempted to run a totally separate fused wire (fused to limit the current) to the back of the truck and jumper that to the power pin of the fuel pump connector itself. You could also jumper a grounded wire to the correct pin of the connector with the connector off at the fuel pump.

By applying 12vdc and ground to the correct pins you can determine if the pump runs or not. Use a separate car battery if you have one available.

Another thing that comes in handy with a multimeter is making resistance readings with the battry ground disconnected so no power can be in the circuit. Or totally disconnect the battery. Make ohm readings on the wire to ground to see if any are shorted to ground that should not be. Verify continuity (0 or very low) readings where you should have power when it is on.

You could also read the resistance of the fuel pump motor to see if it is open circuit indicating it burned up. Not sure what resistance to expect, but it should be very low if the little internal pump motor is good.

Hope this rambling was somewhat helpful.

 

Haha, no I know you didnt mean that. I was just tryin to say that I have a little feel for whats going on, but Im not great at it.

I just took the battery out and ran jumper cables right to the pump. I had it on the wrong neg yesterday. Pump runs fine. Whew.

I checked resistance with inertia switch at both wires. One was open (expected) and one was 166 lol. Is this a short or a bad connection or something?

Also I checked continuity at the open connection with the key on and it closed, so I guess the fuel pump relay is working properly? I dont think you are supposed to check ohms with current in the circuit... hope I didnt break the meter.

Anyway, I then tried to check volts, and continuity at the different pump plugs. At the pump connector, I think I got about 9 volts, .1 amps and continuity(an accident) with the circuit on.
When I went to test the next one in the wheel well, in the hubbub of turning the key on and scrambling to hit the connections in the 5 second window, I broke one of my multimeter pins.

So, gotta go replace those and wait for my wife to get home so she can turn some key.

Any thoughts on what I got so far?