Bad fuel line

  • 3.6L
  • 170,000 MILES
We have found that there is a hole in the fuel line somewhere, before it would start and run alright until the engine heated up, then it would start dogging and sputtering and at a stop light when at an idle would just simply shut off. It has sat for awhile, we would start it about every 3 months or so, this last time we started it to move it it seems that the leak has gotten a lot worse because it took 1/4 tank of fuel to move it from one side of the yard to the other with a trail of fuel behind it on the ground. What else could it be besides a leaking fuel line? And what else should I replace besides the fuel line in order to make sure I'm getting the proper fuel flow and best possible gas mileage?
Do you
have the same problem?
Sunday, August 29th, 2021 AT 3:58 PM

1 Reply

This is a return-type fuel system. The pump in the gas tank sends the gas through the filter on the right frame rail right ahead of the right rear tire. From there it runs up next to the right strut tower. That is a metal line that can rust out. A rubber hose runs from the end of that line to the metal fuel rail on the engine. One on each side feeds three injectors each that are plugged into those rails. The front rail also has the fuel pressure regulator on the end. You'll see a small vacuum hose attached to that.

The pump produces fuel volume that's real much higher than what the engine uses. About 99 percent of that volume goes through the regulator, then back into the tank. That line also ls rubber where it leaves the fuel rail and transitions over to the right strut tower where it connects to another steel line. That return line is smaller diameter than the feed line. This is another line that could develop rust holes.

Once the return line enters the tank, it runs down to the bottom, and around a bowl welded to the center of the tank. The returning gas leaves the end of that pipe, then flows up a ramp curved around the outside of the bowl. As it does, that flow draws in more gas from the tank to flow up and into that bowl to keep it full, even when the level in the tank is real low. There's a pick-up screen, or "strainer", often called a "sock", to filter the gas that is being sucked up by the pump. The pump and strainer sit in that bowl to prevent gas from running away while cornering or stopping abruptly when the tank level is low.

The common places for a leak to develop are the two rubber hoses by the right strut tower, then the steel feed and return lines, and finally, a rusted-out filter. I had all of those over the years on my '88 Grand Caravan. Both lines are connected the the tank with short runs of rubber hose too. Those don't develop leaks very often because they don't see the sun or the heat from the engine, and they don't flex and twist like the two up front do as the engine rocks. Of course the tank can rust too, but if a hole develops on the bottom, it will leak gas all the time. If the hole is on the top, you'll smell the fumes, but you won't lose much gas and it won't leave a trail. Leaks in the tank don't affect engine performance.

These systems typically run around 45 psi. One clue to the location of the leak is how hard it is to start the engine. That fuel pressure should hold for weeks. If the feed line is leaking, that pressure will drop off within seconds or a minute or two. The fuel pump runs rather slowly while cranking the engine, so it builds pressure back up very slowly. That pressure has to have enough time to get high enough for the engine to run. To say that a different way, you'll need to crank the engine much longer than normal for the engine to start.

If the feed line has a large leak like you described, chances are the engine won't run at all since fuel pressure can't get high enough. The better suspect with a real bad leak is the return line. There's no pressure in that line, and what's flowing in that line has little to do with how the engine runs. With a leaking return line, pressure in the feed line is still normal, so the engine still runs well. The exception is if the level is low in the tank, it won't be high enough to spill over into that bowl and keep it full. The pump might start sending air along with the gas, and that will lead to sputtering or stalling.

As a side note, remember that bowl has to stay full to keep the strainer submerged in gas. The returning fuel is what does that, until you run the tank empty. I know from experience that when I added gas to my '88 Grand Caravan, the gas I'm putting in exits the filler pipe and falls right into that bowl. I only had to add a quart of gas for the engine to start and run. That wasn't the case with my '94 Grand Voyager. That gas being filled missed the bowl and just went into the tank. For that and similar models, it takes a good five gallons of gas, (after running the tank empty), for the level to get high enough for some gas to spill over into the bowl. Once that happened, the engine would run, and the returning gas would keep the bowl full, so you could run it low again, like some of us do. It only took that five gallons to get the system started.

Another point of interest, unlike on many other models and brands, you will never solve a running problem on a Chrysler product by replacing the fuel filter. Except for diesel engines, they last the life of the vehicle unless they rust out. It's the strainers in the tank that become plugged or collapse and block fuel flow. Most commonly the symptom is the engine stalls when the largest volume of fuel is being pumped, which is during coasting down from highway speed. The engine runs best at higher speeds and when accelerating. That plugged strainer is a very elusive cause of this problem. For some models the strainer is about a $12.00 part that snaps onto the bottom of the fuel pump housing. For some other models, it is only available as part of a new pump / housing assembly.

The last place to look for a leak is next to each injector. They're plugged into the fuel rails with rubber o-rings. Some other models had a problem with those o-rings shrinking and leaking real cold weather. That wasn't a problem on the Dynasties, but I did run into two that had a cut o-ring. One was on a brand new car just delivered to the dealership. Typically the first symptom is the fuel smell. You have to look close to find the leakage because it's usually slow enough that the gas evaporates rather than leaving much of a wet area.

Do you have the 3.3L? I have a '93 Dynasty with less than 5,000 miles. I put another mile on it this summer. Otherwise it hasn't been started in over five years, and the gas is over ten years old. Still runs great and is so comfortable. Makes me remember why I bought it.
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Sunday, August 29th, 2021 AT 5:45 PM

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