166 issue

[alfagtv152]

Hi Guys,
Anybody experienced with 166 issues that sound like this?.
My 166 went nuts today after a burst of acceleration it started to miss,run rough and extremely lean. I say lean as the rear extractors were glowing red!.Spark plugs are not old and I dont believe it is coil related as No check engine light or fault codes and when connected to Alfa Obd I cant log anything except injector signal, does this sound like ECU?, or could it just be air flow meter related even though it only produces the code for it if you disconnect it.

[colcol]

Has the heater sprung a leak?, and is leaking on to the ECU?, Colin.

[alfagtv152]

Hi Colin,
No. The transmission functions ok.

[giulia_veloce]

Just a thought.

We chased a similar problem with glowing exhaust.
Fuel smelt funny.
Drained an refilled the tank with reputable 98 and problem fixed.

Robert

[alfagtv152]

Hi Robert,
Thanks for the thought,it has had that tank of fuel for about a week and only 40km but the symptoms appeared suddenly after a full throttle burst in bottom. The fuel was from a local OTR which is busy so I would expect the fuel to be fresh.
Today I managed to get it to log data and the only obvious thing I can see is one very low cat reading compared to the other 3 so I will suss that out tomorrow.
Cheers
Andrew

[alfagtv152]

Can anybody tell me what sort of values you would expect to see on the 4 sensors at idle?

[johnl]

A lean mixture burns hotter, so could possibly overheat headers. A rich mixture burns cooler, but not all the extra fuel may burn in the cylinder, so fuel could still be burning as it enters the header, causing higher than normal header temperature (a somewhat similar condition can be caused by very retarded ignition timing).

That there appears to be a problem that affects the entire header on only one bank suggests a problem with metering on that bank only. Not knowing the V6 engine, I expect it has at least one O2 sensor per bank? Problems with O2 sensors are often not recognised by the  ECU...

I'd be checking spark plug colours.

Regards,
John.

[Jekyll and Hyde]

Running like a bucket of bolts and one side extractors glowing red, all after giving it a bootfull? First place I'd be looking if it were my v6 is checking cam timing...

[bazzbazz]

I had the EXACT same thing happen to our old magna when the catalytic converter melted and was almost completely blocking of the headers. Worth a check?

Baz

[alfagtv152]

There are 4 o2 sensors as I said earlier, I have one reading lean pre cat right bank and the other 3 normal range values.
I disconnected them all and it defaulted to a value of 437mV each with no change in running.
Cam timing is still spot on.
As far as checking the plug colour I will have to do it but checking the back plugs requires the removal of the complete inlet plenum and intake system which is a little arduous.
Yes I assume glowing extractors indicates lean mixture which is born out by the pre cat oxy sensor for that bank but I have also heard of blocked cats causing similar issues. Pitty that bank is the one squeezed up against the fire wall.
Fuel pressure is good in both rails. It just really annoys me that the ecu doesn't give me any fault codes or clues as to what the issue may be, I thought what all this electronics was supposed to be good for!.
Oh well,I will just have to keep plugging away.

[johnl]

I had the EXACT same thing happen to our old magna when the catalytic converter melted and was almost completely blocking of the headers. Worth a check?

Baz

Baz,
A melted cat is I think quite unusual, and would suggest pre-existing excessively high exhaust temperature...

Regards,
John.

[bazzbazz]

Ahhhhh, Catalytic Converters ARE NOT melted by temperature, but by fuel poisoning! Once poisoned the small holes in them become blocked restricting the exhaust gas flow, turning the exhaust manifold/extractors into something akin to a Kiln, thus the reason why they glow bright red.   

And plugged/fractured cats are VERY common, I should know, I diagnose/repair them quite often. A glowing bright red exhaust is the classic indicator of blocked exhaust, the reason is the hot gasses are held in the header space for a protracted period, super heating the metal, instead of being carried away quickly.

But as new cats are not cheap, I would love to be wrong, and hope I am.

Baz

[Darryl]

But as new cats are not cheap, I would love to be wrong, and hope I am.

Baz

Special lightweight free flow ones may not be 

[johnl]

Ahhhhh, Catalytic Converters ARE NOT melted by temperature, but by fuel poisoning! Once poisoned the small holes in them become blocked restricting the exhaust gas flow, turning the exhaust manifold/extractors into something akin to a Kiln, thus the reason why they glow bright red.   

Then can an affected cat be described as having been 'melted'? Surely it is 'blocked'...?

And plugged/fractured cats are VERY common, I should know, I diagnose/repair them quite often. A glowing bright red exhaust is the classic indicator of blocked exhaust, the reason is the hot gasses are held in the header space for a protracted period, super heating the metal, instead of being carried away quickly.

I've yet to encounter an obvious problem with a catalytic converter, which is why I said "I think". I'm not disagreeing with your experience, I'll accept I've just been lucky so far...

Regards,
John.

[bazzbazz]

Lets hope the good luck holds for as long as you own your beloved Alfa 

Baz