3.0 Xantia misfire

Stempy · Unread post by **Stempy** » 21 Apr 2004, 00:30

Well since replacing the thermostat and spark plugs it's like a different car and runs up to temp quickly as it should and is much smoother. However, it still has a rough period between 1500 and 2500 rpm especially bad at just over 2000rpm. It is much worse when cold but it's still noticeable very slightly when hot. There's nothing wrong with the performance otherwise.
On the back of the throttle body there's a cylinder which Citroen call a 'compensator'. I assume this is an air bypass valve but don't know how to test it as it is completely sealed.
I'd be interested to know if anyone knows any test procedures for the various input sensors for the injection ECU, and where the diagnostic plug is situated so I can perhaps read any fault codes.

Richard Gallagher · Unread post by **Richard Gallagher** » 21 Apr 2004, 00:58

The diagnostic socket is the long 30 pin one in the fusebox where the handbook is kept. You will need a proper code reader, the LED type will not work as 'pulses' are not generated.
If I'm not too far away from you, Iver Bucks (M25/M4/M40 triangle) you are welcome to 'pop in' and I will put my Sykes ACR on it. This will not only read fault codes but also give the "readings" that the ECU is receiving from the various sensors, such as temp(coolant/air)/ignition timing etc etc.

Unread post by **philhoward** » 21 Apr 2004, 01:16

Does the ECU do a self-learning process? In this case, it MAY be worth disconnecting the ECU to reset it and go for a long, varied drive for it to learn its new optimum settings...I'd wait for some other opinions on this first before doing it incase there may be something sinister in doing so!

Stempy · Unread post by **Stempy** » 21 Apr 2004, 01:30

Richard, I'm in Guildford, so not a million miles away. I'm glad you mentioned that the LED type wont work as I was going to buy one. If I'm not able to sort it by any other means I may well take you up on your kind offer.

Stempy · Unread post by **Stempy** » 22 Apr 2004, 02:46

Tried the battery off thing today and there doesn't seem to be any difference at all

Richard Gallagher · Unread post by **Richard Gallagher** » 23 Apr 2004, 02:49

Stempy, let me know of the engine code and I will check to see if my code reader covers your V6, like all things useful the spec sheet only shows engine codes, not engine types as in 4 cyl, V6.

Stempy · Unread post by **Stempy** » 23 Apr 2004, 04:56

Engine type is ES9J4

XM-V6 · Unread post by **XM-V6** » 24 Apr 2004, 18:53

Stempy,I have a XM with the same engine and mine is shuddering just at 2100 rpm , sound a bit rough like its only 3 cylinders , maybe it is characteristic for this engine ?

Richard Gallagher · Unread post by **Richard Gallagher** » 25 Apr 2004, 00:46

Stempy, I'm looking at the list and have BFZ/RFX, RFX, LFY/LFZ, RFV, RFY, LFY, RFV, RGX, XFZ, XFX, 3FZ, 6FZ. For the Petrol versions, any similar?
What engine management system does it have?

Stempy · Unread post by **Stempy** » 25 Apr 2004, 05:29

Richard
They all sound like four cylinder engines.
I did find the diagnostic plug in the cabin fuse box.
I believe engine management is a Bosch MP7.0
XM-V6
This is more that just sounding rough, there is a definite hesitation and stutter in the acceleration. Being that it is much worse when cold I'm wondering whether one of the temperature sensors is playing up and affecting the fueling. Though I've heard that MAP sensors and the TPS can go dodgy. What ever it is, it hasn't been enough to make the warning light come on, but it may have registered a fault code.

Richard Gallagher · Unread post by **Richard Gallagher** » 25 Apr 2004, 11:56

According to my list Bosch MP7.0 relates to XFZ. Now using XFZ as the engine code, what I can do is plug the code reader into mine, go through the menu and see if it brings up the V6 model.

deelite · Unread post by **deelite** » 25 Apr 2004, 12:57

<blockquote id="quote"><font size="1" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by Stempy</i>

Well since replacing the thermostat and spark plugs it's like a different car and runs up to temp quickly as it should and is much smoother. However, it still has a rough period between 1500 and 2500 rpm especially bad at just over 2000rpm. It is much worse when cold but it's still noticeable very slightly when hot. There's nothing wrong with the performance otherwise.
On the back of the throttle body there's a cylinder which Citroen call a 'compensator'. I assume this is an air bypass valve but don't know how to test it as it is completely sealed.
I'd be interested to know if anyone knows any test procedures for the various input sensors for the injection ECU, and where the diagnostic plug is situated so I can perhaps read any fault codes.
<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">
Hello Stempy,
I once had nearly the same problem with my V6. It was running bad between 1000 and 2000rpm. When the car was diagnosed with running motor on the Lexia computer, 2 faults appeared : idle speed motor fault and temperature sensor fault. The idle speed motor is the air bypass valve connected with the orange wires : http://xantia.servepics.com/picuploads/ ... c-472s.jpg
When you loose the connector there are 3 pins. From left to right you should measure on the pins 3 and 2 12 ohms and on pins 2 and 1 10 ohms. Mine was dead, so i replaced the unit. Sometimes the valve is blocked by dirt, so you can clean it with WD40 or something.
The temperature sensor was worn to, since the computer diagnosed -45°C with a running warm motor ! So the injection received bad values.
The sensor have a green connector and is placed underneath the airfilter box on the waterhouse. The enigine management is Bosch MP7.0. I got the diagnosis procedure in PDF-format and French language and can send it by mail if you want it.

Richard Gallagher · Unread post by **Richard Gallagher** » 25 Apr 2004, 14:57

Stempy I've just tried to bring up the petrol engine types but with mine being a weasel it wouldn't play ball. However as it does show the Bosch MP7.0 system I would think it will work.
I've sent you an email with phone details if you fancy giving it a try.

Stempy · Unread post by **Stempy** » 25 Apr 2004, 20:55

Thanks deelite and Richard. I think the next thing I am going to do is carry out voltage and resistance checks on the various sensors/actuators etc to see if that throws any light on the problem.
Richard, if you sent a mail via the forum it's likely that won't ever leave. I have had problems sending and receiving mails from the forum in the past. My email is [email protected], if I get no joy with my static tests I may well give you a call.

Stempy · Unread post by **Stempy** » 05 May 2004, 00:30

I've narrowed down the poor running to the point where I can predict it is going to happen, and that is at low engine speed, ie below 2200 when under load, generally accellerating slowly up hill. Any ideas wouls be welcome.
I haven't forgotten you Richard, tried you a couple of times but didn't leave a message.