2003 56K Siemens Hdi90 poor slow running

[piglet]

Good afternoon and seasonal greetings, I am new here and am just 3 months into 406 ownership having 'migrated' from the 405 community. Nothing against you 406ers, but the 405 was a damn fine car.

I don't appear to be unique in my complaint but some specific guidance would really help.
so
great at tickover, pulls clean at power but in between it's hesitant, inconsistant, difficult to get smooth gear changes and just recently starting to Kangaroo for no reason while slow driving.
Economy is steadily dropping, now under 40 mpg on the pump, computer saying 35. Performance, dull.

I have got as far as removing, inspecting and refitting the EGR with a BLANKING PLATE at the inlet manifold end, this mod gave a slight enhancement low down but didn't seem to improve the 'fault'.
I have removed inspected and refitted the MAF which looked clean, perhaps too clean, I am wondering if someone has had a go and given up.

Am I correct in understanding that the Siemens Hdi90 does NOT have a cat/fap device, hope not!
Where next? get codes read, disable clutch switch, run with MAF disconnected, it's all a bit muddling really, XUD so simple.

Thanks in advance!

[jasper5]

Hi and welcome

First thing I would have done/do is to replace the fuel filter and fill the fuel filter housing with injection cleaner and fit a new air filter....apologies if you already did that.

I would carefully and very gently spray brake cleaner or injection cleaner onto the tiny filament in the maf sensor.

Give the car a good blast and see how things are then.

No, the 90 does not have the fap system.

[rwb]

I found the turbo kick (from 1800) on my HDi 90 to be much more noticeable than it was on my previous XUD 406 (can actually lift off gently while still accelerating).

When I got mine it felt slow at low revs, turned out to be a flat spot on the throttle position potentiometer.
This should thow an "Engine anti-pollution system defective" exception, but not always.
In fact, I'm now on my third throttle position sensor.

Another possibility is air ingress into the fuel lines.
I keep wondering about this since I see quite a lot of air bubbles in the transparent plastic tubes into and out of the fuel filter. Been like that for years though and if it was serious then I'd expect to have errors being reported.

If it's juddery at low revs then change gear! Actually, easing off a little and then back on again works for me. I'd expect it to pull from about 1200... but not very much.

My trip computer under-estimates too, but by about twice as much!

Economy drops in winter. Here's my graph with 5 years of data:


Cat: yes.
FAP: no.

I think the EGR blanking is a bit of a red herring and recommend to leave it alone. Don't upset the sensors!

A clean set of filters mightn't go amiss and -- provided you know the cam-belt is good -- a good blast down the motorway at 4000rpm in 3rd usually makes mine feel a bit perkier.

[piglet]

Thanks Jaspar, a new filter set wouldn't hurt though the air filter looks very clean, I'll see if I can get some injector cleaner too and do like wot you said.
Since my 1st post I have driven 40 miles with the MAF plug off and there is no perceivable difference to the feel of the car or performance or economy (computer says no difference). What should that tell me about the MAF?

Cool graph RWP, are those figures your calculations from odo and fuel receipts? I'm not even getting close to that.
Mine has no turbo kick at all, very flat and boring. The XUD had a satisfying whoosh from about 1800.
How long is the cat supposed to last?
Interesting comment about the throttle pot. Are they expensive? Mine has a dead spot at the start, when I tried to take it out by moving the cable clip I got an Anti-Pollution Fault message. The cable clip is at the limit of it's adjustment anyway.
I also have bubbles in the clear pipe. They don't get any bigger. If it were a black pipe we wouldn't be discussing it!

Thanks for the interest, I will report back next week when I've bought some bits.

[rwb]

Throttle potentiometer was a £15 eBay job. £25 is more typical; I got lucky.
As you've found, they complain if you take up too much slack. This is very irritating -- I'd like to adjust it up by another notch but computer says no.

I always brim-to-brim and compute it myself. They're not readings from the computer. The data in that graph is about 300 miles per week of gentle motorway driving. I'm getting mid to low 50s now that I'm only doing two 10 mile journeys per day.

I've never had to and can't remember anyone who has had to replace a cat.

[piglet]

OK, new fuel and air filters, filled the filter bowl with Comma Diesel Magic injector cleaner.
Also took sons best Airfix brush and delicately brushed the MAF sensors with injector cleaner and carefully airlined off.
I havent been near any motorways but I have been able to give the motor a couple of short beastings at 4000-4500 rpm.
Overall the car does seem a bit perkier so worth doing, however the fault still persists.
At 1500 rpm there is a marked dead zone and/or tries to oscillate/kangaroo.
Economy still crap.

Could this be a turbo issue?

Thanks for advice so far, very helpful.

[Doggy]

I've never had to and can't remember anyone who has had to replace a cat.

'scuse my 2d worth. My old Xsara HDi 90 came from a lease company, who provided a very detailed service history. There wasn't a great deal of note, but there was a bit of a pantomime around 70,000 miles / 3 years, where it went to several garages to cure a 'power loss'. The final entry for this sorry chapter was a cat replacement.

I ran the car for 4 years, from 85k to 185k and towards the end, I think it needed doing again. It didn't really loose power, but the turbo lag was a lot more pronounced, also the exhaust smelt like a non-cat diesel. Never did the job, so can't be certain, but that was how it looked to be shaping up.

Having said all that, I seem to remember someone saying Siemens equiped car don't have a cat?

[Captain Jack]

I would tempted to replace the MAF as you say disconnecting it doesn't make a difference. Not sure on the cost of these though...

[rwb]

turbo lag was a lot more pronounced

Interesting