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Discussion Starter #1
...real mpg 27mpg.

Hello,

I recently purchased a low mileage (48k) 2005 Peugeot 407 SW 2.0HDi 136 Auto (4 speed) on a 54 plate with FSH.

I do quite a lot of miles and noticed in the first week that the fuel guage was going down pretty quick, despite the fact that the onboard computer was reading 45mpg. When I manually calculated the MPG it came out as an abysmal 27mpg. The second tank came back as 28mpg and the third 30mpg.

I've taken it to an independent garage and they couldn't find anything wrong. No fuel leaks, no diagnostic errors. It was fully serviced after the second tank of fuel, but the fuel economy has not really improved as the third tank where I got only 30mpg included a long trip, including motorway from Shrewsbury to Banbury.

The mechanic said it might be the diesel particulate filter (DPF) that is to blame.

Shouldn't a blocked DPF throw up an error?
Would a blocked DPF not allow the onboard computer to calculate the MPG correctly?

Any help/suggestions would be greatly appreciated. Anyone else experienced this? Absolutely love the car, but I only got it as I needed better fuel economy than the 29mpg I was getting from my V6 Rover 75!

Thank you
Gladius82
 

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Hello Gladius and welcome :cool:
first the obligitory
http://www.peugeotforums.com/forums/introductions-28/brief-faq-guide-new-members-83170/
have a read of those, it will help :thumb:
Right now i'm no expert on the auto's but im on my 3rd 2.0 hdo 407 and all have averaged about 45mph, with a mix of town and motorway miles. My first suggestions have been covered when you said fully serviced as i assume fuel filter and air filter were changed?? The dpf would throw up errors and shouldnt affect your mpg by that much (if at all). what i have found with my last 2 is when i bought them they felt sluggish and needed a bit of dare i say it energetic driving to clear them out. My latest (wish i could say last but with my reputation thats pushing it) was owned by a funeral directors wife so the first tankful got a tin of fuel system cleaner (your choice of which) and it improved it drastically, so much so i havnt checked to see if the egr is blanked on this one yet.
 

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Discussion Starter #3
Right now i'm no expert on the auto's but im on my 3rd 2.0 hdo 407 and all have averaged about 45mph, with a mix of town and motorway miles. My first suggestions have been covered when you said fully serviced as i assume fuel filter and air filter were changed?? The dpf would throw up errors and shouldnt affect your mpg by that much (if at all). what i have found with my last 2 is when i bought them they felt sluggish and needed a bit of dare i say it energetic driving to clear them out. My latest (wish i could say last but with my reputation thats pushing it) was owned by a funeral directors wife so the first tankful got a tin of fuel system cleaner (your choice of which) and it improved it drastically, so much so i havnt checked to see if the egr is blanked on this one yet.
Hi trem1 and thanks for the reply.

I cover 300 miles a week, mixed driving - about 10 miles of small winding roads (deepest darkest Shropshire) until I get onto the main roads for about 17 miles then about 3 miles of driving around Telford - in the mornings, then reverse that in the evenings.

The weird thing is that there are no issues with performance. The car pulls extremely well.

All filters were changed at the service. I've tried two lots of Redex (simply because it's the most easily available) but that's not made a significant difference. The current tank of fuel is BP Ultimate to see if that makes a difference and I have been driving it a bit more 'enthusiastically'. The onboard computer is showing 40.3mpg, but I will have to wait until next week now to work out the actual mpg. I've also ordered some Forte Advanced Formula Diesel Treatment which has been recommended to me as being particularly effective at blasting out the gunk build ups.

Even if that is the issue, why do you think the onboard computer is reading so dramatically different to real life?

Thanks again
Gladius82
 

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have you reset the trip computer since youve had it ??
 

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I have a 2004 407 2.0 HDi and it did not throw up any fault codes, despite the DPF was totally blocked, reading about 60mbar diff pressure at idle and up to about 600mbar when driving along.

The trip computer was way out, I believe the trip computer calculated about 0.7l/10km while the actual consumption was 1.0l/10km.

Everything improved when I had a new DPF mounted. It had clogged down due to faulty glow plugs and faulty glow relay so the regen process didn't work.

Watch your oil level and see if it "rises". This means it injects diesel to clear the DPF, but lots of it might end up in the sump.

The onboard computer apparently don't include the DPF cleaning injector cycles in the calculations, at least that was my conclusion when I was struggling with this.

Get the car onto PP2000 and read the codes, possible faults might be glow plugs, glow relay, fuel flap sensor faults.
 

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Regarding trip computer accuracy, mine seem to be underestimate the actual fuel consumption by about 7-10%. My tires have the correct rolling radius.
 

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Discussion Starter #8
I have a 2004 407 2.0 HDi and it did not throw up any fault codes, despite the DPF was totally blocked, reading about 60mbar diff pressure at idle and up to about 600mbar when driving along.

The trip computer was way out, I believe the trip computer calculated about 0.7l/10km while the actual consumption was 1.0l/10km.

Everything improved when I had a new DPF mounted. It had clogged down due to faulty glow plugs and faulty glow relay so the regen process didn't work.

Watch your oil level and see if it "rises". This means it injects diesel to clear the DPF, but lots of it might end up in the sump.

The onboard computer apparently don't include the DPF cleaning injector cycles in the calculations, at least that was my conclusion when I was struggling with this.

Get the car onto PP2000 and read the codes, possible faults might be glow plugs, glow relay, fuel flap sensor faults.
Hi there. Thanks for the reply.

What's the difference between the PP2000 and any other scanner? Why would the PP2000 show error codes that the scanner the garage used hasn't?

Thanks again!
 

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Discussion Starter #9
Regarding trip computer accuracy, mine seem to be underestimate the actual fuel consumption by about 7-10%. My tires have the correct rolling radius.
That pretty much what I've found with other cars I've owned with onboard mpg calculators. My Rover V6 used to show 32mpg, then when I manually calculated it would be 29mpg - about 10% discrepancy.

So, I'd be expecting actual MPG of 40-42mpg based on 45mpg (10-7% less), which would be absolutely lovely. Current discepancy is 40%!

I think I'll go back to the garage and get them to check the DPF etc, that you mentioned in your first reply.

Thanks for the help
 

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If the car is remapped with durations changed or has a tuning box fitted it will screw up the trip MPG calculations
 

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Discussion Starter #13
Honest John's real mpg: Peugeot 407 SW 2004 - Real MPGs | Honest John always useful for checking what you should be getting.

I'd check the MAF Peugeot 407SW MAF Cleaning - YouTube and replace the air-filter.
Thanks PureJoe, I'll check the maf. The air filter was replaced at the service.

Filled up with diesel over the weekend - covered 201.8 miles and used 35.23 litres of fuel = 26.04mpg. The onboard computer was showing 39.3mpg.

I'm going to see if my local garage knows anyone with the correct diagnostic equipment to see if it throws up any codes.

Cheers.
 

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Discussion Starter #15
on board computer trip meters are hopeless.
Have you tried a calculation using dash trip?
I've been manually calculating all my mpg figures.

Just a quick update - the car went back to the garage on Monday. They checked the dpf additive fluid levels and topped it up as it was low. They got a guy from Shrewsbury with PP2k to come down on Wednesday and it was producing fault code p1435. He's managed to track down the fault to a possible wiring issue which he'll be investigating further this coming Monday.

Still no guarantee that this is the cause of the abysmal fuel economy, but at least it's a start.
 

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When they have it on planet get them to do a gearbox fault code check as well. Maybe you have issue with torque convertor lockup clutch or similar
 

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Discussion Starter #17
Touch wood, the car is now fixed. Peugeot Paul, my friendly neighbourhood PP2k owner with the help of my local indie mechanic managed to track down the fault to the DPF ECU. Turns out it wasn't fitted properly and was hanging down pulling on the wires. So, they refitted it and replaced a ton of the wiring. The car is now fault code free.

They think that it was like it out of the factory, so the DPF system has never worked properly. The previous owner did very few miles, so probably didn't notice the terrible fuel economy.

I will report back next week with fuel economy figures, but so far the fuel gauge appears to be going down slower than it was. :D
 

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Discussion Starter #19
Looks like the issue is at least partially fixed. The onboard computer was reading 44.7mpg but the actual mpg was 37.6. A significant improvment.
 
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