what would a cause a cossy to run on 3 cylinders on ideal and when reved it runs on 4 perfect

 

leads breaking down?
plugs?
cap?
or head gasket leaking water into the cylinder

 

Ceramic centre electrode surround on the spark plug cracked and dropping down shrouding the spark possibly...

Take them out and hold them in their natural running position and see what happens....

 

furry
i rebuilt the engine with new every thing apart from leads cap plugs or rotor but it does run on 4 but sounds like on 3 but when your driving its its runing perfect

 

check/replace them then fella, cheaper then pulling the head off again.

 

right .took all the plugs out and ther all dry and clean cap rotor and leads were new about 4 montha a go and looked mint .its defo number 1 cylinder .but plugs arnt wet .

 

could the plugs off fucked up as they were still in the head when it was steam cleand and washed

 

Burnt valve would cause a low speed missfire

 

Champion C57's?

 

Stu @ M Developments
nope i use 071

 

i have a littel more info if i drive the car lets say for 30 min or go for a long drive its fine no misfire or nothing .even when idealing but once it gets cool it starts to get a littel misfire on idel. but its not like a misfire coz all 4 cylinders are working no coolent loss no oil buring and no high fuel consumption all 4 plugs are working leads are giving the spark injectors well i only just but in the light blues about 200 miles ago with the right chip rebuilt engine about 200 miles ago changed every thing

 

tell me about it, gets worse over time too

 

b19bal defnatly not burnt valves as i hade it apart 2 days ago and replaced all valve guides and seals the rest looked mint .i think it must be a miss seated valve or the valve is staying open .coz its only should like its missing at 900 rpm as soon as you rev it its perfect

 

that is shocking!

 

abs was actually talking about my escort csbrio runabout

i bought it 18 months ago with a burnt valve, keep meanimg to fix it but never bothered, its worse now

not everyone on here likes to have cheap digs mate

 

essexrsturbo
what is shocking

 

b19bal
no offence taken m8 just a littel stuck

 

think hes talking about full rebuild yet keep the 8 quid rotor arm that always causes high rpm missfires

 

b19bal
thers no high rpm misfire .at all .plus its not worth changing the cap rotor or plugs as i did so 2 weeks ago befor the rebuild so no point in changing agine spent silly money to as i changed all sensors to

 

then its technically a new engine then

 

If u KNOW its no1 thats missfireing then swap the plugs/leads around making a note of where u move them too.

If it then missfires on the cylinder u have moved the plug/leads to u know its 1 of them.

If it doesnt then u know its something else and go from there!

 

SORTED

 

And it was?

 

all just a dream

 

Stu @ M Developments
its gona sound stupid but changed the oil from 15/50 to 5/50 and its a dream must off been to do with the grade of oil it wouldnt allow the hydrolic lifter to fill up after the rebuild sounds stupid but it worked .thanks guys

 

Lol

 

What make of oil are you using ?

Steve.

 

5/50 valvoline fully synthetic

 

Cheers

Steve.