Bucking at WOT after dealer unnecessarily replaced fuel pump

Eric Fuller

Eric Fuller

Greenie N00B Member
Hey ya'll...awesome forum here, wish I'd found it years ago. This is kind of a weird story, so bear with me. Hoping someone can help point me in the right direction.

I have a 2013 MS3 with ~70k miles that's always run like a champ. No issues, ever. Dead stock with no mods. Not even a DD; it's my "fun" car. I was driving it with a friend and the low fuel comes on. I pull over at a gas station where my friend remembers me filling the tank (as do I).

After I fill it the fuel light is still on and the gauge hasn't moved. I figure there's a bad sensor or fuse and make a note to check it. The next day the car dies, acting like it's out of gas. Now I'm thinking there's a larger issue with the car.

I tow it to the dealer, tell them the car has a full tank but is dying and the fuel gauge isn't responsive. They diagnose a bad fuel pump and a bunch of other garbage like coolant and transmission flush. I tell them to just install the pump since I have a mechanic I trust who can lmk about the other stuff. They end up installing an aftermarket pump because I guess they couldn't source an OEM? $800 later I pick the car up.

When I pick it up the tank still reads empty. I talk to the tech and ask if he had to drain the tank to replace the pump. He tells me the car came in empty. After he added a gallon of gas it started right up and he pulled it into the bay. I ask why they replaced the fuel pump and he mumbles something about excessive resistance. They knew I thought the tank was full and at no point disclosed that it was actually dry. I wouldn't have known if I hadn't asked the tech. This is the first time the car had ever run out of gas and I don't believe that one instance burned out the fuel pump.

The next day I drive the car and there's a strong gas smell. Back to the dealer where they say the gas tank was damaged during the fuel pump install. They install a new tank. I pick up the car again. No gas smell but now the car stumbles under anything more than 70% throttle. My long-term reliable mechanic is now telling me there's an issue with the turbo.

IDK what to do here. No way I'm bringing it back to that same dealer, but this seems like something that may be over my mechanics' head since he had to call a friend who's a Mazda tech to figure out it's the turbo.

Thanks for putting up with this long-ass message but I figured all this info was relevant. Any advice you guys can give would be hugely helpful. I love this car and just want it back to it's normal condition.
 
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First thing to do is check for fuel leaks. If the engine isn't getting enough fuel then it can result in not being able to go full throttle.

I had a Mitsubishi Starion that I bought for a spare which ran and drove. But any time I tried to boost it then it would fall flat on it's face. I put a fuel pressure gauge inline with the fuel rail and taped it to the windshield. Took it up the road and instead of fuel pressure rising it fell down. Turns out the in tank pump was bad. I installed a new 255lph pump and it ran great.

So you could have an issue like that. Either there is a pinched fuel feed line preventing enough fuel to get to the HPFP.

Or you could have a wiring concern where not enough current can go to the fuel pump so it can generate enough pressure/flow.

Check your logs and see what your fuel trims are. They would be excessively lean. Not saying this is the concern but something for you to check off.
 
Sounds like that Mazda dealership is a gem, start with what these guys have said hopefully that gives you something tell point them at.
 
I'd want to get some disclosure on what "aftermarket" fuel pump they installed. If they were going to install an aftermarket fuel pump I'd at least want a say in what was going into the car, personally.
 
Onto the problems:

Emissions systems can prevent depressurization of your tank when you are filling up. You probably never filled the gas tank in the first place. Usually it is assumed if the pump gun clicks off, your tank is full. But do you remember how many gallons/liters you put in? The temporary solution, if this is the problem, is to modulate the gas pump gun to a very slow rate, that will provide time for air to escape through the filler neck.

If you are telling me the car ran before and it doesn't now, and the only thing it touched was the fuel pump, then I would get your mechanic to monitor the low pressure fuel, both at idle and when applying load. If everything checks out there, check high pressure fuel under load. What do you see?

I bet they did touch your fuel pump, but they did something wrong in the process or installed a unit that is defective or incorrect.
 
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