Xantia HDi power gremlins

[Edhertz]

The power gremlins have arrived for Xmas. Many threads on this subject so to say it’s not uncommon is an understatement. In a nutshell the power and nippiness have been noticably reduced to the point of frustration when considering overtaking. I have checked the usual suspects with the help of past threads,
This is what I’ve found/done so far:
Wastegate and EGR hoses …..no damage….. high vac
Turbo solenoid valve functioning normally ….. Vac: 26 in Hg
Visually checked turbo lever smooth operation over full range ….. holds high vac
Vac pump measured: 26 in Hg
Lexia readings:
Induction air flow idle: 458mg/cp
Induction air flow 70mph: 570mg/cp
Actu.turbo P at 70mph: 1223mb
Boost solenoid OCR idle 89%
Boost solenoid OCR drops to 58.5% - when accelerator flat floored
(boost control?)
No warning K lights or Lexia resets required
Thanks in advance for replies and suggestions,
Cheers, Alan

[Rp0thejester]

Hmm, everyone here knows what I'm gunna say...MAF sensor, unplug it and see what happens.

[CitroJim]

Good call on the MAF Ryan

Also, any whistling noises when on boost? The 110HDi has a nasty habit of making holes, often not easy to see, in its big rubber pipes that go to and from the intercooler. Also, the little rubber stub pipe that links the end of the plastic pipe to the turbo compressor output can split and leak boost.

Any small boost leaks like this can impact performance without necessarily raising fault codes...

[Edhertz]

Thanks for replies and here is an update so far.
Run with MAF disconnected …. no change
Checked all induction and turbo pipework …. no obvious cracks or leaks
Jim … couldn’t find a small stub pipe.
MAF and MAP sensors checked in situ …. Functioning normally and checked against spares.
Checked MAP sensor output on a run over a range of accelerations and speeds and found no response so there appears to be a leak somewhere possibly through the intercooler or pipework.
Blanked off turbo outlet to manifold inlet pipes and pressure tested complete system via the MAP sensor connection to approx 10psi.The blank seals were not 100% so the pressure went down slowly, with no sounds or signs of a leak from intercooler or pipework.
Could it be that it only requires the smallest leak in the intercooler to collapse the pressure drop required for the MAP sensor? What would the effect be if the wastegate was not seated correctly?
Cheers, Alan

[CitroJim]

Could it be that it only requires the smallest leak in the intercooler to collapse the pressure drop required for the MAP sensor? What would the effect be if the wastegate was not seated correctly?
Cheers, Alan

Yes, it only takes a tiny leak Alan...

The stub pipe is got at by crawling under (taking necessary precautions) and looking at where the plastic turbo hose that passes under the engine interfaces to the turbo outlet. It should be about two inches long and have two Jubilee clips around it... It goes soft and leaky.

Often when there's a leak you can hear a whistle when you really give it some welly...

Else that, I'd start looking at your cat as a potential cause... I've known diesel cats start to block at high mileages and any resistance in the exhaust system will not do performance any good...

You could bypass it as a test (bypass pipes have been and may still be available) but be aware it must be present for legal and MoT reasons...

[Edhertz]

Jim..... double checked the pipework with fairy liquid solution including the stubpipe and couldn't find any leaks.
Next step is to have the intercooler off and give it a good looking at ..... hoping I find something. Could try the cat next but as it was renewed only appox 40K ago I'll hold back a while,
Cheers Alan

[CitroJim]

Gosh, that's being a bit of a puzzler Alan.. No, it won't be the cat if only swapped 40K ago. Does that go for the silencers too?

The intercooler is a good call. it can have a tiny leak and may contain a fair of bit of oil and that can impair its performance, as can much dirt and grime on its external surfaces... An intercooler that cant effectively cool for whatever reason will make a 110 HDi feel more like a 90 HDi

I well recall how flat a 1.9TD with the top-mounted intercooler could feel if the car had been sitting in a traffic queue for any length of time. The intercooler would get very hot (heatsoak) and the engine would feel like it was robbed of a cylinder or two when you could move off again. All fine once some cooling air got to it...

[Edhertz]

I’m back on the case. Following your suggestion Jim I removed the intercooler …. between showers just to make it easy.

Looking at the state it was in I doubt it was operating at more than 50% so removed nearly 25 years worth of highway crud and pressure tested everything along with complete pipework and found no leaks. The Mg alloy finning was on the fragile side but other than that it was in amazingly good nick. So job was worth doing and where am I now? Been out for a spin and nothing has changed. I’ve tested the MAP sensor on the road and the highest reading I got was 2.7volts. The reading at idle is the same with the engine off 2.35volts. What am I looking for? I am expecting to see a voltage corresponding to atmospheric pressure with ignition on and a small voltage drop due to the slight vacuum at tick over with a steady linear increase to approx 4.5volts at approx 2 bar around 3500rpm. MAP sensor is fully tested and functions correctly so guess its Waistgate , EGR , CAT next. Thanks for replies and suggestions in advance,
Cheers, Alan

[myglaren]

Did you check the internals of the intercooler?
On my last C5 the 'performance' was absolutely rubbish.
I had the intercooler, turbo, EGR and all associated pipework removed and cleaned.
The difference was astounding.
I took it from the garage at lunch time, downhill to work, only ¼ mile.
Later, leaving work, i applied the usual throttle up the hill and scared myself, it took off like a scalded cat. Immense improvement and much improved economy too.

[CitroJim]

Gosh Alan, the muck there on that Intercooler

I'm thinking you mean the MAF sensor. How did you test it? The MAF sensor is easily tested by running with it disconnected. If no discernible difference then it's dead. They are very delicate little flowers.

EGR and Cat are good candidates...

[PaulC5]

This is from post 4 'Run with MAF disconnected …. no change' as well as 'MAF and MAP sensors checked in situ …. Functioning normally and checked against spares.' I am not sure what these mean, either the MAF is faulty or it is not ?

[CitroJim]

Good point Paul...

[Edhertz]

Apologies if I have caused the fog to descend here. The MAP and MAF sensors were tested and found to be functioning correctly. MAF sensor is a quality Hella, new out of the box. Sensor outputs were found to be functioning in a linear, proportional, smooth manner and compared favorably with functional behavior of spares.
As suggested car was run with MAF disconnected and found very little difference in performance between connected and disconnected. Since the clean however I can now report a noticeable improvement, particularly in the lower gears. So Jim the clean is a definite plus! No change in get up and go to report at this stage. Connected an air pressure gauge to MAP sensor pipe and noted turbo air pressure change with increase in engine speed. The maximum pressure was found to be around 7psi which is around half of what it should be at 3500rpm. Operated EGR with hand vacuum pump, found to be working smoothly with a definite sound of the internal gate closing,
Cheers Alan

[CitroJim]

That's good Alan, a lot excluded in the search... Pleased an intercooler clan has helped a little...

To prove the EGR, you could temporarily block it off... Note that it cannot be left in this state but like disconnecting the MAF, it's a good test.

Really now, given the EGR tests good as above, all that's left is either persistent small leaks in the turbo hoses or a leaky turbo wastegate...

[SwissTony]

On mine (ex Jim's) HDi, the large pipe that runs over the top of the engine had split on the underside, but upon inspection didn't look like it had at all. It was only when I removed it and manipulated it with force, that the split showed up. It had me baffled for a few days.