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Jerry
Jerry, Master Mechanic
Category: Dodge
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Experience:  ASE Master tech, 30 years exp. troubleshooter, driveability tech
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I have a 99 ram 1500 5.9 4wd when I turn the truck off

Customer Question

Hello I have a 99 ram 1500 5.9 4wd when I turn the truck off sometimes I can hear the gas gurgling in the tank?
Submitted: 1 year ago.
Category: Dodge
Expert:  camerontech replied 1 year ago.

hi there

im cam, a licenced diagnostic tech.

there is a good chance it is just the fuel pump module releasing pressure when the pump is not running.

there is a pressure/ backflow valve inside the fuel pump module assembly, and these can leak pressure.

the only way to check this is to hook a fuel pressure gage up and shut the vehicle off. it should hold pressure.

I would not be too concerned about this if the truck is starting ok and not extended cranking.

monitor to see when you take the fuel cap off, if this stops, than this is just the tank into a vacuum from the purge valve and this is normal untill the tank equalizes pressures.

if its either of these, i would not be too concerned as long as it starts ok and the fuel cap is not excessive issues when removing

Customer: replied 1 year ago.
New fuel pump and it did it before and after and was a factory fuel pump replacement,
Customer: replied 1 year ago.
Truck has 225k hard miles on it and it is only recently this problem happened fuel pump failed replaced it and it still does it
Expert:  camerontech replied 1 year ago.

do you have any trouble codes stored in the evap system?

Customer: replied 1 year ago.
No codes and no evap leaks checked via smoke leak tamer and innova scanner
Customer: replied 1 year ago.
New rollover valve oem installed at time of fuel pump
Expert:  camerontech replied 1 year ago.

when you remove your fuel cap, does it sound like it has excessive vacuum?

Customer: replied 1 year ago.
No more than normal
Expert:  camerontech replied 1 year ago.

ok,

im going to open your question up for another tech.

sorry i could not help you any further, but another tech will jump in to assist you further

Expert:  Dodgerench replied 1 year ago.

Hi, this is Ed. Thanks for sticking with us!

Are there any symptoms besides the gurgling noise?

Cameron's thought about the fuel system reversion is completely valid, but it would also involve a very long crank time to replace the liquid fuel being pushed backward and into the tank.

Does the truck start easily after sitting with the gurgling sound?

Or does it take longer to restart, possibly with rough running at first?

And I have to ask; how sure are you that the sound comes from inside the fuel tank?

The truck is run hard and that's all good. Does it matter if the truck was driven lightly or not for the sound to happen?

Talk in a bit,

Ed

Customer: replied 1 year ago.
Starts no issues no matter how driven and when gurgling
Expert:  Dodgerench replied 1 year ago.

Thanks. I saw your response on my email notification but for some reason it hasn't shown up here.

So it starts OK when gurgling.... that strongly suggests that the sound isn't being caused by fuel reversion from a hot engine. It will always, always take longer to get an engine to start when vapor replaces liquid fuel.

What about engine heat, engine load or outside temperature when you hear the sound?

Does it happen only after the truck has been run hard or is it the same when just driven to DQ?

And... how certain are you that the sound comes from the tank?

Ed

Customer: replied 1 year ago.
100% positive it's coming from the tank put a stethoscope up to it and hear it in the filler neck when I take the gas cap off doesn't matter towing driving empty it does it all the time
Customer: replied 1 year ago.
Has a hd fan clutch on it and a heavy duty radiator and an additional remote mounted trans cooler so it never gets above 190* no matter the grade or weight
Expert:  Dodgerench replied 1 year ago.

Interesting. Taking a sound sample right from the tank is a great piece of info.

How soon in a drive cycle can you go before the noise happens?

Does it HAVE to be run hard?

Customer: replied 1 year ago.
Driven grandma or loaded down seems to not matter worse in the summer but still prevalent in colder weather short or long drive only time it seems to not do it is when it's on a low fuel light and I pull up to the tank
Customer: replied 1 year ago.
Pump sorry
Expert:  Dodgerench replied 1 year ago.

I guess that fits. Less fuel means less opportunity for bubbles to gurgle up through tank volume.

Is there an exhaust pipe that has been moved closer to the tank than it originally was?

Or the loss of a heat shield?

Customer: replied 1 year ago.
No sir does have headers and cat back exhaust but still all on factory hangers on the other side of the driveshaft in factory location
Customer: replied 1 year ago.
It's been to dodge and they had the situation occur and still could not give me an answer
Expert:  Dodgerench replied 1 year ago.

I'm running out of ideas myself!

Gurgling does suggest that vapor (or air) is being introduced below fuel level. The engine runs on vacuum alone, so unless you have a blower on the 5.9 I'm running out of ideas.

Give me a few minutes to agonize and I'll get back to you.

Customer: replied 1 year ago.
Hahahahah I'm in the same boat
Expert:  Dodgerench replied 1 year ago.

Dang, didn't help.

These units regulate fuel pressure from inside the tank and only send usable fuel volume forward. Gas isn't exposed to engine heat and returned like in the old days, so unless the fuel gets boiled and overcomes a check valve in the tank, it's not a possibility for the gurgling sound.

And you'd absolutely have trouble restarting the engine, so we can cross that off the list.

Another quick question.

Does the gurgling stop after you start the truck?

Not sure where that'll lead, but I'm running out of ideas.

Customer: replied 1 year ago.
Obviously couldn't tell u when driving but when I start the truck it still does it
Expert:  Dodgerench replied 1 year ago.

Ow.. Brain hurts.

I think you've already stated this, but for clarification purposes...

Does removing the gas cap influence the noise at all?

Customer: replied 1 year ago.
Yea normal sound u get from all vehicles
Expert:  Dodgerench replied 1 year ago.

Some hiss but it doesn't change the gurgling?

Customer: replied 1 year ago.
Same hiss and doesn't stop the gurgling if I leave the cap on or off the gurgling will continue some where between 10 and 20 min and eventually goes away have had this issue a long time doesn't seen to affect the drivability, I'd like to think it effects the fuel mileage but it's the 5.9 gutless gas hog and avg of 14 is prob the best it gets
Customer: replied 1 year ago.
I exhausted all my knowledge and thought maybe I'm not thinking outside of the box and that's when I turned to just answer
Expert:  Dodgerench replied 1 year ago.

Thanks. I'm still running the info but don't have a good answer at this point.

The hiss tells us that a pressure differential is being equalized. It can be from vacuum inside the tank or pressure being released-- both are possible with evaporative purge flow and heat buildup.

If you wouldn't mind taking more time, put your nose next to the gas cap the next time you have an opportunity to twist the cap when the tank is gurgling. If you smell fuel odor, it's a pressure release. If no smell is noted, it's likely vacuum and air is being drawn into the tank.

The difference in possibilities is great. If the tank is being cavitated, you may be boiling fuel at low temperatures due to the loss of atmospheric pressure. A release of gas fumes from the cap suggests that the tank is being pressurized from heat, but I can't identify the source at this point if that's true. It's most likely a cavitation problem, but it should stop almost immediately when the cap is cracked. Boiling from heat would likely get worse with loss of cap pressure and I'd expect the noise to increase at that point.

So... no, I don't know the answer. If you wouldn't mind taking the sniff test when convenient, I'd be interested in hearing the results. It would at least identify whether the tank is operating at a high or low pressure, which may make it possible to diagnose.

It's a weird one, I'll give you that!

Customer: replied 1 year ago.
Absolutely
Expert:  Dodgerench replied 1 year ago.

We're in agreement. Let me know what you find.

Customer: replied 1 year ago.
I did not receive an answer so why is it I'm being charged a week later 38?
Expert:  Dodgerench replied 1 year ago.

The last time we talked, we agreed that you would do a sniff test of the gas cap area and I've been waiting to hear back from you.

Customer: replied 1 year ago.
It's going to smell like gas cause it's a gas tank
Expert:  Dodgerench replied 1 year ago.

Not if the hiss is air being drawn into the tank rather than vapor rushing out. What I'm trying to establish is whether you have vacuum or pressure in the tank. You won't smell anything if it's vacuum.

Customer: replied 1 year ago.
It expels out no vacuum
Customer: replied 1 year ago.
The gurgling in the tank tells that answer says to me that there is air entering the fuel in the tank
Customer: replied 1 year ago.
not to be rude but it seems I'm repeating all the steps I have already taken, I understand u have to do a diag run thru to get the info to try and diagnos the problem but it seems we are both stumped seems I should get my 38$ back
Expert:  Dodgerench replied 1 year ago.

That's cool. There should be a tab to connect with JA customer service somewhere on your screen. They'll take it from there.

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