Mr Noisy

Coming in your ears.

• Jun 20, 2011

• #21

ok mate cheers

tbh i didnt get time to pull a plug today, i wil try to do it tomorrow night!

misfire sounds more likely than the fuel system running lean. it does sometimes go off on a cylinder, but only for a little while when its not had a run for a few weeks and its been in and out of the workshop most days.

will get some pics up.

cheers!

 

oldskool

Well-Known Member

• Jun 20, 2011

• #22

eightinavee said:

Take all the plugs out,I think you have a partial misfire which you cant hear/feel. Scoping the plug leads would show it up in seconds,it might be enough to show a darker colour on the plug tip..

Click to expand...

How does a PARTIAL misfire cause the Co to drop? im assuming 0.14 is lean im not an eggsput on these engines

 

Mr Noisy

Coming in your ears.

• Jun 20, 2011

• #23

i aint an eggsput at all so there's no point asking me!

 

oldskool

Well-Known Member

• Jun 20, 2011

• #24

Mr Noisy said:

i aint an eggsput at all so there's no point asking me!

Click to expand...

Was asking the eggspurt 8inav i don't know how a missfire can give low Co readings thats all perhaps James can tell us he's an eggspurt in everyfing LR

 

E

eightinavee

Well-Known Member

• Jun 20, 2011

• #25

Because overall the possibly seven good cylinders are running lean,the bad cyl has incomplete combustion - not always burning all of its fuel charge on every firing stroke so unburnt fuel goes out the exhaust port.Also remember this engine is running open loop so there is no oxy sensor to see the unburnt fuel which confuses the situation further.
I have seen mot failures on v8's like this where I have changed a single plug or lead and transformed the emission readings - but in driving there was no perceptible difference.One of those things its easier to see on an actual car rather than typed on a page,also one of those situations where a decent scope really shines - you dont even have to touch the engine or get your hands dirty to do a 100% accurate diagnosis.

 

jamesmartin

Well-Known Member

• Jun 20, 2011

• #26

i would have said thats fairly good description

 

oldskool

Well-Known Member

• Jun 21, 2011

• #27

I can see how a missfire can give high Hc's but i still don't see how it give's low Co

 

joe1972

Well-Known Member

• Jun 28, 2011

• #28

Are the injectors all fuly opening and closing as they should?
Noid light to check the contacts are getting a signal, and UEFI Quick probe to check they are clicking open then closing