98 4.0 Fuel Issues

[Jaimec]

Hey guys,

My wife's 98 ex 4.o sohc has developed an issue that has me scratching my head. First off, we've only had this rig for about 5 months, but it seemed well cared for, and other than this issue, zero problems.

Started about 2 months back. Going up slight hills, it would hesitate mildly, as if the fuel filter was needing a change. This happened in my 99 ex 4.0 ohv, and it was the filter. I finally got it changed yesterday (The fuel draining from the filter looked like coffee, just as it did mine) and it ran smoother and better than the day we bought it. For a day. Now it seems to be doing it again, which leads me to think fuel pump. BUT....here's the odd part. It only seems to happen when the tank was below 1/8 (my wife noticed this before I changed the filter, as well). The fuel light was on before I got it home today, so I put 4 gallons in (didn't want to fill it if I have to drop the tank) and it made a pretty good improvement, though I couldn't test it on a hill. Still, pretty obvious there's a problem that needs addressing.

I don't have a fuel pressure gauge, but I'll go to autozone tomorrow and check it. If it's below 35, with a new filter, then definitely a new pump, right? Anything else it could be, before I spend the bucks and do the job in a gravel driveway????

Thanks!

 

[ranger7ltr]

You are seeing the classic example of a rusty metal fuel tank and the resultant rust issues the fuel pump and filter are catching... Hopefully the fuel pump is still good but I would recommend replacing the tank, the filter sock on the pump, and depending on the look of the pump the pump as well... I have seen this scenario play out and I even had the original tank boiled out by a radiator shop to remove the rust but it came back as the level of the tank drops the rust reappears... I should have bought stock in Fram for the fuel filters i replaced but after replacing the tank I had no more rusty fuel and clogged fuel filter issues..

.The pics are what the inside of my tank looked like when I pulled it for the last time... The other pic is what the fuel looked like coming out of the supply side of the filter...When it looked like that, not enough fuel was coming through to run the engine with a load on it... It would actually idle but would die with any throttle position...And with my electric fuel pressure gauge mounted in the cab I could watch the fuel pressure drop as well...

View attachment 91815

View attachment 91816

 

[J_C]

Don't let the tank get that low on old vehicles with metal gas tanks. It causes interior rust and is hard on the fuel pump for cooling and refueling contraction reasons.

Otherwise, yeah, it's up to you how much to replace and gamble on whether you did enough and how long that lasts. It's easiest to suggest replacing everything but it makes less and less financial sense the older a vehicle gets. If it still has the original pump then I would replace it while you have the opportunity to do so easily, whether the pressure is low or not... since it's now 17 years old.

 

[Robman]

the rubber fuel lines between the pump and regulator could have cracks.

I run my tank low all the time, usually rare when I fill it right up, it always sucks from the bottom anyways

 

[J_C]

^ It's not that it sucks from the bottom, it's the air with water vapor exposed to bare metal and the outside of the pump not helping to cool it as well when not submerged.

 

[Robman]

STPs suck from the bottom, regardless of fuel level, particulate will be heavier than the fuel and sink to the bottom.
An STP can have cooling by sucking the fuel up, sure it probably isn't kept quite as cool as also having all the fuel around the pump. I'd imagine while functioning, it's usually kept within its tolerances for temperature.

The pump can be starved for fuel when ascending or descending steep hills on a very low tank, yes.

This tank full/tank low for fuel pump health is not much more than a wives' tale and I'd be interested in seeing solid scientific evidence and research into this matter to see how the life span of the pump is really affected. If you're driving around with a full tank all the time to keep your tank healthy and pump cool, you may be likely just hurting your fuel mileage carrying around extra weight.

Low tanks rust? They do if you're storing the vehicle for extended periods of time with a low fuel level. When you're driving fuel tends to slosh around.

Your metal tank will rust, and your mechanical fuel pump will eventually die. There's no need to put overdue thought into it.

In my opinion

 

[koda2000]

The fuel pickup is pretty much sitting on the bottom of the tank, so sucking up fuel and whatever from there is what's happening all the time, regardless of the tank's fuel level.

Several issues can occur which will damage the fuel pump:
1. They eventually will wear out. I find this typically happens somewhere around +/- 200,000 miles.
2. Ethanol blended fuels pull moister out of the air. This moister causes rust in the fuel system/tank.
3. Running your tank very low is hard on the fuel pump because the gasoline in the tank helps to keep the pump cool.
4. Running on a clogged fuel filter is very hard on the pump.

I have changed 6 or seven fuel pumps in my Expl's and Mountaineers in the past several years. In each case the vehicles had between 175,000 and 200,000 miles on them (with the exception of our '97 Sport which had over 260,000 on it's original fuel pump, which was actually working prefectly). In each case I examined the inside of my fuel tanks and found absolutely nothing inside of them. They were all clean and rust free.

Ford recommends you replace the fuel filter at 30,000 mile intervals, which I do.