Intermittent Gas Flow Problem

[supertack]

I just had my second such incident of what I believe is some sort of gas flow problem. The first time I got it, my gas light had just came on as I pulled into work. I figured I get gas on the way home; however, when I started to drive home, the car hesitated constantly, like it wasn't getting enough gas, then the 'check engine' light came one. I stopped & got gas & the problem and light went away. Then yesterday, I had the same problem after starting the car on my way home from work again. This time a had a little over 1/4 of a tank of gas. I stopped at the nearby gas station, turned off the car, let sit 2 minutes & started back up to find the same problem. I then put in more gas, & the problem went away. The second instance came over a week after the first & both times the 'check engine' light came on, then reset itself after I got gas. I've had thoughts from a faulty gas gauge to clogged fuel injectors, any ideas before I take it in & get the fault code read?

Thanks.

[n.10.z]

I had a simillar problem several years ago. Every time I'd get low on fuel the car would start missing and hesitating and just generally running awful. After I'd fill it back up, it'd be fine. After the second time, I took it in to have it looked at. The diagnosis was that I'd either gotten some bad gas from somewhere or had somehow otherwise gotten water in the fuel. The mechanic had some stuff that he poured in to dry out the water, and all was better. Don't know if it's the same thing, but sure sounds familliar.

[Dave at Pelican Parts]

Yup. Could also be dirt or rust inside the gas tank. Older cars with metal fuel tanks are known for the rust problems, but dirt can get into any tank eventually.

--DD

[supertack]

So what can be done to fix rust/dirt in the tank? I've had the car almost (2) years, & this is the first time I've seen this.

[Dave at Pelican Parts]

In the old Porsches (and VWs and such), we pull the tanks and either clean them and re-line them ourselves, or have a shop do the cleaning and relining. Not sure how difficult that is with a newer Bimmer.

I'm not sure what I'd do in your place. I suppose I'd first verify that fuel delivery is actually the problem, then I'd start trying to inspect the tank. Isn't there a fuel pump inside the tank of these cars? If so, then you can pull it out or open up its access hole and check the tank through that.

--DD

[blkongry]

Man, I really doubt there is dirt or corrosion in your tank... pretty remote on a newer Beemer unless you were doing something wrong... and I've seen pics of your car... you keep it tight. It really sounds like water in the gas. Fuel and water are immicible, meaning they can't mix. So, the gas floats and when pick-up gets low enough, you start to pick up water. The way to get it out is to either mix in a small amount of dry Ethanol or go get some off the shelf 'fuel drier'. What they do is mix with the water (Ethanol and other grain alcohols are miscible with water... otherwise your Whiskey Sour would separate), difuse its concentration, and carry the water through the engine in the form of trace vapor. It really sounds like condensation... I'd go after something like this: Pyroil Isopropyl fuel drier first.

[supertack]

"So, the gas floats and when pick-up gets low enough, you start to pick up water."

What do you mean by this? I don't understand how I could have gotten water in my gas tank. What's the designed application for that product you mentioned above? Thanks dude.

[blkongry]

When gas and water are put together, they don't mix... they separate, and because the density of gas is less than water, the water sinks to the bottom, and the gasoline sits on top. If you looked at a cut-away from the side of a fuel tank with gas and water in it, you'd see a bottom layer of water, and a top layer of gas.

As far as the fuel pump 'pick-up', many tanks have a floating pick-up that moves with the gas. This is so when you go around a hard corner, or up/down a steep embankment, you don't starve out the engine. I don't know about BMW's design, but I do know there is some strange baffling in there and I presume the fuel pick-up system is similar. With that said, the system picks up fuel from the top... as you use up fuel, the level goes down. If you have a lower layer of water in your tank, the pick-up eventually starts to suck up the water.... and then you get the chuggin' and stalling.

Now, many people say you get water in your tank from condensation, which I think is crap. I mean, your tank is sealed for the most part. You'd have to be in a tropical climate with massive temperature changes and an open gas tank to really get any condensation in it. Where you get the water is from filling stations. Old stations have leaky tanks that can pick up rain water, or they don't seal them closed when the tankers fill them and water seeps in... what ever the reason, that is probably where you get it. If you are getting the tail end of the main tank at a gas station, you could be picking up a lot of water. I don't know if they have any kind of sensor to prevent this, or if they just pump whatever the hell is in their tanks (check out this little story http://abclocal.go.com/wpvi/news/07262001_nw_gas.html ). If your problem is showing up at 1/4 tank... dude, that's a lot of water in your tank. I think there should be a drain plug somewhere on the tank (some one jump in here if you know).

The stuff I posted is a dry alcohol based substance... it makes it so the water and gas can mix, the water gets diffused, and gets burned out (the water passes as vapor). With a 1/4 tank of water, this stuff isn't going to cut it.

If I were you, before you do anything else, go get one of those cheezy little siphons... the ones with the long tube and the squeeze-bulb on it. slide the tube as far down to the bottom of your tank as possible. Suck out the fuel into a clear container. Let it sit and see if you see two layers form (or see if you see anything else like brownish tint, dirt, whatever). If you don't see a difference, you may have just pulled straight water (depending on how much water you have). Try pouring some good gas (on top of what you pulled out of your tank) in the container and then see if two layers form. If you've got 1/4 tank of water, that's like 4 freakin' gallons of water. If you really do have this much water, you may have got a deal like that article link I threw in here. Not much you can do but get that tank drained. If you can truly get down in to the tank with a shiphon hose, you can use a good electric or hand pump (not that stupid little bulb thing) to pump out as much of the tank as possible. Fill it with clean gas, then throw in some of the fuel dryer and that should clear it out. Either way, you've got some checking to do... good luck man.

[n.10.z]

The only way siphoning the gas into a jar to see if it separates is going to work is if you get to the bottom of the tank. I really don't know what the chances you'll be able to do that with a bulb type siphon are, but I wouldn't personally be optimistic that I was really getting to the bottom. Having said that, I don't have a better suggestion of how to determine how much water is in there. I do agree that the chances of it being anything else (i.e. dirt or rust) are pretty slim no older than your car is.

I worked at a gas station for a bit and the one I worked at was pretty modern. There were no sensors to gauge water in the tanks. There IS some paste that you're supposed to use daily when you stick the tanks to see how many inches of fuel is there. The paste is supposed to indicate the presence of water. I worked at this station for about 6 months and was one of the people responsible for sticking the tanks. In the time I was there, I never used the paste, never was told to or taught how to, and to the best of my knowledge, noone else was using the stuff either. I'm going to go out on a limb and say that NOTusing the stuff is probably the norm at most stations. Sticking the tanks really isn't that fun a job to begin with, but that's the only way to accurately "inventory" how much gas you actually have in the underground tanks, so it's a necessary evil. However, using the paste is something you can get around. I can't say with any certainty that this is the case at most filling stations, but my gut instinct says that it is. Under-payed quickie-mart employees are NOT the most motivated people I've ever known.

Also.. and I don't know that I've ever known a station to get busted for this.. I've heard rumors of different stations watering down there gas. (Gas is expensive, water's cheap.. it all comes down to profit) Now, it would stand to reason that if you frequently filled up at a station that was mixing a little H2O with their gas, eventually you'd get enough at the bottom of the tank to start causing a problem.

If it were me, I'd try the fuel dryer first and see if that took care of it. Worst case scenario: you'd still be exactly where you are now. Best case: it'll solve the problem and you won't have to worry with it anymore.

Good Luck!

[supertack]

You guys are frickin killin me.

[Geno325is]

Originally posted by supertack
You guys are frickin killin me.

So whats the update ? Did you pull the code from the CEL you got?

[supertack]

Nothin, problem hasn't come back, so I didn't get the code read.

[blkongry]

So, you just gonna keep it above 1/4 tank and call it good?

[supertack]

No, I'm gonna let it get low enough for the light to come on, then see what it does. If the problem doesn't come back after doin that I'm gonna assume what ever contaminated the fuel is gone. If the problem persists, then I'm gonna get the code read & maybe try your fuel drier additive.

[Dave at Pelican Parts]

The additive can't really hurt... In fact, in some areas of the country ethanol (that's what dry-gas is) is already added as a part of the mixture of stuff that is gasoline. It's not so great in large amounts, IMHO, but in small ones isn't going to do any real harm.

--DD