V6 12v starting issues - sorted at last!!

[MTXM]

Hi All,

I am having a rather a frustrating time with my 1989 V6, which ran happily enough at acquisition, although a few weeks later after sitting out in cold and damp weather there were starting issues and it has not been possible to get her going since, despite very considerable efforts!

In essence the engine turns over well, there is a reasonable spark and plenty of fuel with the plugs getting wet, but only the very slightest splutter of ignition and no real firing. I think I have done all the obvious checks, including replacement of various components with known good parts from another car and here is a brief summary:

- cleaned distributor contacts and all engine bay earths
- changed ignition coil and module and ecu and various relays (petrol pump, oxygen sensors etc.)
- cleaned sparking plug lead contacts and checked plugs
- checked flow of petrol to injector rails
- changed petrol pump
- checked and cleaned connections of various engine sensors and injectors

Interestingly on my other running car it is possible to disconnect pretty much everything electrical including all the accessible sensors and the only things that actually prevent starting (apart from the obvious coil, module and ecu) are the two relays mentioned above and earth wires of course.

It may or may not be significant that the car had a single point gas kit fitted albeit no longer in use and everything is now completely stripped off. All the gas components were connected in parallel/spiced in and fortunately removable without damage, including wiring to the ignition coil and oxygen sensors and another loom against the injectors.

I have spoken with Paul (Citroen XM) who helpfully offered some pointers, but still no joy, hence I thought I should make this wider appeal for assistance. Please do let me know if you have any bright ideas that would be most welcome!!

With thanks and regards,

Matthew T.

[Dieselman]

Make sure you have a good, beefy spark and it is timed properly, then pour some fresh petrol down the intake as you, or a helper, are cranking the ignition. If it spits back with a flame (fire), keep cranking to suck it in.

I wonder if the cold start isn't energising, so the mixture is too lean to fire. Alternatively, is it too rich to fire. (unlikely)

[MTXM]

Thanks Will and I can confirm that the spark is quite reasonable and certainly should be good enough to fire. The exercise you suggest sounds interesting, but would it actually help to start? As the plugs are getting wet I do not think the mix is too weak to fire. I was rather more suspecting the timing of the injectors myself but how could that have been upset or changed? Regards, Matthew T.

[MTXM]

Make sure you have a good, beefy spark and it is timed properly

Are there any other ways I can improve the spark apart from those already attempted and why should the ignition timing not be correct? With regards, Matthew T.

[Dieselman]

The injectors aren't timed, they spray in banks of 2 or three onto the back of the inlet valves, only the spark is timed.

A weak spark can cause none start, but as you have changed the coil, check the distributor for any shorting to Gnd.

You have got petrol int eh tank, haven't you? A friend once put water into the tank from a petrol can.

[MTXM]

That is helpful advice about the injectors Will but where could the distributor be shorting? The distributor cap is almost new and has not been changed and only cleaned but I could try another one. There is plenty of petrol in the tank that I was able to confirm when changing the pump and no water to my knowledge! With regards, Matthew T.

[Dieselman]

Don't trust anything. The distributor rotor arm may be shorting to the shaft, or power may be tracking to Gnd via a cracked dust cover.

Pull off one of the HT leads, stick a screwdriver into it and hold it about 1" away from the engine metal. you need a good fat spark to jump about 1" at atmospheric pressure to ensure a decent spark.

[MTXM]

I shall certainly check and if necessary replace the distributor rotor arm and cover Will as you suggest. So far I have checked the sparks on the plugs and between the ignition coil lead and engine metal, which all do seem fairly healthy. Regards, Matthew T.

[xantia_v6]

If the plugs are wet and a bit sooty, I would suspect that the mixture is too rich, maybe the coolant temperature sensor has failed or disconnected?

In cases like this it is sometimes helpful to disable the injection and try to start the engine just on EZ start or similar to prove that the ignition and timing are OK.

BTW, how was the injection disabled while running on gas?

[MTXM]

Many thanks for the further comments and the plugs are certainly wet but not sooty. On my other car I have disconnected the coolant sensor and various other sensors and it does not appear to prevent starting. I wonder how it is possible to disable the injection? In this case there was no obvious switch for using gas rather than petrol! Regards, Matthew T.