2.0 110bhp HDI Acceleration

[johnway]

Hello everyone,
My 2002 Citroen C5 always had more oomph than my 2003 Pug 406 yet they both have the same DW10 engine (no particulate filter). The Pug starts and runs OK but when I put my gogo foot to the floor (especially in 3rd gear) there is no immediate response - revs stay the same as does the speed, then after maybe 10 seconds or so - whoosh, off she goes !! I have tried gentle acceleration through the gears but it just won't perform as it should even though the turbo is working. I have changed the air filter and fuel filter recently and don't hear any vacuum leaks - any ideas out there please? All the best, John.

[Gibbo_Wirral]

Could it be the EGR valve? You really need a Planet diagnostic to find out.

[Stickyfinger]

Bet its the MAF sensor, unplug it and see if acceleration/pick-up changes, if not then it is

[johnway]

Well done - you win the bet !! Unplugged the MAF and she goes like a rocket. I had spotted that an earth wire had been added by a previous owner and traced it back to the green wire on the MAF plug - something fishy going on here methinks. I have checked the ignition voltage at the plug and there is 12V between the green and adjacent pink wire. Before delving any further into the remaining 3 wires I am wondering why bother repairing/replacing the MAF sensor anyway? Is there any logical reason why these damn things are fitted in the first place and will any harm be caused by leaving it disconnected? The car seems better off without it !!

[Stickyfinger]

There is a point to the MAF, you will either Over-Fuel or Under-Fuel, neither are good for the HDI. Sort the wires and fit a new one (not a cheap one, get an OEM), the cheapos are crap and do not last.

[johnway]

OK, many thanks for the advice Stickyfinger. BTW I love the sheep pic - I should show it to Bruce our local pet ram!!

[Northern_Mike]

I am wondering why bother repairing/replacing the MAF sensor anyway? Is there any logical reason why these damn things are fitted in the first place and will any harm be caused by leaving it disconnected? The car seems better off without it !!

Simply put, the MAF measures the airflow rate going into the engine and tells the ECU how much fuel to inject. If it's not plugged in, it'll be running in a default "safe" mode, probably over-fuelling, which isn't great for the engine. It's probably broken and misfuelling the engine when it's plugged in, hence the lack of power.

You *might*find that your 406 has exactly the same unit on, if it also has the same fuel injection system (Siemens or Bosch,I believe) and you can try it to see if it is indeed the MAF that is at fault and not the wiring. My only concern would be if a wiring fault has caused the failure of your MAF and you might cause damage to the working one, though I very much doubt it's possible.

[Stickyfinger]

BTW I love the sheep pic - I should show it to Bruce our local pet ram!!

I have had that as an Avata for years and years across many games and forums, I even have some flying versions

[johnway]

Very nice !!

[johnway]

Thanks everyone for your input - very helpful as usual. It will be interesting to see how the Pug reacts to the tuning chip, which I removed as a precaution, once the MAF problem has been sorted. The chip worked very well on my C5 before I sold it last year.
All the best,
John.

[johnway]

All sorted !! A brand new Siemens MAF sensor and rubber seal fitted today (thanks to ebay again) - results were outstanding. As soon as I started up the car she sounded different and now accelerates smoothly and on demand. I can now put my foot down in 4th at 50mph and vroom - off she goes - something that has been lacking for quite some time. A little money well spent and just in time for the caravan season.
All the best,
John.

[Stickyfinger]

Great, good you got the real one as well....enjoy your mobile road block