How to make a motor smoother?

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I drive a 2003 Mitsubishi Diamante, 6G74.

It is fairly smooth, with the exception of high load, low rpm driving.
So, 5th gear under 2,000rpm on an uphill and there is a humming type harshness.

Is there any way to get it smoother in that rpm range?
The TCU is hesitant to downshift to 4th when the torque converter locks up, and that is the scenario that it is most harsh at.
 
Shift the trans. I would select fourth. Alternatively, try to tap the brake with your left foot, leaving your right on the throttle. That ought to force the TC to unlock.
 
Make sure the Harmonic Balancer is working properly, check motor mounts, use fuel Octane as specified in owners' manual.

You should not be operating any motor in a High Load Low RPM mode. Downshift, force unlock the torque converter, etc but keep those revs up under high loads. Aside from the harshness you're experiencing, it can lead to detonation and resulting engine damage.

Exactly what RPM constitutes "too low RPM" is going to vary with engine configuration, size, and state of tune. But experiencing unusually rough running is certainly an indicator. Find an RPM level that is as smooth as you expect under normal driving conditions, and don't run below that RPM under heavy loads.
 
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How do I test the balancer?
And is this something that would wear out with time?

Above 2,000rpm it is fine, but it is around 1,500-2,000rpm that it has this humming type vibration under load.
 
Originally Posted By: Spetz
How do I test the balancer?
And is this something that would wear out with time?

Above 2,000rpm it is fine, but it is around 1,500-2,000rpm that it has this humming type vibration under load.
"Doc, my arm hurts when I lift it...." Doc: "Don't lift it".
 
don't use xW-20
wink.gif
 
Originally Posted By: Spetz
I drive a 2003 Mitsubishi Diamante, 6G74.

It is fairly smooth, with the exception of high load, low rpm driving.
So, 5th gear under 2,000rpm on an uphill and there is a humming type harshness.

Is there any way to get it smoother in that rpm range?
The TCU is hesitant to downshift to 4th when the torque converter locks up, and that is the scenario that it is most harsh at.
Sounds like a drone to me. You just may be stuck with it. More prevalent in some engines than others. See if you drop a gear to get out of that rpm range. They tend to lock up the torque converter to increase fuel economy. I drive a 2015 Equinox with a 2.4 Ecotec. It has a drone as well. I run Total FGC 5w30 that reduced that drone some, but it doesn't disappear. You may find a combination that helps you as well. Good luck!
 
under the hood can you see if the throttle uses a cable or is it electronic drive by wire?

if it is cable operated there is usually a second cable that goes from the throttle body butterfly valve to the trans

Try and tighten it up a little, try 1/8 inch at a time then drive around the block to test

that should make the car downshift sooner without having to push down on the gas pedal all the way to the floor

my 2 c
 
Originally Posted By: CT8
Lugging the engine?


That's what I'm thinking, which is why I posted the "don't use thin oil" message.


If you want more torque low down, you'd need to change the cam timing and/or fit other cams, and get a remap aswell.

Or change the behaviour of the transmission, so it won't hold on to low revs as much.
 
If the engine was lugging, wouldn't adding more torque only increase the pressures on the bearings more?
 
Don't drive with that low rpm. Take it down a gear.
My cars and trucks don't lug at even 1000 rpm but they aren't responsive either.
Keep it in 4th when driving in the city. Use the higher gears for the highway.
My trucks stay in 3rd when in the city. Only hitting 4th on the highway.
I slap shift the charger or let it shift on its own at 5500rpm. It's a fun car.
 
Is there any torque converter specialists on this
forum that could explain the causes, cures and symptoms
of a bad converter?

I've known people who have chased what they thought to
be an engine shudder or vibration, only to discover
the problem was in the driveline or transmission
all along.
 
Originally Posted By: Spetz
How do I test the balancer?
And is this something that would wear out with time?

Above 2,000rpm it is fine, but it is around 1,500-2,000rpm that it has this humming type vibration under load.


Physical inspection. They are two metal pieces bonded together by rubber. The rubber can deteriorate.

See:
http://www.underhoodservice.com/harmonic-dampeners-fail-look/

Note: Aftermarket balancers are available. For stock engines without performance internals and/or extended RPM modifications to the valvetrain, they are unnecessary.
 
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Hey guys,

I have had the shift map adjusted so that it gets into 5th later, and downshifts to 4th easier, it seems like when the torque converter is locked it partially ignores the map and does not downshift.

This vibration (it feels like the car has a loud muffler, but it doesn't) is there in all gears, but the more load the more pronounced it is, essentially only being really obvious in 5th gear, up a hill when the torque converter is locked.

The car also has a constant miss at idle, could this vibration be a part of the miss?
 
Originally Posted By: Spetz


The car also has a constant miss at idle, could this vibration be a part of the miss?


Duuuh, bingo!
 
I've been unable to diagnose the miss though.
The car has had new:
Air, fuel and oil filter
New spark plugs, leads, distributor rotor and button
Ultrasonically cleaned and tested injectors
Hooked up to a diagnostics machine and all sensors were reading fine

The only thing that seemed to have made the idle better (but not the vibration in the 1,000-2,000rpm range) is replacing the EGR solenoid. I then have tried blocking the EGR all together but this made no effect on idle.
 
Originally Posted By: Spetz


The car also has a constant miss at idle, could this vibration be a part of the miss?


This is a very important piece of information.
 
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