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C6 2.2 stalling/lumpy idle when cold
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Dan595   
Tue Oct 26 2021, 09:05am
Joined: Nov 26 2010
Member No: #299
Location: Wiltshire
 Looking for ideas on this one as it has frustrated all attempts to resolve so far, and the recently colder weather has made the issue rather worse.

C6 2.2 Manual, 255,000 miles.

Starts from cold perfectly and idles sweetly.
I drive off, it is fine at the first junction (300 yards or so) but when I ease off to idle at the top of town (less than half a mile) the engine falters and usually cuts out. Will always restart immediately, but may do the same at the next few junctions.

Once out of (small) town, may 'cough' which feels like the engine has instantaneously seized, but will then relight and drive normally. May do this once, or a few times. May not do it at all. Once warmed up, won't do it and will run for hundreds of miles no problem.

Sometimes, it may not show the fault at all (most likely to not show it if I can drive off and not have to stop when the car is warming up).

Never shows an EML, never shows any faults on Diagbox, all the live information on Diagbox looks fine when driving, even when the fault occurs. The fuel filter has been changed (twice).

So, does anyone have any ideas what is causing this?

The throttle body, EGR, injectors, injection pump, exhaust, DPF are all original from when the car was new. Crankshaft sensor has been changed, DMF was changed around 150,000 miles. I have recently cleaned up all the fuses and electrical connectors, but this does not seem to have made any difference.
onthecut   
Wed Oct 27 2021, 07:44am
Joined: Sep 20 2016
Member No: #2793
Location: West Mids
 Hi Dan..

Just a couple of random thoughts -- the fact that nothing shows on Diagbox perhaps suggests the relevant ECU(s) isn't seeing anything it views as odd. As there may be a temperature link, is it possible you have a duff temperature sensor somewhere. It may be delivering readings that are within limits, but too soon / late, whatever ?
Your symptoms are very similar to those I experienced on my 1.6HDi Pug and in that case it turned out to be a fuel pressure issue (regulator on top of the pump), but that did show up on a diagnostic, although didn't trigger the lamp.
Again, I would think it would show up as a pressure issue, but just as a precaution, if you can access it without major grief, it may be worth checking the pick up gauze on the end of the pipe in the tank.
If the fuel filter has only been done twice in the mileage, definitely worth diong again. It's worth avoiding cheap filters, too -- we've had one fail and block the system. (TJ make). Only use Purflux or similar, now.
Finally, there was a piece a few months ago in one of the trade mags - and unfortunately I don't recall which or exactly when -- about a mystery injection issue that (I think) wasn't showing up on the normal diagnostics. That was resolved by a specialist and his oscilloscope, which picked out the fault that was beyond the reach of the ordinary kit.

Good luck with it. Mike.
Jas16   
Wed Oct 27 2021, 09:13am
Joined: Feb 07 2017
Member No: #2994
Location: West London
 On my 2.2, I have changed both crankshaft [was this changed recently?] and camshaft sensor [easy to do].

As per previous post, change the fuel filter too, but remember to bleed the air out as well

Reading from your post, it looks like there is no issue when warm? what I did to help is to ask a mechanic with a good quality scan tool, is to have it connected and drive the car, and record the live data stream. Review this afterwards as the error may not be "significant" enough to trigger a code.
Dan595   
Wed Oct 27 2021, 06:26pm
Joined: Nov 26 2010
Member No: #299
Location: Wiltshire
 Thanks for the input on this.

I perhaps didn't make the fuel filter changes clear - the car has a full main dealer service history (I've paid for them all!) and since this issue has arisen the fuel filter has been changed once as part of a service and again as a standalone replacement.

To me it feels like a fuel issue, but my experience is with (literally) agricultural diesels where there are very limited electronics, so I don't trust my intuition here.

From what we can tell none of the sensors are showing anything untoward, either as raw data or enough to trigger an EML or fault code.

Crankshaft sensor was changed about two years ago, the fault being an engine cut-out (none of the stalling/hesitancy) and sometimes not an immediate restart. This seemed to be cured. I am certainly one to 'beware the brand new' so a good call.

Thanks.
JohnB   
Thu Oct 28 2021, 02:35pm
Joined: Dec 09 2014
Member No: #1968
Location: Bath
 I posted this on another thread, but might be worth considering…
I had a similar, although not exactly the same, problem with my 2.2hdi auto. The engine would cut out, usually during a long journey, with no error code. I’d also noticed it was taking a fraction of a second longer to start, whether hot or cold. I took it to BL Autos, who found an intermittent problem with the throttle. I’ve now driven about 20k miles on a new throttle and it’s been perfect on both issues. All credit to Robert at BL Autos as I don’t think anyone else would have found that issue until it had completely failed.
Regards
John
 

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