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Mazda3 Trouble starting after filling up

I have a Mazda 3 5-door and I believe it is a 2010 model year, with between 50k-70k miles. I’ve been, I believe, consistent with regular maintenance schedules, and this is the first issue I’ve had, and I’ve been having it for a bit of time now (a few weeks). I’ve tried various things to try and understand the issues that bring it up. I hope that, after reading this, someone may have some suggestions.

First, I don’t remember if this started before or after, but my “Check Engine” light popped on. I brought it in to have the code read and it was the one for the gas cap not being on properly. The person reset the diagnostic code, tightened the cap, and I went on my way.

A few hours later it came back.

Okay, but that’s not the issue, and I mention it only because of the other things I’ve observed.

The real problem is, after I’ve been driving for “awhile” at highway speeds, and I add fuel, the car has a very difficult time starting. I have to really press the accelerator down to get it to start, and even then it can take a good 5 seconds of holding the key to “start”.

Things I’ve noticed:

  • If I fill up at the start of a trip, so that the car hasn’t been running long, I can fill up and the car starts immediately.
  • I thought it might be a problem with fuel spilling over into the overflow, so I’ve added less fuel (so I ended with the needle pointing between 3/4 and full) but it still had trouble starting
  • After I start it, it runs rough for a bit and I feel like I have to rev it to keep it from stalling, though I haven’t left it to idle to see if it actually will stall.
  • After the difficult start, if I drive as little as down a city block, turn the car off, and back on, it has no trouble starting, nor does it stutter like it does when I fill it up.
  • If I take a long drive but don’t add any fuel, it starts up right away.

I’ve always used 87 octane fuel, which seems to work fine, and I feel as though that’s the recommended grade, isn’t it? I also try to fill it up when the needle reads 1/4 of a tank or a bit more, but I do notice that, if I allow the pump to auto-shutoff the car will accept 9-10 gallons (and I thought it was a 10.5 gallon tank, which is less than 1/4 left… I’m not sure how bad that is…)

Does anyone have any thoughts for what it could possibly be? Or even additional tests I could try to narrow it down?

Thank you very much for your time!

Have the computer checked for any stored codes, and if you still have the shop order post the code that previously tripped the CEL.

In the meantime, I’ve posted some documents for my own emissions system and fuel delivery system. Yours should be similar.

Honestly, I’m thinking that perhaps filling the tank is stirring up some sediments that are interfering with the filter on the pickup tube of the pump. But I’m thinking that others might come up with some other ideas by perusing the attached.

A problem with the fuel tank emissions and venting system should be considered. If a vacuum develops in the air space at the top of the tank, it prevents the fuel pump from delivering fuel to the engine. It’s like if you put water in a coke bottle say, then turn it upside down and put the small end of the bottle in a bowl of water, the water will appear to magically stay in the bottle and never drain out. With a car, it is easier for this to happen when the tank is full. The venting system is supposed to prevent it, but somelthing may have gone askew. If it happens again, you might see if loosening the gas cap allows the car to start. If so, this would confirm a tank venting problem. Here’s some general info on this topic fyi.

You are correct. Mazda calls for regular unleaded fuel. You can get the emissions computer codes read at a chain auto store, like Autozone or Advance Auto Parts for free. Call ahead to make sure that they have one and it is working. You just plug it into the connector under the dash board and above the the gas pedal. The store clerks should be able to help you if they are not too busy. You may have to leave a credit card for security, but it won’t cost anything. They should give you a printout with the codes o it. Post them here and we can help you decipher them.