Changing ATTESA Accumulator: Depressurize System First?

[accel junky]

Hey Folks,

Been looking around for help with this but I’m not on social media now and info is slim out here in the Internet wilds.

I’ve got the subframe out of my R32 GTR and preparing to proactively replace the accumulator on the 4WD pump. Info out there suggests I need to depressurize the system before I try to remove the original. Is this as simple as having the ignition off (hasn't been started in weeks) or is there something else that needs to be done? Prefer not to screw something up or make a huge mess.

And further, would it be necessary to bleed the system after the canister is swapped?

Much appreciated.

[Duncan]

Firstly, let me say, I've got no idea and never done this.

If the subframe is out of the car, then the hydraulic system is disconnected and therefore the only potential pressure in the system is inside the accumulator/nitrogen cannister that you are trying to replace. That cannister surely is sealed (or that seal has failed in some way which is why you are looking to replace it) so it is just a case of unscrewing the cannister.

Unfortunately the workshop manual says the attessa unit "cannot be disassembled" even though nissan sells the cannister as a part.

[accel junky]

The pump and lines are all still connected as it was I just bungee’d them up after I lowered the diff/subframe down. I read the same thing in the manual, it wasn’t much of a help. I feel like the pump probably depressurizes once the car is turned off (I hear sounds all the time post-shutdown) but I don’t want to assume and create a disaster.

[joshuaho96]

https://www.gtr.co.uk/threads/attesa-accumulator-nitrogen-canister-change.572973/#post-5815458

Quote

Disconnect battery. Open bleed nipple on Attessa unit above diff to release pressure.

 

[accel junky]

41 minutes ago, joshuaho96 said:

https://www.gtr.co.uk/threads/attesa-accumulator-nitrogen-canister-change.572973/#post-5815458

 

Thanks! I poked around there but somehow missed that comment.

[TXSquirrel]

2 hours ago, accel junky said:

The pump and lines are all still connected as it was I just bungee’d them up after I lowered the diff/subframe down. I read the same thing in the manual, it wasn’t much of a help. I feel like the pump probably depressurizes once the car is turned off (I hear sounds all the time post-shutdown) but I don’t want to assume and create a disaster.

Is it a mechanical whirring sound you are hearing post shutdown?  Like some kind of pump running?  

 

[accel junky]

21 hours ago, TXSquirrel said:

Is it a mechanical whirring sound you are hearing post shutdown?  Like some kind of pump running?  

 

I isolated that noise. It's like a foghorn sound and there is a little damper ahead of the fuel tank in the area where the 4wd pump normally sits.

I got the new accumulator on. Ultimately I got impatient and used a 3 prong oil filter adapter to turn it by the end cap but unfortunately that unthreaded from the base and discharged the nitrogen sending the canister flying. There was some fluid involved but not a ton. In the future I'd wait for the steelman socket to arrive and take it off by the base.

I attempted to bleed the system with the ignition on, plug under kick panel unplugged and whatnot but ultimately the pump never came on. Best I could tell it was just the noisy Nismo fuel pump priming when the ignition turned on. I'm guessing that because I have the subframe and diff dropped the grounding straps unhooked will keep the pump from running? Also the rear ABS sensors are unplugged (attached to diff currently). I hope either of those would be why the pump doesn't sound like it runs and that I did not mess up something. No prior 4WD dash light or known 4WD issues before dropping the subframe. I'd hate to put the subframe back in, hook up those grounding straps and then discover something on the 4WD pump is shot.

Edited July 26, 2020 by accel junky

[TXSquirrel]

I am having a weird sound coming from the back post shutdown as well.  It sounds a little different from both the fuel pump and attesa pump, and it could be described as fog horn.   I notice it usually happens after I drive extensively. 

But a couple weeks ago when the weather got pass 100°F and I was out in the front yard, I heard the sound just came on for no reason, even though car has been sitting in the garage for over a week.  Then I heard it again last week, also when weather was very hot and car hasn't been moved for some time.  

I am still trying to figure out what it is, but it's impossible to replicate as it just comes on randomly when (I presume) weather is hot.  My friend thinks it's because the fuel tank evap line is clogged and the noise is from fuel pump, but I'm not sure how likely that is with car just sitting there untouched.