92 1.6 Oil Filler Cap question

[magic torch]

I get a bit of oil on top of the crank case, causing a misfire when first fired up.

I reckon it's coming from my oil filler cap, looks like the cap should also have a washer.

Anyone know if it should?

Thanks

[MX-5 Lazza]

I think the oil-filler cap should have an oil-seal but how does a bit of oil on the crankcase cause a misfire?

[skinny]

don't think mine has a washer?

i have a little oil on the camshaft cover but that comes from teh crap sealing around the back (despite replacing the gasket twice and using silicon sealant)

doesn't cause any probs tho (well, i hope the water pipes underneath are ok...)

Edited by skinny on Sunday 30th March 00:36

[magic torch]

Cheers, I'll investigate further...

MX-5 Lazza said:

I think the oil-filler cap should have an oil-seal but how does a bit of oil on the crankcase cause a misfire?

Goes down HT leads....

[MX-5 Lazza]

But oil does not transmit electricity. I've seen cars that had leaky cam-covers so bad that the spark-plug wells were full of oil but the car didn't so much as misfire!

If your car is misfiring it's more likely that you have dodgy HT leads. The oil is a separate problem.

[magic torch]

MX-5 Lazza said:

But oil does not transmit electricity. I've seen cars that had leaky cam-covers so bad that the spark-plug wells were full of oil but the car didn't so much as misfire!

If your car is misfiring it's more likely that you have dodgy HT leads. The oil is a separate problem.

What do you mean by "oil does not transmit electricity"?

New HT leads, and it was fine until they've been contaminated too. The old ones had oil at the bottom, when removed them, in a couple of cylinders.

New plugs as well.

It's a toy for me, so I don't use it that often. It only misfires when left for a day or more, and then only for a few seconds. Made me think whatever the contamination is, oil, water, whatever is being burnt away.

[skinny]

think he means that it's unlikely the oil is 'shorting' the spark signal

[Hovis]

If it only occurs after being left for a while, and then goes, I'd say it's more likely that your leads are going (or at least one of them is) high resistance, or the insulation is starting to break down. Once things warm up, slight HR or Low insul can disappear. Swap the leads and see it disappear!

And on previous notes - engine oil is not a particularly good electrical conductor, nowhere near as good as water, so if there were any shorting going on, I'd suspect water / condensation long before oil.

[magic torch]

Hovis said:

If it only occurs after being left for a while, and then goes, I'd say it's more likely that your leads are going (or at least one of them is) high resistance, or the insulation is starting to break down. Once things warm up, slight HR or Low insul can disappear. Swap the leads and see it disappear!

Like I said, it's brand new leads, same problem.

It literally lasts a few seconds...

[HRG]

Next time before you start it pop the plugs and clean the leads etc. If it doesn't misfire that'll confirm if it's the problem or not.

[magic torch]

HRG said:

Next time before you start it pop the plugs and clean the leads etc. If it doesn't misfire that'll confirm if it's the problem or not.

This is what is leading me down that route...

Swapped the leads was fine starting from cold, not been used for 48 hours.

Started it up a couple of days later, misfire reappeared.

Had already changed the plugs. Puzzling.

ETA: HRG? Didn't realise it was you Rob.

Edited by magic torch on Monday 31st March 19:14

[HRG]

I was hiding a'la Saturday And HRG = Horn Rimmed Glasses... Anyway, the car, I seem to recall an o-ring on my old MX, but I could be wrong about that.