Misfiring/Smoking - Expert Reassurance Sought!

[UpTheIron]

Picture the scene...I left work a happy TVR owner, top down, smug wave to workmates and roar off down to road (ok, so cold engine and Central London means I roar about 3 yds).

No problems on the way home, pull onto the drive and car cuts out. Nothing *that* unusual, I've had the odd idling problem that I haven't attended to.

Just to check all is OK I restart and car is misfiring quite badly when engine is not under load. Suddenly not such a happy TVR owner - especially when I notice the odd cloud of black smoke that coincides with the misfire.

I had a misfire or two a few days ago and I thought I had cured it by reseating the HT leads and giving the dizzy cap a good clean.

So, in summary:

.Car (58k 93L pre-serpentine 4.0) misfires badly
.Idles poorly (no surprise given the above)
.Smokes (black) whilst misfiring but not whilst under load and running OK.
.Spark plugs show signs of mixture being too rich.
.HT Leads aren't brand new, but aren't too bad either.
.Car burns virtually no oil

Is the concensus of opinion that this is something more serious than will be fixed by new HT leads, dizzy cap and spark plugs?

Or is likely to be something more serious, in which case does anyone have a Griff 500 engine I can have?

Paul

[Darrens]

Seems more of a ignition prob rather than engine

Darren

[GreenV8s]

quote:Picture the scene...I left work a happy TVR owner, top down, smug wave to workmates and roar off down to road (ok, so cold engine and Central London means I roar about 3 yds).

No problems on the way home, pull onto the drive and car cuts out. Nothing *that* unusual, I've had the odd idling problem that I haven't attended to.

Just to check all is OK I restart and car is misfiring quite badly when engine is not under load. Suddenly not such a happy TVR owner - especially when I notice the odd cloud of black smoke that coincides with the misfire.

I had a misfire or two a few days ago and I thought I had cured it by reseating the HT leads and giving the dizzy cap a good clean.

So, in summary:

.Car (58k 93L pre-serpentine 4.0) misfires badly
.Idles poorly (no surprise given the above)
.Smokes (black) whilst misfiring but not whilst under load and running OK.
.Spark plugs show signs of mixture being too rich.
.HT Leads aren't brand new, but aren't too bad either.
.Car burns virtually no oil

Is the concensus of opinion that this is something more serious than will be fixed by new HT leads, dizzy cap and spark plugs?

Or is likely to be something more serious, in which case does anyone have a Griff 500 engine I can have?

Paul

Black smoke with the misfire is probably unburnt petrol from the misfire, not too worrying in itself.

The symptoms sound like too much fuel, not enough spark or wrong spark timing. Hot favorites would be stuck injector, broken HT lead or dizzy vac advance unit coming adrift, but there must be a hundred other faults that could cause these symptoms.

You checked the plugs, did you check all of them or just one or two? If it's just one cylinder you're looking at the per-cylinder bits - plugs, extenders, leads, dizzy cap, injectors. If it's one bank that suggests the injector driver circuit/wiring or a lambda sensor. If it's the whole engine, could be air flow meter, temp sensor, coil/coil mounting, dizzy ignitor pack/rotor arm/vac advance unit, king lead, ignition LT supply, immobiliser/wiring, you name it.

Suggest you start off checking that everything is firmly attached where it should be - coil, plug leads, dizzy firmly clamped and vac advance unit securely screwed on. Check the condition of all the vac lines, just on principle, although problems here will probably make it run lean not rich. Consider getting some spark trace lights (little strobes that you put in line with the ignition HT leads) and see if the spark is fluctuating.

Hopefully when you've got more information about which cylinders it's affecting we can start to narrow it down.

BTW (and I always seem to be saying this) if the problem isn't obvious and you aren't an experienced motor mechanic, I recommend getting specialist help. Running with a misfire can damage the engine, and you may end up causing more damage in your attempts to find/fix the fault - not to mention time and money replacing bits by trial and error. A professional is also more likely to fix the underlying fault rather than cure the symptoms.

Hope this helps,
Peter Humphries (and a green V8S)

[UpTheIron]

Pete,

Thanks. You pretty much confirmed what I thought.

All the plugs I've checked (3 from one bank, 2 from the other) show carbon fouling - which although doesn't appear bad enough to cause the misfire on it's own it certainly won't help if I've got a weak spark.

I'm willing to gamble that both lambda sensors are OK, rather than both being knackered.

The car is running fine now, just as it was this morning, so I'm inclined to think that the problem is heat related (aren't all TVR problems heat related?!!!). So this may point at a failing ignition coil.

I suspect I may have more than one problem - I don't actually do that much town driving, so the carbon fouling isn't just from crawling in traffic - it just could be down to the coil, or the culprit could also be air filter (cheap!), or temp sensor (cheap!) or air flow sensor (not cheap!). I am sure you will throw a few more bits and pieces into the equation.

Anyway, I suspect this will result in a rest for the car until I have time to check everything at the weekend before possibly seeking professional help and perhaps an early 60k service.

Thanks


Paul