Misfire

[Tigs]

Hi Guys!

I joined the start of the blat to Cheddar Gorge today but lasted less than a mile after developing a misfire 

Had a 20 mile journey to the start point where the car was running perfectly and parked up for about 15 minutes and after setting off on the blat the engine was running horribly rough and developed a strong smell of oil for a short bit. Pulled up and bailed on the blat and decided to limp home where the misfire cleared and the engine was back to running as normal. Have been out in the car again to see if I could replicate the misfire but it's now running great! 

It's a 1.8l K series in a Superlight R which has been fettled by Dave Andrews in the past. The only thing that we have done to the car recently is top it up with a bit of oil. Up until today, it's been running absolutely fantastically. 

If anyone has any tips or suggestions on what to start looking at that would be great!

Tigs

[garybee]

Strong smell of oil and misfire after topping up oil.  I'd usually suggest you've overfilled your oil and it's breathing into the intake but would expect your car to have a catch tank system.  

How is your crankcase vent routed.  Does it go back to the intake?

[Tigs]

I did wonder about that but there was no more oil in the catch tank than there has ever been. It vents via the catch tank - pic below showing the setup

[garybee]

Ta, was fairly confident an SLR would vent to a catch tank but not 100% so seemed worth asking.  

Overfilling could change the oil properties due to the crank thrashing around in it but I don't believe that it would cause the symptoms you describe.

You'll probably get people telling you it's valve stem seals.  People always blame oil burning on valve stem seals but that tends to be more on startup (trickles down the valve and pools in the cylinder).  I think it's one of those things that many say because they've heard someone else say it.

It could potentially be an oil control ring on one of the cylinders that's got a bit stuck in its groove and freed itself but there'd be no way to prove that.  I can't think of anything else that would cause an intermittent heavy burning of oil after warm up on an engine with an external crank case breather.  I'd just run with it and monitor its oil usage closely for a while.

[Tigs]

Thanks. Think it might have to be a case of keeping a close eye on things and hoping it doesn't happen again!

[revilla]

Just a thought on the oil smell (but not the misfire); is it possible when topping up you spilled a bit of oil and it dribbled down somewhere like the exhaust and burned off when things got hot?

[Tigs]

No, no oil was spilled when filling up. Absolutely no sign of any rogue oil in the engine bay anywhere

[Colin Cooper]

 Hi Tigs, Shame you couldn't make it; perhaps it just needed a bit of right foot to clear it. Pleased its sorted now though.

See you next time .

Col 

[elie boone]

Can't see how overfilling would affect the crank trashing on what seems a dry sump ? what where the weather conditions on your stop ?

[Tigs]

Hi Colin. Yeah, shame I couldn't carry on but not worth the risk of getting further away from home. Hope you guys had a good blat!

[Tigs]

Hi Elie

Weather conditions were great - bone dry, sunny but a little chilly. Good engine temperature though.

[garybee]

"Can't see how overfilling would affect the crank trashing on what seems a dry sump ?"

It wouldn't.  Anyone finding the thread in the future through the search engine who had similar symptoms could have a different setup though.  I've also made comment on other potential suggestions that it won't be with an explanation why.