If it's not one thing it's another. Truck ran fine yesterday morning. Sat all day. Then wouldn't start last night. Like it was out of gas but I should have half a tank. My first thought was that some a-hole sucked my gas. I can't go too much off the fuel gauge cause it is out of whack with this elcheapo dura-crap unit. I hear the pump turn on but it won't start. I through some more gas in and it started up. This morning tried to start it and it didn't on the first crank but did on the second. So aggravated right now.

 

sound like the valve on the fuelpump is gone. it should be ok if you don't mind priming you fuel system before you start your truck.

 

It had started fine since my origional post. I went 4-wheeling on Saturday without issue (thank God!!). Then Sunday on my way home in town it just died going down the road. I tried starting and staring nothing. Realized the fuel pump wasn't turning on. Switched the fuel pump and A/C solenoids and it started right up. But so did the A/C. I went ahead and bought a new solenoid for the fuel pump and am now crossing my fingers that this is a permanent fix and this won't happen again and leave me stranded. I do not know what the current draw difference is between the A/C and fuel pump. That'd be good to know.

 

do you mean that you switched the relays in the power distribution box?

 

Yep, under the hood.

 

Other than checking the fuel pump wiring, replacing the relay in the box should be a "permanent fix". If the problem comes back, you have narrowed it down to the fuel pump.

 

the relays barely draw any power. the way they work is power goes to the relay (from a switch, or in the fuel pumps case from the pcm), that power closes the contact between the incoming power from the battery and allows it to flow from the battery to whatever is receiving power.

if you look at a relay you will see that you the 30 and 87 posts are not connected and the 85 and 86 are.

85/86 get power from a switch or the pcm (doesn't require much).
when they are energized they magnetically pull the switch between the 30/87 terminals closed which allows the power from the battery to go into the 30 post and out of the 87 post.
since the 30/87 terminals are not connected to the 85/86 terminals then your switch is only powering the relay itself (closing the switch).

i'm trying to explain how the relays work because i thought it was pretty cool when i finally realized how they work, thanks to jasonw.

so basically you had a bad relay (the switch inside got stuck and thats why the ac powered up when you started it), it should be good now.

 

The past few times I've driven it I've just turned the key to On before starting to see if the pump engages. I've had, I think, twice now where it did not. I turn the key off, turn it to On again, I hear it, then crank to start and it starts fine. That doesn't give me much confidence that the problem is fixed. What's the ACD relay do? Someone posted they had starting problems and it turned out to be that.

 

The ASD relay runs all the power to many circuits in the vehicle. A relay is a switch in laymen terms ok, and, that switch routes power to multiple items in the truck.

Check out the schematics for your truck. Look under fuel and ignition systems. Under that one section alone, that relay is at the heart of the system.

VDC flows out of the battery, into the Power Distribution Center through 20A and 30A fuses depending on the circuit. From there, one feed goes directly to one side of the ASD, through that to your PCM. This controls your ASD in case of fault. The PCM will kill power by disconnecting this relay. Again, it's a switch that is powered. That's all a relay is- it's a simple electro-mechanical switch that, depending on the configuration, can be *SPST, SPDT, (*Single Pole, single throw, Single Pole Double Throw etc)

There are metal contacts and, over time, they become oxidized if the switch is not hermetically sealed. At time of manufacture, some switches are back filled with nitrogen (an inert gas), to remove all O2 from within. The presence of O2 and water molecules leads to oxides on the contacts. This inhibits electrical contact. It also raises contact resistance.

When you put hi DC current through those contacts, it draws excessive current and burns through the oxide layer to make contact. This can burn the pins over time making it worse as time goes on. Keep in mind, that if there's a bad connection, the items that are off that circuit will not be getting the proper voltage. If they don't see the correct operating voltage, they don't put out the proper voltage that feeds the PCM thus creating an imbalance in air/fuel ratio.

The other thing is that there's an electro-mechanical mechanism used to drive the switch to make the contact to the other pins. That is also prone to binding, or shorting, or partial shorting of the coil thus preventing full contact or, no contact if it's open- meaning the wires around the coil popped like a fuse.

In such case, the end user would not be able to start the vehicle at all- there would be no power applied. These cases are easy to fix but, when you have an intermittent switch, this can be difficult to diagnose.

In that case, when in doubt, simply replace the relay and retest.

Below is a small list of circuits that feed off the ASD:

Connected to the ASD is the Fuel Pump Module. This is the emergency shut down for the pump in case of fault.

There's many splices off that line too. One of those is Splice 138 (S138). That is where the injectors tie into. All the fuel injectors feed off of that splice.

IF there's bad or fluctuating voltage due to high impedance at the relay, well, it's not going to be stable at the injectors. Then a code is generated. The user troubleshoots and assumes it's a bad injector when, in fact, it's a bad ASD.

Also off of that same splice is S133. That feeds the O2 sensors.

The coil is fed from the ASD as is the generator.

There's so many splices off the ASD relay, that there's a lot of things that are being fed off that one device. This should give you an idea of how involved that one simple component is in the electrical system.

What I touched on above is a mere fraction of the total number of circuits involved.

 

thats a good bit of info.
you forgot to mention what asd stands for though. its automatic shut down, which is exactly what it does when that relay has problems.