Car Sputters After Gas Station Fill

[Viper5]

Hey Forum,

I've got an '04 GT that sputters whenever I fill-up at a gas station. It doesn't matter if I take it down to empty or not. Meaning, I can add 15 gallons or I can add 2 gallons with the same effect at the end. I can pull out of the gas station but after about 3-5 miles of driving, the car begins to sputter and the RPM's drop. The car will stall out unless I press in the clutch and rev up to about 4k. The sputtering only happens for about a day or two in city driving or about 15 miles on the highway.

The car was actually running fine until I put in some System Cleaner. The car started sputtering then, but I figured it was just the gunk going through the injectors, so I didn't pay much attention. Even after 4 fill-ups (see above), I'm having the same problem. I tried switching out the fuel filter, different gas stations and even took it on a 4-hour highway drive to empty out the tank but no luck.

Any suggestions?

 

[wmburns]

Are there any check engine codes (DTC's) at all?

If no DTC's, my best guess is the vapor evaporative purge system and IAC are not playing well together.

After a fill up and all other conditions are right, the PCM will call for a vapor purge. It is normal for the extra vapors to cause some rough running. Normally the Idle Air Controller (IAC) will adjust.

I suspect there is a problem with the IAC. The problem is not bad enough to cause noticeable problems driving. For the 2004, the IAC does not have the black vent and can be cleaned. If no improvement after cleaning, replace.

Another possibility is a leak in the evaporative vapor purge system. For a test after your next fill up, disconnect and PLUG (important) both ends of the vapor purge vacuum line. The line should be a 1/4" line on the rear of the throttle body.

This may throw a new DTC but it's OK. What we are trying to do is see if the drivability improves.

It is not a great idea to drive around with the vapor line plugged. It may cause damage to the charcoal canister. If replacement is needed, you will find it $$ and a PIA to change. Therefore, do the test immediatly after filling up. Restore the vacuum lines after the results are known.

Also consider looking for vacuum leaks. Perform a through visual inspection. Inspect the PCV system, oil dip stick, oil filler neck, valve covers, air tube, and all hoses, and vacuum lines. Even the smallest vacuum leak will cause problems.

 

[Viper5]

NO DTC codes as of yet, but I do have MIL eliminators on the O2 Sensors which may mask the reading? I'll try the above right after next fill-up and keep you posted.

Thanks!

 

[patman0911]

MIL eliminators won't affect anything.

 

[wmburns]

Upon re-reading your post, there may be more than evap purge going on here. The evap purge last only a few minutes and then it is over. If the driveability concerns goes on for minute after minute mile after mile, then it is not just the evap purge causing this.

Suggest that Mass Air Flow sensor (MAF) be cleaned. Use cleaner made for the job. The sensor is easily damaged. Take care.

Inspect the spark plug holes for moisture.

Consider replacing the IAC. I suspect it will come to it anyway. Autozone makes a less $$ after market replacement that works well.

 

[bhuff30]

Maybe a long shot, but have you ever changed the fuel filter? Maybe filling the tank stirs up the debris in your tank, and it gets sucked into the filter. No reason it would later start acting correctly though.
I only say that because to me, it sounds like a fuel starvation issue.

 

[Icemanstang]

Definitley change your fuel filter because they can get clogged
over time.
What gasoline station are you giving your busniess to?
I would hope you are running a name brand Top Tier gasoline
in your mustang.

 

[MaxedGT]

Try fueling up without filling. Add to maybe 3/4 tank. If it doesn't act up, somehow the evap system is drawing in fuel when the tank is full. If it still acts up, there's likely dirt in the tank that's churned up when you fuel up, and it's being drawn into the fuel pump pickup. After the car sits it can settle back down to the bottom of the tank, without plugging the pickup.

 

[Viper5]

I changed the fuel filter last week and filled up, yet the issue persisted. My initial guess was just like many of yours. That maybe me filling it up is stirring up the sediment at the bottom of the tank, however why hasn't the new filter taken care of this? I may need a new MAF, but the issue only occurs after about 3 minutes of the car being on rather than the entire drive.

I've been running 93 octane since day 1. Usually I fill up at BP or Chevron, but last fill-up was Shell.

I didn't check the sensors just yet, but I'll try the 3/4 fill-up first.

Like I said, the problem doesn't last for too long. It takes about 2 days of city driving (randomly stutters here or there) or about 10 miles on the highway (continuously bucking from mile 2-10). Either way, it's definitely noticeable when it happens, as the car jerks back and forth like it's hiccuping.

 

[wmburns]

IMO, if debris in fuel tank, it would not suddenly get better. Once the debris is in the filter, it is there. Further, one would have expected some improvement (if only temporary) when the new filter was installed.

However, this can be ruled out by monitoring the fuel pressure with an ODB2 scanner. Look for the FP to be a constant 40 PSI (38-41 is OK). This will also help rule out a weak fuel pump.

Suggest staring off with a CLEANING of the MAF. Use the cleaner designed for it. This step is cheap and easy and will help rule out one more item. Note, the MAF could still be bad.

Monitor the Air flow, Long term fuel time (LTFT), and Short term Fuel trim (STFT) with an ODB2 scanner. Look at the air flow and see if it jumps for no apparent reason. Also look to see if the numbers are reasonable. A reasonable number is 0.6-0.9 lb/min at idle for a stock SOHC 4.6.

Look for LTFT to go from big negative values at idle and large positive values under load. This will indicate the MAF is dirty.

Look for big differences between LTFT bank1 (right) and bank2 (Left).

This could also be the evap purge system, EGR system, spark, injectors, IAC, or several other items (some are more/less likely than others).

The evap system is easy to rule in/out. Nothing fancy there. Optionally, monitor the EVAP purge PID and see if the PCM is calling for EVAP purge when the problem occurs.

This could also be a gas tank venting problem. Consider if the EVAP vapor valve (VMV) is stuck open. After some period of time, the charcoal canister is empty of vapors. But the VMV is still open. This will apply engine vacuum to the gas tank creating a partial vacuum and starving the FP.

Monitor the IAC duty percentage. Look for changes esp when the AC is turned on/off. Disconnect the IAC electrical connection. The engine should die (IAC with no black vent).

Good luck.