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[terry paget]

My favourite Omega, the 2.5 petrol CDX, X reg, mileage 153162, bought from OOF member ajsphead in March 2014, has developed a misfire under extreme load, i.e. full throttle 20mph in 4th gear. No EML on.

Service records show plug change Feb 2013 140000 miles.crank sensor at 144K. e-bay advert stated 'the breathers and plenum have been cleaned at 140K and all the belts etc. done at 133K. the cam cover gaskets are fine too. I've never had a problem with the coil packs'.

Last week I posted my suspicion of leaking scuttle. I have since sealed it, anyway it was dry last night.

Oil/water in plug holes? Plug leads? Coil pack? My money is on coil pack, but I would welcome expert advice.

[chrisgixer]

Have you checked the codes?

If no codes suspect missfire. Which means checking all you listed.

Full throttle in 4the gear though .... Are you sure it's not stalling?

Coil pacs some times split if nothing else is visible. But that usually means the missfire affects pairs of cylinders and the car sounds like a Subaru flat four.


....full throttle in fourth.... Wow. I presume it's a manual?

[terry paget]

paper clip codes: 1 2 1 2 1 2 1 9 1 9 1 9  1 2 1 2 1 2 1 9 1 9 1 9 ignition on engine not running Not OBD2 so code reader no help. What does that mean?

[chrisgixer]

Crank sensor, according to that.

[terry paget]

Thanks! That's easy to change. I assume it will be a Siemens, in which case I have a spare. I will change that first.

[JamesV6CDX]

Miss under load almost always HT related and won't log a code

[terry paget]

Sensor locating screw was loose. Am having difficullty disconnecting the connector, may have to remove either plenum or scuttle. I wouldn't like to do it at the roadside.

Could the loose screw cause my problem?

[05omegav6]

It could create an intermittent earth fault as the sensor rattles around

Probably not very good for the sensor either...

[terry paget]

I have reassembled, with crank sensor screw tight. I shall find out next Friday if fault is cured or not. Will report back.
Thanks. My feeling was if I change the crank sensor for good spare and fault has gone, it could have been either sensor or loose screw. Either way I would have discarded original sensor, which might be OK.

[chrisgixer]

Why not test run the car before Friday when it's needed?

[terry paget]

Fair question. This is the same car which the previous Friday caused me to post the thread 'scuttle leaks causing misfires'. It only misbehaves after a 60 miles thrash along the A34 and M4 late on a Friday night. First I thought it was leaky scuttle; then I thought it was failing coil pack; now thanks to your advice on codes I think it is crank sensor or loose crank sensor. To test I need a 60 mile thrash; I shall get one on Friday.

I love these seasonal emoticons!

[terry paget]

Misfire is still there! Driving hoe form Wells tonight, 10 mile journey, it again misfired under full throttle at 20mph. So it was not the loose crank sensor. It did not do it when it was cold, but after 10 miles it did. Sounds like crank sensor, doesn't it? And code 19.

Sunday I found it difficult to reach the crank sensor lead connector without removing scuttle or plenum. Al tipped me I could change plugs on left hand bank if I first unscrewed the vacuum pipe to servo, then unplugged the rear dual ram plug, unscrewed the harness locating screws and popped the harness box on top of the vacuum pipe. I could not see how to unplug the dual ram plug, Al. I would need long strong fingers. Is there a trick?

[05omegav6]

I squeeze the spring clip together and wriggle the plug off...

Are we still talking the 2.5 though? no need to disturb anything to pull the leads off and unscrew the plugs, surely...

Just because the scuttle is sealed, doesn't mean the DIS pack isn't gradually failing... the fact it only does it when hot, suggests that summat is expanding... ie the coils in the dis pack...

[chrisgixer]

Is code 19 still there?

[terry paget]

I squeeze the spring clip together and wriggle the plug off...

Are we still talking the 2.5 though? no need to disturb anything to pull the leads off and unscrew the plugs, surely...

Just because the scuttle is sealed, doesn't mean the DIS pack isn't gradually failing... the fact it only does it when hot, suggests that summat is expanding... ie the coils in the dis pack...

Yes, we are talking 2.5. I cannot get access to the plugs without moving the wiring harness. You said recently procedure wsa as to unscrew the vacuum pipe, harness locating screws, unplug rear dual plug, then prop the harness on the vacuum pipe and then remove plug leads and plugs. You say I can put a hand through to the dual ram plug, squeeze the spring clips and wriggle it off. I have always found it hard to remove in the past, usually doing it after I have lifted the plenum off the manifold.

I agree fault may be coil pack. It still could be water/oil in plug holes or plug leads. It wsa code 19 that suggested crank sensor. Engine has never stopped, it just misfires under heavy load, when hot.