C5 Facelift Vacuum issue (Fixed)

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MGmike
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C5 Facelift Vacuum issue (Fixed)

Post by MGmike »

Hi All,
I'd really appreciate the your input on the above problem as I'm a little stumped and, short of throwing parts at it, I'm not sure how to diagnose the cause.

The problem is... on first start-up of the day it takes about 2 mins to build up vacuum for the brakes and, I guess, all the other items that need it. On subsequent start-ups the vacuum is there within a couple of seconds. The only error code is P2120 which I believe could be related to a lack of vacuum on the air heater inlet circuit.

So, is it a lazy vacuum pump or something else and how do I set about confirming where the problem originates?

I do have one other problem I'm struggling with! I'll start a separate thread for that as I believe it's unconnected but I'll mention it here for complete disclosure. That problem relates to the gearbox not always shifting from 2nd to 3rd on strong acceleration. That is, until the steering is turned to the right! Steering angle sensor?

Thanks in advance.

Michael
MGmike
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Re: C5 Facelift Vacuum issue

Post by MGmike »

Possibly fixed... I'll find out for sure in the morning.

Last night I had a bit of a light bulb moment when I remembered I've just bought a vintage vacuum gauge for setting up my MG's!
This morning, I attached it to the output of the vacuum pump and watched as it struggled to rise to 20 in/Hg. It was very slow to get started then crawled up to a about 15 in/Hg before slowing down again until it finally reached 20 in/Hg after a couple of minutes.

I've swapped in the vacuum pump from my spares car and will see how things go on a cold start tomorrow. fingers crossed...
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MattBLancs
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Re: C5 Facelift Vacuum issue

Post by MattBLancs »

Ah good thinking!

There's plenty of second hand ones on eBay for not much.

I took the lid off the 1.6 HDi one here. There's an O-ring around perimeter of the lid, wonder if that has perished and so air leaking in on yours? Perhaps a bit of "O-ring cord" cut to length could replace it?
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MattBLancs
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Re: C5 Facelift Vacuum issue

Post by MattBLancs »

P.s. and quite off topic, and indeed quite silly, but...


"Facelift vacuum issue" sounds like some sort of failed cosmetic surgery horror story! :rofl2:
MGmike
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Joined: 29 Aug 2020, 18:29
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Re: C5 Facelift Vacuum issue (Fixed)

Post by MGmike »

Matt, thanks for the comments and I like your thinking :rofl2:
I might think about stripping the old unit just for the fun of seeing what was at fault. For now the replacement from the spares car will suffice.

Mods, could you change the thread header to ***fixed*** pls?
Confirmed fix at start-up this morning with fully working brakes from the off :-D