Now I am confused. I have a black & a grey wire on the outside terminals of the connector. The center wire is green.
Black is ground. Battery voltage 12.88
With the connector not attached to the fuel pump I get no voltage at the green (center wire) I get 4.88 volts at the grey wire. I thought I would switch relays to see if the relay was causing the voltage drop. There are 3 relays in the glove box but I don't know which one is the fuel pump relay. I pulled them 1 at a time and still get 4.88v. I even pulled them all and still 4.88v ??????????
I hooked my jumper cables to the battery and substituted the jumper cable for the ground wire at the pump and I get 4.98 v. Then I connected the fuel pump ground test lead back up to the wiring connector and connected the + lead from the tester to the jumper cable and I get 12.58v.
I believe this shows the ground is ok. I was going to check voltage at the fuse but the owners manual does not list a fuse for the fuel pump.

I 'm not sure what to do next and I don't know what the center (green wire is for. The wiring diagram I have only shows a black & a grey wire.

 

There should be 4 wires going to the pump. I won't be able to tell you which colors are for what because honestly I am colorblind and couldn't tell you if my life depended on it.

However two of these wires are for power to the pump and the other two are for your fuel gauge. The best I can offer for differentiating between them without crawling back under my own truck is that the thicker two wires are for power to the pump and the two thinner ones go to the gauge.

if you connect a volt meter to the two thicker wires you should get the same voltage as your battery. That being 12.whatever volts. If you have that at the connector then more then likely your pump has gone bad.

The fuel pump relay on most model years of this vehicle that I have worked on is actually located under the hood rather then in the glove box.

A sticking relay is a possibility for your hard starts and/or early pump failure but with only 45 psi output it certainly seems that your pump is no longer usable. I always recommend replacing both the relay and the connector to the pump when you replace the fuel pump on these trucks.

Though if you get a good pump you will have no choice on the connector replacement as it has been redesigned on most decent aftermarket pumps to help prevent the corrosion problems that plague OEM connectors.

 

DUH--------- I was thinking the 4 wire connector was the sending unit for some reason??? The manual said grey & black to the pump and since I had grey & black at the 3-wire connector I thought I was on the right one. I will get under it tomorrow and check the 4 wire connector.

 

I'm not an expert on all model years of this truck so it may be different in some years. But it sounds as though you may have the plug for the tank pressure sensor which is right next to the fuel pump/sending unit plug.

It is an easy mistake to make when you are checking the wires with the tank still mounted in the truck.

 

I have not had time to check the voltage at the pump yet. But the omment about the tank pressure sensor got me to thinking. I have had trouble with P0446 and P1441 codes. Could the tank pressure sensor have anything to do with these codes? I clear the codes and in a week or 2 one or maybe both will come back. The P0446 seems to show up most often.

 

Those codes are unlikely to be set by a bad tank pressure sensor as far as I am aware.

Those two are usually caused by a clogged valve on the evap canister and or a bad canister purge solenoid. I have once or twice also seen those codes pop up with a faulty gas cap as well.

If you are getting these codes then they may actually be the root cause of your problems as it means that the venting and evap systems are not functioning properly on your truck.

If the venting/evap system is not fully functional then fuel delivery will suffer and can cause low fuel pressure in some instances and can sometimes prematurely burn out a fuel pump.

I would replace the canister purge solenoid right off and check to make sure that all of the lines and check valves on the evap canister are squeaky clean before doing any further testing with the fuel pump itself. Though as I said, the pump may have been damaged already by the evap system being nonfunctional.

 

Where are the purge solenoid and evap. canister located? I have been so busy I have not had time to check the pump voltage but want to check the canister and solenoid at the same time. Hope to get it done by this weekend.

 

Ok, I finally got out to check it again. I was on the wrong connector before.

Here is what the voltages are.
at the Battery not cranking 12.5 v
at the fuel pump connector not cranking 11.7 v

at the battery cranking 10.8 v
at the fuel pump connector cranking 10.4 v

I know the battery is down from sitting but it cranked over fine. Is this voltage drop acceptable?

(Also the fuel pump relay is the one on the far left in the glove box.) I swaped it with another and no change in the voltage drop.

I decided to put a new fuel pump in. Then I had 70 psi at the filter. It was 33 psi when it would not start. So far so good.

Then I checked it at the engine and I had 55 psi the same as when I was having trouble getting it started. But it started right up and the pressure dropped to 50psi ???? It runs ok and starts right up every time I shut it off. Will see how it starts in the morning and how it drives.

 

Update>> I have been driving it for a week now and it starts instantly and runs fine. I know many recommend not using an aftermarket pump but I put one in anyway. The pump I took out was an aftermarket and it lasted 40,000 miles but the factory pump lasted 140,000 miles. So if you plan to keep the vehicle it would be best to put in a AC pump.

I do not understand what is going on but here is some info. on the fuel pressure. Maybe someone can explain waht is going on.

1. When I was having troube with hard starting the fuel pressure was 53-55 psi at the engine.
2. When it finally refused to start the fuel pressure was 33 psi at the engine and 45 psi ahead of the regulator. This makes perfect sense as to why it would not start.
3. With the new pump the pressure is 70 psi ahead of the regulator but only 47 psi at the engine. This is less pressure than the old pump but now it starts perfectly and runs fine???????