Hi forum,

So I have been dropping info here and there about my issues, but I realized I havn't really started a focused, to the point thread.

My truck is having starting issues, it is a fuel delivery issue set on by electrical problems. I have pulled the connector that runs from the engine compartment down underneath the truck. This is one entire wiring harness that has connectors for the fuel pump, ABS, and rear lights. I have the entire harness loose from the truck, but i can't pull it out to bring it in and go through it; a few connectors are too big to snake thru the frame/cab mount.

Electrical problems are sort of blowing my mind, lol. It is a lot to go over and test. The main thing I want to test is for continuity from the beginning of the wiring (the connector in the engine bay, c207) to the fuel pump, and beyond if needed.

One thing i found interesting was when the truck would be turned to key on, the voltage at that connector would vary. I assume it needs to be giving 12v down the line for the fuel pump. I got ranges anywhere from 0 to 10v thru the line. I actually used the meter to bridge right from the battery to the pin i was testing, and while this gave me 12v, there was no activity at the fuel pump.

I guess in summary, I just need some help as to what direction I should go with this. I have been using the FSM quite a bit and it's an amazing resource, I am just finding that i seem to be having trouble following exactly how things work.

Thanks for any help everyone, I'm chomping at the bit to get this truck up and running!

 

The easiest way to test the wiring harness is see if you have voltage at the relay terminal output to the pump. Then if you do have power test to see if you have power at the pump connector. If no power at the pump then you have a brake in the line.

If you have no power at the relay terminal output then make a jumper wire to the battery power. Then test at the pump connector for power.

 

Crazy,

Thanks for the quick reply! I want to make sure I am following you properly.

Here is the diagram i have been using the most



so when you say relay terminal output you are referring to the Fuel Pump Relay pin D, correct? Put the multimeter positive on that pin, and then ground out the negative, read voltage.

Pin Reference for relays


If there is no power and i make a jumper wire, I am going to jump from the positive terminal on the battery to where?

Thanks again for the help, I think I am going to reconnect my lower wiring harness for now to keep it up off the ground and all. I had really wanted to pull that out and go through it just to check everything and clean it up, but I'm out of time for this week.

Thanks again!

 

bump......

 

I'm getting back at this hopefully later today. I will keep everyone updated on what i find out. I'm going to start by reconnecting the lower harness and checking things thru there.

 

So just a mini update for everyone.

The battery in my truck is too low to crank the starter now. I checked a few things in the PDC and the fuel pump connector and here is what i found.

I connected a lead to the Fuel pump relay output and to the negative terminal on the battery. turned the key, no power or anything. In retrospect i feel like that is correct though. The next thing I did was make GHETTO (but functional) jumper wire. Put one end on the positive terminal and the other on the same pin in the PDC (pin 5D, fuel pump relay output.) I checked the fuel pump connector and found it was piping 10v down the line. I moved the harness some and didn't see a drop in voltage. I left this setup in tact and was planning in cranking the truck up. That is when I found the power too low to crank. Not sure what im doign to do about that yet since i cant very well jump the truck since it wont start; the way my driveway is I couldnt get a car up to the front of it to jump it anyway.

Thats all for now. thanks for helping everyone!

 

Alrighty everyone, Heres an update.

So i tested a few more things at the fuel pump relay in the pdc. reading the wiring diagram the other day i realized that a relay is just an electromagnet (I'm sure a lot of people are going "no kidding" right now) and that one circuit powers the magnet to pull the relay into place to create a closed circuit to power the fuel pump circuit.

So i test the circuit that powers the magnet. when the key turns on, the power shoots to 10v, then drops to 5v and holds steady around 5v.

Next i tested the output ciricut that goes TO the fuel pump circuit. This gave me right around 10v. I then used a jumper wire to power the fuel pump circuit. I tested the fuel pump connector and got 10.2v, then it dropped to 10.1v. I tested this while an assistant gave the wiring harness a good shake all through it. the lowest the voltage dropped to was 10v. If i remember correctly the fuel pump needs 10v to run, right?

Anyway, I have now pulled teh battery out since it is dead and need to find a way to charge it back up. a buddy of mine said to hook jumper cables to it to charge it with my car but I feel this is a bad idea. I don't have a charger or anything so I'm gonna look around and see what I can find.

I am made a little nervous in seeing that powerwise everything looks legit going back to the pump. It doesnt prime when the key is turned so I don't really know what to make of all this.

Help? lol
Thanks everyone!

 

I fixed the charged battery issue. I bought a new Duralast battery at the autozonez, lol. I had them test the battery I had in the truck and it tested mega fail. So i used my $20 bonus card money and got a 80 dollar battery for 60. sux but oh well, no i can get back to troubleshooting the pump.

 

Ya that $20 rewards is great. I get it all the time.

 

**UPDATE!!** i found something interesting! this may help me! at the PDC the "hot" wire that powers the fuel pump thru the relay gives off 12.3v, however when i jump the circuit usign the multimeter it outputs 8.2v!!!! wtf is happening here?! when i pipe from battery positive terminal (B+ right?) to the fuel pump relay output it is ALSO 8.3v! I feel like this is a major break in the case so to speak, lol. I just do not know how to use this information now.