Acting like it's out of fuel

[Ryan Cowper]

I drove my truck up to 8000' on Mount Lassen in northern California yesterday. When I reached a parking lot near the summit and stopped to look at my map, the truck hesitated a couple of times at idle, exactly the way it does just before it runs out of fuel. My gas gauge don't work and I know I can only pull 9 gallons of fuel out of my rear tank because of a broken straw. I glanced at my trip odometer to see that I had driven 138 miles ... I'll usually get about 160ish off of that tank when I'm driving around in the flatlands. I assumed that the steep mountain terrain dropped my mpg down significantly and I had blown through my rear tank. I switched over to the (completely full) front tank and the hesitation stopped. I then proceeded to another parking lot about 10 miles down from the summit. I turned the truck off and went for a few hour hike. When I returned, I turned over the truck. It started and immediately died ... exactly the way it does when there's air intrusion. I rebuilt my return lines a few weeks ago and haven't had any air intrusion trouble leading up to this. I cranked it for about 8 seconds, got out and pressed the Schrader valve on the filter housing, it hissed, and I cranked it again ... no go. I repeated that process a few times, assuming I had some air intrusion and I just needed to reprime the fuel system. On the third cranking cycle, there was no hiss from the Schrader valve and no fuel came out. I unscrewed the fuel filter and saw that it was only about 1/3 full of fuel. I tried cranking it with the filter off and no fuel came out through the filter housing. I switched to the rear tank, still no fuel. I thought possibly my tank selector valve may be at fault ... maybe it got stuck on the rear tank. So, I grabbed my 5 gallon fuel can and I poured into the front tank first, the tank I knew was full ... yup still full. I dumped the remaining 4.5+ gallons in the rear tank and cranked the engine once more ... nothing. At this point I pretty much gave up, called a tow truck and now my truck is sitting in front of my house.

I imagine it's one of a few things but I want to run it by everyone before I start messing around with it. I'm pretty new to the wonderful world of working on my own vehicle ... keep that in mind.

Either ...
A) It sucked up some broken straw bits or crud and got plugged up somewhere
B) the lift pump gave up the ghost
C) something is wrong with my tank selector valve

What do yall think? Where should I start?

Thanks in advance!

 

[The_Josh_Bear]

Your lift pump is toast most likely.

*Typically* the FSV will fail to switch all the way but the lift pump will still be pulling fuel some way or another. Especially now that you have plenty of fuel in both!

The odds of both tanks getting bits clogged into them are pretty low, but one broken lift pump would fit the bill here. I recommend a Ford pump as the aftermarket ones are generally hit and miss. They are only $30 on Ebay last I checked.

Edit: By the way I appreciate your attention to detail and method of testing! It sure makes it easy to help out when the post is so easy to follow and full of detailed info.

 

[Ryan Cowper]

Your lift pump is toast most likely.

Will any 6.9 or 7.3 idi lift pump fit my 1989 na?

 

[IDIBRONCO]

Yes. They are all the same.

 

[Ryan Cowper]

So, it's better to get a used pump in questionable condition from Ebay than to buy a new aftermarket pump from a parts store?

Also, do you all know of a decent write up (or video) online for replacing the lift pump?

I have the Haynes manual for my truck but it doesn't cover the idi. It's very frustrating not having a 6.9/7.3 engine manual in situations where internet service is not available, like on the top of a mountain! Is there truly no shop manual for our engine?

 

[Cubey]

So, it's better to get a used pump in questionable condition from Ebay than to buy a new aftermarket pump from a parts store?

Also, do you all know of a decent write up (or video) online for replacing the lift pump?

II have the Haynes manual for my truck but it doesn't cover the idi. It's very frustrating not having a 6.9/7.3 engine manual in situations where internet service is not available, like on the top of a mountain! Is there truly no shop manual for our engine?

Yes, there are manuals, the official Ford factory/dealer service manual is one. I think there is a Haynes manual too for diesel engines specifically.

 

[IDIBRONCO]

So, it's better to get a used pump in questionable condition from Ebay than to buy a new aftermarket pump from a parts store?

I believe those are new Ford pumps although I haven't looked.

 

[IDIBRONCO]

As for the replacement, it's not too difficult. I always do it from underneath. I unhook the ground, wires, and transmission lines on the driver's side. Then loosen and remove the two fuel lines. Next unbolt the two bolts that hold on the pump and remove it while avoiding the spray of fuel that likes to come out when you break loose the seal against the block. Clean up the gasket area very well and install the new pump in reverse order.
Helpful hints: the old pump usually stays sealed against the block and requires a light tap to break it loose. This is the only part that I'd recommend doing from above to avoid the aforementioned fuel spray.

The nut part of the steel fuel line that runs up to the filter is 5/8". Use a line wrench on this to help avoid rounding it off. The part of the lift pump that it screws in to is square and an open end 3/4" wrench fits on here to help break the nut loose if it's really stubborn. After it's broken loose, you can unscrew it the rest of the way with a standard open end wrench.

The trickiest part of this may be making sure that the arm on the new pump is positioned underneath the eccentric on the camshaft. Usually, I have no problems with this. All I do is tip the pump up while I slide it into the hole in the block. This will tilt the fuel pump arm down towards the bottom of the oil pan and make it slide underneath the eccentric on the cam. If you encounter one of the rare instances where you can't get the pump to bolt to the block after you're sure that the arm is underneath the eccentric, you can rotate the engine (maybe about 90 degrees) to move the lobe on the eccentric and making it easier to install the new pump.

Lastly, I've had the best luck by actually completely removing the steel fuel line that goes to the fuel filter. The nut at the top takes a 3/4" open end wrench. You may want to have a new 3/8" olive on hand in case this one isn't in the best of shape when you remove the line. It wouldn't be good to have a new lift pump and then have an olive that doesn't seal. Sometimes, the nut on the lift pump is kind of hard to get started while the line is attached at the top. This is why I'll remove this line. You can start the lower nut into the lift pump and then start the upper one onto the fitting on the filter housing.

 

[Ryan Cowper]

@IDIBRONCO hey, thanks for the advice!
I really don't have time to wait around for a delivery from Ebay, this truck is my only vehicle ... I think I'm just going to get an aftermarket pump from the parts store today.

 

[IDIBRONCO]

I guess that was sort of a write up. Aside from the hints that I came up with from experience, it's fairly self explanatory once you start doing it.

 

[Cubey]

Step by step photo instructions, and it lists the (recommended?) fuel pump part numbers at the beginning.

http://www.dieselhub.com/maintenance/6.9-7.3-idi-diesel-fuel-pump-replacement.html