Nissan Micra misfiring

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Trikeshed

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Hello, I'm new to DIYnot and I don't think this issue has been covered. I have a 2004 Nissan Micra (K12) with a long-standing misfiring problem. A well-regarded garage has looked at it (including bringing in an auto electrician) and has drawn a blank after trying all the usual things (plugs, coils, battery, connections). The engine diagnostic light comes on (sometimes) and the code is "Random misfire". Sometimes the car will run fine for weeks on end, with or without the warning light on. But in very damp conditions it misfires badly and sometimes, like yesterday, gives up completely though it is OK again when it has dried out a bit. A local Nissan garage says they have seen the problem on 3 cars of similar vintage recently and each time they have had to give up and scrap the car - even a new ECU hasn't helped. We are about to give up but I wondered if anyone had actually managed to solve this problem. Thank you.
 
It is obviously an HT issue, so I'm surprised a garage would be unable to find it. Coil, HT leads, distributor (if it uses one), or plugs breaking down.

Have a look under the bonnet, when it is misfiring with engine running, on a dark night - some arcing might possibly show up the issue.
 
Thanks! Harry, there aren't HT leads, there's a pencil coil for each plug. Mottie, the diag doesn't show the cylinder.
 
If Mr. Nissan can't find it then that makes it pretty difficult for us!
However - if it's diagnostic comes up with 'random misfire' then it's not usually the coil pencils at fault....if it was then the specific cylinder would have been identified.....the same applies to the fuel injectors.
I have heard of wiring loom problems with these, particularly that which goes across the top of the cylinder head, heading for the ECU (eventually) via the numerous block connectors so I'd be looking at that. Just guesswork, of course but any connections which are green can give a clue.
John :)
 
On the K12 you have to remove the large air box on the top of the motor.....a good few bolts!
This has to be done anyway to access the plugs, and you’ll find the wiring loom there.
John :)
 
You could maybe try running a really good earth from the engine block to the battery negative and trying it for a few weeks. Obviously, after the spark has "done its thing" you need to get rid of the energy somewhere. It relies on their being a big potential difference between the tip of the electrode and "earth" (which really means the battery negative). If there's a high resistance somewhere, some of the spark energy will be wasted in overcoming it. At least it's cheap to try!

Also, less cheap to try, is an upgraded plug (say a platinum or iridium one)? I agree this isn't fixing the root cause of the problem though.
 
Avocet said:
You could maybe try running a really good earth from the engine block to the battery negative and trying it for a few weeks. Obviously, after the spark has "done its thing" you need to get rid of the energy somewhere. It relies on their being a big potential difference between the tip of the electrode and "earth" (which really means the battery negative). If there's a high resistance somewhere, some of the spark energy will be wasted in overcoming it. At least it's cheap to try!
Click to expand...

If there was a poor earth to the engine block, cranking would be an issue and so would battery charging.
 
Avocet said:
They're both low voltage, heavy current situations though.
Click to expand...

Which will usually show up a poor engine black ground. A favourite, was a bad earth to the engine block and when you tried to crank it, the choke cable would begin smoking.
 
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