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Originally Posted by PhilV
Hi IMHO. Not sure to be honest. When driving it feels like it is starving itself so I assumed both. Fuel pressure all checks out ok and they have changed the pump. I have not witnessed the issue in the workshop as it was dropped in for a service and I assumed a tweak to the mapping. They found a couple of other issues that we hoped had cured it but this warm up issue remains. I’ll ask them tomorrow as I am due my weekly update.

War Bird - Currently running on standard plugs but again they have been changed. Any recommendations on alternatives?


Iridium plugs may be worth a try. Same heat range used on my car, NGK DCPR7EIX. Due to fine tip they spark at lower voltage.


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Some easy things to try before delving into more complex issues -

To see if it’s on one cylinder -
Start the engine and hold your hands over the exhaust outlets, they should feel the same or you could feel the colder blast of the miss-fire.
Swap over HT leads and see if the problem moves.

Check the pulley timing position Is correct on each cylinder.

If it’s on both, how old/good is your fuel?


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Moody 41 (2013)
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Wouldn’t swapping the spark plug lead mean the cylinders are trying to fire on exhaust instead of firing on compression?


2019 M3W Sold and is now in Las Vegas enjoying the showgirls :-)

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The way I read IMHO's post, is to exchange the complete lead left for the right to eliminate the leads themselves?
Not sure how that would help diagnose a misfire when cold though.

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You can unplug them from the coil pack and the spark plug.


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Nippymog, I just wondered if one of the leads improved when hot. I know it’s a long shot but if the diagnostics isn’t picking it up then it sounds like something at the end of the process and physical?


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Also could be a dodgy spark that’s not so problematic when the engine is hot.

PhilV, when running along with a hot engine do you get any intermittent backfires / popping from any of the exhausts? Could be a dodgy coil pack which is easy to check with a cheap spark indicator.

Good luck!


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Someone has already asked is it just one cylinder misfiring - is this the case or is it both?
edit just seen this has been answered as unsure

Last edited by nippymog; 28/11/19 07:01 PM.
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Ask KH to run it on the rolling road whilst COLD with the ProTune connected & watch the live data


Jon M
IMHO #605460 28/11/19 08:12 PM
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Originally Posted by IMHO
Nippymog, I just wondered if one of the leads improved when hot. I know it’s a long shot but if the diagnostics isn’t picking it up then it sounds like something at the end of the process and physical?


I once owned an AH Sprite that would not start or if it it did start when in the cold damp air of our beach community it would run very ragged until it got warmed up.

I found the problem when trying to start it ( someone else using the starter) while observing the wiring in the dark. There was arcing coming from degraded insulation and hairline cracks (invisible to naked eye) in the plastic parts. The UK can get pretty damp so it might be worth a check.

Last edited by LightSpeed; 28/11/19 08:13 PM.

2019 M3W Sold and is now in Las Vegas enjoying the showgirls :-)

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