S2 intermittent bad misfire - any ideas?

[frontfloater]

On Friday I did a 100-mile journey in my S2 with the 2.9 Cologne engine, the first 70 miles being on motorways. After lots of very slow-moving traffic on the M6, I started to get sudden jerking as the engine misfired and lost power - as if I was rapidly flapping my foot off and on the throttle pedal several times. It happened at extended random intervals for the rest of the journey, sometimes just once in 10 minutes, sometimes several times. And it was still happening half an hour after I left the motorway and got onto A-roads where I was able to drive without delays.

I'm using fresh high-octane petrol, and for the rest of the time the engine felt as smooth and powerful as normal. The temp gauge was within normal limits, although it hit the white line regularly in the slow moving traffic ; and the voltage gauge also looked normal. The oil pressure gauge seemed to be reading pretty low (25-ish) during idle and slow crawls, but around 48 at speed. The return journey yesterday was problem-free, but I'm worried that this may happen again.

The only vaguely similar problem I've had, many years ago, turned out to be a faulty throttle potentiometer - but the symptoms then were one sudden cut-out at around 3000 revs, picking back up at about 2000. It wasn't like the rapid "fluttering" that I had recently.

Any ideas please?

BOB

[GreenV8S]

Heat related ignition component failure would be my first guess, although there's also a huge range of sensor and wiring faults that could produce similar symptoms.

[phillpot]

Ignition coil breaking down? Try a new one and move it from sitting on top of a hot engine


Ignition module fixed to the distributor (and a pig to get at) should have heat sink paste where it fits to the dizzy so that the dizzy acts as the heat sink. When I took mine off a while back the paste over time had dried out to a white powder and therefore not doing its job!

[frontfloater]

I should have said that I have no technical knowledge or ability, and would be paying X-Works to diagnose and fix. Thus wondering whether it is likely to recur, and I should book it in ; or perhaps it was a one-off due to 20 miles of 1st & 2nd gear crawling ...

BOB

Edited by frontfloater on Sunday 29th August 19:03

[phillpot]

May well be fine until the next traffic jam, and it will be difficult to diagnose if not doing it!

[frontfloater]

Heath at XWorks just completed the MoT jobs plus this misfire. He said he had to "pour the oil out of the coil" , so full marks to those who pointed the finger at that component. Fingers crossed, the new one will now cure it.

[phillpot]

Ignition coils are meant to be full of oil?

Perhaps he meant it was leaking and he could pour the oil out


You're sorted and back on the road, that's the main thing

[Mr Clifford]

Make sure the fuel injectors are clean !
Same happened on mine years ago.

[v8s4me]

frontfloater said:

Heath at XWorks just completed the MoT jobs plus this misfire. He said he had to "pour the oil out of the coil" , so full marks to those who pointed the finger at that component. Fingers crossed, the new one will now cure it.

The oil is there to cool the coil. I'd have thought any competent mechanic would have know that? Anyhow, if the coil was faulty then you're sorted

[frontfloater]

I probably misreported what he said - I have no mechanical knowledge at all. Maybe what he was saying is that he was ABLE to pour the oil out of it, ie it was defective and needed replacing..