Thoughts on SOHC not being able to idle with low gas tank level.

[sehaare]

After warning my daughter repeatedly not to trust the gas gauge on a vehicle built in 1998, she ran it down to less than a quarter tank on the gauge. When I went to start it, to move it out of the way of my car, it would start every time, but would not idle on its own. I ended up having to keep one foot feathering the gas pedal and putting the other on the brake to shift out of park and then continue to give it gas or it would die. I figured that something else was wrong with the car and I'd be freezing my ass off soon working on it.

After she filled the gas tank up, it ran like a top. You can even reach in through the driver side window and start the car and it now idles like it was brand new.

There obviously was still gas in the tank or it would not have started and would not have kept running with my foot feathering the Gas peddle. Any thoughts on why a low gas tank would cause it to not idle on it's own?

 

[Mbrooks420]

The fuel pump would be the first thing to suspect. They will often run intermittently before completely failing.

If you replace it don’t buy the Airtek, or other cheap pump assemblies, or you’ll be replacing it again in short order.

It’s unlikely there’s anything wrong with the gauges accuracy.

 

[sehaare]

The fuel pump would be the first thing to suspect. They will often run intermittently before completely failing.

If you replace it don’t buy the Airtek, or other cheap pump assemblies, or you’ll be replacing it again in short order.

It’s unlikely there’s anything wrong with the gauges accuracy.

The pump was replaced 8 years ago, when it failed on the side of the road while driving my daughter down to college. Got it towed and had to leave it there while they replaced the pump (not sure what brand pump they used but hopefully it was oem).

If the pump were starting to go bad again, I could see how less fuel height in the tank would reduce the pressure at the suction to the pump somewhat and make the pump work harder, but not sure how big an affect the fuel height would have on that pressure. but anything that makes a failing pump work harder isn't good.

 

[CDW6212R]

Fuel pumps don't always fail completely, they often slowly have reduced pressure or capacity. Testing the pressure is the quickest clue of the pump's condition. But as said, the tested pressure may pass the minimum limit and be called good. There is a better test which a shop manual describes, but it's slightly longer to do, and most people don't consider it.

It sounds like most likely the pump. You can test it the right way by the shop manual, or give it the quick pressure test and guess the condition, or just skip testing and change the pump, or keep driving it until it fails. Those are the actual choices, and most of them are not given fully in these threads. We, I, and most of us, take one of the easiest routes, and skip the proper shop manual testing.

 

[German Engineer]

These fuel pumps that we have in our Explorers are sadly designed to be submerged in fuel (Whoever came up with that?). If they're not submerged in gasoline then they're not cooled and lubricated properly. This pump also isn't regulated but runs on full power all the time. The fuel pressure regulator just lets any excess pumped fuel run back into the tank. So for the pump itself it makes no difference whatsoever if you drive at full speed, or if the engine runs idle in park.

It's a poor design many cars more or less share, but the pumps on our explorers seem to be especially poorly designed.
So as a result, if you run the engine of the car with an empty or nearly empty tank that will kill the fuel pump rather quickly.

If you look at how the pump is located on the pump assembly 'standing upright' in the tank and how tall the actual fuel pump itself on this assembly already is, then you will see why for our Explorers several people recommend to avoid driving around with a gas tank that's not at least 1/3rd filled, in order to avoid having to replace the fuel pump over and over all the time.

There's practically no telling how precise your fuel level sensor and gauge in your truck are when they show 1/4 of fuel left. But even if it were absolutely precise then at that point fuel pump will clearly not be fully submerged in fuel anymore but will only partially submerged, if at all.
That will cause it to run much warmer and with less lubrication than it would otherwise run when submerged. And if it's already an old pump on it's way out, then that easily explains the symptoms you and your daughter are experiencing.

So look for a new fuel pump and try to keep enough fuel (best more than 1/3rd) in your tank at all times. I put a Canadian made fuel pump assembly from Spectra into mine and it's runs great for 4 years now and it has a better fuel level sensor on it than the previous one had. But you can of course also just get the pump and not replace the full assembly.
I for myself rarely drive around with anything less than half full tank, not only because of the poor design of the fuel pump, but also because I live on an Island where the highway floods now and then at high tide and you can end up stuck waiting for a while.

 

[donalds]

Bosch only
Replace the pump only not the whole sending unit assembly

 

[Mbrooks420]

The low fuel level hurting the pumps is a myth. I run my tank to the fuel light every time. I’ve never replaced one before 150k which seems to be a pretty solid lifespan for them. Fuel is running through them, and they don’t run hot, anyways.

 

[donalds]

I solved all my problems by buying a good pump
In my case a walbro
I recommend a bosch

 

[CDW6212R]

The pump itself is about 3" from the bottom, to about the center of the pump. The 95-01 tanks are especially long compared to other gas tanks. That exposes the pump more often then shorter or deeper tanks. The old 91-94 tanks are much shorter and larger in profile area, and the same capacity.

Fuel sloshing around inside the tanks is a big help to cool the pumps, but also there is a set of walls around the pump area to help contain some fuel at the pump pickup. So there are many factors affecting the lifespan of the pumps. Filling up more often will help, and the quality of the pump is important. Avoid cheap brand parts, Bosch and Spectra seem to do well, but there are many many brands, try to listen to experience of other people.

Here's an old 93 Explorer tank, and a 98 model, they both hold 22 gallons(both are 4dr models);

 

[imp]

I could see how less fuel height in the tank would reduce the pressure at the suction to the pump somewhat and make the pump work harder, but not sure how big an affect the fuel height would have on that pressure

" I could see how less fuel height in the tank would reduce the pressure at the suction to the pump somewhat and make the pump work harder, but not sure how big an affect the fuel height would have on that pressure"

This is a sort of engineering consideration based on "head" of a contained liquid. Water and gasoline are not too far apart, and "head" pressure for water is 0.433 pounds per square inch per foot of depth, so gasoline a bit less. Thus, if the pump were submerged 1 foot deep in the fuel, it's inlet pressure would be about 1/2 psi, pretty small, and neglecting the fact that the pump is "sucking" fuel in at a vacuum, that 1/2psi "helps" it.

So based on that, no, .....fuel depth is immaterial. But pump ability is VERY REAL. Some pump motors are permanent magnet type, others are series-wound containing brushes. Just as in an alternator, brushes making poor contact result in impaired performance.

 

[German Engineer]

" I could see how less fuel height in the tank would reduce the pressure at the suction to the pump somewhat and make the pump work harder, but not sure how big an affect the fuel height would have on that pressure"

This is a sort of engineering consideration based on "head" of a contained liquid. Water and gasoline are not too far apart, and "head" pressure for water is 0.433 pounds per square inch per foot of depth, so gasoline a bit less. Thus, if the pump were submerged 1 foot deep in the fuel, it's inlet pressure would be about 1/2 psi, pretty small, and neglecting the fact that the pump is "sucking" fuel in at a vacuum, that 1/2psi "helps" it.

So based on that, no, .....fuel depth is immaterial. But pump ability is VERY REAL. Some pump motors are permanent magnet type, others are series-wound containing brushes. Just as in an alternator, brushes making poor contact result in impaired performance.

The pressure difference is totally irrelevant, but with little fuel in the tank fuel contaminants in bad gas tanks may play an increasing role, also air and air bubbles getting into the pump when the fuel sloshes around. And as mentioned cooling and lubrication of the pump and as you say contact issues and corrosion etc. with older pumps.

First and foremost of course, it's really a matter of how well (or not) the pump is designed and manufactured though.

 

[sehaare]

Looks like the consensus is, that it is the fuel pump. Just checked on line and even the Bosch ones are cheap. The only problem is that I'd have to drop the tank to replace it. I've never done that before, but with it being up here in the land of winter salt rust in Chicagoland, I'd be real worried about snapping rusted fasteners and welded studs.

I wish Ford had done what VW did on their older cars and built in a accesses to the fuel pump under the rear seat. That made replacing those (and inspecting the tank) a snap.

 

[German Engineer]

Try to arrange it so that you drop the tank when the tank isn't all full but just about empty instead.
That'll make the job a lot easier.
You'll find plenty of good advice on how to drop the tank and replace the fuel pump in older threads here.
Just please don't cripple your Explorer by cutting an access panel under the seat.
It's really not a very difficult job other than the usual issues with rusted bolts and the likes that you have with older vehicles.
Getting those clips on the fuel lines open is probably the most challenging part about it.
It's supposed to be easy, but I've somehow ended up buying two different special tools for it, and in the end I ended up doing it with a wrench and a piece of rubber hose, because I somehow just couldn't get one horribly stubborn quick connector to release.

It's most likely the fuel pump, but the proper step by step way to diagnose the issue, would indeed be testing the fuel pressure and testing the electrical connection to the fuel pump first, before replacing it.

You may also want to replace the fuel filter along with the fuel pump and keep the receipt of that. For one, simply because the fuel pump manufacturers will recommend it in their instructions. And secondly you might need to have it as proof of a proper fuel pump installation in case you'd need or want to claim any warranty on the pump.

When you replace the pump and put it all back together, take the time to make sure the big seal at the top between the whole pump assembly and the gas tank itself is still in perfect condition and all the surfaces are clean.
You wouldn't want to create a fire hazard with gas fumes leaking out into your garage.

 

[C420sailor]

Remember that return vs returnless is also a big factor in pump longevity.

BMW did experiments and realized that fuel temps could be up to 70°F higher in traditional fuel systems, vs returnless. Fuel in a partially filled tank will heat up much faster than a full tank. Now imagine that hot fuel flowing through an exposed pump in the dead of summer.

This is why I try to keep my ‘98 above 1/2 tank.

 

[CDW6212R]

There is one main bolt to remove which holds the one tank strap on. The is the largest worry of a seized bolt among all of the tank bolts to loosen. Be sure to spray that one and others with a really good penetrant, like Kroil etc. That bolt will be tough to remove, so go at it slow and expect to spend five minutes or more getting it out. If the truck has a skid plate, there is also an additional bolt similar to the strap bolt, nearby to the other one. Those have captured nuts in the hole up near the truck floor, so you don't want those threads to strip.

The fuel line connectors are a PITA, go slow at those and be patient. Don't force them at all, damaging the fragile internal locking clips creates a big problem. You don't want to go back at it again to replace the fuel lines.

 

[C420sailor]

There is one main bolt to remove which holds the one tank strap on. The is the largest worry of a seized bolt among all of the tank bolts to loosen. Be sure to spray that one and others with a really good penetrant, like Kroil etc. That bolt will be tough to remove, so go at it slow and expect to spend five minutes or more getting it out. If the truck has a skid plate, there is also an additional bolt similar to the strap bolt, nearby to the other one. Those have captured nuts in the hole up near the truck floor, so you don't want those threads to strip.

The fuel line connectors are a PITA, go slow at those and be patient. Don't force them at all, damaging the fragile internal locking clips creates a big problem. You don't want to go back at it again to replace the fuel lines.

I had to carefully cut the lines where they exited the tank, before the connectors. Turns out the fittings were somehow crushed oval ever so slightly, and were an absolute bear to separate...but cutting the rest of the tank/pump assembly away helped give me room to work.

Had to replace the entire assembly (pump and level sensor), but I had planned to do that anyway.

 

[donalds]

Is my fuel pump bad 1999 ford explorer shoc 4.0. Lots of pictures on the replacement

How can I explain this

www.explorerforum.com

Here ya go

 

[sehaare]

Is my fuel pump bad 1999 ford explorer shoc 4.0. Lots of pictures on the replacement

How can I explain this

www.explorerforum.com

Here ya go

Awesome, that makes it look almost easy. unfortunately it has become a little too cold in chicagoland to be laying on the ground right now and wrenching on a car. Since this has only happened once, when the gas level was extremely low, and since the pump appears to be happy once the tank was filled, and had no further issues, I think I'm going to tell my daughter to keep the tank above 1/2 full, and roll the dice until spring.

I know that will have some of you shaking your heads, I'm not a big fan myself of just crossing your fingers and hoping, instead of fixing what needs to be fixed, that plan usually ends up biting you in your ass. If I see any more pump related issues before spring, that will force my hand, and I will have replace it then and there. But right now, I have visions of me having to suit up in my carharts, lying on my back on the ground in 30 degree weather, and snapping off a bolt on my daughter daily driver.

And on a side note to donalds, congratulations on having a son that likes to wrench. I've got a lifetime of tools (I'm 58) that I would have killed to have back when I was younger, and right now my two potential son-in-laws, who would stand to inherit all of them, probably couldn't change their own oil.

 

[Mbrooks420]

In no way way are you “crippling” your car by adding an access panel. I’d absolutely cut one when the tank was down, so you never have to drop it again. (I’d cut it with it in there, but I’m wild)

 

[donalds]

Btw the strap and hardware kit is available cheap
At napa