Better MPG at 70 than 55, dodgy EGR???

[landymad]

Hi

I have a 2002 406 90bhp Hdi 72k.
I get about 50mpg at 70 and low 40's at 55.
It does have a bit of a flat spot on light throttle between 1800 - 2200 rpm, but fine on full throttle.
Could this be a sticking EGR valve?
Can you blank the EGR off as i was thinking of putting a blanking plate in place of one of the gaskets in the EGR pipework as I thought this would not kick in any fault lights on the dash as nothing has been disconnected.
Does the EGR serve any other purpose like keeping the combustion temp down or is it just emmisions?
It is due a cambelt service, would that make any difference if it had stretched a bit?


Any help to a newbie would be great.

[swiss]

Not sure about the specifics of the HDI90, but her indoors' 2.5TD Omega is way more efficient at 80 than around town. Like, 400 miles to a tank instead of 200.

And it only needs 2700rpm to do 80

[supafrisk]

I used to drive a 90 bhp with the EGR blanked, up til then it was a common conception that you couldn't do it because the engine management light would come on. The mechanic that modified it fitted a small ball bearing to the pipework, probably between the solenoid and the EGR.
It is also possible to take the EGR off and clean it, though I am lazy and haven't done mine yet
The MAF (mass air flow sensor) is always worth a looky, although remember the filaments inside are FRAGILE and break easily (Yes I did it), swabbing it lightly with a cotton bud should do the trick.
Landy, when you say you have a flat spot is it flat as the proverbial pancake but if you back off the throttle slightly and re-apply it steadily it starts to pull?

[landymad]

Hi Cheers for the reply.

Is cleaning the EGR a git as all the exhaust manifold is right up against the bulkhead and it looks like double jointed wrists will be required.

To clean the MAF - is it just a bit of wire that is heated up? Can I do it with a tin of spray cleaner?
The cable to the plug coupler on the airbox seems to be very tight. Any known problems with cable breaks?

The flat spot on a light throttle varies to how bad it is - but it is always there to some degree - can be quite bad. Can sometimes help by coming completely off the trottle and back on again.

Fuel consumption seems variable even when doing the same regular trips, it had spates of doing 35mpg on the flat on the motorway today, and then would do 55+.

[supafrisk]

Hi Cheers for the reply.

Is cleaning the EGR a git as all the exhaust manifold is right up against the bulkhead and it looks like double jointed wrists will be required.

To clean the MAF - is it just a bit of wire that is heated up? Can I do it with a tin of spray cleaner?
The cable to the plug coupler on the airbox seems to be very tight. Any known problems with cable breaks?

The flat spot on a light throttle varies to how bad it is - but it is always there to some degree - can be quite bad. Can sometimes help by coming completely off the trottle and back on again.
Fuel consumption seems variable even when doing the same regular trips, it had spates of doing 35mpg on the flat on the motorway today, and then would do 55+.

That's what I was expecting, your 406 has the same symptoms as mine
The main stealers have looked at it twice and can't find any fault codes, they know it is flat as a pancake but they can't say why.
They tested all my solenoids by substituting a new one and just hooking the pipes up in situ, it wasn't any of those. Also the MAF was checked, there's a switch that sits on top of the radiator bracket about an inch long, I replaced that and it didn't cure it.
The main stealers pulled the intercooler and turbo hoses off and inspected inside with a lead lamp to check for the pipes imploding and they seemed to be fine.
Before all of that the local main stealer diagnosed it as a faulty air doser, which I duly replaced and found to be untrue. I replaced the MAf and got power back for 6 months then it went again. i know it wasn't the MAF second time round cos I snapped the filament cleaning it and had to replace it
Plus when the MAF goes it's like there's no turbo at all
I was then told by some shytehole Citroen approved dealership in Coventry that it was the turbo and I duly pulled my pants down and let them shaft me for £800 only to find it wasn't the turbo
They then had the car back a month later to attempt to find what was actually causing it, had it for three days, clocked up over 80 miles in it (using a sat nav and I know that cos of the ring on the windscreen in the corner and I don't own one) and had the cheek to tell me as far as they were concerned there was nothing wrong with the car and it was running normally
Sadly the original thread had to be deleted recently owing to a prat reading my posts, otherwise you probably would have eliminated a lot of what it wasn't from the thread, which was about 20 pages long.
All i can say is start from scratch, check your solenoids and more importantly the pipes running from them.
Clean your MAF lightly (a squirt of carb cleaner and LIGHT application with a cotton bud does wonders).
Check your doser (if you have one for ingress of oil/dirt etc) and clean accordingly.
Check your intercooler pipes for correct operation (lean under bonnet, open throttle with right hand whilst squeezing your hose with your left, you should feel it swell in your hand) (Yes I know I'm leaving myself wide open for a double entendre there). Check for splits, holes and leaks if possible.

One thing I forgot to ask you, at night when it is running "properly", when flooring it can you see smoke in the rear view if you have headlights behind you?
(Or has anyone reported seeing it smoking when abusing the throttle, I say this as I was sat in the 306 watching someone drive the 406 and when booting it it was noticeably coughing out black smoke, at night when I drive it I notice when it's running crap there's no smoke).
Before anyone else pipes up, yes I know some smoke in the rearview at night is normal, but what I saw coming out of mine during daylight definitely isn't.

I personally am poking the finger at the EGR but at £300 odd quid I think one garage quoted me for a new one, I will clean it first and see if it improves.
My old samarkand blue one had the EGR cleaned out and I remember the mechanic saying it will smoke less, have quicker accelleration and fuel economy will improve now that's been sorted out.

Either way, let us know how you get on, what you replace and more importantly, IF YOU CURE IT!!!!!!

[alladdin]

does it only happen when engine is hot? car pulls ok when cold ?