Club 80-90 Forums

This problem just started after real cold spell.
Not running on No. 3 despite getting spark and having good compression on all 4 cylinders.
Already changed plugs, leads, cap and blocked servo hole in manifold. Still no joy.
Suggestions please.
Thanks

Manufold to head gasket failure perhaps?

you haven't had a rusty spark plug on that cylinder have you?

http://www.brick-yard.co.uk/forum/rusty ... 43480.html

Have you tried swapping a plug from a known working one ? Ditto the plug lead ? Remember not all new parts are good ! That's why you should always keep the last known-good set so you can always do a 'system restore'.

itchyfeet wrote: Manufold to head gasket failure perhaps?

What the blithering heck ?

Ian

Ian Hulley wrote:

itchyfeet wrote: Manufold to head gasket failure perhaps?

What the blithering heck ?

gasket fail draws in air rather than air/fuel from the carb, path of least resistance

So you mean failure of the gasket between the inlet manifold and the cylinder head then

yes

Already done the WD trick to look for leaks...

OK so how do you know you have sparks on No3?
how do you know it's not 'running' on no3?

perhaps he removed the lead and the engine did not falter/misfire/rock?

yeh perhaps but interesting to know exactly what tests were done becuase it does not add up.

Assuming sparks are Ok, no air leaks, it isn't firing on No3 but is on all other cylinders, then perhaps it's a duff or badly adjusted inlet tappet on No3?

This would prevent fuel/air being drawn in but would still give good compression

I would expect it to be noisy and this was not reported.

May be exhaust tappet No3 would do the same.

No. 3 is next to the brake servo hose if this is leaking air then it might affect the mixture.. along with No. 4

Sorry for the delay people.
I checked spark with a spare plug on loose lead so put this in knowing it was OK.
I know it's not running on no. 3 because the exhaust doesn't get hot - until heat transfers through the 'head.
Sprayed wd all around when servo hole on manifld was blocked, no difference so don't think it's an air leak.
All thoughts appreciated.
Thanks

gjy55split wrote:This problem just started after real cold spell.
Not running on No. 3 despite getting spark and having good compression on all 4 cylinders.
Already changed plugs, leads, cap and blocked servo hole in manifold. Still no joy.
Suggestions please.
Thanks

A few thoughts

What are the compresion figures?
Does it achieve the compression figure on number 3 in the same time as the others?
What is the compression figure on this cylinder with a little oil added to the bore?
Have you removed the rocker cover to see that the valve is actually moving up and down sufficiently enough i.e valves adjusted correctly - maybe cam lobe worn away on that cylinder. (outside the box maybe over the horizon!)
Other things to consider - sock in inlet manifold on that cylinder!!
Very bad air leak on the inlet valve stem allowing air to be drawn in
Is it possible that the plug is not earthing on the head on that cylinder? (This would be a million to one shot!!)
Until we see compresion figures etc -