Could cat probs be related to petrol?

[andysat]

Hi all,while i am waiting for my emission light to come on again :roll: -i read that the cats can become 'clogged'-would putting the dearer type of petrol help in any way?-i am thinking the dearer stuff has more engine cleaning additives?-or am i way off the mark in my thoughts?-i never touch supermarket petrol,nothing wrong with it just the way i am.
I would appreciate any thoughts,thanks.

 

[tabbie]

I have only ever heared of problems with supermarket fuel. I only ever use 95ron in my Zed its pointless putting in super unleaded in a 2ltr

 

[mrlozzer]

Hi all,while i am waiting for my emission light to come on again :roll: -i read that the cats can become 'clogged'-would putting the dearer type of petrol help in any way?-i am thinking the dearer stuff has more engine cleaning additives?-or am i way off the mark in my thoughts?-i never touch supermarket petrol,nothing wrong with it just the way i am.
I would appreciate any thoughts,thanks.

What kind of driving do you do? Lots of short, local journeys. Motorway miles? Is the car left standing for fair periods of time?

 

[lacroupade]

The biggest single cause of damage to a cat is unburnt fuel igniting on the cat itself, so its has nothing whatsoever to do with the grade of fuel, and lots to do with how the car is driven and ECU telemmetry malfunctioning. e,g, the MAF could be faulty, giving faulty readings back to the ECU which squirts more fuel in than is needed for a given volume/density of air. Or maybe the car just does too many short journeys and doesn't get thrashed enough......

This 'supermarket fuel' thing is a fallacy by the way. I mean does anyone know where the 'supermarket fuel refinery' is?

Err no, because there isn't one....its all comes from the same place and the only thing that differentiates what comes out of the pump is the additives put in the tanker.

 

[lacroupade]

Actually this is a pretty good explanation...

Catalytic Converter Failure

Catalytic converter failures typically fall into one of four categories:
1. Thermal failure (overheating)
2. Plugged substrate
3. Thermal shock
4. Physical damage

Thermal failure is most often caused when excessive raw fuel comes into contact with the catalyst, and "burns" in the converter instead of in the engine. The high quantity of fuel generates temperatures well in excess of the capacity of the converter, causing meltdown of the ceramic monolith. The melted ceramic could block the exhaust path, leading to a significant loss of engine power. Visible symptoms include heat-related discoloration of the converter shell.

Potential causes of thermal failure include: misfire, malfunctioning oxygen sensor, fuel delivery issue, improper choke setting/operation, and ECU malfunction.
A plugged or contaminated substrate can be the result of an overly rich air/fuel mixture, radiator sealant, and oil or antifreeze entering the exhaust flow. The resultant carbon deposits restrict the operation - and ultimately the flow characteristics - of the converter by coating the unit's reactive surface. This degrades the converter's ability to perform its chemical conversion process, leading to potentially illegal levels of HC, CO, and NOx.

Root causes of this problem are a malfunctioning O2 sensor, plugged or inoperable fuel injectors, piston blow-by, leaking head gasket, broken or frozen choke or carburetor float, excessive cranking time, and repeated incidences of running out of gas.

Thermal shock occurs when a fully heated converter suddenly is "cold-quenched," such as coming into contact with snow or ice. This leads to sudden contraction of the converter housing, which can cause cracks and disintegration of the ceramic substrate. Symptoms include a "rattling'' sound when the converter is tapped with a fist or mallet (monolith-type converters only).

Physical damage, caused by running over road debris, collisions and other impacts, is usually easy to diagnose. This type of damage can break up the ceramic substrate or cause restriction that changes the flow characteristics of the converter or impacts the efficiency of the catalyst.

 

[andysat]

Wow thanks for that in -depth analysis,i drive 5-6 miles to work,then obviously home again with the odd hoon on a weekend.

 

[Ewazix]

Spot on

Premium fuels, such as Shell V-Power and BP Ultimate etc have additives that may benefit the running of the engine and therefore the Cat', but all UK fuel exceeds minimum requirements for proper operation of the BMW engines so won't be a cause.

As mentioned on another thread corrosion, splits and the interior falling apart due to the damage/thermal shock mentioned by Lacroupade are the most common causes of full breakdown, but I'd be interested to know if additive fuel treatments can really clean 'plugged' or contaminated cat surfaces? I would have guessed a good hot run should do the trick in theory?

 

[Gargybloke]

The biggest single cause of damage to a cat is unburnt fuel igniting on the cat itself, so its has nothing whatsoever to do with the grade of fuel, and lots to do with how the car is driven and ECU telemmetry malfunctioning. e,g, the MAF could be faulty, giving faulty readings back to the ECU which squirts more fuel in than is needed for a given volume/density of air. Or maybe the car just does too many short journeys and doesn't get thrashed enough......

This 'supermarket fuel' thing is a fallacy by the way. I mean does anyone know where the 'supermarket fuel refinery' is?

Err no, because there isn't one....its all comes from the same place and the only thing that differentiates what comes out of the pump is the additives put in the tanker.

I don't think it has all come from the same place in the past. Wasn't it about 5 or 6 years ago there was that batch of petrol some supermarkets had bought that affected o2 sensors?

I think from Tesco and Asda. My friend at work was affected. In the end the garages were replacing so many sensors, the stock ran out. They realised that cleaning with ultrasound could get the sensors going again. It was a really big news item at the time. Whether they still source from just the cheapest they can find now I am not sure. I had heard Tesco had some deal with Esso to supply the cheap unleaded but not sure how true that is.

I don't put supermarket fuel in the Z. The closest garage to me is an Esso one. It price matches a Tesco as it is so close. I put their super unleaded flavour in which is about 97 Ron I think. Just under the 98 Ron limit as marked on the filler cap.

Thinking about, it perhaps some of our guys who have replaced sensors themselves could buy an ultrasound cleaner and try that first before forking out on new sensors.

 

[mrlozzer]

Wow thanks for that in -depth analysis,i drive 5-6 miles to work,then obviously home again with the odd hoon on a weekend.

The reason I asked is that there was a very interesting case recently in the papers, which echoed problems I have had recently (though not with the zed). A guy fom London bought a brand new XF. Had repeated emissions problems, kept going into 'limp home' mode etc. Back to the dealers several times. Eventually, they told him he car wasn't being driven quickly enough! Very amusing.... In his case, it was a diesel, but the problem as lacroupade said is unburnt fuel. In his case, lots of stop start slow driving meant the car was always running rich.

Mrs lozzer used to have a diesel Peugeot 307. She stuck 40k miles on it, pretty much trouble free. Replaced it, but we kept it as a workhorse. Used occasionally and locally. Starting playing up really badly. Emissions problems, sensor failures, the works. Having exactly the same problems at the moment with the petrol Vitara that replaced it. Blocked EGR valve, O2 sensor issues. Mechanic asked how often we drove it, and how far. Cut a long story short, we had a delay in delivery of Mrs Loz's new car, so she used the Vitara for a couple of weeks. She commutes 70 miles a day. Warning lights have gone off and stayed off....

 

[andysat]

Interesting mate-hmmmm