Adjusting driving style to avoid clogging inlet and EGR?

[WesBrooks]

General topic for how to keep diesels running well. My daily isn't Land Rover, but I guess many of these topics are transferable to vehicles with EGR and DPF.

I've a 2 litre 2009 170bhp Skoda Superb that I use for commuting and get do high mileages compared to Joe Blogs. I've always recorded brim to brim mileage and fill levels just to keep an eye on costs and have an extra advanced warning of anything heading towards the tits-up side of the spectrum!

In the past I've been able to get high mpg figures (55 on the tank average, and one 700 mile tank full with a 55l fill) between the quoted urban and extra urban when on motorway traffic that was limited to 50 by average cameras. I guess a lot of this was slip streaming. After a couple of months of driving like this the car became unhappy and often stalled and refused to start until temperatures dropped below 65C and the everything was as if nothing had happened. Nothing showed up on the computer and DPF issues would have shown up as there are plenty of sensors on that. The general consensus is probably EGR getting a little gunged up, but it is an pain of a job to get to, so not really worth attempting until confirmed. I swapped my commute to a longer faster route and the car seems to have cleared itself. MPG average for tank full is now more like 45-48 brim to brim. Reduction in MPG mainly down to a 5mph increase in target cruise from a GPS validated 65 to 70.

While modern diesels seem to be able to be driven comparatively economically for a given maximum power of the engine, it appears as if even with motorway miles unless there are a little higher up their % loading the EGR system and inlets tend to gunge up.

So. Main question is when plodding along in slow, but flowing traffic at say 50mph which gear would be best for reducing the rate at which everything blocks up? My guess has been to drop to a lower gear which would keep the revs and airflow up, but the ECU would probably reduce the weight of fuel per shot as it doesn't need the same amount of energy from each combustion event. Higher gearing would slow the engine and airflow down keeping the hot stuff in the cylinder longer, but in turn any requirement to speed up would require much more torque due to the lower engine speed and therefore would likely run toward the rich end of the spectrum without getting much acceleration.

Thoughts? I'm tending towards keeping the revs around 2000 when holding a speed for a long period of time but would be really interested to see if anyone knows of some driving style advice that is a little more in depth than the standard generic advice for economic driving!

[honitonhobbit]

Interesting. Our family hack is a 2.0litr Audi A4 178bhp 6 speed. It's just coming up to 180k. We've not had any issues with EGR blockage - just DM flywheels, water pumps, sensors...  It's still getting 60mpg plus - but that's my wife's daily commute which is mostly motorway out of traffic times. At 65mph it is relatively uneconomic - about 52mpg; at 80mph it happily runs above 60mpg. My mum has the same car but with a 140bhp 2.0ltr/six speed. She finds the same - at over the legal limit it is always more economic. She not had any EGR issues in her 140k miles. Neither car is fitted with a particulate filter

[WesBrooks]

Is that brim to brim more economic or dash display. The latter is inaccurate in my car. Maybe consistent with itself and indicates whether one day is more economic than the last but normally over 10% inaccurate!

Mine is at 228k. It has been very good money wise, but as you'd expect had much done. Turbo actuator, full clutch kit, gearbox casing & selector, lower control arms (bushes failed), cruise control stalk, shockers/springs/bushings, and all the usual consumables. Coming up for it's second cambelt/water pump service.

Edited February 1, 2017 by WesBrooks

[WesBrooks]

From internet searches I've found so far responses generally say avoid cheap fuel and driving style advise varies from 'you can't do anything about it, it's just a time/miles issue' to keeping the revs up.

Not found anything that really shows a detailed study.

It's a result of trying to get the emissions within limit (along with their cheat ECUs ;-) ) but 25,000 miles per annum (thankfully less than it used to be) in a petrol isn't too appealing. Like for like swap with the now 1.4 petrols with cylinder deactivation would be about the same on fuel but the 1.6 TDI eco models of the same age would still have the fuel costs of the 1.4 petrol beaten.

[Cynic-al]

A lot of cars have an inbuilt program which burns off the soot certain conditions have to be met before it will start regarding engine temperatures and speeds so if you don't meet those criteria it will never run the program. Mercedes had a problem a few years ago where the program was starting to run but if you stopped the car before it finished it would remain on and cook all the sensors etc in the exhaust.

Garages have a machine now to clear it, I've never seen it done and it costs a fair chunk but I know people who have had problems which the machine has fixed.

[WesBrooks]

That's specifically for the particulate filter. The problem with the EGR is the gases don't get hot enought to ever do much cleaning. As far as I'm aware the EGR gas is sent through the intercooler. This has the added side effect that if your EGR is clogged enough to be a problem you intercooler is also generally clogged! EGR may be cleanable by the determined DIYer, bu I think intercooler is another mater! EGR and intercooler replace is around the £800 mark. Not the most expensive service I've done recently but not cheap!

[Cynic-al]

The EGR went wrong on my 1600tdi Citroën a few years ago, the car ran fine but had a warning light, the garage took it off and cleaned it but it wouldn't recalibrate apparently so it had to be replaced. 3 sensors in the exhaust system had to be replaced too  Their advice was to drive it hard from time to time to get things as hot as you can. That was also the advice of the Nissan main dealer to someone I know to clear the warning lights on the dash... their engine clogged up and blew up a week out of warranty

I had the EGR fail on my 2001 fiat 1900tdi and the garage just blanked it off, although I'm sure I read that they were tightening up on people doing that?

[WesBrooks]

Yeah the EGR defeat and ECU reprogram would solve it but it would make the NO emissions worse still. The MOT guys are becoming more hot on that and I'm not willing to take that route. Having said that if you disable it with an ECU tune I would think it would be very difficult to spot. My understanding it the EGR is used to reduce NO emissions but this is a trade off and it makes particulate emissions worse.

[honitonhobbit]

Wes

 

Both - the dash display on both motors is surprisingly good. We both tend to use shell fuel (closest garage and air miles) with every third tank being Shell sooperdooper (always gives better mileage). I drive both motors on a fairly regular basis. The sheer get up and go of the 178 is rather entertaining - although the 140 is better at 6th gear 70+ acceleration. The 178 is an S line so minor issues with suspension bushes very noticeable and not ignorable.

[WesBrooks]

Very odd!

[mickeyw]

When it comes to an engine's ability to clean itself, I would have thought that the harder you drive it, the better the cleaning process. Engine revs at cruising speed can't affect much apart from fuel consumption.

I am really just thinking of an engine that gets a good workout must see hotter exhaust gasses and everything else, which will consequently burn the crud out better. Maybe this is a rather old school idea, I don't know... I realise that it does bear some validity when it comes to DPFs though. My mum's FL2 gets a clogged DPF from time to time, but she only ever tootles around, with very few longer trips. The garage's fix seems to involve giving it a proper wake up.

In my mind this means you end up using more fuel just to keep the engine clean, which kinda negates the whole driving frugally principle...

[honitonhobbit]

I was chatting to the guys form Yanmar Diesels at a trade show recently. They have a pretty comprehensive range of engines for re-engining plant. All are modern style with DPF's and all the gubbins. It was interesting talking to them about the placement of the exhaust being critical within the engine compartment, for emissions figures - they run the exhausts close to the intake to warm the intake air...

[WesBrooks]

I think the logic behind warming the intake is about ensuring the fuel doesn't condense out of the fuel-air mix. For most power cold and dense is best, but guess that may lead to an increase in unburnt hydrocarbons in the exhaust as the condensed fuel doesn't burn as well or simply gets pumped out.

[honitonhobbit]

That was pretty much what they said...  Nice engines mind

[mmgemini]

21 hours ago, mickeyw said:

When it comes to an engine's ability to clean itself, I would have thought that the harder you drive it, the better the cleaning process. Engine revs at cruising speed can't affect much apart from fuel consumption.

I am really just thinking of an engine that gets a good workout must see hotter exhaust gasses and everything else, which will consequently burn the crud out better. Maybe this is a rather old school idea, I don't know... I realise that it does bear some validity when it comes to DPFs though. My mum's FL2 gets a clogged DPF from time to time, but she only ever tootles around, with very few longer trips. The garage's fix seems to involve giving it a proper wake up.

In my mind this means you end up using more fuel just to keep the engine clean, which kinda negates the whole driving frugally principle...

Nothing new about flogging an engine to clean it. A friend 30 years ago would do this to his mothers Mini. He would flogg it up the A19 and back 20 miles each way. When returned his mother would say. " I don't know what he does to my car but it runs better"