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Steve_RI

no start

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Trying to chase down an issue again with the truck cranking but no start.  Fuel pump is definitely not getting power and I'm starting to go through the manual procedure to diagnose.   In the diagram below, does this indicate a jumper between the two contact points?

Wiring.jpg

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No power at the fuel pump is the broken ground wire or a chaffed wire loom between the exhaust on the left side and the tank guard. The diagram is of the connector at the fuel pump at the top of the tank back to the main harness, to be checked with the key on and engine off, there should be voltage at terminals 2 and 3( sequentially, no jumper needed). If you have 0 at both then it's the ground for sure.

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I had repaired that ground wire in the past, so it may very well be the issue again, thanks.   And thank you for clarifying....test sequentially...understand now.

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Okay, stumped on this one.  Went through the factory service manual procedure and can not figure this out.  Started with this from above.  I have 12 volts at those terminals at the relay.

 

CH01GWr.jpg

 

 

 

Next went through these steps - all checked out.

QQC3MCu.jpg

 

Swapped in  new relay and checked the fuel pump - got between 1.6 and 1.9 ohms.

PEqEirU.jpg

 

I went through the wiring in the rear near the exhaust and replaced all the wiring I fixed from 2005 or so because it was looking rattly.  Went through the procedure again, no change.

What the heck am I missing?

 

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I noticed the fuel light working again, so that was fixed when I went through the wires on the back fender above the exhaust.   There's two yellow wires for the gauge and light.  I noticed one of them didn't have continuity from the harness the fuel pump plugs in to, so that solves a very minor but inconsequential issue..

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Just throwing crap out here...I should be able to run two wires - one for power (blue/white) and one for ground (black/red) to the battery and get the fuel pump to kick on, no?  

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Since you have looked at fuses and relays, and your previous wiring repair, I'd try that. Running a power wire from a 12V source and a ground to the fuel pump plug should tell you if it'll work or not.

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Okay, I get the fuel pump to run with a 12v source and ground directly on the fuel pump harness.

 

I also found this:

If you jump a BLACK/WHITE from the 12V source at the relay (that’s terminals 2/3 at the relay) to the WHITE/BLUE wire at the fuel pump and the key is "on," you should have power to the fuel pump. If you don't, you have an open circuit in the WHITE/BLUE wire and it needs to be traced and repaired

 

I don't get the fuel pump to run in this case, so it looks like that is the problem,  I have continuity in all the new wire I replaced, so this break or short must be somewhere else.  I'm stumped now.

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Right, so now the procedure is to follow the WHITE/BLUE wire along its path in the harness from the relay back to the fuel pump. This is going to be a visual inspection for broken and cracked harness covers, missing tape and exposed wires....  I would start at any place where the harness makes a turn or passes through a panel. I would personally start at the harness in between the front and rear doors and check for continuity in the white/blue wire there ( make sure your equipment is working AND that you get a good ground!). If you have low ohms there, then your problem area is at the rear of the truck. Move halfway along the wire from the middle of the truck to the fuel pump and check for continuity there: low ohms again means that your problem is closer to the fuel pump, high ohms means that you passed the spot where the wire is broken. The same is true for working in the other direction towards the front of the truck. Just keep splitting the distance in half until you are at the section that is the problem, chop the broken part out, throw some heat shrink on both ends and solder yourself some wire in there!

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Thanks for the help, I do appreciate it.  Intuitively, it doesn't make any sense to me.....

If you jump a BLACK/WHITE from the 12V source at the relay (that’s terminals 2/3 at the relay) to the WHITE/BLUE wire at the fuel pump and the key is "on," you should have power to the fuel pump. If you don't, you have an open circuit in the WHITE/BLUE wire and it needs to be traced and repaired

I would think that since you have 12v at this point ground is the issue if it doesn't kick on.  This is probably where the ECM comes into play.  

 

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The white blue wire is the positive wire to the fuel pump. If there is a fault along that wire, then you don't have your 12v+(nominal) at the pump. The ECU simply turns on and off  the relay. 

If you run a wire from the positive terminal of the battery to the white/blue wire where the relay plugs in, you should have battery voltage at the fuel pump regardless of the key position. If you do that and you have battery voltage at the pump, then it is likely a failed ground. 

I only say this because you said the pump runs when you feed power and ground at the pump, so that shows the pump is ok. So either the ground wire has failed, or the positive wire between the relay and the pump is your failure. Checking the ground wire is easy, with an ohm meter measure between the ground wire at the pump and a good body/chassis ground, it should be very close to 0 ohms. If so, the ground is fine and you can focus on the positive wire. Not complicated, just a bit tedious. 

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10 hours ago, Mr_Reverse said:

The white blue wire is the positive wire to the fuel pump. If there is a fault along that wire, then you don't have your 12v+(nominal) at the pump. The ECU simply turns on and off  the relay. 

If you run a wire from the positive terminal of the battery to the white/blue wire where the relay plugs in, you should have battery voltage at the fuel pump regardless of the key position. If you do that and you have battery voltage at the pump, then it is likely a failed ground. 

I only say this because you said the pump runs when you feed power and ground at the pump, so that shows the pump is ok. So either the ground wire has failed, or the positive wire between the relay and the pump is your failure. Checking the ground wire is easy, with an ohm meter measure between the ground wire at the pump and a good body/chassis ground, it should be very close to 0 ohms. If so, the ground is fine and you can focus on the positive wire. Not complicated, just a bit tedious. 

 

Yes, thanks, I do have 12V with a wire from the battery to the white/blue at the relay.  I checked with the key on, but it shouldn't matter based on what you said.

 

Also, I think you meant (from the bolded statement above) ...if you don't have voltage at the pump, then likely it's the ground.

 

I've got all the wire exposed from the front wheel well to the pump.  The only place I can't get to is inside the dash along the engine compartment.  In a worse case scenario, I should be able to run a new wire from the relay back to the pump, correct.  Easy enough to check...gonna be doing a lot soldering and heat shrinking, anyway.

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Nope, ground has no effect on the white/blue wire. If you have + battery voltage at the relay end of the white/blue wire, you should have + battery voltage at the fuel pump end of the wire. If you do in fact have + battery voltage at the pump end of the white/blue wire and the pump won't run, then the problem is with the ground side. 

If you really want to be confused, just know that the power flows from the negative post through the load(in this case the fuel pump) up the white/blue wire to the relay. When the relay is closed(energized) the current continues on through the fuse and then into the positive post of the battery. Lots of backwards thinking but that is how DC works. Basically the ground(the chassis and body of the car) is a big buss bar supplying the current that then flows back to the battery through all the wires. 

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Posted (edited)

Alright, ran a new white/blue wire from relay to the pump, nothing.  Jumped a wire from +positive at battery to the  white/blue at relay connector, pump has power like before.  So, with a new wire from relay to pump, time to look at the ground.

 

At the pump I  checked the ground to the pump (blue/red) and the ground for the sender (black) - marked in red.  Both read 0 ohms from the plug to the underside connections.  So, that's fine.

 

pjxoFNP.jpg 

 

Now at the Harness, I checked both ground connections (circled in red) with a good chassis ground and get 1.5 - 1.7 ohms on both.   These should be zero, or at least one of them?

 

7HkltlV.jpg

 

Thanks for the continued help.

Edited by Steve_RI

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Ok, so the pump runs when you run a wire from the + terminal to the white/blue wire terminal for the relay? If so, the wiring to the pump and the ground is ok. The problem is either the relay is not operating, the contacts in the relay have failed, or the positive wire to the relay has an open. Do you have power on both sides of the fuel pump fuse? Does the fuel pump relay click when the ignition is turned on and off?

I will try to remember to look up the diagram tomorrow at work to refresh my memory of the system. 

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Posted (edited)

Yes, relay clicks and tried a spare.  Not sure how to check power at both sides of the fuse?

 

From the wiring diagram (L for blue)

Both B/W feed to fuse at ignition.  R/L goes to pin 104.  And W/L goes to fuel pump.

Edited by Steve_RI

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Ok, sorry it took so long to get back. 

With the ignition in the on position, you should have battery voltage on both black white stripe wires at the fuel pump relay. If so, power supply is good. If you put a jumper wire from positive post of the battery to the white blue stripe wire at the relay socket, you should have battery voltage at the fuel pump on the white blue stripe wire. If so, the wire is good between relay and pump. Should have less than 2 ohms when measuring between black wire at pump and good ground. If so, ground is ok. 

 

The ECU controls the ground for the fuel pump relay. If the relay clicks when the ignition is turned on, the relay drive circuit is ok. 

 

With the red blue stripe wire at the fuel pump is grounded with the ignition on, the relay should click on and you should have battery voltage at the fuel pump on the white wire with blue stripe. 

 

As for testing the fuses, pretty simple. Using a test light or volt meter, connect the negative to a good ground and of you look at the top of the fuse, you will see a small hole on each end. Poke the tip of the positive probe into the hole on one end and then the other. Both should give the same battery voltage if the circuit is on. If one side is "hot" and the other is not, then you have a bad fuse. 

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