RE: bog, stumble, stall, recover
 

Ron: (and anyone else still reading this saga)

I would consider it a rough running/misfire, almost to the point of not running at all. It is a serious bogging, stutter, close to stall, shaking type of misfire. The last time it was running so poorly, I swung around with a U-turn, let it set a second to compose itself from the turn, and slowly went back to a near gas station (Shell). I had actually wondered about bad fuel that does not show itself until the tank is low. The theory being that the good fuel sinks to the bottom and is picked up by the pump, while the contaminated fuel separates and floats on the top only to show itself as the good fuel is used up. The only hesitation that I have with this theory is that I judiciously buy from the same two stations, both top tier gasoline, Chevron and Shell. Of course, anyone can get a bad delivery though in their underground tanks. It almost acts as a floating diesel fuel. I will definitely investigate this thoroughly. I hope I can get the tank sufficiently low this time before trying to siphon all of that out.

I also should have mentioned that I ran a bottle of Techron Fuel Injector cleaner in the tank as soon as the problem first appeared. No help there, and I have had very good luck with this brand of cleaner in the past (contaminated flutes on the intake valve(s) of a Toyota Camry cleared right up).

Do you have an idea what the fuel pressure regulator may be seeing on a low tank? I read the manual and it seemed that the regulator opened when there was a disparity between fuel pressure and manifold pressure, but I can’t tie that into the lower fuel in the tank correlation, especially since the tank seems pressurized as evidenced by the “whoosh” when removing the filler cap.

This will be interesting. Thanks again Ron, your approach is both logical and intelligent, and I appreciate both.

Ed Fisher
Dallas, Tx

RE: bog, stumble, stall, recover
 

Yeah, I guess the best fit is contaminated fuel, particularly fuel contaminated with water (or some aqueous solution) as earlier suggested by mk. I think that gas and diesel fuel would be fully miscible, so this would not fit as well. In the former case, water is more dense than gas and therefore would be at the bottom of the tank.

Here's a possible scenario:
When the tank is full of gas, the fuel pump draws only gas, which is in vast excess over the small amount of water at the bottom of the tank. As the gas level falls in the tank to 1/4 full, there is a much smaller amount of gas mixed with the same amount of contaminant water and, in addition, the lower total fluid level permits more sloshing and mixing of the two fluids, allowing uptake of water by the fuel pump and causing engine bogging.

RE: bog, stumble, stall, recover
 

I have found the definitive fix for the problem of bogging/stalling when the fuel level reaches below somewhere under ½ to ¼ of a tank-full of gasoline. The fuel pick-up screen, or in tank fuel filter had detached from the fuel pump. The slip fit of the plastic components would not adequately hold the filter in place, so I used an epoxy called ‘tank repair’, which is two-part, to adhere the plastic elbows/fittings used for the filter to pump pickup. The car now runs down to 1/32 of a tank with no problems.

My theory: air bubbles from sloshing and low fuel could get into the orifice for the fuel pick-up and cause the sputtering/bogging/stalling conditions. The bubbles are more pronounced and closer to the pickup when the fuel level is low. Even with the in-tank baffle in place and secure, the small bubbles in the fuel are picked up by the pump inlet. The fuel filter, with its very small mesh screen, acts as a sieve to keep the bubbles out of the pick-up tube and therefore out of the fuel circuit, which of course includes the injectors. Air bubbles are simply too big to make it past the screen.

Thanks for reading, and thanks to Ron J for sticking this out with me.

RE: bog, stumble, stall, recover
 

Nice fix. Congratulations. Did you happen to shoot any photographs of the filter/screen so that you could post them for others to see?

RE: bog, stumble, stall, recover
 

Ron:

I did not get any pictures, actually I never thought of it, but I will know better for next time. It is all pretty straightforward once you get the pump out. I fished out my filter from the bottom of the tank with a pair of forceps and when test fitting I could see that it was a loose fit. I believe my pump had been changed out by the previous owner, and just the motor was replaced which necessitated removing the screen and putting it on the new motor/pickup. This was probably where the problem originated. Anyone replacing the pump would be advised to epoxy the filter/screen to keep it in place.

Thanks again Ron.

Ed

This really should be a sticky post
 

Ed,

First, let me congratulate you on your fine detective work and perseverance in trying to isolate your issue. Ultimately this led you to your problem source and solution.

Second, others might have this issue in the future and I'd hate for them to have trouble finding your solution.

Third, would you be willing to start a new thread, copy some of your descriptions and then your solution you posted here at the end? that way, no one will have to look at 3 pages of posts b/4 seeing the solution. Perhaps, label the subject as Problem Solved:...

Lastly, would the mod be willing to post this as a sticky or under the "Look here first" section?

Thanks.

RE: This really should be a sticky post
 

I would be willing to start the thread, and post it as a 'lessons learned', or 'solved', of something as such. I don't know about a sticky, as this seems to be a rather isolated occurence, but I will let others decide about that line of reasoning.

I will also add that a 'problem solved' section is a good idea. After a search, I read pages and pages of someone chasing a stumbling/bogging problem and the fix/solution was never posted, not even at the end of those several pages. It was, admittedly, very frustrating.

Thank you for the kind words.

Thanks for posting all your info, Ed.

I am having the same issue with my 99 Civic EX. It will bog down, jerk, and come close to stalling while I try to accellerate while under 1/2 tank of gas. I had it at a Honda specialistist for diagnosis/repair yesterday. So far I believe plugs, distributor wires, and some other electrical things have been changed out, to no avail. I have a return diagnosis appt. Monday and will be taking a copy of your fix and problems for them to look over. I Techron'd last night as well as filled up, so maybe my problem won't duplicate until I get under 1/2 tank again.

I think you likely have the solution though and again, thanks for posting.

Thanks for the post. I have a similar problem but is very intermittent but never really paid attention to the gas tank level when it happens. It happened last night and my tank was at 1/3 full. However, it may have been full at one time but not really sure because I wasn't paying attention to it. I started a thread but didn't update it because problem is very intermittent. In fact I went through two gas tanks and didn't really sputter to bad, just a little unresponsive to 1st or 2nd gear acceleration a couple times.

Regarding the new posts on the stumble, stall, recover. If you remove the rear seat of your car and lift the cover on the tank you can easily see the screws holding the fuel pump to the tank. Seriously, the hardest part of this was removing the rear seat as I didn't know there was a hidden screw. All in all, 30 minutes should reveal whether your pickup tube/screen has become detached from the pump. In my case, the pump had been replaced by the previous owner. Replacement pumps are motor only, which means the pickup tube from the original pump must be used on the replacement. It is a loose fit when re-used. Best of luck.