Puzzling fuel problem on '96 Dodge van

dodge
gasoline

#1

This could be a great PUZZLER…I have a 1996 full-size Dodge van that has developed an aggravating problem in the last few years. When the fuel gauge gets to about the half-tank level, the vehicle starts sputtering AS IF it were running out of gas. It is barely driveable but can usually reach a service station. When the tank is refilled, the problem disappears and I’m good to go - as long as I keep the tank more than half filled.

I’ve tried to rationalize what could cause this:

Bad fuel pump - why would it only fail when the tank reaches half full?

Water in the tank - wouldn’t it mix while driving and cause the problem intermittantly?

Bad fuel gauge - if it were really getting empty and the gauge were just off, why can I only put 15 gallons in the 32 gallon tank?

To add another layer of mystery, this problem is worse when it’s cold - happens at about 2/3 tank. Also, if the van is driven only on local stop and go roads, the problem does not appear until maybe 1/4th tank. In other words, highway driving in freezing temperatures makes the problem worse.


#2

i would guess (and this is a WAG at that) your fuel pump is going. it sounds like as long as the fuel pump is totally submerged, it is doing ok, but when it starts to become exposed it either loses prime, or possibly an inside tank fuel line is leaking, so it cant get full pressure up to the engine.

it sounds like you need to have the tank dropped, and have someone check out the fuel pump, and the lines to and from it.

out of curiosity, when you get in the van, and turn on the key, has the fuel pump noise changed from what you remember? has it gotten quieter, or louder?


#3

To get my stupid question out of the way first; are you absolutely positive the van has the optional 30 gallon tank?

If so, any chance the tank could possibly be developing a vacuum inside and the pump is having difficulty overcoming this in its attempt to pull fuel from the tank?
Maybe the stops for fuel, and the variation in speed along with bumps, relieves this vacuum to some extent and this is why the problem disappears.

Try leaving the gas cap loose, drive it, and see what happens.

I’ll also throw something out there I’ve seen about half a dozen times on VWs but have no idea if this could apply to a Dodge or not.
Look underneath at the tank and make sure it is not buckled inwards, which will decrease the capacity.
Some of the older VWs had a tendency to “vacuum the tank flat” due to an emissions glitch and one could insert their fist between the tank and straps that hold the tank in place.

In these cases a 15 gallon tank may have only held 2 or 3 gallons when full and a number of VWs were towed in because of this anomaly. The owner would fill up, drive about 75 miles and run out of gas even though the gauge reads FULL.
(Think of taking a 1 gallon milk jug, crushing it down some, and then reinstalling the cap tightly. The crushed jug will maintain its shape. I’m not saying this is your problem but is something to consider anyway.) Hope this helps.


#4

I would vote for a fuel pump, filter or pick-up. It is harder to pump from a half full tank than a full one. If I am correct, the problem will just get worse.


#5

“If so, any chance the tank could possibly be developing a vacuum inside and the pump is having difficulty overcoming this in its attempt to pull fuel from the tank?
Maybe the stops for fuel, and the variation in speed along with bumps, relieves this vacuum to some extent and this is why the problem disappears.
Try leaving the gas cap loose, drive it, and see what happens.”

This sounds good to me


#6

When there are questions of fuel supply, or pressure, this is why there are FUEL PRESSURE GUAGES made. MEASURE the fuel pressure with the fuel tank FULL. MEASURE the fuel pressure when the fuel tank is HALF full. If there are differences, new theories can be produced.


#7

Thanks for all the feedback. Now that you mention it, I have noticed that the fuel pump is much quieter than in the past, having gone from a quite noticeable hum to quiet. A vacuum problem does make sense also. I will try loosening the gas cap and seeing if the problem continues at the same fuel level.


#8

Try leaving the gas cap loose, drive it, and see what happens

I’m not positive when Dodge went to OBDII with this vehicle but if it’s so equipped, this would set a CEL for evap leak. You probably already considered this in your answer. Either way, an alternative is to drive it until the problem occurs, pull over and remove the cap with the engine still running. A larger than normal whoosh of air being sucked into the tank and the problem going away would indicate a venting problem or weak FP without having to mess around with inadvertant CELs or running with the cap loose.


#9

This is actually a known problem. The fuel tank breaths in as the fuel level drops through an activated charcoal bed in the charcoal canister under the hood. If the charcoal bed gets saturated (on some cars overfilling, adding more after the pump stops, can cause this), the tank can no longer breath in. In that case, as the pummp pulls gas from the tank a vacuum forms in the air space. This vacuum can make it hard for the pump to draw gas out. In addition to your symmptoms it can cause premature pump failure.

The next time this happens, remove and replace the gas cap. If you hear a whooshing sound and the symptoms disappear, then suspect a saturated canister.

By the way, if this gas cap test does not work it is possible that the fuel pump is weak. It’s possible that the pump requires the “head pressure” from the gas to maintain enough line pressure. “Head pressure” is the weight of the gas pushing the fuel up into the pump, essentially assisting the pump in pressurizing the system.