Ford Power Stroke Nation banner

Do I need to replace my lift pump?

4448 Views 39 Replies 13 Participants Last post by  paramax55
I have a '95 7.3 and I'm pretty sure the lift pump is bad. I just bought it and I got it cheap because it was running like crap. It wouldn't go over 45 MPH and it was running like it had a bad fuel filter. I replaced the filter and limped it to the gas station. I filled both tanks and drove it around a bit. After a couple of miles, it came back to life. I went home, got the wife, picked the truck up several hours later, and drove it 90 miles back home. It ran great the whole time. After a couple of days of sitting, I started it again and it was back to the same thing... running like garbage, no power, just like a clogged fuel filter. Since the filter is brand new, and the old one looked brand new as well, and the only change is that it was sitting, I'm thinking lift pump.

I have an electric pump that I want to use anyway for this thing. My big question is... If I put this pump before the mechanical pump, is there any reason to replace the mechanical pump? Is there any diaphragm or something to start leaking fuel into the crank case? Will I ever notice the difference? I've used a couple of these pumps before to pump diesel and WMO. They pump 140 GPH at 15 PSI and they never complain.

1 - 20 of 40 Posts
Check your fuel pressure before you do anything
Well, I don't have a 4,000 PSI gauge yet, and I have the electric pump, and I want to install the electric pump anyway... I'm going to install the electric pump and see if that fixes the problem. If it does, it's pretty certain that it's the lift pump... but I appreciate the idea about checking fuel pressure... makes me think I should check the HPOP.
There is no lift pump on an OBS PSD. The pump in the valley is a two stage pump, one for low pressure that goes through the filter, then back to the pump, where it hits the second stage into the fuel rails.
I would also clean the fuel pressure regulator screen
And the electric pump isn't a good idea, I know 15 psi isn't Mich, but I believe its enough pressure to crack your fuel bowl.
I don't know if it would crack the fuel bowl but you would have diesel spraying out of the lid.

If you want to go to the electric pump you need to go all the way and eliminate the filter housing in the valley. But before I did anything else I would find out what the fuel pressure is either while the truck is running or cranking the engine over to determine if it is the fuel pump.
Well, whether it's the pump or not, the pressure is low. It starts right up, but rruns like it has a clogged fuel filter, or air in the lines. But it was running fine when I shut it down, and nothing but diesel comes out of the schrader valve while it's running. I don't see how the screen can plug up while it's sitting. I'm suspecting some sort of small hole somewhere in the mechanical pump. When it sits, that could let air into the system. Once it worked itself "primed" it could be OK.

This pump is adjustable. You can lower the output pressure. It's just that it comes set at 15 PSI. It also lets you flow through it if you don't power it on. So I can use it to prime, then shut it off. These have worked well for me to push fuel through a clogged fuel filter as well so I can get to the next exit instead of changing the filter on the highway...
So are asking what to check for your running issue or just letting us know you are putting on a electric pump instead of doing a "lift" aka fuel pump? If you are just putting the electric pump on I would listen to these guys who have done efuel conversions as they have experience with them. And I bet it's the fpr screen that's plugged full! And if your just adding the electric pump that screen is still going to cause you issues of its plugged. You would be amazed at the gunk that gets in there!
Well, now that I think about it, I guess I fully intend to put an electric pump before the mechanical one. I'll use it as needed and I'll check for fuel spraying out of the cap and/or a cracked bowl. I'm going to be running WMO and I've noticed it can help push cold oil through a fuel filter. I'll also check the fpr screen as well as putting a glass in-line filter before everything. They catch a lot of crud and they're easy to clean.

So... I guess the biggest question now is - Is there a pathway to get fuel down into the crankcase and thin out my oil if my lift pump is bad?
There is definitely something going on with the lift pump. I cleaned the fuel screen... What a duh-brained idea Ford had when they put THAT thing in there! I's so miniscule, ANYTHING will plug it up. The classic AC orifice filter or power steering filter would have been MUCH better choices.

Anyhow, after I cleaned the screen, there was no difference. So I put the electric pump on and the problem went away. There is a leak somewhere related to the lift pump, though. The valley is full of fuel and it leaks all over the ground under the truck. Aparently, whatever is leaking lets air into the system while the truck is sitting. Then, when you start it, it runs like crap until it works itself out.

The next thing I need to do is find where the leak is coming from. I guess that'll have to wait until Tuesday.
the fpr screen gets plugged with pieces of your injector orings
you do not ned a 4000psi guage to check your fuel pressure, if it is at 60psi it is working fine
I love it when guys come on here asking for help, but they never take the advice
Fuel bowls are notorious for leaking, the pump itself can leak from the weep hole, multiple rubber lines to leak, etc. Wash the engine, dry it off good, and start the truck back up, crawl under the hood with a flashlight and mirror, and you will find your leak.
My fuel restriction sensor was leaking on my fuel bowl. Pretty bad, about 1 drop a second and made a huge mess in that valley. I put a plug in place of it and problem solved.
damn this guy posted this same question in every spot in the forum.

Putting the electric pump before the mechanical pump will do nothing but supply pressure from the electric pump to the mechanical pump. the mech. pump would become a restriction. It is not going to boost pressure in any way. especially if the mechanical pump is bad.
"This Guy" did not post this same question in every spot in the forum. "He" didn't see that there were two seperate 7.3 sections and posted in the wrong one first. Then "He" corrected "his" mistake and put the question in the right place because there are people who like to flame instead of help.

If you had read through the thread, you would have seen that, indeed, an electric pump can help, because it did. The mechanical pump supplies pressure in pulses. The electric pump is more constant. It does not supply as much pressure as the mechanical pump, but it supplies more volume. It also makes it easier to prime a system when it has become comprimised for any reason - changing the filter, fuel leak, etc... And, as a diagnostic tool, I wouldn't want to be without it - especially when you're driving down the road in and something starts to act wonky.

Thanks for the tips on finding the fuel leak. There's about 1/2 a yard of dirt in the valley right now. I need to get in there with some degreaser and get down to a level I can work with. I felt all around the fuel bowl and didn't feel any diesel. I think the banjo bolt at the back of the fuel pump looked like some of the grime was washed away. I'm kinda hoping that's where the leak is. I've heard about the baby powder method of finding leaks. I like to use paper towels. I just stuff them everywhere and look for where they get wet.
See less See more
I've heard of the banjo bolts copper waahers leaking as well. And I suggest power washing the engine. Obviously don't get carried away on the wires and swnsors, but the actual motor, and valley especially, is free game. It looks better, and makes finding leaks super easy. Plus when you do have to work on the motor, you don't get nearly as dirty.
My fuel restriction sensor was leaking on my fuel bowl. Pretty bad, about 1 drop a second and made a huge mess in that valley. I put a plug in place of it and problem solved.
This is exactly what I dealt with this weekend. Time-consuming, but an easy fix. Knee pads help, while you're kneeling up on the rad.

Lots of possible leak sources in there - crack in the bowl, rubber lines between the bowl and pump, weep hole in the pump, sensors/heater in the bowl, etc. Yeah, get a back hoe in there and get that half-yard of dirt out, then dry it out good and sprinkle baby powder in there (I used baking soda, since that's what we had), and crank the engine. If it's a bad leak, you don't even have to start it; just a remote switch on the starter relay to crank it over several times might reveal it.
I'm glad I'm not the only one who's thought of kneepads. I was feeling a little "sissy" for wanting them.
1 - 20 of 40 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.