Strange loud knocking noise ACD pump
 

Hello Lancer RALLIART / EVO tech specialists!


I have a very special problem with my `09 Lancer RALLIART sportback:


My mmc dealer installed a new ACD pump because mine was broken (corrosion).
The new pump made a very strange loud noise after building up pressure. So i`ve got a new pump under warranty. Now i have the second NEW pump installed and the noise is still the same. My dealer does not know how to fix it .What do you think: Is there a Problem with air in the pump? Or is there a problem with the software, or are some pumps already faulty when the are new?? The link with the video will show the problem i have with these pumps. Listen to the noise when the pump has built up pressure and switches off. Has anyone an idea what the cause for this loud knockung noise is???


https://vimeo.com/182702589


Thank you very much!!


Georg from austria

Are you concerned about the whining as it builds pressure? That sounds normal.

i know that the whining is normal. the problem is the loud "knock" after building up pressure. the whole car body is vibrating when the pump does this...it cant be a normal operating noise of the pump...

Bad batch of ACDs?


Normal Operation is:
Pump builds pressure in the accumulator which; a. stores pressure, and b. absorbs pressure shocks. Pressure remains in the accumulator with a check valve (pressure goes in/can't bleed back out to reverse-drive the pump). An electric solenoid opens on command to allow pressure to the Active Center Differential to pressurize actuators to release clamping force ("open the axle") and allow front wheels to spin at a different speed than the rears. Once steering wheel returns to center - solenoid closes and relieves pressure on the ACD clamping actuators.


So...
What could "bang?"
1. Accumulator gas charge depleted and system is experiencing pressure spikes as in 'hammering'...
2. Solenoid is loose/out of tolerance and 'slams' open or shut ( I hear this in my TC-SST on the shift to 6th gear if I am not applying some gas pedal to 'load' the shift).
3. Air in the system (not properly bled enough) and the pump cavitates or the air bubbles make noise in the system.
4. Check valve leaks pressure which causes the pump to counter-rotate until the motor tries to spin in it the correct direction...


Next Step:
1. Bleed the system again with a different tech - in case tech #1 did both bleeds incorrectly... I would assume nothing about their skill and ability at this point.
2. Have the mitsu tech "listen" with a stethoscope for where exactly the banging is coming from. If it is the ACD pump assy - replace again with a known/good one (from a car on the lot if necessary).


DO NOT ACCEPT AS NORMAL OR "OKAY". This kind of noise indicates a real problem that will get worse until the system fails.


Good luck! Be persistent.

Dear Veronica,


Thank you for your very detailed answer!
The master technician in our austrian mmc headquarters will decide what to do next, because it is under warranty. If i would try to repair something on my own it could happen that warranty is extinguished...
But you are completely right that i should not accept this noise as normal. Sometimes i think the ACD pump is exploding when this "bang" appears.
It could really be that there are faulty pumps from factory because i was there when the second new pump was bled. They bled it 4 times with MUT-III so i do not think that there is air inside the system. Also the "whining" when the pump builds up pressure is normal. If there is air inside it that noise would be different or what do you think?
The main problem to diagnose the reason of this noise is that we have very few of this cars running here in austria most of techs are overwhelmed with the technology of these cars. Today our master technician told me that he has sent the video to a special technician in japan wo will hopefully know what the problem is...i will post again when i know more...


Greetings from Austria,
Georg

When you say he bled it four times, what exactly do you mean by that? Can you be more specific?

The reason I ask is I believe that is the sound of an improperly bled pump. It may very well be that there was a bad batch (though highly unlikely) and even after being bled it is somehow allowing air into the system, but one way or another, I am almost certain that is the sound of the unit compressing fluid and then all of a sudden compressing air.

It actually makes that sound and/or a similar, yet longer groaning sound during the fluid bleed procedure if the system still has air in it. I have done plenty, myself, and that would be my first guess.

They did the bleeding procedure as following:


One tech was sitting on driver seat of the car with the MUT-III, another was under the car located at the draining nipple at the center differential and the third one at the container in the trunk. They started the bleeding procedure with the MUT-III four times. MUT-III starts the pump and after some minutes it sais "bleeding complete". So four times Mut-III said "bleeding complete". The tech said they did it four times for safety that it is 100% properly bled. There is one more thing i saw when they were bleeding: They ALWAYS turned the steering wheel from left stop point to right stop point while the whole procedure. IS THIS CORRECT OR COULD THIS CAUSE THE PROBLEM??
If there is still air in the accumulator/pump what would be the correct procedure to bleed it??


Thank you very much!!

You must turn the steering wheel to activate pressure at the nipple at the diff.
Sounds like they did it correctly.

Sorry to revive a kind of old thread. My ralliart is doing exactly this. Did you ever find out what was the problem with your awc pump? Thanks in advance.

mine has also been doing this sporadically, and only during heavy acceleration.