back to basics, RELAYS

[NITROUS]

I asked my bro to post the fuel pump schematic, yall can look at it and give the nod as to where the red wire should go.

I think I've posted more than once where the red wire goes. That's straight from GM's manual and the way my 97 is setup. Red is the fuel pump prime connector - Pin 87A on the relay. If you want, I'll post the schematic also.

[NITROUS]

This is the 96 C1500 schematic, unless I'm missing something this should be all of the info you need.

[LSXmyford]

well for one, you are missing something, your attachments are too small to see, you acknowledge this in past threads, maybe its time to remedy the situation.

second, your just not getting what is being asked, its understandable, its alot easier for me to see my POV than it is for you to put the pieces together and see my perspective.

im tired of trying for now.

when and if the pcm arrives and a new relay is found, im sure we will post something.

[NITROUS]

Someone here on LS1Truck will have to correct the file size issue because it's full screen on my end. If you took a picture and posted this 4 pin connector your talking about it would sure make things simpler. You say you have a 5 pin relay correct? If so it would still be wired just like I posted above and shouldn't be any different. I can't explain where the wires go any easier even if you only have 4 wires because you must be missing one which I understand to be the red prime wire. I hope someone can help you out since I'm not able to.

Good Luck!

[r6z4o6]

Are you still getting no juice from the red wire, key on OR key off???


"I better correct something. The fuel pump relay in the nelson harness, has five terminals on the relay itself, however, on the electrical connector it attaches too, theres only a place for four wires, so there is no way to connect the red wire to the wrong relay terminal."


PLEASE PLEASE PLEASE check that fifth terminal on the relay for 12v when you hit the key


Ask for a "foglight relay" at the parts store...I had the same problem and kept getting some 30$ relay until one of the girls who worked there and KNEW what was going on told the little snot nosed oil stock boy where to go, i think they are near the headlights/fuses/lightbulb area and found a generic 30a relay, like 5 bux.

Her is a biggie-size of what Nitrous posted:


Here is life-size schematics for 2001 5.3..may or may not be of interest to ya.

[NITROUS]

Terminal 87a is the prime terminal. The only time you should have +12 volts on the prime terminal is when you apply it. It's a test terminal. By applying battery positive (+) voltage to the jumper wire with the relay plugged into the fuseblock, you can verify whether the fuel pump runs or not. This was driving me crazy so I had to verify it for myself, because I was going by the diagram and not looking at my vehicle. You don't need to hook this up to anything even though the diagram shows it.

[r6z4o6]

Terminal 87a is the prime terminal. The only time you should have +12 volts on the prime terminal is when you apply it. It's a test terminal.

On my 91 the RED wire PRIME(TEST), it goes to ALDL connector G.

My final absolute end of all problems answer that will fix it for SURE....
The red wire should do NOTHINGGGGG!!!!! When you put 12 volts on it with the KEY OFF, it will put power to 87, which is the GRAY WIRE that you have never mentioned, LSXmyford!!! Probably because it fell off of the mysterious fifth terminal of the relay!!!!!

In conclusion...
================================================== ===

KEY ON, your mystery fifth terminal on relay shows 12volts, yes?????
KEY OFF, you put 12v TO your RED wire, your mystery fifth relay terminal now HAS 12v, yes??
================================================== ================

[NITROUS]

BTW, this reply is for myself!! Yep, this wire is about 8-10 inches long and has a small female spade connector on it right behind the fuse box by the firewall going nowhere. I apologize for sounding a little harsh above but I was helping another member and glanced at this schematic not to mention no pictures.

[RedHeartbeat]

Do you still have the factory original fuel pump relay installed in the truck? You mentioned that when you attempt to start the engine you can smell fuel, if it wasn't wired correctly then you wouldn't be getting fuel. Have you put a fuel pressure gauge on the rail to see what fuel pressure you're getting and if its holding pressure after crank?

[LSXmyford]

r6z4o6

Thanks for the relay info, hes gonna check that out, makes total sense. However, man oh man, I would be lying if I didnt have all kinds of colorful language come to mind when I read your post. Gonna make this short and sweet. There are 5 terminals on the relay itself. However, here comes the key part to this, the pigtail in which the relay attaches, only has four openings, if a person wanted to use the 5th terminal on the relay, they would have to literally drill out the pigtail...there is no missing 5th wire. Stay tuned, cause Im gonna explain to nitrous why I think nelson used four wires instead of 5. Its a theory but a damn good one.




redheartbeat

Yes. We had the fuel pump wired to the old relay/ harness, this is how we know the fuel injectors were working with a cranking engine, yes it holds line pressure. We are trying to eliminate as much of the old as possible, so we are trying to get the fuel relay on the new harness to work. He has recently tried to confirm spark and again, no spark.




nitrous

Reason I didnt post the shematic, I stated this issue would be dropped until the pcm arrived, Im glad you revived it, I have what I believe is reasoning for the four wires.

First off, we found out the gray chassis wire is power to the fuel pump.

Now for the fuel pump relay on the NEW harness.

He confirmed ground, constant 12v, then put a hot wire to the switched wire (green)....

then checked for power at the red wire, again nothing. As stated to r6z406, the pigtail only has provisions for four wire attachment, the fifth is physically blocked. Logically, this tells me, the red wire should go hot with the key forward...Im sure you would agree, its a bad relay, if not, it defies logic.

Now for the epiphany that leads me to believe four wires is ok in this scenario.

My bro put a test light on the switched green wire that leads from the pcm to the fuel pump relay. When he turned the key forward, the 12v switched green wire from the pcm, went hot, then after about a second went dead. I believe the fuel pump prime is built into the 03 pcm programming. Thats the only logical explanation of why that wire would be live, then go dead after a second, it behaves much like you would expect a pump prime to behave and also explain why nelsons only used a four wire connection. I can only assume at this point, should the engine crank and fire, the pcm would energize this green wire as needed, ultimately activating the relay, ultimately sending power to the fuel pump.

Apparently, your five terminal is needed for some damn reason, whereas the 03 5.3 pcm doesnt require it. This is theory, as the engine has yet to idle.



Can we get a group agreement here?