Citroen AX (1987 -1997) - '95 1.0 Dimension, cold start problems.

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Mon 3 Dec 2007 16:17
'95 1.0 Dimension, cold start problems. - Maceman
Hi all - My first post, can anyone help?

Just bought 95 AX and have noticed a problem just after starting up. If I don't leave it to warm up for a few minutes, the engine bogs down when I use the throttle. Release the throttle and it revs again. Only happens when it's cold. As soon as it warms up it runs well. There was a slight burning smell whilst trying to run it cold and some smoke around the exhaust pipe (not coming out of it)

I thought it was the autochoke needing adjusting or sticking, but the engine has a Bosch monopoint fuel injection system, so no choke.

Have a receipt from 1 week ago for investigating starting problems - garage said exhaust was blocked causing spark plugs to foul up. They replaced the sparks and fitted new back box. Not sure if it's related?

As I say it runs fine once its warm so not too bothered but am worried about doing nothing and things getting worse.

Any advice much appreciated!

Maceman

slt

Edited by Pugugly {P} on 03/12/2007 at 18:11

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Mon 3 Dec 2007 16:38
'95 1.0 Dimension, cold start problems. - Screwloose
The engine coolant temperature sensor would be a good place to start.

It can be tested with an Ohmmeter; but checking it's reading in the engine management's live-data is better.

Edited by Pugugly {P} on 03/12/2007 at 18:12

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Mon 3 Dec 2007 16:47
'95 1.0 Dimension, cold start problems. - Maceman
Thanks Screwloose.

I take it a reading from the engine management live data means an expensive trip to a Citroen dealer?

Maceman

Edited by Pugugly {P} on 03/12/2007 at 18:12

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Mon 3 Dec 2007 22:47
'95 1.0 Dimension, cold start problems. - Screwloose

Anyone with a scanner. Most garages have one.
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Tue 18 Dec 2007 10:48
'95 1.0 Dimension, cold start problems. - Maceman
Have bought myself a fault code reader and it came back with one fault - the oxygen sensor.

The car has a four wire hego and I'm thinking that the fact that the problems occur when it's cold suggests that the heating circuit or element is faulty??

Do you think it's worth getting a new lambda or should I carry out more tests first? I suppose it's possible that the something else is causing a mix problem which in turn means the lambda would send a signal that the ecu doesn't like.

Any thoughts on how to progress on this one?

Thanks!

Maceman

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Tue 18 Dec 2007 12:02
'95 1.0 Dimension, cold start problems. - Screwloose
Maceman

The oxygen sensor has no part in start-up/warm-up. In that phase, the system operates in open-loop just running on a pre-set warm-up map - mainly controlled by the coolant temp sensor.

Only once the oxygen sensor is fully up to temp [2-8 mins] will the system swap to closed loop and start adjusting itself to suit the exhaust oxygen level.

What was the exact code number? Check and clean the sensor's plug; they're well known for getting corroded down there.
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Tue 18 Dec 2007 12:20
'95 1.0 Dimension, cold start problems. - Maceman
Hi Screwloose,

The code was 51 - no other codes present

The notes with the fault code reader suggest that if the ecu records this fault code it will enter LOS mode and 'limp home'. I'm wondering is this is what is happening and why I'm losing power?

I wonder whether previous owner has put wrong fuel in car and killed it?

Today the car was running rough for nearly 30 mins before it settled down. Black deposits from exhaust pipe are also present. . .unburnt fuel?

Could the cat be blocked and openeing up once it gets hot?

Will take the sensor off and check for corrosion and deposits on the tip.
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Thu 3 Jan 2008 12:27
'95 1.0 Dimension, cold start problems. - Maceman
Screwloose,

Thought I'd let you know that I seem to have fixed the fault. I replaced the O2 sensor with a universal part and know the car is running really well. The old sensor tip was cracked and covered in carbon. Looks as though it had never been changed in 12 years. Thanks for your advice.

Maceman
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Thu 3 Jan 2008 13:16
'95 1.0 Dimension, cold start problems. - Screwloose
Maceman

Sorry; your previous post seems to have slipped past without me noticing it - probably a Christmess thing.

Yes; 51 is a catch-all HEGO code - the only one in the list. No LOS facility fitted to these; but if the over-fuelling was persisting for 30 minutes, then it could, maybe, be involved in your black smoke/soot.

I'm still thinking faulty coolant temp sensor - which won't normally leave a code for the coolant sensor - but may flag a code for the HEGO/Lambda because it's not sweeping, just reading too rich.... [Simple this ain't.]

If you've got a meter, then it's in the end of the head next to the coilpack [maybe a white or green clip-on plug?] and should have 3,500 Ohms across it's two pins [disconnected] when cold and 240-ish when hot.
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