MK1 Cab 1.8i Intermittent Misfire

Hi all,

I have a bit of a problem which has just started. Car starts fine, then misfires for about 5 mins, then clears.

I have changed the spark plugs, rotor arm and cap.

Has anyone else experienced this and found a cure? I've never had any other problems with the car whatsoever.

Cheers,

Hi, might be worth checking your ht leads as these can break down and cause a misfire, also might be worth looking at the injectors to make sure there  working ok, plus renewing the seals is always a good idea. There is a injector test plan on the site somewhere which is good. Also worth noting that the bucket tappets can wear, usually noted by rattling after start up, this can also cause a misfire. Hope this helps

Thanks for the advice, i'll give the leads a whirl 1st then the injectors. I'll keep ya posted

Ok, new HT leads and its still not happy.

However, on top of the throttle housing there is a black microswitch thingy with two wires going to it. if i press that the pump (i think its a pump) on the side of the airbox starts to work and cures the misfire. I need a solution to fix it without keeping the switch closed.

hmm, is this a k-jet or digi car? pics?

The arrow is pointing to the Microswitch, i have closed it with some wire

ok, if thats an idle switch it looks to me like the metal arm has snapped off? if so you'll need to get a replacment. im not sure but the digifant wot switch may fit?

The metal arm is actually tied back, i did that so it would run (same as bridging the two wires), as this seems to enable the pump at the side of the airbox to operate (gives off a buzzing sound). if i let the switch open it seems to misfire / want to stall

Can you show us pics of the "pump at the side of the airbox", I didn't know it had one. It might be a different component. Whichever, buzzing is never that good, and it might solve your running issue.

I cant quite get a pic of the pump thingy, the electrical connection can be seen, i'll have to start taking it apart to get a good pic. By the way, is it a K-jet?

hmm, i might be wrong but is that a fuel injector, could it be you have a k-star + fuel setup…

can you try to get a better pic of it so we can figure out what it is?

I've googled the k-star setup and your absolutely right, it does look like a k-star (is that a good thing?). its raining quite heavy so another pic will have to wait.

So, if the throttle switch is open the k-star injector stops working, close it and hey presto it works and it runs fine.

There must be something else in the equation which also makes this injector work, so i need to find out what that is i guess.

I really do appreciate your help with this bud.

looks like it needs tuning, if that is indeed a k-star + fuel then your engine may be running lean, hence why bridging the WOT switch fixes the problem as injector chucks in more fuel.

trouble is not many people can tune it now! if it is the k-star + fuel though its worth good money to the right people. you could return your car to standard and retune the idle/co/timing to suit super unleaded.

if it was me, id start by checking carefully for vacuum leaks, then move on to checking idle, co and ign timing to make sure all is well. then if still not right pull the injectors and do a flow/spray pattern test, plenty of info on that on here

Ok, i'll start with the vacuum pipes then injectors. i'm busy for a week but i'll get onto it straight after and i'll let you know the outcome.

If you or anyone does know a good tuner not too far from Leicestershire then please let me know.

Cheers,