R400 Duratec: occasional misfire -- plug problem?

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John Vine
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R400 Duratec: occasional misfire -- plug problem?

On my trip south through France, every so often the engine suffered a short bout of misfiring on one cylinder.  This tended to occur after a longish period of 4000+ rpm running, followed by a potter through a 50kph zone.  Giving it some beans tended to clear things again.

The plugs are NGK BR7EFS, fitted new about 3k miles ago, and gapped to 0.9mm (37thou).

This morning I took the plugs out.  #1 (and #2 less so) showed a slight black "shadow" on one side of the ceramic insulator:

This was quite hard-baked and would not simply scrape off.

The other plugs were the same colour, but with no "shadow".

Is this evidence of anything untoward (the spark tracking sideways to earth, for example)?

So far, I've replaced plug #1, and will test things out at the earliest opportunity (Monday).

The plug loom itself (connectors, wires etc) looks just fine. The coils are clean and grip the plugs firmly. The plug cavities are also clean and dry as a bone.  In every other respect the car goes exactly like an R400D should.

JV 

 

 

rj
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I've had an 485R with a similar behaviour in the garage. It turned out to be one of the injector connectors.

The cable was routed in a way that caused tension to the plug resulting in the pin to be loaded and in the end the spring effect was no longer sprung :-p

Car behaved well at idle, but it registered an OBD code indicating that the injector was short to ground. This was an EU car, hence the OBD.

I didn't check the plugs though.

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revilla
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Sounds remarkably similar to the issue I've been having with a K Series VVC 160 here https://www.lotus7.club/forum/techtalk/mysterious-occasional-misfire-vvc-160

I'm running BCPR7ES plugs at the moment but I've realised the original Rover NLP100290 is equivalent to an NGK 6 range plug and the misfire only happens at time when the plugs would be running at their coolest. I've also seen numerous references to larger plug gaps causing very similar issues on the 1.8 K. So I'm about to try some BCPR6ES with 0.7mm gap just to see if it makes a difference.

SV VVC 170 - 170.4 bhp @ 7100 rpm - 142.4 ft.lb. @ 4900 rpm

Jim 123
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John is it a trick of the light or is there a small dimple recess in the center electrode on the surface facing the camera? 

Jim

John Vine
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Trick of the light, Jim (the flash, I suspect).  The electrode is as new.

JV

John Vine
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Thanks, chaps.  I hadn't considered an injector problem, so I'll check the loom.  A more detailed check will have to wait until I return and can record an Easimap log.

...the misfire only happens at time when the plugs would be running at their coolest.

Thanks for the pointer, Andrew.  I'm beginning to suspect that that may well be my problem, as the misfire tends to occur after a spell running on a light throttle.  My original plugs were Ford/NGK TRAP6-13.  I moved to BR7EFS for two reasons: (a) to follow a  recommendation from the Two Steve's for a Duratec, and (b) to reduce the plug gap as there had been reports of coil failure due to voltage stress caused by the large 1.3mm gap.  Certainly I suffered a coil failure a few years ago while using the TRAP6's.

I don't have the original TRAP6 plugs with me.  I've got a new set of BR7EFS on order, and if the problem persists, I'll put the TRAP6 ones back in (re-gapped to 1.0mm) and see what happens.

JV

Geoff Brown
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JV - Has the miss fire continued back in Blighty?

When I took my R400D to France last year it became very grumpy idling in traffic & would blow itself out if left to idle in stationary traffic for too long in high ambient temperatures. When restarted or pulling away it would 'miss fire' for a heart beat then back to normal.

Also the performance changed but not for the better though higher ethanol content fuels are supposed to improve performance........

I put these symptoms down to the high ethanol content in French 95. As soon as I was back in the UK the tank was brimmed with UK 95 & the symptoms slowly disappeared.  

And yes my plugs were unusually dark when inspected somewhere around Soissons having run on French 95 for a few days & brimmed the tank twice.

Is it the Lambda giving different feed back due to the combustion properties of the high ethanol content?

John Vine
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Thanks for the input,  Geoff.

I'm still in France at the moment (SW -- Gers).  Your ethanol thought intrigues me.  So far, I've filled up with quite a variety of fuels: Esso 98-E5, Avia 95-E10, Intermarché 95-E5, Intermarché 98-E5, Carrefour 95-E5.

The misfire happens only very occasionally. The first time was after I left the A26 at J11 after running at 80-ish for a round 70 miles (after filling up with Esso 98-E5 just south of Saint Omer).   I've used French ethanol-laced fuel many times before without misfires, so I don't think it's fuel-related.  Certainly, the plugs are anything but dark.

I'll be trying out the replacement #1 plug tomorrow....

JV

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A fellow member had a similar misfire on his Duratec recently...... his also became 'very grumpy', particularly upon entering a car park..... his too resulted in a significant change in spark plug colour and could also be linked to a change in the burn characteristics of the fuel....

.....but then he had just topped the tank up with Diesel......

.. Getmecoat 

Geoff Brown
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JV - The area I was driving in - Soissons, Arras & southern Belgium only sold 95 E10 or higher. I believe that UK 95 is a maximum of E5.

I note that you did top up with 98 occasionally. A bog standard R400D ECU is programmed for 95 maybe could be part of the problem?

Intriguing though I hope you find the source & get a cure.......

 

John Vine
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Thanks, Geoff.  I normally use SP95 exclusively, but take SP98 when the 95 isn't available.  But I've done that in other years without problems.

I took the car our for a 40-mile blat on Monday after fitting a new plug in #1.  It ran well, so maybe the old plug was the problem?  I'll be watching closely over the next few days....

PS: Nice one, Neil.  Très amusant!

JV