Help! Citroen c4 2.0hdi 136hdi, lack of power.

[Richard85]

Hi, ive had a lack of power with my c4 2.0hdi 136bhp, it seems to have no boost until around 2500rpm. Then its minimal at best, but noticable. However when you get into 4th gear or above the lag is problematic, especially on the motorway. Ive done a lexia scan, and no faults logged. I did some live data running and have noticed some discrepanceys regards turbo boost pressure measured and reference value, the turbo hits 2050 mbar max when the reference is showing it should be 2400mbar, also the reference shows it should be at this for way longer than it actually is. It seems to peak at 2050mbar for a split second. Also the turbo electrovalve is showing weird values, spiking to 100% when there is no boost showing. I wish i could add a picture of the live data to show you. Any ideas? I did change the electrovalve for one i had spare for the egr electrovalve but its a different part number and very slightly different appearence, but all this did was move the boost to 3500rpm and above and very sluggish and no boost below.

[Chris570]

My wife's c4 has a similar problem and a very common fault on these is the turbo boost sensor. What it is is a little needle sensor and it it senses how far the actuator rod has actually been pulled versus how far it should have been. The problem is water gets down the back of the engine and destroys the sensor. I'm on my mobile at the moment so I hope I've explained it well enough to further your search. Citroen don't list the part separately but you can find them on a popular auction site. I have one on the bench waiting for my patience to get to a point where I fancy sticking my hands up the back of the engine....

[Richard85]

Thanks for your reply Chris, i did read that the turbo copy sensor can cause this issue. Im gonna order one and fit this week. I will also buy a new turbo electrovalve just to be sure. It makes sense regards water ingress, the scuttle panel below the windscreen doenst fit well at all and you can see water has made its way down the back in the past. Do you know if its normal for it not to log a fault for the sensor if its failing? I would of expected it to, but hey citroens have always been misterious regards sensor faults! Richard

[Chris570]

No problem. Let me know how you get on fitting the sensor as there's not a lot of room! My wife's c4 has logged a fault but the light isn't on.... I imagine like most sensors it will only log a fault if the received reading is drastically different to the expected one so perhaps yours has failed in a new and fun way.....

[Richard85]

Just a bit of an update, the turbo sopy sensor is being fitted in the morning, but i did some more live data sessions and have noticed the turbo pressure drops first on each press of the throttle, then boosts to 60% of what it should. So should be 1001 mbar on idle but shows 980 mbar. When i accelerate it should go to 1500 mbar on a quick blip but instead it goes down to 930 mbar and then up to 1150 mbar. Weird. The turbo pipes vacuum instead of pressurise first. In othr words they suck in, then later slowly pressurise a little. I hope the copy sensor is to blame.
Will update tommorow.

[Mandrake]

I would think a brief dip in pressure when you open the throttle quickly which then recovers and goes higher than what you started at a moment later is normal for a turbo engine - it's called turbo lag

At the instant you open the throttle the engine vacuum pump will increase but the turbo inertia prevents it instantly spinning faster so boost drops. As the turbo spools up due to increased exhaust flow the boost will recover.

Of course an excessive dip/lag could indicate a problem but without a known good to compare against there's no easy way of knowing whether the amount of dip you see is normal.

[Richard85]

Update,
Fitted new turbo copy sensor, the old one was full of orange dust (rusty water) etc. It has made a diffrence regards the turbo now boosting around 2000rpm in each gear, but it hasnt fixed the issue completely. The boost still isnt as the reference value on lexia suggests, by around 250mbar lower than reference, so 2400mbar reference 2150mbar actual. Doesnt hold that figure for long neither, it spikes and then reduces. Still getting surging when holding around 2000rpm, or on cruise control. Also stuttering when at low rpm like its kangarooing slightly. Boost is better and more responsive in each gear but, come off the power and re apply it and the boost has gone and acceleration is noteably slower. I tryed changing the turbo electrovalve again, as i have a couple of spares and i got PO2565 turbo copy signal voltage to high.

However when i put the origional electrovalve back on the fault cleared and didnt return. It did this before when i changed just the electrovalve before changing the copy sensor and the same fault occured. Using either of my spare electrovalves shows the p02565 and boost pressure at 980mbar and expected 1400mbar, and near no turbo boost.

So replaced or checked so 8far:-
New turbo copy sensor
Turbo electrovalve
Changed Maf sensor (No difference)
Airfilter / fuel filter oil etc
Checked vacuum hoses and connections
No faults showing in ecu apart from p0495 fan high speed coherance. Which i beleive is the fan resistor pack.

Pretty fed up of the car now, its a pristine c4 vts hdi and would be a shame to part with but its starting to look like the old peugeot 406 money pit.
Any ideas or help would be appreciated

Cheers
Richard

[Richard85]

Also i forgot to say, im getting a fair amount of black soot up the bumper, and soot on acceleration. Like its running rich.
Cheers

[Chris570]

I can't remember the lexia terms now but do the copy sensor values and expected values now tally up? If so I'd be looking for a boost leak somewhere and if the values are still slightly out I'd look again at vacuum. My c5 split in the join just behind the starter motor and a 407 that I know had a split in the little vacuum black box about 2 inches from that join....

[Chris570]

Also how much of a pain in the bum was it changing the copy sensor?

[Richard85]

Hi Chris,

i will be reinvestigating the vacuum system, however im wondering what this vacuum box is that you mention? Ive checked the little rubber link pipes to the electrvalves that control the throttle butterflies (air doser), they are fine, also the rubber links to the turbo valve by the cambelt side of engine. I really could do with maybee taking the metal pipe from the actuator to turbo valve off and flushing it through as its got rusty water and dust in it.
If there is some sort of vacuum resevoir do you know were it is? Ive also checked the vacuum from the pump and the little pipes all check out ok.
I just blanked the egr and its made a big diffrence regards hesitation and running. Still boost problems.

Cheers
Richard

[brookesmk4]

SOrry to dig up an old thread but di you ever manage to get this sorted?? ive recently bought a CGP and have black soot over boot and not to very little power its a 2.0HDI auto

[Chris570]

Best to start a new thread if not already done so, if you can list any fault codes if known and also symptoms that will help massively.

[brookesmk4]

Best to start a new thread if not already done so, if you can list any fault codes if known and also symptoms that will help massively.

Cheers Chris, i will get it scanned later. the EML isnt lit up so im not sure if it will give me anything. plus i've not the foggiest idea as to how to make a new post lol

[GiveMeABreak]

Just click on the French Car Forum banner at the top of any page.
Select from the available Forums which one is most suitable to post your Query in (I'm guessing 'CITROEN' in your case)
So in this case, click CITROEN
From the Citroen Forum at the top you will see the 'New Topic' button to create a new thread: