O-series EFi coughing and spluttering?

[G51 NAV]

I seem to be plauged with problems where a car parked-up on the drive at night, running perfectly, either runs badly or completely refuses to start at all the following morning. Twice in succession it's been the timing on the HLE which had drifted off overnight because of a dizzy-clamp which had mysterioiusly come loose, now it's the turn of the EFi...

Symptoms are that it's basically missing, coughing and spluttering at all revs, same as how a carb engine often does when you first start it up, but on those cars holding the throttle in for a few seconds clears it. This never clears, with the engine hot or cold.

I've cleaned the plugs, checked the breather-pipes and swapped the ignition ECU (admittedly for an MG Turbo one) but it made no difference.

As I'm typing this I realise that if I was answering someone else posting this problem, I'd tell them to try different pulgs and leads, so I may well do that (but not for a while because the missis has gone shopping in it).

Any ideas in the meantime? Just what can go wrong overnight?

[tony]

have you checked the crank angle sensor, if it was me i would whip that baby out, and check and clean it.

[G51 NAV]

At this point Tony, I'm going to have to confess to being a technical numb-skull: where exactly will I find that? Be as specific as you can when explaining its location in relation to big, obvious items! The most technical I've ever got with an O-series EFi is resetting the throttle-pot with a multi-meter.

The more I think about it, the more I think the problem is electrical/ignition-related: every 'miss' is followed by a puff of smoke out the exhaust (unburnt fuel), but the misses aren't rhythmic (ie just one plug not constantly firing). However I'm prepared to try anything.

[G Force]

At this point Tony, I'm going to have to confess to being a technical numb-skull: where exactly will I find that? Be as specific as you can when explaining its location in relation to big, obvious items!

The crank sensor is located in the gearbox adapter plate towards the bulkhead side of the engine bay. If you look down the back of the engine below the throttle body you can see the crank sensor multiplug attached to a small bracket, then you can follow the wire to the sensor where it is bolted to the gearbox adapter plate. Sometimes the plug can get coolant dripping on to it from the coolant pipes in that area if they leak slightly, giving misfire problems.

Roll back the boot of the harness plug and check the wiring is ok and that the pins have not backed out of the plug.

[G51 NAV]

Thanks to both of you :) Plug located & contacts cleaned, but I think I've sorted it: turned out to be dodgy leads. Not sure which one because I changed all four for some spare ones I had in the garage. I had already tried new plugs, which helped a little, though not much: certainly won't do any harm to change them though as they're of unknown mileage and vintage.

Only thing I've not been able to test is any lumpiness or misfiring when cold (this morning's first symptoms), as all today's running around has got the engine warm. Any more problems, I'll let you know :cool: