We just bought a 2004 Mazda 3 that wasnt running right, thinking it was a catalytic converter. It's hard to start, as in, I turn the key, it cranks a few times, will rev up, but then just die. After about 5 times, it starts and idles. But, when you press on the gas pedal, it bugs down real bad. If I press the pedal slowly, it accelerates normal. Last owner said the fuel pump, and I believe one coil pack was changed, as well as the battery. I removed the exhaust manifold, and no change. Almost seems like a fuel problem, but not sure. Does smell a little like too much fuel though. Any help would be greatly appreciated.

 

Any check engine codes?

I would not say it was fuel pump. Usually, fuel pump will start and idle fine but them hard accel or heavy load will sputter.

Can you check for vacuum leaks? While idling, spray around the engine intake with carb cleaner.

Check the MAF. While idling tap the MAF and jiggle the connector.

With no code its some pure guessing here. My first guess is for replacing the TB.

You need some luck.

RGAZ

 

No codes. Dont hear any vacuum leaks. Previous owner said the fuel pump was replaced. Will check MAF, and clean. I do have MAF cleaner.

 

Engine noise drowns out vacuum leaks. Use the carb spray and if the engine races when you spray near it, then you know.

 

So far changed coil packs, spark plugs, MAF sensor, cleaned throttle body, checked for vacuum leaks. Still the same. Will idle fine, but if I press on throttle all the way, it gets to 1,500-2,000 RPM and bogs down. It pops, shutters, until it gets above 3,000 RPMS, then runs again. When driving, if I get it up to speed, when I fully press the peddle, it bogs down and feels like the transmission is holding it back. Tired of throwing money at this with no change.

 

This sounds like something is happening when the two major engine transitions occur. I cannot tell which is causing you the problem. Here they are:

At about 2500 rpm the intake manifold runners activate and change the intake manifold from a short run to a long run. Something is happening when that transition occurs on your car causing it to miss.

Also at about 2500/3000 rpm, the VVT actuator is fully advanced on the intake valves. This is when the engine changes the valve timing for increased high rpm power. Something is happening when that actuation occurs that is causing a miss.

I am not sure what to tell you. You can disable the intake runner control by disconnecting the electrical connectors to the two vacuum solenoids on the intake to test, but it will shortly throw a code. ITs not so simple on the VVT, I don't recommend disconnecting the solenoid as it controls the oil to it. You could replace it for about $40 to try.

Other than that, I am out of ideas, but if you figure it out I am curious to hear what it is.

RGAZ

 

If this is an automatic transmission, it is no doubt the tranny. I own the manual from 04' and have replaced the fuel pump, as well as several other fuel feeding components, and she runs fine. With that kind of drastic push back, you could keep a relic from the original body line, or take your chances of investing in beyond anything after 2007. But if it's had regular oil changes, you still have a gem despite the elephant in the room.

cheers,