Fuel pump help

[master53yoda]

The other possibility is a oil pressure/fuel pump switch that is going bad but hasn't completely failed yet. If the resistance is high on the oil switch it will slow down the pump reducing its pumping efficiency.
Can you use your primer button to bypass the pressure switch with the engine running. If so when you have low flow, energize the pump with your prime switch,if you get increased flow then that would verify a bad pressure switch.

If it is the switch it will progressively get worse, until it won't work at all. When i put transfer pumps on i energize the pump through a relay that is operated by the switch rather then using the switch to drive the pump.

good luck

[arveetek]

Thanks guys! I appreciate the responses. I am running Kennedy's OPS relay harness, so the pump is energized by his relay kit, and not directly off the OPS. I have verified that the pump is receiving good, steady power with the engine running. I have a button on the firewall that allows me to energize the pump whenever I wish. I have also tried running the pump manually with the engine running with no change.

Casey

[JohnC]

OK, so we can probably assume the pump is working to the best of its ability.

That leaves 2 questions:
1) how is the air getting into the filter?
2) why is the volume of excess fuel so low when the engine is running?

The first one is easy. It has to be getting in on the suction side of the pump.

The second one is more puzzling. Could the injection pump be bypassing too much fuel?

[DmaxMaverick]

If the IP were bypassing (returning) too much fuel, it would do it at idle too, and temperature would be a much bigger player. Sounds like a weak lift pump, coupled with an otherwise insignificant air leak (only leaks under suction, which is quite common). Or.... You have a big leak between the lift pump and tank.

[JohnC]

If the IP were bypassing (returning) too much fuel, it would do it at idle too, ...

I agree, but I think he said he had good flow out of the filter breather with the engine off, but just a trickle at idle and nothing at higher RPM.

[arveetek]

I have checked, rechecked, and triple checked for leaks between the lift pump and tank, and cannot find a thing. I'm really suspecting a weak lift pump.

I picked up another lift pump today, and am going to swap it out tomorrow night. Hopefully that will take care of it.

Fortunately my current pump is still under warranty, and the parts store has no problem swapping pumps with me.

Wish me luck!

Casey

[racer55]

I didn't read all of the posts,but if it has not been mentioned the dip tube on the sending unit has been known to get pinholes from rust inside the fuel tank that allow air entry when the fuel level falls below the hole.

Also the lines leaving the sending unit are prone to rust from moisture and debris settling on them.

The rubber O-ring where the fuel line from the tank enters the LP if damaged or dried out can also be a source of air entry.

[arveetek]

Swapped out the pump tonight. I immediately noticed more flow, and now when the engine is idling or even at high idle, fuel squirts out pretty strongly when I open the bleeder valve on top of the fuel filter.

Cross your fingers and hope that this was the problem all along!!

Casey

[More Power]

Was the first replacement lift pump an imported unit? I've heard from 6.5 owners these past 2-3 years about imported (China) pumps not performing very well or failing soon after installation.

[Burning Oil]

Swapped out the pump tonight. I immediately noticed more flow, and now when the engine is idling or even at high idle, fuel squirts out pretty strongly when I open the bleeder valve on top of the fuel filter.

Cross your fingers and hope that this was the problem all along!!

Casey

Should be good to go! (for 9 months)

[arveetek]

Drove to work just fine, went to lunch, came back from lunch and she ran out of fuel in the parking lot.

This pump is an Airtex brand, probably a China model. I haven't looked closely at the box.

Recap of the symptoms:

Engine started sputtering under load. Checked pump (Airtex brand with 45K on it). Did not appear to be pumping well, replaced pump. Did not solve issues. Still running out of fuel (filter is empty). Can manually prime filter and runs great for a while until it starts sputtering and bucking - check the filter and it is empty. Replaced pump with another unit, still running out of fuel.

I have verified pump is running and has constant power when engine is running. I have dropped the tank twice to check for leaks, and the sending unit/pickup assembly only has around 18K miles on it. "Sock" on pickup is clean as can be. Symptoms appear no matter what level the fuel is. New diesel fuel cap on tank.

I'm getting really stumped on this one...unless I am just getting crappy pumps that are no good.

Casey

[racer55]

Have you checked the screen in the filter manager that sits on the mast/fuel heater under the filter?
If it is plugged it might be enough restriction to let the IP empty the housing?

[DmaxMaverick]

While "outgassing" can occur with fuel under vacuum, you are seeing too much, too quick for that to be the issue. You have a leak you haven't found, likely between the lift pump and tank. Check all the connections, and the line, again. You may have a leak that only leaks under vacuum, but doesn't under pressure. I know it sounds like a broken record, but it keeps coming back to this.

[Burning Oil]

My gut keeps telling me the sock. Only other thing I can think of is a problem I have had. It Would make the truck not able to exceed 30mph, but it would not buck. The problem was the hard line going from LP to FFM was pluged. I ran a hose into a clean bucket and blew compressed air from FFM side (where the rubber hose connects) down to the bucket. All kind of crap came out of there. Truck has run great since.
You can also blow back to tank at the LP connection (remove cap first)

You really need to hook up a fuel gauge!!

[arveetek]

I'm going to have to take a harder look at the line between the filter and the lift pump. It was running so bad tonight, I didn't think I was going to make it home! I have a 22 mile drive home from work, and I had to stop 3 times to bleed the filter. Each time it got worse and worse, to the point that fuel would not pump up to the filter. The last time I couldn't get more than 3 miles. Then it wouldn't pump fuel hardly at all. I ended up taking the filter out, and it took maybe 2 minutes to get the filter housing full. Fuel was barely trickling into the housing. What's funny is that there were no air bubbles in the housing when the pump was running.

The pump sounded like it was working hard too. Almost sounds like a restriction between the pump and filter....

[Burning Oil]

Could be a restriction on the suction side to. Blow the lines out.

[a5150nut]

Have you got any algie growth in the tank?

[Robyn]

You need to unhook the line at the filter and then at the pump, blow that sucker out with air and make sure its OK.

The line sets used on these trucks have a metal component as well as a rubber section.

What may have happened is that the rubber portion of the line has degraded inside the CORE and has basically swollen shut.

I have seen this before and the symptoms sure fit the problem.

Have you used Bio diesel in this rig. Some Bio stuff can cause issues with hoses.

The fuel lines sort of snake up and over the back of the tranny and then connect to the filter and the return line.

What I did on one rig was to cut the feed line to the filter right near the lift pump and then installed a ferrul on the line. ( just used a ferrul fitting, tightened it then removed the fitting and cut the nut off.

You could take the line out and sweat solder a ferrul on.

The ferrul will allow a safe install of a Heavy duty rubber fuel line without it being able to slip off when clamped.

Run a new rubber line up under the drivers side floor board (clamp as needed) snake it around the Hydro boost and then across the LH VC and connect it to the filter.

I do not recommend running the rubber line across the tranny.
Too much chance of it getting worn through due to vibes and engine movement.

Now, If you want to fiddle around, you may be able to remove the old rubber line from the fuel line harnes and then do the ferrul thing and install new rubber and leave the lines where they are.

I swapped locations on mine while the engine was out due to the line bracket being such a PITA to get the nuts on an off of the studs at the top of the bell housing.

Check this area out and keep us posted.


Missy

[arveetek]

Yes, I have run quite a bit of home-brewed Bio Diesel through this rig over the past 5 years. It's been a few months since I've run any, due to cold weather, a busted pump on the processor, and low oil supply.

It crossed my mind that perhaps the fuel supply hoses may be be swelling internally and restricting flow, just like the brake line hoses do from time to time....

Casey

[Robyn]

I would certainly have a peek see at the hoses. The metal lines are imune to most stuff other than water and corrosion rust through.

All it would take would be a little flap of rubber thats flipping into the stream and closing off the flow.

Unhook the feed line from the lift pump and then fire off the pump and see what shakes.

Betcha the fuel flows good right at the pump

Good luck


Missy