Subaru Outback Forums banner

Hesitation after fueling

17K views 14 replies 9 participants last post by  Akok subi 
#1 ·
02 5spd. After fueling the car will hesitate for 2-3 miles. Occasionally it will do it immediately when I'm pulling away from pumps but mostly when I get up around 30-40mph. It will do it for a couple miles then stop and wont happen for the rest of the tank. I have noticed that when removing the cap there is no pressure release like on other cars I've had. Could that have something to do it? I've replaced gas cap, fuel filter, plugs, wires since I first noticed it but with no change.
 
#2 ·
I have noticed that when removing the cap there is no pressure release like on other cars I've had.
Has there been pressure release with this car?

Tank pressure release when removing the cap is not correct with the current evaporative emissions control systems. The tank should be at a neutral pressure most of the time -- the exceptions are when the emissions control system is running through a self-test. At this time, the tank might be subjected to a small vacuum which checks for leaks, i.e. air coming in when it shouldn't. Air coming in would indicate a path for fumes to go out to the atmosphere, which is just what the systems are seeking to prevent.

When you fill the tank, do you "top up" after the nozzle goes off automatically? This is generally not a good idea, because raw fuel can get into the emission control charcoal canister. When the engine is running, the rich fumes from this fuel are drawn forward through the purge valve and into the intake manifold, where it provides an over-rich fuel mix. The purge valve normally opens only after the car is cruising.

Another possible cause is the purge valve is stuck open (full or partial). It should be closed when the engine is off. When filling the tank fumes from inside the tank are forced out to the charcoal canister by the incoming gasoline. The fumes are trapped in the canister, for recycling to the engine later when the purge valve opens. But if the valve remains open during filling, the fumes can travel to the intake manifold unimpeded, where, again, they will cause a rich fuel mixture and poor engine performance, especially when first starting the engine after a fill up.

I can't say that these are the cause of the hesitation, but the symptoms are consistent.
 
#3 ·
I can't say its ever had a pressure release so I guess that's good according to your info. I was just comparing it to a previous subaru and a 95 accord we have. Both did it every time you opened the cap.

When filling, I never top off the tank. Always stop when the nozzle shuts off. I'm not sure what the purge valve is. Is that something that is easy to access/test to see if its working correctly? From reading your description it sounds as if it wasn't working this problem should occur every time the car was started? That doesn't happen, its only after filling up the car. Maybe I should try just partially filling the tank and see if the same hesitation occurs.
 
#4 ·
this problem should occur every time the car was started?
Not necessarily.

When the car is just stopped and started in regular driving, but no fuel is being added, the tank is already at a more-or-less neutral pressure, so the gas fumes in the tank just stay there. It's when fuel is being added to the tank that the air inside, which is laden with gas fumes, has to be vented out somewhere. The design would have the air vented to the charcoal canister. The charcoal in the canister absorbs the gas fumes, and the remaining "clean" air is vented to the atmosphere. (This is the whole idea of evaporation emissions controls.) But if the purge valve remains open when the engine is off, the fumes have an alternate route out of the tank, and this is what can cause hesitation when the car is started after refueling.

A dealer, or well equipped mechanic, can use Subaru diagnostic tools to test the operation of the purge valve. I don't know if there is any other way.

Not sure about the partial fill idea, but it might be worth a try. If the car doesn't hesitate, or doesn't hesitate as much, in repeated tests, it might suggest the venting of the fumes during filling is the source.
 
#5 ·
-I can already tell you what is wrong: The gasoline that you have in your tank.

It is 10% ethanol [or so it says....]

I come on this forum because I have a work car, a 2001 Subaru Outback H6 that I keep in Memphis. I live in Fort Lauderdale, and for the past day my Porsche 928 has been hard to start! I had to crank it and crank it for 30 seconds tonight at an investment house. It is full of Chevron-Texaco CRAP!

Chevron used to be good gas. Then they mandated ethanol, and the station went downhill immediately. The Techron additive is good, but now the individual stations are cheating and adding more alcohol. I know it- I drive my 928 every day, and it starts just fine. But today I had to crank and crank the 928 to get it to start-

Sorry, that never happened a few years ago when we drove with PURE gasoline.

This stuff is still available: Ethanol-free gas stations in FL

I'd start there!

N!
 
#6 ·
The gasoline that you have in your tank.
That's quite possible, whether ethanol or just a bad batch of gasoline, but if this were the case it would happen almost every, if not every, time the car is started up and driven.

However, the original post is clear -- it happens only immediately after filling, and doesn't reappear in subsequent starts/drives:

"After fueling the car will hesitate for 2-3 miles. . . . It will do it for a couple miles then stop and wont happen for the rest of the tank." [bold added]
 
#8 ·
That's conceivable, if the new fuel almost immediately replaces the fuel that's in the line from the pump (in the tank) to the filter, the contents of the filter, and the rest of the fuel from the filter to the engine. It's only when the new fuel hits the cylinder and resulting knocking, misfires, or exhaust gases cause the emissions controls to start adjusting things. It doesn't adjust based on what's in the tank.

I'd add that if this were the cause, then there could well be similar searching for the sweet spot every time the tank is filled from different stations or with different brand fuels, which doesn't seem to be the case.

Sure, it's possible to fill up at a station where the added ethanol exceeds the spec (generally = or < 10%) and this could lead to performance problems. But it wouldn't likely happen every time the tank is filled as the fuel at the station would have been replenished with new stock, or the car might be filled at a totally different station. I don't have a sense that this is happening.

It's also possible that a car with "pre-existing problems" (fuel or ignition system) will be more sensitive to different fuels, but again, in this case, I would expect related symptoms to show up at other times -- cold starts, heavy engine load, damp environment etc.

I won't say I'm absolutely sure it's not the gas, but I don't see a pattern the leads me in that direction. On the other hand, hard starting and hesitation immediately after filling the tank is characteristic of problems in the evaporative emissions controls, including the purge control valve.
 
#9 ·
I don't think its fuel. Although I do use the same station a lot, we don't drive a lot so the fillings are spaced apart so it would be different fuel. Not that it matters but I've never had a problem with the other car or motorcycle at the same station. Its also happened after filling at other places outside the area and at different times of year (ethanol is used mostly in the winter isn't it?).

The car starts fine all the time. Even after fueling. The hesitation only happens for a couple miles immediately after fueling then not again the rest of the tank.

Thanks for the comments so far.
 
#15 ·
I don't think its fuel. Although I do use the same station a lot, we don't drive a lot so the fillings are spaced apart so it would be different fuel. Not that it matters but I've never had a problem with the other car or motorcycle at the same station. Its also happened after filling at other places outside the area and at different times of year (ethanol is used mostly in the winter isn't it?).

The car starts fine all the time. Even after fueling. The hesitation only happens for a couple miles immediately after fueling then not again the rest of the tank.

Thanks for the comments so far.
Did you ever solve this issue? I am having what seems like the exact same problem with my 2005 outback.
 
#10 ·
(ethanol is used mostly in the winter isn't it?).
Most gas suppliers/marketers in North America are now pumping gasoline with up to 10% ethanol all year. This is usually indicated somewhere on the pump. (There are also pumps with 85% ethanol -- it can be used as a fuel, and some newer cars are specially-built to run on regular gasoline with up to 10%, and the 85% type and are often identified with a plaque on the back, such as "FlexFuel".)

There are, however, seasonal changes in the gasoline formulation. For winter, the base gasoline is refined and blended so that it will be better able to vaporize in the cold, which is needed for rapid starts. In summer, the ability of the fuel to vaporize is made lower, reducing the tendency of the fuel to evaporate too readily in the gas tank (which could lead to the gas fumes escaping into the atmosphere). This is independent of the addition of ethanol or other, often company-specific, additives.

Incidentally, have you ever seen the Check Engine light flash/come on when, or shortly after, the hesitation appears? (I presume the CEL does work, and does come on when the key is set to ON but the engine isn't started.) In some cases, when a problem appears for the first time, the on-board-diagnostics will record a "pending code", and then wait for the next drive cycle to see if it appears again. If it does, it sets a permanent code, and turns on the CEL. If it doesn't, it clears the pending code. If you have access to a code reader, it could indicate if/when a pending code is set. Some auto parts stores such as Autozone or Advanced will read the codes without charge, and they can see a pending code. The important thing though in either case, is to not turn the car off, otherwise when it starts again and runs well, the code might be erased. If there is a code, it could help identify the problem.
 
#11 ·
I use Sta-Bil in every tank of gas due to ethonal. Some mechanics I know say that ethonal based fuel can start to go bad in as little as two weeks. Another product I add every 3,000 miles is Techron Concentrate. This keeps the injectors and lines clean. Never had hesitation problems.

Another cause could be a catalytic convertor that's clogging up. I've seen this happen on other brands of cars.
 
#12 ·
My '02 outback has the same problem. Every time I fill up my tank, the car hesitates and jumps for the next few miles. The car feels like it is going to fall apart for those few miles, but it is completely fine after that. I have tried all kinds of different fuels, and they all react the same.
 
#13 ·
My '04 does it too, but not every time I fuel and I always fuel at the same Shell station. It's weird - I always figured it was a pressure issue. Since it doesn't do it all the time, I've never really worried about it. Same thing though - somewhere between 2nd and 3rd gear - when I up-shift and accelerate, it's fine.
 
#14 ·
My 04 did this the last two refills at the same station after running the tank down to less then 1/4. The same exact symptoms. I thought it was water in the tank but after reading this thread, I am thinking its because I am topping the tank off as Plain OM suggests not to do. I never do that but I know I did the last two refills. I did add some HEET because of the suspected water but I will experiment the next few refills.


This is on an 04 OBW 5 speed. Is the fuel filter in the tank or the engine compartment?


Just read about the driver's door mirror/trim wind fix. This site is awesome!


Thanks.


Jeff
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top