2007 XLT fuel shuts off intermittently....relay or pump??

[Planebldr]

So I have a 2007 XLT and loved it all the way up to this point. It has approx 170k miles and was reliable. I stopped at the gas station to fill it up and tried to restart after and it would just crank. No fire or sputter. It cranked at a normal rate so it wasnt a battery. Towed it home to take a look at it. I hooked up my f250 diesel with jumper cables to make sure battery wasnt below voltage and was the same...crank no start.
Following day, it started up and ran for a little while. Now it starts right away, but shuts off intermittently now. Fuel pump 20a fuse is fine, swapped the relay with another (same part number), and still shut off. I checked the inertia switch and it seems fine. I took a volt meter across the two wires at the inertia switch because I read that gets voltage from the relay? Anyway when it is running I get a little voltage reading. Once it shuts off I have none. Would that point to the relay even though it does it with 2 different relays. I hate to drop the tank...especially since I JUST filled it lol. I'll dig more into it tomorrow but I figured I would ask. Thank you in advance!

 

[Trainmaster]

Fuel pumps only go bad after filling the tank... you should know that.

 

[tommyddsr]

Pump. Had the same exact issue in my 2000. Sometimes the motor in the pump would catch and it would be ok, then it finally dumped me. If you get it started it stays, but turn it off and next time it's a crap shoot. Just gotta drop the tank. And that's a lot of gas to transfer.

 

[Planebldr]

That is what I am thinking, but the fact it now starts everytime right away....but then shuts off after running a little has me baffled. I was thinking if it was the pump I would get a crank but no start sometimes. It starts normally...no long cranks. How long before it shuts off varies.

 

[Trainmaster]

Find a schematic and check voltage at different points down the chain when it's stopped. You have to find where the power's stopping. Only that way will you know if it's a relay, switch or the pump.

If you can get at it when it's dead, you must check voltage at the line going to the pump and find it live before you drop the tank. Without diagnostics, you're throwing very expensive parts at it and doing a hell of a lot of work.

 

[Planebldr]

That is the plan for today....follow the wires all the way to the pump.. just didnt have time yet. Meter will be my friend today for sure...

 

[Trainmaster]

If the failure is reliable enough to shut the truck down in your driveway, just check for voltage at the pump's leads and you'll know right away.

 

[Planebldr]

So I only had a few minutes and didn't research wire colors for the pump itself yet, so pinned around the pump relay with a meter. That is what feeds power/signal to the pump correct? Anyway, once again it started right away, and then would shut off randomly. The one terminal on the relay is always hot like it should. The other is ground and had very low resistance which is good. The output gets 12v until engine starts then goes up because alternator is charging which is good. When is shuts off I loose all power out of that terminal. So am I correct in thinking that even if the pump is bad, it would still read voltage since pcm/ecm whatever it's called would be still trying to spin the pump? Going to try to find the wire color to stab into for the pump connector tonight...unless someone knows that by chance? Lol.

 

[Hamfisted]

Does it still have the original fuel pump drive module on it ? Those tend to roast or fail from corrosion. Might be in the early stages of failing.


https://www.amazon.com/Mounting-2004-2010-4L3Z9D370A-5L8Z9D370A-6C2Z9D372A/dp/B07PYN1FV9

 

[Don Hall]

Does it still have the original fuel pump drive module on it ? .....

Hamfisted, would a faulty fuel pump drive module set a code?

 

[Planebldr]

So after pinning around wires to see if the pump is being supplied with consistent power. Turns out it was fluctuating. The relay was turning on and off at will. So after some reading some people were saying that the pcm/ecm or whatever it's called on the firewall lol, tells the relay to turn on or off. So I tried the easiest thing to do first, check the ground that is mounted directly to the box. Wouldn't you know it? It was jumping from next to no resistance to over 15ohms between the case and wire connector. That was without moving the test leads...it would just jump all over. So I cleaned it all up under and over till it didnt jump around. Guess what, it runs fine now. So the pcm must have been glitching and turning the relay on and off???

 

[ChrisRCNY]

That'd do it. My 08 had a bad connector at the fuel pump, damaged both the pump and connector. Former police service vehicle, probably has a lot of hours idling. Fuse was so brittle from slowly being baked before it blew that I had to pry chunks out with a toothpick.

In the process, I discovered that my truck does not have a driver module, just a relay. Pump assembly has a pressure regulator, pump supplies full flow to filter, fuel filter has 3 connections, with the third being the return to the regulator, dumping excess back into the tank. Dealer parts list still shows a driver module, even if it's not on the wiring diagram anymore.

 

[plumcolr]

Probably the pump controller, mounted on LR frame rail. The factory originals were mounted in a way which encourages corrosion. Most replacements come with a shield to prevent electrolytic corrosion.