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Q4 Viscomatic "bad piston movement" while bleeding

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Q4 Viscomatic "bad piston movement" while bleeding

Postby AlfaWhiz » Mon Jun 05, 2017 7:24 am

I've had some success with my Viscomatic system during the weekend. I was able to plut in the F/L Tester with the correct module and identify the code causing my 4x4 light to come on. It was a "faulty" brake switch. I have measured the continuity of all wires and voltage registered by the Viscomatic computer, and while the continuity between the brake switch connector and Viscomatic plug was fine, one of the two brake switch signals was not triggered correctly. Remember, the brake switch gives both the "pedal pressed" and "pedal released" signals to the Viscomatic, for a sort of a double-check.

Faulty brake switch fix: remove the brake switch by unplugging the connector and rotating it 90 degrees. Take it out to your workbench and disassemble (very easy, just some locking pins on both sides). The spring inside will pop the housing out. Clean thoroughly and adjust clearances. Reassemble and measure with a multimeter, one circuit should be interrupted while the other one is connected at the same time between the pins. It's a very simple device.

So no more warning light and no more error codes, success! :mrgreen:

The pressure is regulater correctly between 95 and 85 bar (dropping slowly because some air is in the system, then re-pressurized by the system back to 95 bar).

Well, not entirely. I have been trying to bleed the Viscomatic system after replacing some of the copper gaskets by the accumulator using the F/L Tester and the "Ölablassung" (as written on the tester) or "Reinigung Öl" (as written in the module manual). Keeping the engine revs around 2000, the test runs correctly for about 5 minutes, keeping the pressure around 100 bar. Then unfortunately the test stops with a message "Bewegung Kolben falsch", meaning "bad piston movement" I guess. The test stops and no error code is saved ("no errors found"), the warning light does not go on.

I have checked the resistance of the piston sensor on the coupling and registered above 1k Ohm between two of the pins and around 2k Ohm on the third pair, which according to some old post by Wilco should be correct.

What does this mean? What do I look for? What should I check? :?:
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Re: Q4 Viscomatic "bad piston movement" while bleeding

Postby Alfan » Mon Jun 05, 2017 8:27 am

I have had some similar error codes (viewtopic.php?f=22&t=1135&start=75) and have not found the reason. One thing I have noted when trying to bleed the system (which fails), is that it starts at around 100bar, then drops to around 80, goes back up to 100, then drops and fails.

Error codes are the following (French module):

- signal course piston = signal piston stroke -> course trop courte absent = movement too short
- pressure systeme hydraulique -> variation signal trop importante absent

So if you find out what is happening with your system, I would like to know :)
1994 Alfa Romeo 164 Q4 Proteo Rosso 535.000km
1989 Lancia Thema 8.32 Verde Indy 260.000km
2015 Alfa Romeo 4C Rosso Competizione 75.000km
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Re: Q4 Viscomatic "bad piston movement" while bleeding

Postby AlfaWhiz » Mon Jun 05, 2017 9:20 am

Your piston stroke signal error seems to be similar to what I'm getting. As far as I see, this error is only mentioned in the active diagnosis / oil bleeding section of the MA12A manual, and not in the defects section. Mine does not register as an error code and the light does not go on, it only shows up when running the bleeding procedure.

Where did you get a spare piston stroke sensor, if you don't mind sharing? Swapping it out could be worth a try.

No problems with removing it from the housing?
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Re: Q4 Viscomatic "bad piston movement" while bleeding

Postby Alfan » Tue Jun 06, 2017 6:15 pm

I actually did replace the sensor from another rear diff I have. This did not change anything, so I am still stuck with this error.

Because of the mileage of my car, it might be something mechanical, so I am not sure what the next step will be...
1994 Alfa Romeo 164 Q4 Proteo Rosso 535.000km
1989 Lancia Thema 8.32 Verde Indy 260.000km
2015 Alfa Romeo 4C Rosso Competizione 75.000km
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Re: Q4 Viscomatic "bad piston movement" while bleeding

Postby AlfaWhiz » Mon Jun 12, 2017 7:53 pm

So believe it or not, I got some advice from alfisty here (thanks!) to basically run the car good and let the oil warm up etc., then repeat the diagnostics.

And guess what? At lest this time I was lucky! The bleeding procedure went through and completed successfully. No more errors and no more Viscomatic light on the dash, system working perfectly! :D

At some point I will have to approach replacing the Viscomatic lines though as they are getting a bit rusty, and it seems that it can't be done without removing the fuel tank. This is a separate story though. At least my drive works correctly now. :)
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Re: Q4 Viscomatic "bad piston movement" while bleeding

Postby Alfan » Tue Jun 13, 2017 12:33 pm

Great that you got the light to disappear!! :D

If only mine was that simple....
1994 Alfa Romeo 164 Q4 Proteo Rosso 535.000km
1989 Lancia Thema 8.32 Verde Indy 260.000km
2015 Alfa Romeo 4C Rosso Competizione 75.000km
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Re: Q4 Viscomatic "bad piston movement" while bleeding

Postby AlfaWhiz » Fri Jun 30, 2017 10:59 pm

So the bleeding problem with bad piston movement disappeared, Viscomatic bleeds itself correctly now. I have repeated it several times already.

I have another problem though. The 4WD light comes on after a couple minutes of driving over 100 km/h with error "Druck Hydrauliksystem, Variierung Signal zu groß", meaning "hydraulic system pressure, too large variations of the signal".

It is very interesting as the system works correctly on speeds below ca. 100 km/h and the error never appears when driving slowly. I was observing the piston movement using the F/L Tester, which works correctly, and pressure is regulated between 95 and 82 bars, dropping over a 10-15 second period or so and being replenished to 95 bars repetitively. This leads me to believe that both accumulator and pressure regulator work correctly.

The possible causes as listed by the MA12A manual are a defective hydraulic pressure sensor, defective accumulator, or electromagnetic interference on line to pin 18 of the Viscomatic ECU.

As the pressure seems to be regulated correctly, and the error only appears when driving 5-10 minutes over 100 km/h, I don't really know what to make of this.

Do you guys have any ideas? :?:
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Re: Q4 Viscomatic "bad piston movement" while bleeding

Postby Alfan » Sat Jul 01, 2017 8:54 am

I don't know what could cause this, based on the speed relation, you mention.... But an electrical issue seems most likely to me.

Fluid level is ok?

So the light stays on, until you restart the engine?
1994 Alfa Romeo 164 Q4 Proteo Rosso 535.000km
1989 Lancia Thema 8.32 Verde Indy 260.000km
2015 Alfa Romeo 4C Rosso Competizione 75.000km
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Re: Q4 Viscomatic "bad piston movement" while bleeding

Postby AlfaWhiz » Sun Jul 02, 2017 10:17 am

Yes the light stays on until the engine is restarted and the drive is disconnected (no 4WD). Fluid is OK. I'm really puzzled by this. I was thinking maybe some electromagnetic interference is possible as they do mention this specifically in the manual, but absolutely no idea what could cause this. Some rotating mass? Rotating wheels? Driveshaft? Or maybe just some electrical gremlin. I'll try cleaning all connectors first, but it will be tough if this doesn't help.
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Re: Q4 Viscomatic "bad piston movement" while bleeding

Postby krrobrock » Tue Aug 01, 2017 6:53 pm

Hi there. I am about to go through the bleeding process on my Q4, which has been apart for many years and is finally up and running again. This thread is fantastic, and should help me out a bunch. I have the tester equipment. Does anyone have the MA12A manual they could share with me? Happy to share my email address via direct message if that makes most sense.

Thanks!

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Re: Q4 Viscomatic "bad piston movement" while bleeding

Postby Alfan » Tue Aug 01, 2017 7:59 pm

I have tried attaching the manual, together with some translation to English, hope it works.
Attachments
ma12a text.pdf
separate translation
(42.88 KiB) Downloaded 35 times
Marelli Tester MA12A Module 164Q4 4WD Viscomatic.PDF
Module description
(531.71 KiB) Downloaded 34 times
1994 Alfa Romeo 164 Q4 Proteo Rosso 535.000km
1989 Lancia Thema 8.32 Verde Indy 260.000km
2015 Alfa Romeo 4C Rosso Competizione 75.000km
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Re: Q4 Viscomatic "bad piston movement" while bleeding

Postby krrobrock » Tue Aug 01, 2017 8:18 pm

Thanks a bunch Alfan! Will give this a go.
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Re: Q4 Viscomatic "bad piston movement" while bleeding

Postby Alfan » Fri Aug 11, 2017 2:44 pm

Did you get any further with this, Karl?
1994 Alfa Romeo 164 Q4 Proteo Rosso 535.000km
1989 Lancia Thema 8.32 Verde Indy 260.000km
2015 Alfa Romeo 4C Rosso Competizione 75.000km
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Re: Q4 Viscomatic "bad piston movement" while bleeding

Postby wilco » Thu Sep 28, 2017 4:56 pm

what oil are you using.. could it be wrong viscosity ?
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Re: Q4 Viscomatic "bad piston movement" while bleeding

Postby AlfaWhiz » Fri Nov 24, 2017 10:53 pm

Thanks for your replies guys, I've been quite busy lately without much time to poke around this issue...

I'm using Motul Multi HF in my system, like this one: https://www.motul.com/us/en-US/products/multi-hf It has virtually the same viscosity at 40 and 100 Celsius as Tutela GI/R, so it should be fine I guess.

Any other ideas? :?:
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Re: Q4 Viscomatic "bad piston movement" while bleeding

Postby Alfan » Mon Nov 27, 2017 4:47 pm

I hope to tackle the 4WD issues on my Q4 during winter, so no news or ideas from my side...
1994 Alfa Romeo 164 Q4 Proteo Rosso 535.000km
1989 Lancia Thema 8.32 Verde Indy 260.000km
2015 Alfa Romeo 4C Rosso Competizione 75.000km
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Re: Q4 Viscomatic "bad piston movement" while bleeding

Postby AlfaWhiz » Wed Nov 29, 2017 6:57 pm

Honestly the only thing I have for my problem is that I will try to clean all contacts... If the problem persists, the next thing is to replace all hydraulic lines, fittings and seals. If it still persists, replace the accumulator/hydraulic group.

No good chance for educated troubleshooting with so little info we have about those errors. The only thing I've noticed which got me thinking a bit is that there are 2 errors related to hydraulic pressure mentioned in the manual of the MA12A module in 2 separate places. One is called "signal hydraulic pressure" and reasons lean more towards wiring problems, while the second one a bit further down the text is called simply "hydraulic pressure of the system" and this one mentions also faulty accumulator as possible cause. I'm getting the second error in my case.
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Re: Q4 Viscomatic "bad piston movement" while bleeding

Postby alfa east » Thu Nov 30, 2017 3:08 pm

I would certainly look onto the possibility of wire loom leakages. Happens sometimes with my ECU of the Auto gear and then the car goes into limp mode. Happens mostly when driving through a tropical downpour where the wiring gets damp. Putting it out into the sun for a few hours clears it up.

These wirelooms are now around 25 years old, the insulation material has deteriorated. Mostly it's not a sensor malfunction.
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