Diesel................Or Petrol?

[JonnyG]

Errrrrr, yet again a missed piont, the Egr problem was first highlighted years and years ago, on a ford scorpio PETROL engined car,in otherwords its not just a diesel engined problem, i would be interested to see this new additive to the MOT list for compliance, as i cannot recall NOX being measured [i could be wrong] but if i am not, then whether an EGR vavle actually opens and closes, would have no bearing, unless the NOX reading was high,and was being read. and bearing in mind, once i blanked off my Egr valve on my Alfa, it used to pass the emmsions test in one hit, unlike when the EGR valve worked, where it used to need to have 5 goes!.
Also the seems to be a fare few reputable companies offering ECU type work to shut off the EGR vavle and indeed that new champion of faults the DPF.....So if new euro 4 rules took into account the EGR valve, one would assume the DPF would also be covered.Anyway my Euro4 2.2 mondeo has a erg blanking plate fitted, it passed its MOT in july, so i will see what happens this coming july,although i cannot recall plugging in diagnostic equipement to be part of the mot...upto now.........interesting if it does become so, maybe more petrol engined problems will be highlighed and make the forum rounds......

 

[seth1]

From what i understand one of many new mot stipulations is that off any warning lights illuminated on the dash will be a failure.I expect this means the MIL light as well.But not all diesels will flag an engine fault with the EGR blanked off and there seems to be no pattern to it either.
Im not sure whether anybody on here has ever monitored EGR opening periods,i have since the introduction of euro 2 engines fitted with EGR.EGR only opens/activates under no load/down hill conditions.In other words at during a smoke test the EGR is shut.Besides the Mil warning lamp it would make no difference to a smoke test.

 

[otherclive]

I undertsand that plans are afoot to test DPFs so those who have the DPF removed and the software changed might find themselves with a problem. Although how the MoT tester knows that the DPF has been removed must be by the measure of fine particulates. I think in Germany such a test is already in, so with the harmonisation of testing expect it to crop up in UK.

 

[JonnyG]

Again this will be interesting, as not to have a cat fitted on a diesel car is not an mot failure, as long as it passes the emission, which a good engine will pass easy. So i wonder how the DPF is going to fit into this, as again like seth stated concerning the EGR valve being closed during a smoke test, the DPF also will not be doing anything to clean up emissions,during smoke test so how are they testing its functions at 100%.?

 

[seth1]

Its a mockary.Many years ago i had a conversation with a friend who worked for the same employer back then as me but in reseach and development.It was when euro 1 engines were starting to come through mainstream.Our euro 1,s were spotless to the point on a smoke test we had use a stethascope on the exhaust silencer to indicate to the smoke tester the engine was running.But back then he indicated things were going to tighten up.My responce was,what will you do?He said we will turn the dangerouse gas into another gas.Then when they test for that,we will turn that gas into something else.Here then comes adblue then.But the funny thing is reading commercial motor last month,they said exactly the same thing.Yet we had been on about it over 10 years ago.As for Particulate filters(DPF) it takes 30 mins for them to start working once they,ve warmed up.

 

[otherclive]

I think you have the wrong understanding of how a DPF works. It filters the very fine particles out immediately the engine starts up and continues to work whilst the engine is running. So if you accelerate hard the DPF catches the particles emitted whilst accelerating. The 30 minutes etc when warm, refers to the time required for the DPF to regenerate itself. So I would not expect regeneration to be part of any MoT test as it does not affect the exhaust emissions.

 

[Martin24]

So Terry, are you any further forward???

 

[seth1]

LOL .I understand how a DPF works.If a regen takes half an hour i,d be a bit worried.Ive done a few forced regens to burn the oil out of Particulate filters after turbo failures saying that.

 

[TerryIvybridge]

Errrrrrrr! not sure? opened up a can of worms there .didn't I? Good debate that looks like it may go a little longer too. For me tho' reckon diesel still the best tug engine. I have a 1.9 205 gti for back and forwards to work and whilst that is turning over at a busy 3000 rpm at 60, the Golf in 6th, lollops along at half the engine speed and has so much more torque. My dilema is the Golf, a '04 plate only has 70K on it and worth £4K tops. Looking at a Mk5 Golf or a Passat, they all been to the moon and back and a £9K+ price tag.

 

[xtrailman]

LOL .I understand how a DPF works.If a regen takes half an hour i,d be a bit worried.Ive done a few forced regens to burn the oil out of Particulate filters after turbo failures saying that.

I understood the xtrail took at lest 20 mins to regen?

 

[otherclive]

It depoendes very much on the DPF regen system and what the driving conditions are. Some systems use over-fuelling of the engine suuch that excess fuel goes through and burns in the DPF. On Volvos this has led to various recalls as sump levels were rising due to unburnt fuel in the oil. The fix seems to be to lower the sump level to 2/3rds upadet software so the electronic dipstick shows oil at max when actually it is at 2/3rrd level. And also reprograme the fuelling maps. It seems to have worked, although i never had a problem in the first place. I believe that later Nissans now have an injector direct into the DPF which overcomes over-fuelling. Fords/PSA/Citroen use an additive which burns directly in the DPF but which needs topping up around 50K miles depending on driving environment. Nothing further to say on DPFs from hereon!! LOL

 

[RogerL]

It depoendes very much on the DPF regen system and what the driving conditions are. Some systems use over-fuelling of the engine suuch that excess fuel goes through and burns in the DPF. On Volvos this has led to various recalls as sump levels were rising due to unburnt fuel in the oil. The fix seems to be to lower the sump level to 2/3rds upadet software so the electronic dipstick shows oil at max when actually it is at 2/3rrd level. And also reprograme the fuelling maps. It seems to have worked, although i never had a problem in the first place. I believe that later Nissans now have an injector direct into the DPF which overcomes over-fuelling. Fords/PSA/Citroen use an additive which burns directly in the DPF but which needs topping up around 50K miles depending on driving environment. Nothing further to say on DPFs from hereon!! LOL

Most cars use an automatic combination of passive and active regeneration - only the active regeneration uses extra fuel.
Every time the engine is worked moderately for around 20 minutes a passive regeneration takes place, the exhaust simply gets hot enough to burn the accumulated soot away. No extra fuel is added.
The problem areas occurs with cars used on short, light-duty runs like commuting for which diesel is the wrong choice but that's another argument - in these conditions passive regeneration doesn't happen often enough (or at all in some cases) so the ECU detects when the DPF is getting full and starts an active regeneration which involves over-fuelling the engine so that the burning carries on into the exhaust, thus increasing it's temperature to burn the soot away - the real problem occurs when the engine is stopped before the active regeneration is finished so a small amount of diesel drains down from the cylinders into the sump. Now since it's likely that short, light-duty runs are frequent for some drivers, the ECU is frequently trying, but failing to complete, an active regeneration so the sump overfills with diesel which doesn't do any good at all.
A few cars use a different system which injects a special fluid into the system - it needs replenishment every 60,000 miles or so - AFAIK Ford/Peugeot/Citroen no longer use this system but I could be wrong.
The real principle to remember about diesels and DPFs is NOT to buy a diesel if it's only used for short, light-duty use - diesel is NOT the panacea for all drivers.

 

[ProfJohnL]

Hello Terry,
The discussion thats been going on I think proves there's good and bad in both petrol and diesels, and theres no guarantee any car you get will suffer from the problems that have been brought up, so I don't think you need to be overly concerned.

It wasn't clear from your original post whether you were looking for a new or secondhand car, but you have now given that point to us so your looking for second hand.

With that in mind, and the limited budget it gives, then it tends to crystalise my thinking. I agree with you that diesel is almost certainly the best solution for you. VAG cars do seem to hold their value quite well, but have you considered teh Skoda varients. The Octavia is essentially a golf, and the Superb a Passat, alternatively a marque that has sone strong diesels but tend to loose their value disprortionatly are the Saab 9-3 and 9-5. There are some bargins out there.
A virtually identical drive engine ad drive train can be found in the Vauxhall (GM) Vectra on which the later 9-3 was based, and I belive the GM/Saab 1.9Lt engines are derived from Fiat, so theres another marque you might consider.
In answer to your original question about petrol vs diesel, there are some excelent petrol engined cars that will tug a caravan pretty well, but it is likely that whilst the solo car may produce mpg's approaching disels, under the extra load of towing will probably affect t mpg worse than a compartaive diesel.

 

[xtrailman]

I can only repeat that i have only done 18.5K miles in three years.
That's 90% short journeys.
The car will go to the Asda tomorrow that's around 4 miles there and another 4 back.
Never had a DPF light, ever.
Unlike some 2007/8 xtrails,mine is a 2009, so the system must have been modified, i understand the 2012 version does have the extra injector for the DPF, but can't say for sure.
Also after the dealer second service the oil level was indicating only level 4, on the dashboard oil level indicator, while on the first service it was showing level 5.
So either less oil is added, or the electronics has been moded to show less.
What ever, the outcome is i can now use the dash board oil level indicator to detect any rise in sump level.
I've had none over the last year.

 

[RogerL]

Towing will get the exhaust hot enough for a passive regeneration so the light use issue may not be a problem if you tow regularly.

 

[otherclive]

I believe that most DPFs need to regenerate about once per tankful of fuel in mixed solo use. But changes if used on longer fast journeys or when under load when towing. Where hot exhaust aids passive regeneration.

 

[xtrailman]

Towing will get the exhaust hot enough for a passive regeneration so the light use issue may not be a problem if you tow regularly.

I'm not sure as "experts" on HJ site say differently.
But anyway my caravan had its wheels taken off at the end of Oct, and will be back on again next march.
In use it will only do about 7 weeks holiday, mainly tours under 2.5 hours drive.

 

[seth1]

Regarding the PSA group cars,the fluid is known as Eloys fluid.The system has one major flaw and that is that it works on the belief that every time you replenish the fuel tank,you fill the tank full.As it injects once per full tank and it recognises this by means of a magnet in the fuel cap and thus when the cap is opened it carrys out an injection.But a lot of people dont fill the tank to the brim so it uses Eloys fluid like its going out of fashion.
Regarding regens,my car hasnt done one in 12months.The reason being i would think is the difference between the two differencial pressure sensors(temp sensors) in the trap must be equal,as this is what controls when a regen happens.The amount of regens also dictates oil change intervals.

 

[RogerL]

Towing will get the exhaust hot enough for a passive regeneration so the light use issue may not be a problem if you tow regularly.

I'm not sure as "experts" on HJ site say differently.
But anyway my caravan had its wheels taken off at the end of Oct, and will be back on again next march.
In use it will only do about 7 weeks holiday, mainly tours under 2.5 hours drive.

I don't understand how any "experts" can work out that towing isn't working the engine hard enough - I'd have thought that a half hour tow would be enough for a passive regeneration.

 

[graham8408]

hi , we have a 1.6 07 seqential ford focus.it tows our 2001 abbey harlech quite nicely,but does strugle on inclines on the motor way.going to try and find a cheap vauxhall omega .as ive been told it will pull a house down.