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Misfire On Cylinder 3

electrical engine

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#1 JBZero94

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Posted 16 November 2018 - 05:12 PM

Hi there

 

I have a 1988 Mini Jet Black, 998cc Carb model with Electronic Ignition.

 

There is a problem with cylinder 3 on my Mini.

 

The problem began 3 weeks ago when I went out on a drive in the Mini and it suddenly started running rough and losing power which was a result of both cylinders 3 and 4 misfiring. I limped the Mini back home and me and a friend later confirmed that my distributor cap and rotor arm needed replacing. So we replaced the cap and rotor arm and that managed to fix cylinder 4, however, cylinder 3 still seems to be misfiring.

 

We confirmed cylinder 3 was misfiring since when I briefly took off the HT lead on it when the engine was running, it made no difference in behaviour.

 

Later, we changed the HT leads (Which we knew were working) which made no difference; Then we checked for sparks in cylinders 2 and 3 and both of them were sparking.  One thing we did notice was that despite the sparks, cylinder 3's spark plug in particular had been fouled quite a bit.

 

I have new spark plugs on the way but I am thinking that the problem may be something other than the ignition system.

 

Any Ideas?

 

 

 



#2 Wiggy

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Posted 16 November 2018 - 06:48 PM

Swap the spark plug into a different cylinder, and see if the misfire moves.

#3 mk1leg

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Posted 16 November 2018 - 08:40 PM

new leads and cap



#4 Retroman

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Posted 16 November 2018 - 08:50 PM

Set of new BP5ES NGK's gapped to 0.035"

 

If that doesn't cure it ;

 

Do a compression test,  see if the head gasket has gone



#5 gazza82

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Posted 16 November 2018 - 11:08 PM

Or ... valve ...

Had a Midget that ran on two cylinders ... remove 3 & 4 lead and continued to run. Burnt exhaust valves.

Says a lot for the A-series though!

#6 Steve220

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Posted 17 November 2018 - 03:14 AM

Swap the spark plug into a different cylinder, and see if the misfire moves.


This would be my first port of call!

#7 JBZero94

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Posted 17 November 2018 - 06:38 PM

After further investigation, The new spark plugs made no difference.

 

we then adjusted the timing, still no change.

 

Then we adjusted the valve clearences on cylinder 3, alas, still no change.

 

So then we decided to take off the cylinder head and low and behold, there was a split in the head gasket between cylinder 3 and 4.



#8 JBZero94

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Posted 17 November 2018 - 06:41 PM

Or ... valve ...

Had a Midget that ran on two cylinders ... remove 3 & 4 lead and continued to run. Burnt exhaust valves.

Says a lot for the A-series though!

I was considering your symptom but the valves seemed ok, however, I feel the head does need to be reconditioned including the addition of unleaded valve seats. 

 

The real problem turned out to be a split in the head gasket between cylinder 3 and 4. 







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