S1 V6 auto back on the road at last!! - Problem solved!!

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White Exec
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Re: S1 V6 auto back on the road at last!! - fourth time luck

Post by White Exec » Tue Feb 21, 2017 4:15 pm

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Chris
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Re: S1 V6 auto back on the road at last!! - fourth time luck

Post by MTXM » Tue Feb 21, 2017 7:38 pm

I am sorry to report that we are not quite there yet! In the last day I had been getting inlet manifold leak codes on my reader and I thought that must be it, a poor seal between the manifold and cylinders, which would explain the weak mixture. There had also been quite a dramatic deterioration in the tickover and the engine hardly ran, plus there was a definite hissing from the rear bank.

Anyway I resealed the manifold and in the process discovered a severe split at the bottom of the sensor pipe that I believe was the real culprit! The pipe had been good when removed a few days before but must have been damaged on refitting.

I did have some good help from Dave last night with his Lexia but there were no additional fault codes revealed. It is also possible to attach photos of the Lexia data at rest and with engine running at tickover and revving to the max and I would appreciate any enlightening comments.

The manifold pressure reading will obviously be effected by the split pipe but the mixture is interesting with a negative value!

With regards,

Matthew T.
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Re: S1 V6 auto back on the road at last!! - fourth time luck

Post by MTXM » Tue Feb 21, 2017 7:58 pm

In relation to the mixture percentage the figures we obtained were wildly fluctuating, as can be seen, but always in the negative! I understand the optimum is around 1:16 (petrol: air), or 0.00625%.

As a general summary the engine is now starting and ticking over at 850rpm spot on very happily, but then basically runs out of power around 2,300rpm, with an occasional surge, as if something, ie. too little fuel or too much air, is definitely holding it back.

Regards,

Matthew T.
1989 V6 Exclusive (Poland car)
1990 V6sei auto (grey auto)
1990 V6sei manual (gold car)
1990 V6.24 Pallas (Germany car)
1990 V6.24v (Scotland car)
Other previous XM sold and broken too many to mention!

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Re: S1 V6 auto back on the road at last!! - fourth time luck

Post by Dieselman » Tue Feb 21, 2017 8:26 pm

Shouldn't the Ox sensor to be around 0.45v?
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Re: S1 V6 auto back on the road at last!! - fourth time luck

Post by MTXM » Tue Feb 21, 2017 8:33 pm

The sensor does have that reading at rest Will, as shown by the first photo. Regards, Matthew T.
1989 V6 Exclusive (Poland car)
1990 V6sei auto (grey auto)
1990 V6sei manual (gold car)
1990 V6.24 Pallas (Germany car)
1990 V6.24v (Scotland car)
Other previous XM sold and broken too many to mention!

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Re: S1 V6 auto back on the road at last!! - fourth time luck

Post by Dieselman » Tue Feb 21, 2017 8:40 pm

afaik, on the Citroens the o2 sensor voltage should be stable at ~1.0v when running. Yours looks to be showing a rich mixtrure, which might account for the leaning of the mixture, to compensate.
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90 2.1SD M.RP 5049 EJV Mandarin
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Re: S1 V6 auto back on the road at last!! - fourth time luck

Post by MTXM » Tue Feb 21, 2017 9:30 pm

The reading appears to be stable at just under 0.9v, which is pretty close Will surely, or am I missing something? Regards, Matthew T.
1989 V6 Exclusive (Poland car)
1990 V6sei auto (grey auto)
1990 V6sei manual (gold car)
1990 V6.24 Pallas (Germany car)
1990 V6.24v (Scotland car)
Other previous XM sold and broken too many to mention!

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Re: S1 V6 auto back on the road at last!! - fourth time luck

Post by Dieselman » Tue Feb 21, 2017 9:58 pm

0.9v is a very rich mixture.

The o2 sensor should fluctuate between 0.1v and 0.9v continuously, giving an average reading of 0.45v.

Have you trieda known good sensor?

Is it being fed with power?
92 2.1SED M.RP5740 ECZ Sable Phenicien
92 3.0 V6-24.Rp 5713 EXY Black
92 2.1SD M.RP 5685 ENT Blue Sideral
Prev
90 2.1SD M.RP 5049 EJV Mandarin
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Re: S1 V6 auto back on the road at last!! - fourth time luck

Post by sdelasal » Tue Feb 21, 2017 10:00 pm

Matthew - some thoughts...

Engine stopped:
-Was throttle closed? 3.82 volts sees high for a 0-5 volt sensor. Assuming even a 0.5 to 4.5v working range, it's still in the middle. It says 'mid' in all three cases.
-Manifold pressure reading is simply indicating atmospheric pressure with engine off.
-The ECU thinks that the transmission is in drive - not neutral/Park. Odd, but unlikely to be that relevant.

Idle:
-Same comment about throttle as above. Why doesn't it say 'closed' (engine at idle) not "mid"? Does the throttle actually physically close?
-Was the Ox sens voltage cycling or steady? 876mV is rich. Either the mixture really is rich or the sensor is poorly.
-Manifold pressure is ~75% of atmospheric - seem high for idle - should be more like 25%. Idle valve is at 38% , it'd be nice to know if this is its minimum value.
-To me this looks like engine is running rich and at part throttle, not at idle.

1856RPM.
-Throttle position only marginally different. Fuel pulse width is less.
-Manifold pressure similar to at idle. Exhaust gas sensor is still reading a rich voltage. The 036% makes no sense to me. I guess the ECU may be backing off the fuel to correct the richness - but i'm surprised it has the authority to actually effectively cut fuel as it does that. Disconnecting the exhaust oxygen sensor should stop it doing that but in an earlier post you said doing that had no effect on the problem. Rail pressure being high could be another reason for excess fuelling for a given pulsewidth - did you actually check that with a pressure gauge?

In conclusion - the throttle position signal seems a simple and obvious oddity along with the Auto Sign: Drive. Rail pressure needs measuring.

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Re: S1 V6 auto back on the road at last!! - fourth time luck

Post by Dean » Tue Feb 21, 2017 10:02 pm

im waiting for the first picture to load but i see a small issue and one that could be significant, the small one is-why does the ecu always think its in Drive? if you have the gear selector in P or N it should detect a neutral state.
The other issue if at 800rpm its saying it is recieving a 3.82v signal and throttle position as MID, at 1850rpm its seeing 3.49v and still showing throttle position as MID, did you have the throttle fully open on the final picture?

Injection timing is a few milliseconds faster at 1850rpm so seems to be injecting some extra fuel but not much, the O2 sensor voltage appears to be constant at 876mv which to me also suggests the sensor is not seeing much oxygen ie reporting a RICH condition, it should read between 100-900mv fluctuating between the two at idle and holding a constant value under load, if its sitting planted at 876mv its junk.

will wait for the first pic to load, dont know why its taking so long.....

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