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Discussion Starter · #1 ·
My new-to me 04 Mazda 3 2.3 seems to have some issues acceleration. The car current has 122k miles on it. My previous 04 ran perfect till I sold it at 220k, so my standards are high. (I do realize that engines aren't consistently reliable when not treated well).

I'm also getting some fairly bad gas mileage. The exhaust smells a little rich. I have an exhaust leak at the flex pipe that comes off the cat currently. This could influence what I think the exhaust smells like.
It's being fixed right now, but I'm unsure if it would contribute to the car hesitating under acceleration. Other than messing with O2 sensor readings. I was under the impression however that the downstream sensor does not contribute to the ECU's fuel calculations.

I've swapped out the MAF, and both O2 sensors, and cleaned the purge valve. My idle has cleaned up since I've cleaned the purge valve, but I'm thinking the purge valve is going because driving the car makes the rough idle come back. I have new purge valve on order.

I've gotten the P2187 and P2195 codes, but since cleaning the purge valve and replacing the upstream O2 sensor they have not returned...yet. Its completely possible that they will return with more driving as I'm unsure if all conditions were met for the ECU to save these codes.

The poor gas mileage and the exhaust's smell makes me think that something is causing the ECU to think the mixture is lean and dump too much fuel. Which in turn causes the hesitation. When I first swapped a stand-alone ECU into my 00 Miata, the TPS "tip-in" enrichment was too high and caused the car to hesitated unless I rolled into the throttle. It had a similar feeling.

On the other hand, the lean codes could actually be true. I received some maintenance history for the car, and it has had its injectors cleaned twice, but not replaced. I have used, but good injectors ready to be swapped in. This made me think that the car has had issues with fueling being too lean in the past. I've read so far that this gen Mazda 3 can have fuel pump issues.

This brings me to asking how can I test the fuel pressure? Is there a test port on the fuel rail? Can I read it via OBD2?
I'm just a little confused because of the conflicting evidence. The poor gas mileage would point to a rich condition. The spark plugs in it were black suggesting rich. However switching to a higher octane fuel improved performance, which points to the car running lean (knocking, and engine pulling timing).

I also have a new knock sensor that I could throw in.

I've got the parts cannon loaded.

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303 Posts
Might be worth cleaning the MAF sensor in the air intake. You can spray clean with the intake hose out and the sensor still attached to the hose. Be sure to use dedicated MAF cleaner as anything else can harm the delicate wire.

And I like the idea of cleaning the throttle body too. If it is sticking, could be causing lean codes.

Are the IM gaskets and the throttle body gasket in good shape?
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