C5 mk1 2.0 HDi power issues

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maxxo
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Joined: 21 Aug 2019, 01:00
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C5 mk1 2.0 HDi power issues

Post by maxxo »

hi all

further to my weird issue with my C5

experiencing lack of power at times and shuddering at low speed acceleration when hot

i'd been convinced it was the gearbox (AL4) but now i'm not convinced

so with the most pressing one, the loss of power, now this usually happens when up to temp and at higher speed, you're accelerating and then suddenly you just lose all power and can barely maintain speed at all, ocasionally the revs will increase just slightly but otherwise nothing until you life off and on again

but these past few days i decided to try something, it happened at 55 mph and i just pushed my foot to the floor, cue the gearbox kicking down and still absolutely no power

today i discovered something else, if it does it and i use the cruise control to speed up then all is fine......

throttle position sensor would be my guess, but as the gearbox seemed to detect it and kick down then i'm not sure

i also had, last week when it was extremely hot the car feeling like it was in limp mode, almost no power at all from any speeds (no vibrations or anything though) and then have it shoot off like a rocket once it reached 3k rpm

unplugged the MAF sensor, no change at first until it put the EML on and then it went properly into limp mode, and also brough up gearbox fault (not surprising due to having to accelerate hard due to zero power)

no starting issues, the odd slightly rough idle, and slightly jerky at around 26 mph

it just seems as though the pedal gets disconnected, yet at the same time cruise control works as an accelerator.....

are these fly by wire?

i should also add, no codes in lexia for anything, autobox pressures looked absolutely fine on my little drive

thanks
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GiveMeABreak
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Re: C5 mk1 2.0 HDi power issues

Post by GiveMeABreak »

You should be getting stored codes if there is a fault, even though it may be temporary. You should be able to consult the log to find the fault codes and how often they have been triggered.
maxxo
Posts: 68
Joined: 21 Aug 2019, 01:00
x 15

Re: C5 mk1 2.0 HDi power issues

Post by maxxo »

nothing in the lexia global test at all

i've just had 31 mpg from the last tank too which i don't find the best (20 mpg less than my XM!)

now, it's stopped allowing me to accelerate through it using cruise control

everytime you load it up when warm now it loses power to the point where you have no acceleration, you can barely maintain speed

once the gearbox kicks down then all the power usually comes back, same as when you lift off and back on

you can also smell it from behind when it's running

i'm also convinced the engine is sounding different now as well
maxxo
Posts: 68
Joined: 21 Aug 2019, 01:00
x 15

Re: C5 mk1 2.0 HDi power issues

Post by maxxo »

lexia parameters and graphical measurements complete

down on boost when it does it, requests 1.8 bar for example and only gives 1-1.1 bar of boost

fuelling looks okay, not fantastic but good enough

only when up to temp.....wastegate solenoid?
maxxo
Posts: 68
Joined: 21 Aug 2019, 01:00
x 15

Re: C5 mk1 2.0 HDi power issues

Post by maxxo »

dug a bit deeper

it's only when fully up to temp, and then intermittent

for example, say if you've been driving 70-80 for a while and the oil temp guage is approacing halfway it is almost guaranteed to lose power

you can go full throttle, and have nothing until the torque conveter locks around 3k rpm then you shoot off in a cloud of clag

now even when not hot, it can sometimes still do the same thing, worse if it's a hot day

the only issue i can really see is the low boost whilst it's doing this, much lower than what the ECU actually wants

vacuum pipes from the electrovalve look fine, no cracking or anything

i'm really stumped here, does anyone have any suggestions?

exhaust smells a bit less claggy today, but then again it didn't act up today, but once it's done it once then it's flat for the rest of the trip and the exhaust stinks

there is soot on the rear bumper