4th gear boom

[AamirMSP]

I am experiencing a strange issue with my MSP with 400 miles on it.

When I shift in to 4th gear from 3rd gear below ~3000rpm, I always hear a very low pitched boom sound from the rear of the car, like a bass note.

It does not happen from 1st -> 2nd, and its less pronounced from 4th -> 5th. It has become very annoying and I hate shifting in to 4th gear.

Any idea what it may be? I am about to go to the dealer.

Thanks
Aamir

 

[jersey_emt]

If you run WOT in too low of a gear (like from below 3000 rpm) this will happen. It puts a lot of stress on the drivetrain and I wouldn't recommend it. Keep it in 3rd gear for a little longer.

I don't shift into 4th until around 40 mph / 3K RPM's during normal driving, and I'll keep it in 3rd much longer for 'spirited' driving.

 

[DiscreetSpeed]

yeah your engine is gone!

 

[jflo]

maybe you should do the recommended break-in period before you bust your balls on your engine...

 

[mazdadan]

Yeah, keeping it below 3K RPMs during the break-in is crazy. The only time my Protege was below 3K was when it was sitting idling. 4 banger engines love to be revved. As long as you aren't redlining it during break-in you should be fine.

 

[Brian MP5T]

I would take it to a dealer and have them look into it. The car is new. Ask to test drive another one and see if it does the same thing.

Later...Brain

 

[funnylittlman]

Since you are in NOVA,

Let me know, we can meet up and we'll see if mine does the same thing

-fnny

 

[CustomMSP]

Could be a backfire?

 

[Brian MP5T]

Normally a backfire is shot out because of a rich condition usually caused by a carburetor.

I think what you are talking about would be fuel passing through the engine un burnt and hitting the manifold and exploding then causing a "Pop" Yes??

I don't think that it would be audible and also not likely on a EFI car and more importantly a "New EFI car".

Good idea though.

The only ones that I can think of is rear bushings or something else. ??? I'm at a loss, hence the suggestion to take it to the dealer.

 

[funnylittlman]

It might just be the exhaust. the MSP's exhaust is a little noisier than others... a little more bassy to be exact

 

[Mach 3.5 Turbo]

In the clutch industry, we have something like this we call "body boom." This might be what you are hearing. Basically, the engine is vibrating the car at it's natural frequency. This shakes certain body panels, much like the cone on a subwoofer (think of what they look like when they play really low notes). Basically, it just makes a subwoofer out of one of your body panels. Once you speed the engine up, the frequency of the vibration moves past the car's natural frequency and the panel quits vibrating.

Does this sound like what you are experiencing? To test it, get the car to the point that it makes the funky noise, then speed up and see where it goes away. Then get it back to that point and slow down. Really bog the engine if you have to. If the noise goes away or at least lessens in intensity, this is probably what you're hearing. See if the noise happens only around a certain engine rpm. If it's "body boom," then that's what you're hearin'

 

[Stormtrooper77]

It just sounds like your lugging the engine (not enough rpms for the corresponding gear).

 

[CustomMSP]

Brian,

I get backfires all the time with my catless dp and no resonator.

 

[garretts77]

Sonic Boom...

 

[AamirMSP]

maybe you should do the recommended break-in period before you bust your balls on your engine...

Please Remind me again how im busting the ball on my engine by shifting at 3k or below? I never said I have redlined it, in fact, the car has not been revved past 4500rpm yet, and for the record, my integra type R doesnt boom in to 4th shifting in below 3k rpms, and most importantly my roommates MSP does not either. So its not because im shifting below some magical point. I thought maybe someone else may have experienced this issue when shifting, but I guess not. I will be taking it in to the dealer. The joy of warranty.

 

[jonnydoe48]

It just sounds like your lugging the engine (not enough rpms for the corresponding gear).

agreed. i think its also the clunk though. its happening because there is a jerk when he shifts and its bumpy.

 

[t3ase]

It might just be the exhaust. the MSP's exhaust is a little noisier than others... a little more bassy to be exact

Our stock exhaust is pretty much silent. The true "Mazdaspeed" exhaust, however, is not.

 

[jflo]

Please Remind me again how im busting the ball on my engine by shifting at 3k or below? I never said I have redlined it, in fact, the car has not been revved past 4500rpm yet, and for the record, my integra type R doesnt boom in to 4th shifting in below 3k rpms, and most importantly my roommates MSP does not either. So its not because im shifting below some magical point. I thought maybe someone else may have experienced this issue when shifting, but I guess not. I will be taking it in to the dealer. The joy of warranty.

sorry doode, didn't mean to sound like a dickhead there...just thought there might be something to do with your break-in period. and when you do take it to the dealer, make sure you ride with the service dept. manager to replicate the "boom" because if they do it themselves, they may claim to not be able to reproduce the problem and just write it off...same thing w/ the lil' oil streaks on my turbo. anyway, hope you get your problem fixed soon !

MACH 3.5 TURBO- that explanation sounds very interesting...so if i took some kind of vibrating thing (say a massager) to my door panel, i could make a sound at a certain frequency ? nutz0rz...maybe if we tune subs to bump at that frequency, our whole car will shake and bump to the phat beats

 

[Mach 3.5 Turbo]

Yeah, you could theoretically "subwoofer" a panel on your car on purpose, but you probably wouldn't want to. The idea of tuning your sub to vibrate your car is interesting, but I think you would just be rattling loose every screw in it. Know why guys put dynamat around their subwoofers? To keep the panels from rattling. The main reason Dynamat works is becuase it moves the natural frequency of what you roll it onto below what your subwoofer can produce. If your engine is causing the vibration, then you could roll some Dynamat onto the panels and it would stop. If you were to excite all of your body panels to vibrate when a bass note hits, you would get some wicked rattling, like one of those ghetto caddies that just sound like a bag of aluminum cans when they hit.

 

[AamirMSP]

A few people have suggested that I am lugging the engine, but this produces a low frequency drone that is apparent as long as throttle is applied at too low a rev range. The car is not lugging at 2400-2600 rpm.

This "boom" is a one time sound as soon as i let out the clutch in fourth gear. It never occurs above ~3200 rpm but almost always below that rev mark.

I'll let you all know what I find out. Thanks!