Low Revs and Preventing DMF Failure

Ultrasonic

patman99 wrote: »

To have the DPF removed and the ECU remapped costs £400 for an Octavia (unless you know someone with the same engine who has already had this done, you can then use 'EcuFlash' and a laptop to copy the modified firmware onto your ECU). You would get about a 10 - 15% increase in your MPG.

My car doesn't have a DPF to worry about thankfully :cool2:. I've only ever casually looked into ECU remaps and must admit I'm a bit skeptical. If the car can trivially be made 10% more efficient then why didn't the manufacturer do this in the first place? Also, I've just done some quick sums, and a 10% increase in fuel efficiency from 56 mpg (my current average) to 61.6 mpg would lead to a saving of about £100 per 10,000 miles at current fuel prices. That would mean I'd need to drive 40,000 miles after the remap just to break even! Think I'll give that a miss .

patman99 wrote:

There is a good market for the fitment of SMFs. I have yet to hear of any horror stories about cars suffering massive damage due to replacing a DMF with a SMF, but I have heard of a lot of people who have had £1,000+ bills when the DMF fails.

Are you advocating having a DMF replaced by an SMF before the current DMF fails? As far as switching to an SMF goes, most of what I've read is positive, but then there are views like GolfBravo's above that raise concerns over the DMF protecting the gearbox, and a dead gearbox could cost thousands to replace. I have also though heard of some main dealers replacing DMFs with SMFs under warranty, although I guess if the gearbox goes a few years later it is less of a problem for them than a possible second DMF replacement in the short term...

patman99 wrote:

At the end of the day, it is down to the way the car is driven as to how long a part will last.

Which is why I'm trying to get out of the mindset of making optimal fuel economy my sole concern - a trap that I suspect many motorists are currently falling into. It's just rather more complicated firstly to work out what the optimal driving style may be in terms of being kind to the car, and then how to possibly balance that with fuel economy concerns.

patman99 wrote:

Btw, I wanted to know how efficient my car is so invested in an App for my iPad. It allows me to keep track of fuel costs and repairs as well. So far, my mpg is averaging 57.6mpg and is slowly creeping-up.

I do the same thing without the expense of an App (or a smart phone come to that!) by using a simple spreadsheet .

Paperbird

Ultrasonic wrote: »

Thanks very much for your comments. What sort of rev range would be sensible in your view?

Given that most automatics ( the ones that have a manual gearbox and flappy paddle auto gear change ) won't let you change up at less than 2000rpm I would say whatever rpm you have after changing up at 2000rpm is the minimum you should use on a level road in that gear.
ie. 2000rpm in third gear change up to fourth and engine is at 1500rpm, = minimum rpm to use in fourth gear is 1500

Paperbird

If the car can trivially be made 10% more efficient then why didn't the manufacturer do this in the first place?

To cover all markets and the fuels available in those markets.
The 1.9 Tid engine fitted by Fiat and GM came as standard with 150bhp, If you bought a Saab with that engine the dealer could remap it to over 180bhp and still give the full warranty from new ( I think they were the only one that would do that )

Ultrasonic

Paperbird wrote: »

Given that most automatics ( the ones that have a manual gearbox and flappy paddle auto gear change ) won't let you change up at less than 2000rpm I would say whatever rpm you have after changing up at 2000rpm is the minimum you should use on a level road in that gear.

While probably safe, that is likely to be conservative I'd have thought? Gear change indicators will presumably be designed with continued acceleration in mind, when there is far greater engine load than required for steady speed driving. Following that approach would also lose a major potential advantage of manual over automatic cars . That said, the suggestion in at least one earlier post to keep above 1500 rpm would roughly fit in with your suggestion in my car.

Ultrasonic

Thinking about it, if automatics have a change down indicator (do they?) I think that would be of more relevance to the steady speed case?