Technical Erratic MPG - Bravo 2 (08 plate) 1.6 Multijet 105bhp

[ianbunyan]

Hi all!

If I describe what's happening, maybe someone who knows might point me in the right direction...

For 3 or 4 years I had an engine light on the dash. An error code reader pointed this to the EGR valve basically being intermittent. Before each MOT I would have the dash light / error code cleared and it would always pass emissions, etc. before appearing again 3 engine starts later.

However, while driving (always display the MPGs, me!) I would often notice MPG fall from about 60-80 MPG on the flat at 40mph, down to 25-35MPG, accompanied by a loud-ish fan noise from under the bonnet - but this doesn't happen on every trip (and pretty much all of my trips are only 12-15 miles). At the earliest chance I got, I would pull over, turn her off and back on again, and MPG would be good again.

The last trip computer readings were about 58 MPG over 2,500 miles, and 63 MPG over 250 miles. I think these are pretty good!

Which brings us to now... I finally got the EGR valve replaced, and sure enough the dash light is out and has remained out - no more errors! MPGs are good, but they still fall off a cliff like they used to (as described above) along with a loud-ish fan noise, all resolved by pulling over, turning her off and on again.

SOOoooo... what's occurring? And are there some fixes I could try?

Thanks!

 

[PaulTT]

What you are describing sounds like normal DPF regens. The fact that you are deliberately interrupting them is a real problem. The process is starting and by turning the engine off it is interrupted. Once started, it should take around 10-15 minutes for it to end by itself, after burning the accumulated soot. Have you ever waited enough so the process is ending naturally and the MPG recovers without the "stop & go"?

 

[ianbunyan]

Hi Paul. Great point! I never considered that. I will take the motorway home today and watch it and report back. Thanks for a quick reply, and I will keep you posted.

 

[ianbunyan]

What you are describing sounds like normal DPF regens. The fact that you are deliberately interrupting them is a real problem. The process is starting and by turning the engine off it is interrupted. Once started, it should take around 10-15 minutes for it to end by itself, after burning the accumulated soot. Have you ever waited enough so the process is ending naturally and the MPG recovers without the "stop & go"?

Well, 4th gear at 60mph all the way home on the motorway... 56mpg and no big drop-offs or massive fan noises. I will build some more motorway driving into my commute every now and then!

This is only one journey, of course, but I will keep tabs on it and report back in case anyone else finds this useful.

 

[ianbunyan]

Just an update on this, to draw a line under it.

@PaulTT must have been spot on, and I have never interrupted it since. Also, building in some higher rev's / motorway driving massively reduces the times I notice this happening. And even on a long run from Devon to Kent with wife and 3 kids, plus all the gear, and cruise control at 70mph where possible, the Bravo managed a solid 74mpg all the way home over 245 miles! So I reckon all is good

Thanks all!