The TLDR description of the problem is that my 2017 CX-5 appears to intermittently have issues pumping the last 2 or so gallons of fuel from the tank. Here's a repost of the whole story;

The Mazda CX-5 sometimes stutters and dies randomly, and it seems to coincide with having less than 1/4 tank of fuel left. It had only done it twice before, once with my wife, and once with me.

I was nervously driving down from the coastal range towards Portland, keeping an eye on when my next fuel opportunity would be. With 22 miles of range showing left according to the car, and 1/8th tank showing from the digital fuel gauge, I wondered if the car would decide to stutter and die again. I passed the small fuel station knowing it wouldn't accept the fleet fuel card I have to use, and continued on downhill hoping to get fuel at the Arco in 10 miles.

1.5 miles later the car stutters, and I immediately know it's going to die, so I pull off at a country store. Unable to start the car again, I hop on the EUC, and at 17 MPH, I quickly arrive at the fuel station, purchase a 1 gallon fuel container and a gallon of fuel. 1.5 miles back to the car, and I'm back on the road again, the whole ordeal taking about 20 minutes.

The EUC is such a nice thing to have when misfortune strikes. I'm also going to keep a gallon of ethanol free fuel in the car, hopefully only using it for other stranded drivers from here on out.

After tallying the fuel put back into the Mazda, it appears to not be accessing the last 2 gallons of the 15 gallon fuel tank, and only occasionally, as I've pushed the fuel towards empty way more than that before (up to 14.5 gallons).

The previous time it stuttered and died I was able to start the vehicle and accelerate just enough to steer hard side to side to slosh things up in the tank, and then I drove another 20 miles to a petrol station. At that time I hadn't really formulated a hypothesis on why the car died, but just took an everything approach to hobbling the car along.

I'm not sure how fuel pickups work in a passenger vehicle. In a motorcycle there is a straw that sticks up in the fuel tank making it so you run out of fuel even though there's more at the bottom of the tank. Then you switch the fuel petcock to reserve, and it bypasses the straw, giving the full tank capacity.

I'm picturing a flexible hose with a weight on it that picks up fuel in a passenger vehicle. Perhaps I have a hole in that hose? Maybe the weight fell off so it kinda floats? Trying to figure out why it sometimes allows the full capacity to be accessed, but sometimes not.

This is one of those problems I'm hesitant to send to a dealer because those monkeys are incapable of using simple math to troubleshoot a problem. They'll say to refill sooner, or replace the sending unit, or something equally pointless to resolve the issue.

 

As a general rule I fill up at 1/4 tank and try to never let it get below that. My understanding is that in many modern cars, the fuel pump in the gas tank is cooled by the gas itself, so letting the gas tank get down below 1/4 full is hard on the fuel pump.

Sounds like you could fill up sooner and avoid the hassle. Your choice?

 

That's obvious. There's capacity that periodically isn't usable, and that's a defect that needs to be corrected. This solution isn't obvious to me as an extensive Google search brought up nothing.

The issue is mainly the intermittency. What if it gets worse and manifests at half a tank? It isn't clear what the problem is, which is the problem.

 

I would take it in and talk to someone. I can't say mine has manifested this issue and I have run it down to zero on the miles to empty gauge (which we know is notoriously pessimistic) in both my '19 2.5 and '21 2.5T models..

 

If the OP really wanted to know how his fuel pickup worked he could google it. Here is a diagram of the in-tank fuel pump and filter assembly, and a link to more schematics. The last few gallons of fuel in any tank are usually full of concentrated dirt and water which can plug/damage the high pressure fuel injection system, it is not intended to be sucked into the engine. Perhaps a Mazda isn’t for him.

https://www.realmazdaparts.com/v-201...tem--fuel-pump

 

Better pessimistic than optimistic. I once went about 75 miles beyond where my 2004 Tahoe reported 0 miles remaining, but I had a 1972 Dodge Dart with the 318 engine that would run out of gas as soon as the gauge dropped below 1/4.

 

My point is you can drive well beyond "0" on the miles left to empty gauge. Of course you are correct, better to be pessimistic with fuel. Interesting comment from Carpe Diem as well. I have never had an issue with ruining the tank down to empty in any of my cars.

 

Any issues will depend on the mileage on the vehicle (number of tank fills), where and when you get your fuel (was the station high volume/was the buried tank filled recently), and how often you run the tank down low - I assume you don’t run until the engine actually quits. The empty mark on the gauge is not zero gallons left in the tank so you may have never actually used the last few gallons. Current high pressure fuel systems are more prone to dirty fuel issues compared to vehicles from ten years ago or earlier. In addition a plugged fuel filter may very be difficult for the driver to diagnose unless he runs at WOT often.

The last few gallons are intended to be “sacrificial” to protect the fuel system. Running the tank down very low has two potential problems: sucking up dirty/wet fuel, and compromising fuel pump cooling in hot weather.

 

I expected people to say "you're the dumb one for wanting a thing to work correctly", which is why I wanted to solicit the experience and knowledge of a dedicated forum. My expectation is that a dealership would waste several days of my time either telling me there's no problem, or throwing the wrong parts at the car because they can't understand that 13 is less than 15 (gallons).

Fuel capacities are spec'd at what they will deliver, not some larger amount that cannot be used.

My 2nd fill-up in the car, I drove 406 miles and filled 14.4 gallons and got 28 MPG. According to specs, I had 1 gallon of fuel remaining, which explains why I didn't run out. Since then there have been several occasions where I fill with more than 14 gallons, each time going past the estimated range remaining.

On 3 occasions now, the car ran out of fuel with estimated range remaining above 20 miles. One of those occasions I was showing 1/4 tank and the low fuel light wasn't on. Car died and I pulled to side of the road. It would start, run for a few seconds, then die again. I did that half a dozen times, and on the last attempt I got enough speed going to rock sharply side to side, and that allowed me to make the next fuel station 20 miles away.

I have 2 pieces of evidence suggesting I'm not getting full use of the capacity:

1. I pumped only 13 gallons into an empty tank, which should have a capacity of 15.4 gallons.
2. My fuel economy was 27 MPG on my most recent trip, and I ran out of fuel at 352 miles. 352 miles / 27 MPG = 13 gallons of fuel used.

These 2 methods of determining how much fuel was used perfectly support each other, making it highly likely I'm not getting all the fuel I'm supposed to, not that there's a gauge malfunction.

There's some chance I'm interpreting things incorrectly, but I don't think so, and am completely open to all hypothesis. Mostly I'm interested to know how fuel is collected from the tank and delivered to the engine, and a poorly detailed schematic doesn't inform my understanding well enough (which again is why I'm on the forum and not easily solving my own problem).

It's a fleet vehicle, so I have little incentive to put my own effort into this, except that I'm curious and like to solve problems. I might pop the fuel pump out and put an inspection camera in the tank to see what's going on... but I'm at 57k miles and it should be under warranty still.

EDIT: A Youtube video shows the fuel pickup tube is attached very low on the fuel pump. Perhaps this has detached and I'm only pulling fuel directly from the pump, and not from the hose that sits lower in the tank. The fuel hose in the tank isn't listed in any parts diagrams I'm finding.

 

Bump to the top

My 2017 CX-5 is doing exactly what’s described by the OP.

Was there ever a resolution found for his issues?

Anyone else ever run into this?

Thanks
-Rob