Citroen XM Forum

The relays are similar to the 12v then Will, which just to confirm are oxygen sensor, engine ecu, injectors and aircon pump. Regards, Matthew T.

Dean wrote: If you have no spark but have voltage to the coil, the coil winding resistances are about right then i would suspect the ignition module as the prime suspect.

D

There is no +12v at the coil.

Is + missing or ground at the two pin plug or both?

D

No + voltage at the 2 pin plug.

+ should be on pin 1 from the ignition switch via the 9 pin brown multi plug under the LHM tank, ground should be pin 2 via the ignition module, i think.
I dont know how the ignition module actually works but when i had to investigate it during one of my many debarcles i came to the conclusion it was just a solid state relay to contol the coil/ignition timing and allow the ECU to control grounding of the O2 heated tip in this application which is powered by one of the green relays in the ECU box, this green O2 heater relay is fed +VE via the green injection relay which in turn is activated by the ignition switch.

D

Dean wrote:+ should be on pin 1 from the ignition switch via the 9 pin brown multi plug under the LHM tank, ground should be pin 2 via the ignition module, i think.
I dont know how the ignition module actually works but when i had to investigate it during one of my many debarcles i came to the conclusion it was just a solid state relay to contol the coil/ignition timing and allow the ECU to control grounding of the O2 heated tip in this application which is powered by one of the green relays in the ECU box, this green O2 heater relay is fed +VE via the green injection relay which in turn is activated by the ignition switch.

D

I'll go and have a look soon.

The ignition control unit is basically a high capacity transistor. I replaced one a long time ago on a FIAT and still remember the transistor number...BU931ZP. I think BU stands for Big-un...

A challenging day today.

The engine won't start one symptom there is no +12v to the coil, so I cchecked there is +12v and trigger signals at the five ECU relays.

There is no trigger signal to operate the main ECU relay, but all relays have +12v.

I shorted the ECU relay to make the ignition relay function and checked for +12v at the coil, which there now was, so the wiring is sound.
I manually triggered the coil -ve terminal and felt for a HT belt on the king lead. It was there, so the coil is working.

I tried triggering the ignition amplifier from the ECU connector, but no avail. There was no power registerd on the lead and my understanding is that to make the amplifier trigger the coil, the ECU shorts the signal wire to Gnd rapidy on and off, just as if points were opening and closing. I find scratching the wire over the battery terminal or engine casing causes the rapid signal required.

From this I assume the ignition amplifier is U/s. Can anyone confirm the ECU shorts the amplifier signal wire to cause the amplifier to trigger the coil?

As part of my investigations I checked the ECU input and found Gnd to be missing on Pin-7. This shows as being a spur from the same wire that feeds the keypad relay, the A/c clutch, the Ign relay...all of whic have good Gnd. What the diagram shows is that the Gnd for the ECU on this pin has a connector in the circuit.
I checked for voltages and resistances and sure enough this wire was open circuit, so I set to tracing where it went.

After much dismantling to get the loom out and the loom tape stripped off, I found this wire goes back to a connector between the engine and n/s inner wing.
The problem I have is that I can't find what it's supposed to connect to.

It is a Blue coloured, single pin conector. Can the V6-24v members have a look.

Picture attached. It is the blue connector centre of picture.

In addition, I found a white three pin connector under the LHM tank,has no corresponding connector, or loom.

Blue connector just left of centre of pic. It hasn't been connected for a long time.



Spare white connector.



Also, when attempting to move the LHM suction pipe out of the way, it snapped off at the pump.

Does anyone have a V6 suction hose they can let me have?

Sounds like good progress, my 12v does not have that blue connector so it could be a 24v specific thing.

D

I suspect it is to give a higher level of security, which is why the 24v has more relays and connections.

The scene of devastation so far. not quite what I'd call progress...

Today has been a case of re-wrap the engine loom, very neatly and refit it and the throttle potentiometer, which I had to remove to get the loom out.

I also lubed the throttle spindles and linkage again as it was still stiff and sticky...which was much better than not being able to move it at all, which was as it was when I got it. After quite a bit of lubing and operatioon, it now operates as it should.

Look a the rust coming out of the ball joints...only the other 999 components to do.



I relocated the loom and connected all the engine to body connections and am still left with the erronious Blue connector. the white one under the LHM tank also appeared to have been disconnected for a long time, but doesn't have a blanking plate, so I believe should be connected.

As an aside, once I took hold of the Blue connector to attempt to clean it out internally and scrape the pin to make a contact, it snapped off the lead.

I'm sure there is something missing undr the LHM tank?

Can anyone with a 24v please have a look.