'03 Baja bucks after fillup

[jseabolt]

I have a 2003 Baja, 5 speed, 72K miles. This all started about 2 or 3 years ago. I first thought it had something do with this E10 garbage but I'm starting to wonder if it has something to do with the fuel evaporative system.

 

Sometimes the car will starting bucking slightly between 2K to 3K RPMs under part throttle. Under full throttle or idle, it runs smooth.

 

Sometimes this happens if the car has sat for a couple of weeks in my garage at half a tank. Then after about 30 minutes of driving it starts running smooth. As if the fuel being sent back to the tank stirs up any E10/water that might have sank to the bottom.

 

I tried running the tank down to where the light kicks on in an attempt to get rid of any "bad gas" then topping off with fresh gas but this doesn't seem to do any good.

 

I also tried topping the last couple of tanks off with pure gas so I'm not sure if E10 really has anything to do with it.

 

When the bucking is at it's worst is after topping off the fuel tank. Then once I drive the car for about 5 miles, the bucking goes away. Once again, the car idles smooth and runs fine under full throttle. It's part throttle when the bucking occurs.

 

One day when the bucking was occuring at half a tank, I loosened the fuel cap and drove around. The bucking seemed to have went away. The check engine light that is suppose to remind you that the fuel cap was off never came on!

 

Also when removing the fuel cap, I never hear a swoosh sound like there is either too much positive or negative pressure.

 

And the OBD II system is not picking up any codes.

 

Otherwise the car seems to run fine 95% of the time.

 

Any ideas?

 

 

 

[Prwa101]

I got major bucking when my front O2 was bad. If i unplugged it, it ran fine. did that until i got the new one. Mixture of bad gas and bad readings from the O2 i could see causing this. 

[1 Lucky Texan]

your symptoms don't theoretically support this, but you might inspect the fuel pump's cap and o-ring.

 

 

http://www.ultimatesubaru.org/forum/topic/139928-2003-h6-30l-sudden-engine-stop-no-start-fuel-delivery/?hl=+fuel++pump++o-ring++cracked

 

 

http://www.ultimatesubaru.org/forum/topic/129528-fuel-pump-leaky-o-ring-other/?hl=+fuel +pump +o-ring +cracked

 

 

 

you might run a bottle of Techron, or maybe SeaFoam through a coupla tanks.

 

cars that sit unused are also at risk for spiders to clog-up carbon canister drain hoses.

Edited May 29, 2014 by 1 Lucky Texan

[Fairtax4me]

I would suspect a stuck open Evap canister purge control valve.

Easy to test. The valve is under the intake manifold on the passenger side. There is a vacuum hose running from the area of the throttle body to the valve.

Remove the hose from the throttle body and try to blow into it. No air should flow. If air flows the valve is stuck open, usually due to carbon from the evap canister.

 

If you have a habit of topping off the tank, pulling the trigger on the fuel nozzle to try to squeeze in that extra 1/2 gallon of fuel, this has likely damaged the Evap canister carbon structure due to flooding it with liquid fuel. The canister will need to be replaced.

[jseabolt]

I got major bucking when my front O2 was bad. If i unplugged it, it ran fine. did that until i got the new one. Mixture of bad gas and bad readings from the O2 i could see causing this. 

 

Actually about a couple of years ago the check engine light kicked on and my OBD II code reader says the front O2 sensor was bad. I replaced it and reset the code and it hasn't kicked on since.

[jseabolt]

I would suspect a stuck open Evap canister purge control valve.

Easy to test. The valve is under the intake manifold on the passenger side. There is a vacuum hose running from the area of the throttle body to the valve.

Remove the hose from the throttle body and try to blow into it. No air should flow. If air flows the valve is stuck open, usually due to carbon from the evap canister.

 

If you have a habit of topping off the tank, pulling the trigger on the fuel nozzle to try to squeeze in that extra 1/2 gallon of fuel, this has likely damaged the Evap canister carbon structure due to flooding it with liquid fuel. The canister will need to be replaced.

 

I'll check that. I'm not one of those people that try to overload the fuel tank, but here has been times when the pump would kick off 10 tens trying to fill the tank and I'd have no idea if the tank was even full. I suppose a better method would be to look at the fuel guage before I filled it up and if it was at half a tank, not put anymore than 8 gallons in it. Or 7 at the most.

 

We don't have an inspection system where I live. If the canister is bad, can I just remove it and replace with a piece of hose? Or will this cause the check engine light to kick on? Any way to get around this?

[jseabolt]

The other day my Subaru's check engine light came on after startup then went out on the way home. I hooked up my code reader and it threw a "air idle control valve" code. Any correlation between the bucking after fill up and this valve?

 

This car sometimes throws missfire codes during warmup. Then the light goes out. It may throw a missfire code then I can clear the code and it won't happen for 2 years.

 

I changed the fuel filter the other day and drove it this morning to work. It seems to be running much smoother. I won't know until I top the tank off on the way home to work to see if the new filter fixed the problem.

 

This was the original filter and had 72,000 miles on it. I probably should have changed it sooner but didn't realize that there was more trash in gasoline than I suspected.

 

I have a 1981 Trabant 601 (as well as other vehicles) with a gravity feed fuel system and a 1/4" fuel line. I used a small stone type fuel filter from a lawnmower and after 500 miles, the filter became restricted to the point the car wouldn't run at full throttle and started backfiring. So I found a filter at Autozone 5 times as large and it runs much better now and no backfiring or loosing power.

 

http://s222.photobucket.com/user/turbofiat/library/#/user/turbofiat/library/Trabant?sort=6&page=0&_suid=140456040222605783692592038441

 

By the way. If you let your Subaru sit overnight, the fuel pressure will bleed off to nothing. So there is no reason to pull the fuse and let the engine run or do anything special before changing the filter.

 

I'll see how it goes and report back.

[Fairtax4me]

Yes it can be connected. If the purge valve is stuck open it creates a vacuum leak which will throw off the IAC adjustment.

 

Misfiring during warm-up is often due to fouled spark plugs. How old are they?

[jseabolt]

Yes it can be connected. If the purge valve is stuck open it creates a vacuum leak which will throw off the IAC adjustment.

 

Misfiring during warm-up is often due to fouled spark plugs. How old are they?

 

I replaced the plugs at some point in time but can't remember. 60K miles maybe? I also installed new plug wires.

Edited July 5, 2014 by jseabolt

[jseabolt]

I would suspect a stuck open Evap canister purge control valve.

Easy to test. The valve is under the intake manifold on the passenger side. There is a vacuum hose running from the area of the throttle body to the valve.

Remove the hose from the throttle body and try to blow into it. No air should flow. If air flows the valve is stuck open, usually due to carbon from the evap canister.

 

If you have a habit of topping off the tank, pulling the trigger on the fuel nozzle to try to squeeze in that extra 1/2 gallon of fuel, this has likely damaged the Evap canister carbon structure due to flooding it with liquid fuel. The canister will need to be replaced.

 

 

I have not had a chance to investigate this. I'm trying to figure out which hose (in the mess of hoses) under the hood.

 

There are a couple of hoses that are attached to a bracket that hooks to the fuel filter. But you said this was on the passenger side.

Edited July 5, 2014 by jseabolt

[jseabolt]

Update. I topped the fuel tank off on my way home from work and no bucking. It seems odd this bucking condition after a fillup would have any correlation to topping off the fuel tank. Although the bucking has happened at half a day and when the low fuel light were on.

[1 Lucky Texan]

OK, anyone else think this could be a problem with the jet transfer pump?

 

when it starts bucking at half tank, opening the fuel tank, closing it, test for bucking. If it still bucks, try adding just 1 gallon and testing again.

 

I think running some SeaFoam or maybe Techron thru a tank or 2 of fuel might have a chance at cleaning the jet pump out.

 

But, I'd say evap issue is also a possibility.

 

Ever have to 'nurse' fuel into the tank? like it won't accept the fuel quickly enough? Evere have any 'whoosh' from pressure or vacuum when you open the tank?

[jseabolt]

OK, anyone else think this could be a problem with the jet transfer pump?

 

when it starts bucking at half tank, opening the fuel tank, closing it, test for bucking. If it still bucks, try adding just 1 gallon and testing again.

 

I think running some SeaFoam or maybe Techron thru a tank or 2 of fuel might have a chance at cleaning the jet pump out.

 

But, I'd say evap issue is also a possibility.

 

Ever have to 'nurse' fuel into the tank? like it won't accept the fuel quickly enough? Evere have any 'whoosh' from pressure or vacuum when you open the tank?

 

No isses with nursing the fuel into the tank, however I do with my '06 Explorer. No whosh sound when I open the cap on the fuel tank.

 

Got a new issue that cropped up and maybe related. The check engine light keeps coming off after a cold startup. It's the idle air auxillary valve or something like that. The device mounted in the throttle body. I can clear the code and the light goes out for a few days then comes back on after a cold startup like this morning. So far I had not noticed any issues like stalling or a lumpy idle until this morning when I stopped at the bottom of my driveway.

 

Even though this is a fuel injected car, it's 11 years old and has almost 75K miles on it. Of course it's going to hickup on a cold start. Looks to me like the ECU would ignore any hickups until the car has ran a least for a couple of minutes. I think it's supposed to ignore any signals from the O2 sensors until a certain temperature to give the converter a chance to heat up but why not the idle auxillary valve?

Edited July 15, 2014 by jseabolt

[Fairtax4me]

The ECU doesn't really ignore the O2 sensors. They don't create any signal until they get hot. Thy need to be about 600°F before they start sending an accurate signal to the ECU. The ECU watches the signals the whole time, it just can't do anything with that info until it becomes stable after the sensors heat up.

 

The idle air control valve doesn't need to heat up. It's always under the command of the ECU. The idle valve opens and closes and adjusts constantly to set the idle speed. When the engine is cold the idle control valve is opened up to increase engine speed during warm-up. As the engine warms, the idle speed starts to lower because the idle control valve is closing.

It's common for the IAC valve to get dirty or gummed up with carbon and crud from the PCV system. When this happens the valve may not move smoothly, or it may not be able to move along its full travel and get jammed. This would cause the valve to stop responding to the ECU commands to either raise or lower idle speed, and will set a code for Idle Control.

 

Vacuum leaks will also cause idle control codes, because the idle valve may move all the way closed and still the ECU cannot achieve the target idle speed. The ECU doesn't have a way to know that the valve is all the way closed, it just knows that its not responding to commands to change the idle speed.

 

A stuck open evap purge control solenoid valve is a vacuum leak.

[1 Lucky Texan]

sounds like the IACV could use cleaning at least. I think I've seen one or 2 youtube vids on it. seems fairly easy. Dunno if a new gasket/seal is required though.

[jseabolt]

sounds like the IACV could use cleaning at least. I think I've seen one or 2 youtube vids on it. seems fairly easy. Dunno if a new gasket/seal is required though.

 

Yeah, I've seen some photos where a guy cleaned one out on WRX that had a coolant passage but mine looks like a sensor that goes into the throttle body with two nuts. Here is a photo from a YouTube video:

 

 

 

Due to filters on my company's internet, I can't watch it but will try to watch it when I get home. Is there anyway to clean the one on my Subaru without having to replace it?

[1 Lucky Texan]

someone with more experience might answer.

I'd say your only other hope might be a SeaFoam Spray treatment - probably not a waste of time even if it doesn't help the problem.

 

 

[jseabolt]

Update:

 

Since the check engine light has come on a couple of times, both times it's the idle air control valve. I have since reset the code and it has yet to come back on since this past summer. Actually the ECU reset itself the first time after a couple of days.

 

Anyway I changed the fuel filter a couple of months ago. No doubt it was probably past due at 71K miles. I'm not sure if I noticed an initial improvement or not. Then back in December I noticed that the engine was struggling a bit to turn over below freezing. Hope it's not my 7+ year old battery about to crap out! So I cleaned the corrosion off one of the battery posts (fixed that problem). Having been unplugged for more than 30 minutes (I usually take my time) it seemed to reset the ECU's memory.

 

I have since topped the fuel tank off two or three times and have yet to experience any bucking. Nor have I noticed any bucking at 3000 rpms in 3rd gear when this problem first occured. I don't know if that was the "fix" or not.