Car says catalyser is blocked

[duncan webster 1Participant @duncanwebster1]

I'm not suggesting anyone tries this, could be expensive if it went wrong, but the routine for decoking carbonised vapourisers in paraffin blowlamps was to take it off, get it red hot with an oxy torch, then turn off the acetylene and direct the oxygen down the inside of the pipe. The burning carbon kept it all hot, and moving the tip of the oxygen torch in and out gave some measure of control. I can't help feeling some enterprising chap could come up with something similar to clear DPFs, in a rather more controlled manner of course

Friend of mine years ago had a petrol Audi with a cat fitted when the law didn't require one. It developed a strange fault when it would suddenly lose power, but then equally mysteriously clear itself. Turned out the core of the cat had come lose and by moving about inside the outer casing it had gradually gone barrel shaped. It could then roll to one end and block the exhaust. Cure was either a new cat, very expensive, or cut the outer case, pour out the matrix, weld the case back together and carry on. As he is no longer with us I can reveal that he took the cheaper option.

[FMESParticipant @fmes]

Hi Clive, apologies for not seeing this post before.

If I may suggest, the way to clean a DPF is high temeperature in the exhaust system and a higher than normal gas flow.

40mph in your car in top gear is not nearly pulling enough revs to adequately provide the oxygen required to burn off the DPF.

During a regeneration, which will only start when the exhaust temperature reaches a set point, the ECU will inject additional fuel into the exhaust along with any regeneration fluid (some vehicles have seperate tanks for this) normally an eolys fluid which will combine with the fuel and additional oxygen in order to raise the exhaust temperature still further and effectively regenerate the DPF.

So, in essence you need revs, temperature and distance, revs should be 2000 – 2500 (40mph in top willl be well below this) , temperature – runnng at fully warmed up on the temperature gauge will normally be enough, and distance – 30 – 40 miles.

Go out for a decent drive and get theengine up to temperature, if possible get on a motorway or fast A road, select a gear that allows the required rev range without intimidating plod, and keep it there.

I normally do around 60 mph in third for the requred distance.and my old peugeot van (146000Miles) needs this every month or so.

Hope this helps, and goodluck.

[old martParticipant @oldmart]

Don't forget, diesels with DPF's also have a cat, so the op may well have a different problem to most of the answers. I have a 7 year old 1.7 Corsa and have had no trouble with the DPF. The car does get a long drive every other tankful to make up for the short hops it has too many of. The trouble is that with my car, an Italian tune up would be unwise as the car can go 124 mph.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by old mart on 21/10/2020 18:20:49:

[…]

The trouble is that with my car, an Italian tune up would be unwise as the car can go 124 mph.

.

Might one be correct in assuming that it has a range of gear ratios available ?

… The idea is surely to thrash the engine, not the drive-train.

MichaelG

[old martParticipant @oldmart]

The trouble with revving the engine in a low gear is that only a tiny amount of throttle is needed.

[Clive FosterParticipant @clivefoster55965]

Posted by Michael Gilligan on 21/10/2020 21:07:46:

Might one be correct in assuming that it has a range of gear ratios available ?

… The idea is surely to thrash the engine, not the drive-train.

MichaelG

Lower gears don't really do it if the DPF system is well clogged. Need to get the motor under decent load and decent revs simultaneously to clear it.

Light footed drivers like me can get the DPF system into trouble even with a theoretically appropriate mix of fast motorway runs. I long ago mastered the art of getting cars with SU carbs settled nicely at motorway / open road cruising speeds with the throttle backed right off. Still applicable to moderating the thirsty Rover / Buick V8 in my P38 Range Rover!

Clive

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Clive Foster on 21/10/2020 21:30:10:

Posted by Michael Gilligan on 21/10/2020 21:07:46:

Might one be correct in assuming that it has a range of gear ratios available ?

… The idea is surely to thrash the engine, not the drive-train.

MichaelG

Lower gears don't really do it if the DPF system is well clogged. Need to get the motor under decent load and decent revs simultaneously to clear it.

[…]

.

I do realise that it’s a balance, Clive … but a lower gear and a steeper hill should do the job nicely without risking a speeding conviction !

Note: I don’t drive a diesel engined vehicle, so the intricacies are unknown to me.

MichaelG.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by old mart on 21/10/2020 21:26:07:

The trouble with revving the engine in a low gear is that only a tiny amount of throttle is needed.

.

Hence my choice of words … ‘thrash the engine’

… Hopefully my response to Clive adds clarity.

MichaelG.

[Clive HartlandParticipant @clivehartland94829]

What I have is an M2 trip down to the West and over the Medway bridge turn around and then drive back up the hill to my turn off.

I power up the hill and can reach a good speed so that should do the trick.

Clive

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Clive Hartland on 21/10/2020 22:05:32:

What I have is an M2 trip down to the West and over the Medway bridge turn around and then drive back up the hill to my turn off.

I power up the hill and can reach a good speed so that should do the trick.

Clive

.

Sounds like a good plan, Clive

“Don’t spare the horses”

MichaelG.

[Robert Atkinson 2Participant @robertatkinson2]

The key point is to get the exhaust and DPF hot enough. This requires a load on the engine. The load is the same for the same road speed and incline / load / wind regardless of engine speed. However higher engine speeds mean more combustions per minute and higher exhaust flow so generally higher exhaus temperatures. And of course if you do it for the same time you will have done more miles.
It's bad to generalise though as different engines have different systems.Some have an additive (which may be hidden from the driver). Others don't need this but my hve to regenerate by injecting extra fuel either directly into the exhaust with a valve or by opening the injectors on the exhaust stroke. How often this happens depends on driving condtions and style and alo fuel quality.

Robert G8RPI.

[FMESParticipant @fmes]

Posted by old mart on 21/10/2020 21:26:07:

The trouble with revving the engine in a low gear is that only a tiny amount of throttle is needed.

There is no actual 'Throttle' on a diesel engine unlike its petrol counterpart.

The amount of air drawn through the combustion system is directly related to the rpm of the engine, not how hard you tread on the loud pedal.

As I referred earlier, a full active DPF clean needs temperature, gas flow and the addition of a fuel bourne catalyst (adblue, or a more potent – and highly nasty to handle chemical like Eolys).

It doesn't really matter what 'speed' you are doing as long as the pumping action of the engine is high.

Many older cars have non-active DPFs which do not need a fuel bourne catalyst additive – when they block the only recourse is to visit one of these specialist DPF / Catalyser cleaning firms that are popping up nowadays, or replacing the whole unit.

Fun this, isn't it?

[LADmachiningParticipant @ladmachining]

Posted by FMES on 22/10/2020 11:18:39:

Posted by old mart on 21/10/2020 21:26:07:

The trouble with revving the engine in a low gear is that only a tiny amount of throttle is needed.

There is no actual 'Throttle' on a diesel engine unlike its petrol counterpart.

The amount of air drawn through the combustion system is directly related to the rpm of the engine, not how hard you tread on the loud pedal.

As I referred earlier, a full active DPF clean needs temperature, gas flow and the addition of a fuel bourne catalyst (adblue, or a more potent – and highly nasty to handle chemical like Eolys).

It doesn't really matter what 'speed' you are doing as long as the pumping action of the engine is high.

Many older cars have non-active DPFs which do not need a fuel bourne catalyst additive – when they block the only recourse is to visit one of these specialist DPF / Catalyser cleaning firms that are popping up nowadays, or replacing the whole unit.

Fun this, isn't it?

I think it is accepted that a Diesel engine does not have a throttle valve in the traditional sense, what was referred to here was a 'tiny amount of throttle' AKA only gently depressing the throttle pedal. However, some Diesel engines do have an ECU controlled throttle valve in the intake tract to increase manifold vacuum and increase EGR flow, and it also closes at engine shut-down to reduce engine shudder as it comes to a stop.

AdBlue is for SCR (selective catalytic reduction) of NOx within the exhaust gas – it is not involved in DPF regeneration.

[Ex contributorParticipant @mgnbuk]

fuel bourne catalyst (adblue,

Adblue is not "fuel borne" & is nothing to do with cleaning a particulate filter.

Add Adblue to your fuel & you will end up coming to a very expensive stop !

Nigel B.

[JohnFParticipant @johnf59703]

Posted by Bo'sun on 21/10/2020 10:00:27:

Interesting comments, thank you. My Ford Ranger has an indicator to suggest changing up a gear, presumably for better fuel economy with reduced engine rpm. Clearly this won't do the cat much good from what I'm reading above.

As a slight aside. I get regular reports from the Essex Police "Neighbourhood Watch" scheme, and I'm alarmed at the number of catylitic converters being stolen. Presumably because of this, and associated problems. I've fitted a "Cat Loc", as the height of the Ranger makes it easier to steal the cat. I know it's probably not very neighbourly, but hopefully the Cat Loc will make the scum bags look elsewhere for their booty.

Theft is not due to the associated problems, its because they contain a considerable amount of precious metals, mainly platinum I believe, thus worth a lot as scrap and the problem is not confined to Essex !

John

[FMESParticipant @fmes]

Apologies on the reference to Adblue, I ony have cars with either a seperate FBC tank or none, and incorrectly assumed that the Adblue additive had the same purpose.

Sorry.

[not done it yetParticipant @notdoneityet]

Posted by JohnF on 22/10/2020 15:50:09:

Theft is not due to the associated problems, its because they contain a considerable amount of precious metals, mainly platinum I believe, thus worth a lot as scrap and the problem is not confined to Essex !

John

Not much Platinum in modern cats. Mostly Palladium. Was always a precious metal but only a fraction of the value of Pt back when I refined them (30 years ago). Now Pa is in more demand for cats, the price differential has reversed. I think it may be less easily ‘poisoned’ than Pt and likely require less mass per cat?

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