Technical Twinair dispersion correction and AFAS

[puntodeltathema]

Hello all

I have a 500 twinair 85 in my care at the moment with a rough running issue. Euro 5, 2011. I know, just another day.

The ECU is giving generic misfire errors. Coil replacement hasn't worked. The plugs were very black so I have a pre-Cat lambda sensor on order.

Just pessimistically thinking ahead to what to do next (!), I'm eyeing the "dispersion correction" procedure on Multiecuscan. I have done oil resets before but not the dispersion correction as I haven't really understood what it does.

MES also says cryptically that this is for cars with "AFAS". (On the MES users' forum there was a vague suggestion this might only be relevant to Euro 6 cars but this wasn't conclusive).

Does anyone know what AFAS is or stands for, and indeed what dispersion correction does that an oil reset would not?

Many thanks!

Nick

 

[Goudrons]

From what I understand.

AFAS is a timing components wear adjustement reset function.
It's performed if you've had the timing chain off.

Dispersion Correction is to do with the Uniair module.

This adjustment is aimed at adjusting dispersion of components affecting the actuators of the air intake circuit (control valve), in particular it progressively eliminates the mechanical error of the camshaft and the dispersion of the UniAir actuator; the procedure shall be executed in the following cases:
Engine ECU replacement
Crankshaft replacement
Rpm sensor replacement
Camshaft replacement
Camshaft sensor replacement
UniAir module replacement
UniAir oil temperature sensor replacement
Replacement of UEGO lambda probe upstream the catalyst
Warning: before executing this control, the AFAS values reset function shall be executed.

There's more info on these functions on various Alfa sites.

If it's got oily plugs and a misfire and it's not the plugs or coil packs, I gather it's pretty much nailed on it's a faulty Uniair module.

 

[puntodeltathema]

Thanks. The engine is quite rattly even for a TwinAir which is a bit of a worry. And it's had some time out of the Fiat mechanic community so no guarantee what oil it has had.

Misfire only affects idle - it's fine on the gas.

Next step the lambda sensor anyway - fingers crossed! Otherwise a difficult conversation with the owner.

Nick

 

[varesecrazy]

Out of interest..
How many miles on it.?

 

[Goudrons]

Misfire only affects idle - it's fine on the gas.

Nick

If there is a problem with it controlling the valve timings it'll tend to be worse at low rpm like idle.

Where most variable valve designs alter a cam profile designed for slow rpm forward to be more efficent at higher rpm, Fiat's Uniair system is the opposite.

Fiat utilises a "hot" cam designed for high rpm and backs it down for slow rpm by use of a fluid link between the cam and the valves.

A fault in the Uniairs operation will effectively see it stuck with a cam profile designed for higher rpm. At low rpm it will run like a bag of spanners!

 

[Goudrons]

How MultiAir works

When the electronic solenoid valve is closed, the chamber becomes a solid body and the valve follows the profile of the cam exactly.

But if the electronic solenoid is opened to release some of the oil, the chamber shrinks to absorb the cam movement and the valve opens less.

Choosing when to bleed the oil from the chamber, as well as by how much, makes it possible to control timing and lift as well as the duration of opening on an individual, valve-by-valve basis.

The mechanical inlet cam profile is 'hot', that is to say designed for high power at high rpm.
For maximum power, the chambers remain full so the valves are opened to their maximum for longer.

At slow speed, the solenoid is opened near the end of the cam's 'ramp' to close the valve early, maximising the amount of air trapped in the cylinder and improving torque.

At part throttle, different strategies are used, partially opening the valves to trap just the right amount of air and speed up air flow.


The oil/fluid link is actually engine oil, so if it's really low on oil or can't pump it around it can't work properly.

There's a oil screen screwed into the system under a blanking plug in the middle of the cam cover, I did a post regarding cleaning out the screen a while ago.

I am not familiar with Multiecuscan, can is log cam position or any of the Uniairs solenoids as the rpm is increased/decreased?

 

[puntodeltathema]

Out of interest..
How many miles on it.?

It's just turned 74k.

Thanks all for the advice.

Predictably perhaps the lambda sensor made not a jot of difference so I guess we are looking at uniair replacement, which I now need to mug up on (being far more used to 1.2s).

I can't help feeling in my bones that all of this started when I reset the oil parameters at last service - is that a possibility?

And I presume cleaning the microfilter is not going to reverse this at this stage?

Ho hum.

Nick

 

[varesecrazy]

It's just turned 74k.

Thanks all for the advice.

Predictably perhaps the lambda sensor made not a jot of difference

And I presume cleaning the microfilter is not going to reverse this at this stage?

Ho hum.

Nick

Clean the filter.. you never know

74k on junk oil might have clagged it up

 

[puntodeltathema]

Hi - so just to close out this for the collective knowledge.

Actuator filter ok (surprisingly clean in there).

Multiecuscan would not let me perform the dispersion correction operation, implying this was not supported on the Euro 5 ECU. Which I think I had read somewhere else. And yes I did wait for the oil temperature sensor to get to at least 83 deg C.

Tried resetting the general adaptation parameters and did another oil change reset* to no avail. Idle (and transition to power in the 1000-2000 rpm range) still rather poor with intermittent misfire errors. Car still pulls quite sweetly like a train however on the gas.

(*I'm starting to wonder if the oil change reset is something to leave well alone if the engine runs OK after an oil change - there's some anecdotal evidence this procedure was expunged from official Alfa diagnostic equipment for Twin/Multiair- does anybody have a view on this?).

Which all points to needing a new Uniair actuator module as previously suspected (last ditch attempts worth a try though).

Suspicion is that 4 or 5 years being serviced at a general local independent garage (with unspecified 5w40) has done the damage. Another cautionary TwinAir tale.

Nick

 

[varesecrazy]

Worth a call to somebody like
'Small Car Services'

Who have LOTS of experience with these units

The £700 pricetag of a replacement unit means its worth exploring the other options

Have you analysed exhaust gasses to see which way it swings ?

 

[varesecrazy]

Hi - so just to close out this for the collective knowledge.

Actuator filter ok (surprisingly clean in there).

(*I'm starting to wonder if the oil change reset is something to leave well alone if the engine runs OK after an oil change - there's some anecdotal evidence this procedure was expunged from official Alfa diagnostic equipment for Twin/Multiair- does anybody have a view on this?).

Which all points to needing a new Uniair actuator module as previously suspected (last ditch attempts worth a try though).

Suspicion is that 4 or 5 years being serviced at a general local independent garage (with unspecified 5w40) has done the damage. Another cautionary TwinAir tale.

Nick

Any conclusions ?

 

[s130]

Which all points to needing a new Uniair actuator module as previously suspected (last ditch attempts worth a try though).

Suspicion is that 4 or 5 years being serviced at a general local independent garage (with unspecified 5w40) has done the damage. Another cautionary TwinAir tale.

Nick

Correct oil for Uni/MultiAir modules is pretty critical. Fiat have changed the specs at least one if not twice. I'm assuming that when you did the oil change you put the current recommended spec oil in?

I understand Early Uni/MultiAir modules has some form of oil flow/return problem. Fiat would replace under warranty but Dean of Small Cars Services also developed some form of fix to solve the problem.

Dean of Small Car Services is highly experienced AND trusted by me so is certainly worth a call with your exact symptoms/problems.

Your only problem might be if you can reliably drive from Kent to Southampton?

 

[puntodeltathema]

Thanks that's a really useful lead.

I did put the correct Selenia KPE oil in (about two months ago now) as recommended for the Euro 5 engine, and performed an oil change reset using MES.

Nick