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Discussion Starter #1 (Edited)
This is a strange one...

Nothing much done mechanically to the car, apart from adjusting the (non-Cat, Lucas) AMM to weaken the massively over-rich mixture off.

However, over the weekend, we did a long run with a heavy trailer on the back - and whilst sat in heavy motorway traffic, with the temp needle a little higher than normal (fan cutting in and out OK, not overheating), it started to miss and cough a bit.

It's kinda predictable in an unpredictable way. If you sit with it idling and warm, it'll miss - and it's a real bigcough-jerk-backagain miss - when you put some load on it. Not immediately. If you're gently pulling away, and trickling up through the gears, it could even be on the change to second.

It got a bit worse on the journey back again, and was noticable when I picked the car up yesterday after a couple of days in dock for the driveshaft tunnel welding. It'd been thoroughly warmed up, test driven, MOTd, then sat for about half an hour off. When I started it, the needle was a little below normal running temp. But it jerked a couple of times.

Didn't do it this morning on the c.15-20 mile run.

Thoughts? A bit of fuel vap? Seems unlikely, given the ambient temps here at the mo... I put a new fuel filter on it a couple of months ago, together with dizzie cap, rotor, HT, plugs, vac hoses.
 

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Discussion Starter #2
TooMany2cvs said:
It's kinda predictable in an unpredictable way. If you sit with it idling and warm, it'll miss - and it's a real bigcough-jerk-backagain miss - when you put some load on it. Not immediately. If you're gently pulling away, and trickling up through the gears, it could even be on the change to second.
Much worse tonight - more frequent, although less intrusive. Usually on a light throttle, sometimes on a trailing throttle. Not predictable in terms of revs, either.

Puzzled.
 

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I might suspect that new amm - other than that, all the usual suspects :D plugs, wires, et al. After that, I'd get out the fuel pressure gauge.
 

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Well if you rule out spark problems (which I would guess are most likely), I'd test the fuel pressure at the rail (I'm assuming the bentley has info on the proper, healthy specs are) - see what it is doing under when the symptoms occur, I would *guess* that's not the problem, if the FPR or pump were failing, I don't think the symptoms would come and go. I suppose it could also be the injectors.

I'd give the ignition system a good look though, though - something corroded or a plug gap getting ever the wider could cause the symptoms.

Of course, as in anything - if you change something and something else changes, chances are what you changed caused that other something. I might try a known good AMM if you have a buddy with one in the area.
 

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On second thought, there's a chance that there was another problem that was making the car run rich, and adjusting the AMM fixed the symptom, not the problem. Now the same problem may be rearing its head in a different way - this would point to fueling rather than spark.
 
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