Last fill-up my car runs about 2 to 3 gallons then really starts running rough. It would act like its starved for fuel for a couple seconds, then run fine a few seconds, then starved a few seconds, good a few secs, etc. I’ve had this problem before on another car with a bad batch of gas so I ran it until 1/4 tank left (more like 0.2 tank based on my gauge) and refilled it with good gas.
Ran fine for a few gallons then the same old symptoms again. Wanting a good diagnosis, I’ve noticed that if it sits a while, I can get 3 or 4 miles of good driving then the symptoms show up again. I think it is either bad gas and leaving 25% of the gas was too much for this batch to run right or a intermittant clogged fuel filter line.
Is it one of those or something else? How do I fix it?
Seriously, with a 2004 car with all its sensors, computers, etc. and so forth, in my opinion by far the best thing you can do is to take it in to a competent auto shop (and these, despite folklore, are not too rare) and have them diagnose the problem. They have equipment for this costing tens of thousands of dollars, are trained in its use, and have seen just about anything that can go wrong with a modern vehicle.
IMHO you’ll save yourself a ton of grief, frustation, and time. Unfortunately, the days of the shade tree mechanic are just about gone forever.
I would definitely start with the fuel filter. Twenty years ago, I don’t remember dirty fuel really being that much of a problem. These days, it seems to be much more common. I don’t know if it’s due to the cheaper ways they are manufacturing gasoline or what, but I’ve had clogged fuel filters on two of my cars in the past five years.
It might just be the gas station I used to go to, though. I switched gas stations and haven’t had a problem yet.
I had a problem with my distributor last year that caused similar symptoms.
I’m also thinking a bad oxygen sensor or maybe an exhaust leak, bad EGR valve or something along those lines might be possibilities.
Many auto parts stores offer free computer hookup and will print out any codes that you throw. THAT is where I would start. Then I would pull the plugs and look at each plug. Any deviation from a normal fuel/air ratio will show up on the plug tip. If it’s a single plug that looks different from the others then concentrate on that cylinder. You could have a bad/sticking injector or the connection to the injector is intermittent. It could also be a bad plug or a bad plug wire or a defective coil. If it’s a loose plug wire you should see discoloration at the point where the connection is bad (usually the plug end).
And while I’m thinking about it, you could have a vacuum leak because of a loose hose or cracked intake (if it’s made of plastic). When the engine warms up it comes out of rich-fuel-mode and is trying to distribute fuel according to normal intake conditions and will then run lean with a vacuum leak. This is easy to find by spraying starting fluid around the engine intake. If there is a leak it will suck up the starting fluid and the engine will change rpm as it reacts to it. Do this while the engine is still cold and running smoothly. Be careful doing this and have a fire extinguisher handy since you’re spraying a flammable liquid on an engine that could be running poorly because of arcing ignition problems.
If it’s not a single cylinder running rough then you should concentrate on sensors that feed the computer such as the O2 meter, any temp/map sensors, and speed or location sensors such as crank/cam sensors.
If it were a bad O2 sensor it would light the check engine light and store a code. Since the OP doesn’t mention a check engine/service light it is probably the fuel filter. Any of the EGR, MAF, MAP sensors etc mentioned above will result in an error code stored and the engine light lit.
If your check engine light is not on, do not waste time taking it to the shop. No engine light on = no codes stored.
If you live in an area with an ethanol blend of gas that ethanol may have picked up water and moved it into your fuel filter. Water and ethanol will combine in solution, not stay separated like gas and water. Ethanol added to gas is the main cause of increased fuel filter problems.
Computers will register codes without turning the light on. They’re generally minor but it’s worth a trip to a parts store to get it checked for free. You can also clear out the codes to see if any future codes pop up.
possibly: a clogged air vent in your fuel tank
(not sure if this applies to your vehicle)
However if clogged, then your fuel pump is drawing against a fixed volume of air, and so performance degrades until the engine stalls.
Opening the gas cap, or letting it sit a while will allow the air to leak in slowly, and everything returns to normal for a while.
I have the same code reader that is going to be plugged into your OBD II data port when you take it to the auto parts store. A dealer MAY be able to read minor codes that haven’t triggered the light, but the parts store is not going to be able to tell you anything if the light is not on.
Do you “top off” your gas tank when filling it? The vent in the gas tank has a charcoal canister which can become clogged if too much gas is added to the tank.
This was my first hypthosis mostly because the cap is harder to get off than it should, but I dismissed it because “vapor-lock” is a thing of the past. :dubious:
Further research indicates that this system in your vehicle is not simply passive - so there is a solenoid controlling things (and adding more things that could go wrong).
The good news is that the computer can detect and capture a code that indicates this.
The even better news is that the problem is often a bad gas cap according to the linked source. Check the inside center of the gas cap (the valve) - if you see rust, this is likely your problem. Solution: new gas cap.
More definitive would be to run it until the symptom appears, then stop and release the gas cap (a big “whoosh” sound would suggest a buildup of vacuum in the tank). Then right away drive it with the cap off and see if the symptom is gone. If so, a cap replacement may fix it (it would certainly be the cheapest and easiest thing to try first). If removing the cap does not eliminate the symptom, it’s unlikely cap replacement would help.
I like that the gas cap matches my disgosis of the symptoms as vapor lock: gas cap tighter to get off, runs ok after sitting a while, etc. My big hesitation is how can a gas cap go bad after 55K miles?
That would be a good Gary-T answer. My BIL just bought a Vibe (actually a Toyota) and the manual said it was normal for the fuel pump to kick on an hour after the car was shut down to test the fuel system. That means the car is actively testing the system and recording any deviations.