Hi, I've been having trouble with my Mazda 3. Around 2 weeks ago I topped it up with fuel (unleaded), then 3 days later it started really loosing power when under load. If i turn it off and on again it has power again for about 2 minutes then the same thing happens. There were no warning lights or codes from the ECU.
I took it into my local Mazda dealership and they diagnosed it with low fuel pressure. But they don't know if its the pump, filter or return valve without further (costly) investigation.

I tried to locate the filter but its not next to the right rear wheel, so I guess it in the petrol tank with the pump? Is my next step to drop the tank and replace the pump along with the filter? Do they come as one unit or do I need 2 separate parts?

Is there any chance the fuel was contaminated?

I'm not great with cars but I'm willing to give it a go!

Many thanks.

 

Do you know if your car even has a fuel filter? I ask because in the mid-2000s most cars here in the U.S. were built without one.

 

Hi, Shipo,

No i'm not sure at all, I was just going off what the Mazda dealership said when they wanted to do further investigation. I guess i just need a new fuel pump then. I'm just confused as to why it would work fine for 2 mins and then start to cut out.

thanks.

 

Hmmm. I am not sure you are on the right track. I have not seen a fuel pump that just slowly cannot keep up with fuel load. usually, they are either dead or totally plugged. I assume you are not seeing any check engine light.
You could go for the fuel pump ($200) but I would not bank on it.

You said "lose power under load" do you mean it missses, bucks, or just is not as fast as your butt-dyno thinks it should be? Does it struggle to accelerate but runs smooth? Only WOT acceleration? I need a better idea of what you mean.

Without knowing anything more and what I would do, is to see if its bad gas. Depending on whats wrong it might take a few things. The most common I see is way too much ethanol. That would be tough for the car to run well. I recommend you go to a gas station that had 100% gas (no ehtanol) and put as much as you can in the tank to push the dilution. The other option is to siphon off a bunch and replace with good fuel.

Personally, if you can tie it directly to a fill-up, then I would pursue dilution.

BTW - I am guessing the reason it runs ok for a few minutes and then gets worse, is because when your car is cold or first started it will run in warm-up mode using a more rich mixture and then after warming it runs on normal feedback-loop using the O2 sensor and its being fooled by the poor fuel.

Good luck
RGAZ

 

Thanks RGAZ, I will definitely try and siphon out as much of the fuel as I can and then put in some decent stuff. Certainly the cheaper option over a new fuel pump.

When it loses power it is as though I'm no longer pressing the throttle, it will just go to idle instead and i'll drastically slow down. If i turn the ignition off and back on, while still rolling, i'll get power back and will be able to get up the next hill until it happens again. It will also only run for around 2 mins before spluttering to a stop while idling on my drive. Again if i immediately turn it off and back on it will go for another 2 mins.

Its certainly got me confused and I'm not sure how turning it off and on again would fix the fuel pump which the Mazda dealership have pointed to.

Thanks for your help,
Saiph.

 

That is an odd one, especially with no codes at all. I had a problem similar to that but it threw codes like crazy. In the end the electrical connector to the MAF had a bad wire so I got a new connector from the salvage yard. Maybe check your MAF connection and if possible can you swap a throttle body? Expensive trial but it sounds like the TB is slamming shut and not moving in response to the pedal input. That should throw tons of codes though.