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 Post subject: 205 misfire
PostPosted: Mon Aug 21, 2017 8:14 pm 
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Clubman

Joined: Sat Apr 29, 2017 8:54 am
Posts: 77
Car Model: None
Hi guys ok quick problem my 205 has a misfire at low rpm only code is 21 so will a dodgy O2 sensor cause a miss
It struggles to pick up unless I give it a boot then it drives ok but starts to miss under light load you can hear it spooling but no go and at idle it has a slight miss
One thing I've just found is that if I have my hand near the dizzy cap I get a belt from either the leads or cap any direction would be a help
Baz

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 Post subject: Re: 205 misfire
PostPosted: Mon Aug 21, 2017 9:28 pm 
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Group B
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Joined: Sat Sep 02, 2006 3:13 pm
Posts: 3580
Location: Bournemouth
Car Model: None
A dodgy O2 sensor is likely to cause incorrect mixture at idle & cruising. A heater failure would particularly cause a problem with prolonged idle as the sensor can cool down too much to work. From my own experience of a failing sensor, leaving the car on idle tends to leave it running very rich after a minute or two.

I never put my hand near ignition leads with the engine running, these ones hurt !! That said, you 'shouldn't' get a belt and doing so may indicate a problem - either poor insulation or a break in the wire leading to a higher voltage at the cap end. Worth doing a resistance check on the leads and inspection of the cap for cracks. It's also not unknown for the rotor arm to come unscrewed, again causing bad connections.

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 Post subject: Re: 205 misfire
PostPosted: Mon Aug 21, 2017 9:40 pm 
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Clubman

Joined: Sat Apr 29, 2017 8:54 am
Posts: 77
Car Model: None
Hi mate could be a few issues at play then
I went out in the dark just now looking for a spark leaping about the engine bay but there was nothing put my hand into the cap area and number one at the cap end leapt out and danced up my arm so how would code 21 O2 sensor and a dodgy cap on the dizzy go right and ok at full throttle

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 Post subject: Re: 205 misfire
PostPosted: Mon Aug 21, 2017 9:45 pm 
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Clubman

Joined: Sat Apr 29, 2017 8:54 am
Posts: 77
Car Model: None
Or is that symptom more likely to be an injector or something
It's easy to run up a big bill and replace all and sundry and still not get the issue solved so I'm watching the pennies as the missus is cursing the 4 at the moment and it's known as the liquidator as that's what it does to the bank account

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 Post subject: Re: 205 misfire
PostPosted: Tue Aug 22, 2017 9:53 am 
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Group B
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Joined: Sat Sep 02, 2006 3:13 pm
Posts: 3580
Location: Bournemouth
Car Model: None
The ECU goes open loop once on boost as the mixture needs to be richer. The O2 sensor is only used during cruising and idle. The heater is only really needed for prolonged idle idle (earlier models didn't have a heater).

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 Post subject: Re: 205 misfire
PostPosted: Tue Aug 22, 2017 10:04 am 
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Clubman

Joined: Sat Apr 29, 2017 8:54 am
Posts: 77
Car Model: None
So it could be the O2 sensor then as it's under light load under boost it clears and once having a blast and it getting hot it's fine only really goes bad when cold and under light driving after start up


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 Post subject: Re: 205 misfire
PostPosted: Tue Aug 22, 2017 2:36 pm 
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Club Staff
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Joined: Wed Jul 13, 2005 5:10 pm
Posts: 1952
Location: Sunny Fareham, UK
Car Model: ST205
Most likely cause is ignition related - suggested change/check order;
1. Clean rotor cap (check the central sprung carbon brush is there)
2. Check engine earth
3. Change plugs (NGK BKR7E)
4. Change rotor arm
5. Change cap
6. Change leads

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 Post subject: Re: 205 misfire
PostPosted: Tue Aug 22, 2017 6:47 pm 
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Clubman

Joined: Sat Apr 29, 2017 8:54 am
Posts: 77
Car Model: None
Ok Done all of that except the engine earth's still Missing
And bogging down really doing my head in now and I'm running out of ideas could this be an injector issue


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 Post subject: Re: 205 misfire
PostPosted: Wed Aug 23, 2017 10:06 am 
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Group B
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Joined: Sat Sep 02, 2006 3:13 pm
Posts: 3580
Location: Bournemouth
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Engine Earth missing ? This would cause loads of issues, unless you just mean the one by the alternator.

Also check the small pipe that goes from the manifold to the top of the fuel pressure regulator. If this were blocked or not connected it would go rich at low load and weak on boost.

The other thing that can cause similar symptoms is knock sensor failure, but if you only have code 21 it won't be this.

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 Post subject: Re: 205 misfire
PostPosted: Wed Aug 23, 2017 10:55 am 
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Clubman

Joined: Sat Apr 29, 2017 8:54 am
Posts: 77
Car Model: None
No I've checked and have three earth's the fuel regulator pipe is ok. what about a vac leak


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 Post subject: Re: 205 misfire
PostPosted: Wed Aug 23, 2017 11:20 pm 
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Group B
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Joined: Sat Sep 02, 2006 3:13 pm
Posts: 3580
Location: Bournemouth
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vac leaks have very little effect other than raising idle on a 205 as fuel is set from manifold pressure. Unless it's in the pipe to the pressure sensor of course.

Another remote possibility is a poor connection on the resistor which is switched in series with the fuel pump at low load. This can easily be ruled out by linking FP to B+ in the diagnostic connector bypassing the whole fuel pump control circuit.

I would still say a code 21 points to O2 sensor, as this also fits the symptoms - assuming of course the ECU has been reset and the code comes back.

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 Post subject: Re: 205 misfire
PostPosted: Wed Aug 23, 2017 11:32 pm 
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Clubman

Joined: Sat Apr 29, 2017 8:54 am
Posts: 77
Car Model: None
Hi mate
Well it's a little too soon to say but I had a fresh O2 sensor sent up from tcb pit it on this morning and went to work runs smoothly went out from work at teatime and again running smoothly came home about an hour back and running smoothly no misfire and throttle seems crisp
I'm holding my breath down hoping that's the problem solved
I'll monitor it over the next couple of days and see how we go and I'll keep you posted
Regards Baz


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 Post subject: Re: 205 misfire
PostPosted: Fri Aug 25, 2017 9:04 am 
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Clubman

Joined: Sat Apr 29, 2017 8:54 am
Posts: 77
Car Model: None
Solved :
It was indeed the lambda sensor


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