After I get my tanks clean, I coat mine with Red-Kote. It helps seals any leaks and it can be used to seal over the "rust" but I like mine to be clean as possible. You can get the coating at most parts stores, but they may need to order it.

 

Well I got the tank cleaned out and got everything back together. New fuel pump installed and wiring double checked and all that. Rebuilt the sending unit and got it working great again. Poured in five new gallons of fuel.

Went to start and still don't hear or feel pump running. Pulled pump wiring connector and checked for 12 volts at the harness, and had that. Jumped Fp and B+ and still had it. Checked for resistance across the pump harness contacts in the connector and got 28.0 ohms. I don't know if this is good or what.

As I kept messing with it over the course of about ten minutes, I lost voltage at the wiring harness. No matter what I do, I can't get 12 volts back at the harness. I tried turning the ignition off and back on, jumping the Fp and B+..and still get nothing. Checked the EFI fuse and it was good. The relay got pretty warm to the touch.

I don't know what else to check. I'm not sure why I lost 12 volts back there.

Getting more and more frustrated. I'm not sure why the pump is not running but I really don't want to have the pull the dang thing back out of the tank, especially now that have more fresh gas in there. It is a new Denso pump.

 

28 ohms is way too much for any connection in series with the fuel pump wiring. No way it will run with that kind of resistance. Should be less than 1 ohm (basically below your ability to measure with a simple 2-wire multimeter.)

I'd say your problem is still in the wiring/connectors. Jumper Fp to B+, turn the key to "ON", and work your way along the wiring to the fuel pump until you find where the 12V gets lost.

 

So why would I have initially had 12 volts at the wiring harness connector and then it just disappeared? I have a hard time believing that something is wrong with the wiring if it was.initially fine. I'mmore concerned about the relay and the fuse box. Should the relay get hot like that?

With the pump, is it possible to have a bad pump out of the box? I almost put 12 Volts on it in free air to see if it.spun. I was afraid to do that though because I thought it might mess it up without it being submerged and actually pumping.

So I guess I am in for pulling the pump back out of the tank.

 

OK it was a bad ground. The ground with the wire coming directly out of the pump plug where it rivets to the frame holding the pump was where the bad spot was. I fixed that and the pump runs fine like it should. Now, i'm still not getting 12 volts at the wiring harness plug.

Could the bad ground issue that the pump assembly had possibly have melted or screwed up the relay? Maybe that is why it was getting hot.

I'll pull the relay tomorrow and test It. It did not blow the EFI fuse.

 

I am not very good with electric but dont think a bad ground would hurt your relay. I could be wrong on that but I think when it lost contact, maybe the relay would not have worked.

When chasing power, I use two tools to help verify what I am getting, a multimeter and a test light. The test light is a crude tool but it helps me make sure I am not getting a false reading. Electric, grrrr.

 

OK I have a good relay and power to the relay base. I'm going to start tracing the wires from the fuse box to the pump I guess. I have a solid blue wire and a white wire with a blue stripe at the pump connector plug near the tank. Trying to figure out where the wires exit the relay box so I can check from there.

 

I'm trying to figure out where the wiring goes. I see the harness going up into the cab, and I'm thinking it could possibly be going into the module in the passenger foot well. Without taking it off I can't say for sure. Does anybody know if the blue 12 volt wire that is at the wiring harness pump connector goes all the way to the fuse box? I checked it for voltage right where it enters the cab, and there is no power there. Obviously it is between where it enters the cab and the fuse box, but I'm not sure if that blue wire goes all the way.

 

So I made strides today. I am still having an issue with the wiring though. First, I bypassed the wiring and just ran a hot wire directly from the battery to the hot wire on the pump. The pump runs fine and I can hear fuel up near the pressure regulator on the motor too. I guess it is the fuel headed back through the return line.

The truck will crank and run in this state, but only briefly. I have the intake and air filter hoses off, and I seem to remember that the truck really won't run unless these are in place. Not worried about that just yet.

But I am still having wiring issues. I cannot figure out where I am losing voltage. I referred back to this post in this thread.

With the key on, I checked +b to ground. I have 12 Volts. If Fp does in fact connect directly back to the pump and is the blue wire, then I should be able to check continuity to rule out a broken wire right? Well, I did and I have continuity so that wire is good.

With the key on and Fp jumped to +b, I still have no voltage at the wiring harness plug at the tank. So if the Fp wire has continuity from the plug to the diagnostic box, and +b to ground is 12 volts, a jumper wire should give me power at the plug. The ground on the fuel pump wiring is good.

The only other wire that is suspect at this point is the other wire on the harness plug. It is white with a black stripe. I'm thinking this could be the ground. If it has a break, wouldn't this cause an issue? If it is a bad ground I think this could be causing it. Is this a ground? I'll have to see if I can find the routing of that wire tomorrow.

 

Not all "continuity" is created equal. It sounds like you have a high resistance connection somewhere between Fp at the diag connector and the fuel pump itself. In an earlier email you mentioned 28 ohms. If that's the case, here's what will happen.
- With no jumper in place, B+ will measure 12 volts with the key on.
- Also with no jumper in place, you'll measure "continuity" of around 28 ohms plus the resistance of the fuel pump from Fp to ground.
- When you connect B+ to Fp, the high resistance in your wiring will drop all of the voltage across the wiring and connectors, leaving nothing at the fuel pump, so you'll measure ~0 volts at the pump.

As I mentioned in an earlier post, you need a good low resistance connection, less than an ohm from the battery to the fuel pump. The pump draws several amps. As an example, 2 amps times 5 ohms would be 10 volts lost in the wiring, leaving only 2 volts to run the pump which is not enough.

 

There are two different wiring areas I'm talking about. The first section of wiring is between the pump and its connector. There is a hot wire and a ground. The 28 ohm condition was on the ground wire right there. That has been resolved.

The second area is the actual harness. The plug that comes off the harness to the diagnostic box. This is the area I am concerned with now.

 

It is a fuel safety shut off in the event of an accident. You have to have the air tube connected. With the engine cranking, the air flow moves the flapper in the Air Flow Meter which then engages the Circuit Opening Relay (located behind the front speaker on passenger side) which then energizes the fuel pump.

 

He's got the pump jumpered, so the fuel switch in the VAF should not be what is causing the short run.

Instead, the VAF vane is reading "no air flow," so the ECM is setting the mixture wrong.

It is generally a waste of time to try to start the engine without the induction plumbing connected, for a lot of reasons.