Fault codes not stored ...

Another possibility is the engine temperature sensor. This caused similar symptoms to what you have described on my carlton. A new one cost about £10 so it might be worth replacing it even if it just rules it out. Cheers NP

I've discovered (through this group) that it's always worth checking all the relevant electrical connectors. Disconnect them, give them a spray with WD40 or similar, and give them a seeing to with a suitable thingy - a needle for the female half, for example.

Cleaning the air temp. sensor's connector magically cured a neighbour's automatic Fiesta recently, when the owner thought she'd have to buy another car because her garage hadn't been able to cure the problem over a period of

6 months.

Electrical connectors seem to be a very weak link for a lot of cars.

Si

Two good suggestions there, thanks both.

The EM light will illuminate when a fault with the system is detected. For a code to be stored, the fault must occur for a certain length of time, usually at least 3 seconds. Once the code is stored, it will remain in the ECU memory for approximately 20 ignition on/off cycles, as long as the fault does not re-occur.

Your fault sounds more like a IACV fault. Problems I have experienced with crankshaft position sensors have given rise to a misfire at high speed, or complete failure. An air leak downstream (engine side) of the mass air flow meter could also be a cause. The idle valve could be gummed up and be in need of freeing off with a good soaking in WD40.

HTH

Anthony Remove eight from email to reply.

Thank you Anthony. Re: the fault codes, I read somewhere this morning that to (intentionally) erase the code you should turn the ignition on and off 25 times. As for the fault itself, having just suffered another failure today, I'm veering towards a view that says it's temperature related.

This afternoon I completed a 2 miles-or-so (low speed, built-up area) journey without incident starting from cold. Then after about an hour's rest, I set out on the return journey and got about three quarters of the way back before the engine died. It occurred on overrun as I slowed for a roundabout. Unable to restart immediately, I went to a friend's house nearby to .. er, .. service the plumbing(!) and returned to the car abour 20 minutes later. It started at the first attempt enabling me to complete my journey home. I had just applied the handbrake after reversing into the drive and the engine stopped uncommanded once again.

The characteristics of the failure are a complete shutdown with (on this last occasion anyway) a momentary and hardly noticeable 'cough' about half a minute beforehand. Having driven fairly slowly in the heat (it's about

26/27 degrees out there at the moment) the water temp gauge was up near (but not quite at) the point where the cooling fan should be cutting in. If the idle air control valve was at fault, I would have expected to be able to restart again immediately - albeit with some coughing and spluttering and protests perhaps (from the engine, that is!) - and not have to wait 10 or 15 minutes and then experience an apparently "normal" start.

I think I'll document all this evidence for the garage tomorrow and hope that it assists their diagnosis.

Thanks for all the suggestions.

Does it idle well?

Si

From reading your text it seems as though the engine is cutting out through lack of fuel or more likely igntion as it drops to idle, rather than lack of idle air- i.e. ISCV being stuck shut, as if this were the case it would fire up immediately given some help from the throttle to maintain an idle speed.

As this sounds temperature related, and is cutting out when hot and refusing to restart until cooled abit, first point of call would be connection and output from the crank angle sensor.- a good starting point is to see if the rev needle twitches during cranking. If not, then you have no primary igntion.- again go straight to the CAS.

Tim..

When it does, it does so perfectly (but see my reply to Tim ...)

Aha! I *have* noticed that in "can't-be-started" mode, when I turn on the ignition, the fault light blinks momentarily and I hear a relay click in the passenger area somewhere. The light doesn't extinguish, just gives a little blink. Then, on cranking, both speedo and rev counter needles give a tiny jump when the engine first starts to turn, but then settle immediately back to zero and don't twitch at all.

Sounds like it's gonna cost me 200 quid - gulp.

Might do, but give the wires a wobble first - it could be that when it's hot the wires keel over a bit and cause your problems.

Si

That sounds like a good idea, but Mr Haynes has omitted to identify the location of the crankshaft sensor on the illustration of the V6 engine ...

The crank sensor is located on the passenger side of the engine, adjacent to the oil filter, near to the flywheel end of the engine. It is almost impossible to access it from above. The cable from the sensor connects into a loom at the back of the engine, behind the manifold, near to the ignition coil. this connection is also awkward to get to without removing the water shield over the bulkhead.

As an aside and some useful information - when cranking the engine, the EM light will go out as soon as the ECU detects a signal from the crankshaft sensor, as long as there are no other faults present that would bring the light on otherwise.

HTH

Anthony Remove eight from email to reply.

(much snippage ...)

Looking more and more like the crankshaft sensor I think. I'll probably find out tomorrow. From the way the location and the access to it is described, it would not have been possible for me to get to it to check the connections, and I've run out of time anyway. The car is now sitting outside the garage (I got there too late and the gates were locked!) waiting for me to drop by (in a borrowed Citroen AX-something or other - awful little car, but it's on free loan and it's better than a 15 mile walk!) in the morning to book it in. I can feel my Barclaycard cringeing already ...

(huge snippage ...)

Got a phone call from the garage at lunch time ... good news! They road tested the car and the fault occurred. Bad news, there was still no stored fault code so they can't be certain it's the crankshaft sensor causing it. Fed up with this I told 'em to change it anyway and I'll ask Mr Barclay to take the hit. But as always, there's worse news ... they don't have a sensor in their stores !!

Another day of the AX-something or other .. groan.

If you can't get it sorted, you can probably get the dealer to connect a separate data logger. I don't know if this is a possibility with an Omega, but I had it done with an Astra of a similar age. They just plugged a box into a connector under the dash and after I'd driven round with it for a week or so, they unplugged it and took a look at the data - not seeing anything to explain the problem (following a top-end rebuild due to an early failure of the cam-belt, it would sometimes refuse to accelerate when booted to overtake, but was fine the rest of the time), they squirted the data off to Vauxhall for further analysis. Don't hold out too much hope though, they eventually decided that the entire engine management harness needed replacing at a cost of about 1200 quid - luckily a mechanic with a bit of sense tried replacing the ignition leads ... problem solved.

Steve W