MX5Ireland

Mk2 98 1.6 here and noticed on long journeys a slight misfire over 60mph, seems totally fine for daily use (35 motorway miles per day). Also on long journey if I stop and fill her up with petrol problem goes away so I thought probably fuel filter issue or something. HT leads are only 9 months old so kinda ruled this out.

So decided to change the plugs yesterday, though these are only 9 months old also and noticed oil in plug hole, second from the rear of engine, slight signs of oil in other plug holes also but nothing like number 2. I,m guessing rocker cover gasket needs replacing, so no big deal, but just wondering is this a common fault with 5's? And would this cause the slight misfire I described earlier?

Any comments appreciated.

Gaskets aren't expensive and it's an easy job to fit one...do it and then see if your misfiring issue continues.

John

Funny how if you stop for petrol it goes away and dosent become apparant on daily runs. Wonder if there is a blockage in the fuel tank breather causing some fuel starvation. Next time you fill up after a hard run see if there is any vacuum in the tank when you unscrew the filler.Just a thought......................

Actually now that you mention vacuum i recall when I stopped for petrol there seemed like an unusual strong vacuum when I unscrewed cap. Is this weird? Could this suggest blockage somewhere? Is there something I could check?

oil on the tips of the plugs is a sign of engine wear. As a side note the spark plugs are nothing to do with the rocker cover gasket so replacing that wont help ( unless you have a pool of oil down each well ontop of the spark plug)

I would change plugs and leads to see if that sorts out the top end misfire. just because they are a year old doesnt mean they are ok. It might also be a sign that your coilpack is starting to burn out especially if you have a 1.8 ( they usually burn on terminal 4 +2 , ( plull the plug lead and peep into it - if you seen a greenish / blueish powder build up , clean it out and it is a quick fix to keep you mobile for a while longer )

also , the sucking sound when you open the fuel cap is normal so dont worry about it. If you didnt have the sucking sound then you need to worry.

Thanks RS it's not oil on the plug itself but rather oil around the outside of the plug which can be seen without taking the plug out

Changed plugs and misfire disappeared.