How much dirt on spark plugs is normal?

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Rich947
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How much dirt on spark plugs is normal?

Post by Rich947 »

I'm trying to get mine to start after a prolonged period where I think it was left flooded (I was away for a few months and someone tried to start it then left it until I came back).

Following advice on here I've removed the spark plugs, I've never done this before and they seem a lot dirtier than I was expecting? Is this normal? They also initially looked wet and there was a strong smell of fuel. I've turned it over a couple of times with them out which produces a large white cloud, strong smell of fuel and liquid of some description dribbling from where the spark plugs go - my plan at the moment is to keep doing this until I stop getting the cloud then try again with a new set of spark plugs?
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Re: How much dirt on spark plugs is normal?

Post by Nickp47 »

Hi Rich, from what I can see they look fairly well used so a good idea would be to change them.

Are you cutting the fuel when turning the car over? Either by keeping your foot hard down in accelerator or removing fuel pump relay?
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Re: How much dirt on spark plugs is normal?

Post by Rich947 »

Aye, I've removed the fuel pump fuse so my understanding is that means no fuel is being added? I'm a little unsure as from my understanding oil is still added, but I don't think that would be enough to cause the smoke?

Sorry if these are basic questions - am very much new to this...!
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Re: How much dirt on spark plugs is normal?

Post by Nickp47 »

I was going to say the white smoke is excess fuel burning off but if the plugs are out I am not sure this would be the case?

Personally, I would keep it simple - put the plugs back in, connect the fuel pump and then turn the car over for about ten seconds at a time five times with foot hard down on gas. It will either start on the sixth time with foot off the gas or if not will come close to starting in which case repeating the process should work.

The plugs look normal for a used set so should be ok to fire it up
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Re: How much dirt on spark plugs is normal?

Post by warpc0il »

You need to keep the throttle pedal floored while you turn it over to clear a flood, especially if you have the plugs removed.

Flooring the pedal stops both the fuel and the sparks.

If you spin the engine over without flooring the pedal then you can still get sparks from the ends of the HT leads, which could ignite the cloud of unburnt fuel being expelled out the plug holes - this would not be a good thing.
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Re: How much dirt on spark plugs is normal?

Post by Rich947 »

Aha, luckily I was keeping the throttle fully down when turning it over anyway.

Can totally see how cloud of fuel and sparks would be suboptimal...

I'm just surprised how dirty the spark plugs are if that's indeed normal, is that indicative of how the rest of the engine must be?!
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Re: How much dirt on spark plugs is normal?

Post by warpc0il »

The spark plugs sit in their own little pockets, back from the combustion chamber, out of the way of the sweep of the apex seals.
This is totally unlike a piston engine where the plugs protrude out into the combustion chamber.

This means that they don't get the benefit of the flame front and scouring action to keep them clean, even when the engine is running perfectly.

A bad flooding and they will get covered in muck that has no way to get clean, in normal use.

Try soaking the plugs nose down in a couple of inches of carburettor clean (or Cataclean) in a jar and leave for a few days.
Put a lid or polythene bag over the jar to stop evaporation.

Remove the plugs and rinse in some clean cleaner.
Wipe with a soft cloth and allow to dry.
Take each plug with pliers or good oven gloves, so you can hold the working end over a gas flame (e.g. cooker hob) for a few minutes until it stops smoking.
Place the hot plug down gently on a surface that's not going to catch fire or be damaged by the heat, but won't draw the heat out too quickly (not cold metal)
Repeat for the other three plugs.

Rotary plugs must not be cleaned with a knife, wire brush, sandpaper or grit blaster, though a soft brass brush can be used to clean the threads.

Ensure that the plugs are inserted in the correct holes, marked Trailing and Leading, when replacing.
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Re: How much dirt on spark plugs is normal?

Post by SmuttyHutty »

Just going to bring this thread back to life for a moment as I have just changed the plugs on my 8 with the new NGK Iridiums from JP4mance going in. Identical plugs have come out and the leading plugs have a nice coating of light brown on them but the trailing both have half brown and half black - as in the tip was coated across its cross-section with one half brown and the other half black.

I should have taken a photo but I've got a tin of MAF spray that I used on my Porsche a couple of years ago (now THAT was a money pit) and have sprayed the plugs and left them to soak.

The plugs have done a minimum of 3750 miles (during my ownership) and a maximum of 5000 miles as I know the previous owner changed them and the coil packs and leads.

So, I guess my question is how many times can I swap these plugs over and still maintain good combustion?

Stupid statement of the day: Blimey, new plugs make a difference!
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Re: How much dirt on spark plugs is normal?

Post by SmuttyHutty »

Having chatted with a few people, the accepted wisdom is that the plugs should be binned after 10,000 miles. So, in my low annual mileage case, I've got my 5,000 milers soaking and brand new ones in. Next autumn I'll swap them over and the year after that bin the older set and put the newer set in.
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Re: How much dirt on spark plugs is normal?

Post by Ainmhidh »

What originally brought me to the club was looking for a source of replacement spark plugs as the local garage place that was doing my service and MOT that year had said that the recommendation was to change them at 30k (and the car had done 28k at that point) but they'd looked and were horrified that they were priced at £35 each!
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SmuttyHutty (Thu Oct 22, 2020 3:23 pm)
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Re: How much dirt on spark plugs is normal?

Post by SmuttyHutty »

Ainmhidh wrote:
Thu Oct 22, 2020 3:06 pm
...they were priced at £35 each!
Ouch! :shock:
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Re: How much dirt on spark plugs is normal?

Post by PaulAV »

Expect to pay around £80+ for a full set of plugs, I changed mine at 10k clean the old ones and keep them safe as emergency spares (I've had center electrodes break before and porcelain crack) in my experience tow starting in second gear at around 20mph is the easiest way to get a flooded car started, trying the Mazda method takes a lot of patience, minimum of 6 repetitions of the process but more like 8-10, to do you need a really good battery, a jump pack and/or jump leads and another car
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Re: How much dirt on spark plugs is normal?

Post by Ainmhidh »

SmuttyHutty wrote:
Thu Oct 22, 2020 3:08 pm
Ainmhidh wrote:
Thu Oct 22, 2020 3:06 pm
...they were priced at £35 each!
Ouch! :shock:
Exactly. Hence I came looking here, and then spent some of the savings on club membership.
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Re: How much dirt on spark plugs is normal?

Post by New Duke »

In general it's simpler if you just get into a routine of putting new plugs in as part of your annual service pre MOT. Along with that oil filter and airbox filter change etc...
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Re: How much dirt on spark plugs is normal?

Post by warpc0il »

Always keep the set of plugs you've just removed, in a safe place, assuming that the car was running fine and there wasn't anything obviously wrong with them.

The bathtub reliability curve shows that the most likely timing of failure is immediately after a new component is installed, known as "infant mortality" - this seems to be especially true for spark plugs.
bathtub curve.jpg
I've lost track of the number of times I've been involved in diagnosing rough running or misfires and the owner has been convinced that "It can't be the spark plugs because I've just replaced them".

It only under cross-examination that that reveal that the rough running started after the new plugs were fitted. #-o

Plugs can be damaged in transit, or while fitting, or just die when they're subjected to service conditions.

At least if this happens to you, having a known good set to substitute is handy for diagnostics, and while waiting for new replacements.

BTW it takes a very keen ear to sense the failure of a trailing plug and they never trigger any sort of CEL, on their own.
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Re: How much dirt on spark plugs is normal?

Post by PaulAV »

I had a trailing coil fail and I could just about hear a difference, the engine/exhaust note was a little deeper, but as already said there was no misfire shown.
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