Hello! I have a 2008 Mazda3. The car has a replaced engine with 24,000 miles on it. The engine was put in before I bought the car.
The car and engine run like a top; except at certain RPMs and when in gear. When I have the car in any gear (auto), the engine makes a rougher noise at RPMs 1400-1700. As I apply more gas, the RPMs seem to get stuck at 1700, then it will break through and run smooth 2000+ RPMs. The engine sounds perfect at all RPMs except 1400-1700 when in gear. When I have it in park and rev the engine, the engine sounds perfect at all RPMs.
Are you trying to describe a misfire at those rpm ranges? Does it lose power during this range and seems to have to overcome something…sort of…to break thru and then continue to rev normally? An 08 Mazda 3 should have coil over plug…how are the plugs in the engine? Tune up history? Fuel filter? Air filter? Did the replacement engine come from the USDM? or was it a JDM conversion? Is this a Turbo charged engine? What happened to the old engine, do you know? I am thinking maybe a misfire or a fueling issue… Is your CEL (check engine light) illuminated?
Lots o questions for you I know…but we need to know.
I agree with Honda Blackbird; a lot more needs to be known before even a guess could be made.
Knowing if any codes are present could help. If I had to make strictly wild guesses, and these would be as wild as it gets with no info, I might take a stab at a MAF sensor problem (either the MAF or air leak in the intake tract) or an EGR system fault.
If you’re accelerating & at 1400-1700 rpm then you’re near the point of engine lugging. This is going to produce a maximum of vibration throughout the entire vehicle. I’d imagine that “rougher noise” you’re hearing might partly be engine, but also anything else that might vibrate. The “break through” that you describe is most likely just what happens when the transmission downshifts. When it does & the engine rpms rise the entire action of the engine & thus the feel & sound of the whole car will smooth out. Slow & gradual acceleration is good for fuel economy. You could be overdoing it.
Of course, any of the other things mentioned could be relevant.
Thanks for all the follow up questions. I am not a car guy by any means, but I will do my best.
I was told the old engine was damaged from too much water coming through the air intake when driving through a flooding puddle at high speed. I do not know the history on the replacement engine; I am assuming USDM. The engine is 2.0L with no turbo.
The check engine light does not come on. I don’t know the tune-up history of the car, the only records through Mazda are when the car was first sold. If it was maintained, it wasn’t through a Mazda dealer. However, I know it went through a full tune-up before I bought the car from a dealer that specializes in rehabbing cars from insurance claims.
The engine makes the extra noise (kind of a deep growl) in the 1400-1700 range when accelerating fast through the range, accelerating slow through the range and when holding speed/gas constant in the range. The car doesn’t seem to lose power (doesn’t drop speed), but it does take extra time to accelerate out of the range. When accelerating out of the range after holding steady in the range, I apply gas, I hear the engine work hard and the RPMs don’t move, then the RPMs jump and there is a burst of speed.
If I hold the engine in the range in park, there is no noise.
I do have a 90 day warranty on the engine and transmission and I noticed this noise before I bought the car. However, the issue seems like it has gotten a little worse in the last week and with colder weather.
I wonder…if when they swapped engines…they used the correct ECU…They’d have had to…I thought for one second that his new engine doesnt like the tranny…but that really cant be now can it? OR…If his new engine is CAMMED for a manual trans…and now its doing Auto duty? Sounds like he is in Overdrive too early or something and the trans has to downshift…to increase rpms and speed…
Perhaps related, I feel like the car likes to up shift real early. This is the first auto I have had with a LED display of the gear. I can see that the car will shift up to 4th gear when driving steady at 30 mph and the RPMs were only 2000 in 3rd.
In general, the car will keep itself in the highest gear possible without lugging the engine, so going to 4th at a steady speed, even if a low one would not be odd. I think that what you have going on is either normal or you might have something messing with the shift points. That could be something with the transmission or engine management as it relates to transmission controls. (E.g. a MAF sensor issue as ok4450 noted, or maybe a flat spot in the throttle position sensor…). I think that someone good with driveability issues will have to drive it - preferably with a scantool attached to collect live data.