jseabolt Posted September 2, 2015 Share Posted September 2, 2015 I thought I already posted this a couple of times but this thread seems to disappear. My 2003 Baja, 5 speed, 76K miles. About two years ago my Baja started this bucking condition, usually around 3K RPMs in 3rd gear. I replaced the fuel filter but it didn't seem to make any difference. The bucking is worse after topping the fuel tank off but can buck when the tank is near empty. When it does buck after topping the fuel tank off, after 5 miles, the car runs smooth. I usually try to run the tank down until the low fuel light kicks on to get that crap (ethanol) out of my tank then start with fresh fuel. I've tried treating the fuel with Stabil ethanol treatment which is supposed to keep any ethanol/water/gas suspended. I don't know if it works or not but it doesn't seem to help any. In case your wondering, I never keep pumping into the tank after the pump kicks off. What does the fuel level have to do with the bucking? I tried driving around with the fuel cap off to see if it makes a difference. I couldn't tell. No check engine light either. But I have not hooked my OBD II read up to the car in awhile to see if there are any stored messages. Any ideas? Link to comment Share on other sites More sharing options...
gbhrps Posted September 2, 2015 Share Posted September 2, 2015 jseabolt, Just a thought, I don't know for sure since I've never had a fuel pump out of any subie I've ever owned. Some fuel pumps that are inside the gas tank of modern cars have a filter on the intake tube. Is it possible that yours could be partially plugged, and at various fuel levels the unit sucks up floating debris to momentarily cut the fuel supply? Link to comment Share on other sites More sharing options...
jseabolt Posted September 2, 2015 Author Share Posted September 2, 2015 Well that's possible. For some reason I keep thinking fuel is getting sucked into the engine through the fuel evaporative system causing it to run lean at times. So I'm not sure if it's a fuel starvation issue or too much fuel at times issue. Link to comment Share on other sites More sharing options...
1 Lucky Texan Posted September 2, 2015 Share Posted September 2, 2015 symptoms aren't a 100% match for a cap/o-ring problem but, I personally feel everyone that wants maximum reliability from a 2nd gen legacy vehicle should inspect the cap on the fuel pump assembly. http://www.ultimatesubaru.org/forum/topic/130624-2000-outback-fuel-pump-assembly-metal-cap-is-broken/ Link to comment Share on other sites More sharing options...
jseabolt Posted September 3, 2015 Author Share Posted September 3, 2015 (edited) I don't know what's wrong with this computer but the copy and paste function does not work! When I try posting a breakdown of the fuel system and the photo CYN_Dave posted from the link you posted using the image button, the computer locks up so I have to hit reload. What is this problem with the fuel pump cap your referring to? When the cap is broken what does this do? Cause the tank to not be under atmospheric pressure and the check engine light kicks on? Causes air to be sucked into the fuel system? I'm assuming the part in question is the metal piece on the bottom of the fuel pump with the ground wire connected to it. By the way. My "03 Baja has the fuel filter mounted in the corner of the engine compartment. It's not mounted in the tank. If that matters. If I had to say when the car starts this bucking: Every time it's after topping off the tank but the problem goes away after 6 miles. Reason being I monitor my odometer and notice it starts running normally at the 6 mile mark. 10% of the time it happens when there is about 1 to 2 gallons in the tank. Very seldom it may happen at half a tank but very seldom. I have not driven the car with the fuel cap loose directly after topping off the tank. If that somehow effects the bucking, what would that tell me? I somehow think that the reason the bucking occurs worse after topping off the tank is the negative pressure inside the fuel tank is worse when full than say half a tank. Sort of like topping off the tank on a lawnmower with the vent closed on the fuel cap. Then after a few minutes the tank builds up negative pressure and the engine stalls. But not as bad if the tank was near empty. In other worse more of an empty void inside the tank. If any of that makes any sense. Am I on the right track or looking in the wrong place? Otherwise I'm never had the engine stall on me. Edited September 3, 2015 by jseabolt Link to comment Share on other sites More sharing options...
1 Lucky Texan Posted September 3, 2015 Share Posted September 3, 2015 so, you actually detect a vacuum when you remove the gas cap? seems like an evap hose may be clogged and, until the purge solenoid opens, you have low fuel supply. I suppose hooking a fuel pressure gauge up that you could monitor while driving might prove that theory. probably need to find the evap DRain hose. On many systems, there is a hose attached to a 2-way valve. It lets air out of the tank when fueling (or maybe when pressure builds up as gas warms?), but is supposed to let air in as fuel is used-up. probably a hose about the size of your thumb, coming from the charcoal canister area. Some cars like Mazdas attract spiders that clog evap hoses. i have heard of mud from off-roading clogging the hose. I suppose the valve could be bad...... Link to comment Share on other sites More sharing options...
jseabolt Posted September 7, 2015 Author Share Posted September 7, 2015 No, I don't detect any vacuum or positive pressure when I remove the fuel cap. Link to comment Share on other sites More sharing options...
Fairtax4me Posted September 7, 2015 Share Posted September 7, 2015 (edited) Could be the evap purge solenoid is stuck open. Find the evap line where it comes up to the manifold by the other fuel lines. It's usually the bottom hose and the smallest diameter. Disconnect the hose and plug it shut or pinch it with some vice grips. Start the engine and see if there is vacuum at the metal line. Just stick your finger over it for a few seconds and you'll be able to tell. There should be no vaccum. If there is, it means the purge valve is stuck open. If you have no vacuum there plug off the metal line and take the car for a 10-15 minute drive and see if it starts acting up. Check again for vacuum on the metal line after driving. Sometimes the valve may stick open after getting warm. Reach under the dash and connect the two green test mode plugs, turn the key to On. Find the evap purge solenoid under the #3 intake runner and see if it clicks on-off in about 1 second intervals. It it does click, find the vacuum hose going to it and see if you can blow air through it. Air should flow then stop in relation to the click on-off. If air flows all the time the valve is stuck open or there's something jammed in the valve seat, and should be replaced. If it doesn't click its probably stuck open, replace it. Edited September 7, 2015 by Fairtax4me Link to comment Share on other sites More sharing options...
jseabolt Posted September 7, 2015 Author Share Posted September 7, 2015 Thanks! I currently have my 68 Ford out this week and my Subaru in it's place. I printed off your instructions and I'll check it and get back with you. I know that sounds like a big deal but I have six cars in my garage and have to strategically park them in order to fit them all in. Sometimes I have to move two of them just to get one of them out! Link to comment Share on other sites More sharing options...
Fairtax4me Posted September 7, 2015 Share Posted September 7, 2015 Sounds like a fun garage! Link to comment Share on other sites More sharing options...
Recommended Posts
Please sign in to comment
You will be able to leave a comment after signing in
Sign In Now