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MG MGF Technical - HT leads - coil lead too?

We've been recently having problems with acceleration and idling, especially when warm. Basically the idle is not even, every 5 seconds or so it seems a cylinder fails to fire and we get a little pop out of the exhaust, accompanied with a dip in revs.

When accelerating, when you floor it there is just no power and what can best be described as a stuttering, farting noise.

I have looked through the archives and narrowed this down to the ignition system. I had the dizzy cap and rotor arm replaced 8 months ago, so I doubt it's that. I for one have not changed the leads and spark plugs for 35,000 miles so I guess it's that.

Anyway the plan is to change the HT leads, and spark plugs while im about it. My question is when replacing HT leads, is it vital that the king lead is replaced too? It's just I cannot get the lead free from the coil as it's in a really awkward position! Is it a pointless excercise replacing HT leads without replacing the coil lead?

regards
jon
Jon

Sorry the car is a 96 MGF, MPi. 67K miles
Jon

I'd replace the coil lead too - the trick is to twist the plug to break the seal first. It really isn't that tricky from the boot - just difficult to see (easy to feel though because the wire is rubberized and thick)

Don't discount the cap and arm, these can be shocking quality (boom tish - i'm here all week), and fail in invisiable ways. Personally I'd do the cap and arm first, cos they're cheap and 90% possibility they'll cure you.
Will Munns

So the distributor cap and arm could realistically fail after 8 months (and less than 5K miles) after being replaced by a reputable MGF specialist?

If that's true it is truly shocking quality!
Jon

yep, an example is rotor castings that end up with air bubbles under the center connector, over time, when the engine is at high load the spark can track thru the plastic to the camshaft, this deposits carbon, which makes the track easier and so the cycle continues. A good arm and cap should last for bloody ages though.
Will Munns

Well I tried your advice about twisting and got the damn thing off! You know what they say about perseverence. Any tips for getting spark plugs out without cracking them?
Jon

the trick with sparkplugs is in the putting in - which is a bit late for you!

If you get sparkplugs from MGR (unipart) then they must be torqued correctly, if you get them from halfords then the instructions are on the pack and DO NOT use a torque wrench. To insert put the plug in a rubber hose and lower into the head _DO NOT DROP THE PLUGS IN_, then you should do the start turns with the hose and pull to withdraw for the socket.
Will Munns

I've suffered from the same problem for some time. My car is a VVC so there's less routine parts to change but I've done the usual plugs and leads without success of preventing the strange periodic lack of power.
Similar to yourself I have checked through the archives and with the exception of replacing the coil packs the only other solution to the problem that others have identified involves replacement of the crankshaft sensor. I finally managed to remove the sensor last night which turned into a much bigger job than it should have done due to the oil cooler fitted on my car making it almost impossible to find a tool that can remove the bolt. Removal of the sensor confirmed what others have previously identified namely a very dirty sensor. The theory is that the although the dirty sensor can function adequately when cold, as the resistance builds up due to heat it eventually fails to monitor the crank speed accurately.
I am really hoping that a new clean sensor will solve the peculiar misfire and I can get back to giving the car good thrashing.

Let us know if you sort it Jon.

Neil
Neil Stothert

Neil - couldn't you get a ratchet spanner on it?

Is it 7mm or 6?
Will Munns

Will - it's 7mm. Unfortunately the pipes from the cooler wouldn't allow any movement for a flat head spanner. I eventually sourced a suitably angled 7mm ring spanner that provide a little more movement between the pipes but as I can't actually reach to touch the bolt with my fingers it was a slow process. Putting the bolt back in was a horrible job because I couldn't reach to feel when it had located the hole and the sensor just swivels and I couldn't see anything.

I just hope it's sorted the problem.

Neil
Neil

I must admit that in may car it's a whole lot easier to reach, being front engined, not having a water pipe run round the back of the engine and not having any of this new-fangled oily stuff
Will Munns

This thread was discussed between 09/08/2005 and 10/08/2005

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