does anybody inspect their spark plugs ?

[peanut]

does anyone still use this useful diagnostic these days ? Reading your plugs can tell you everything about how your engine is running and performing.

I suggested reading the plugs on another forum where a 944 had a intermittant misfire or hesitation on acceleration. It might have identified if one particular bore had different fuel and ignition characteristics than the others.

I was met with ............. nah the plugs were all clean mate ?[] clearly not grasping the diagnostic potential .
I wonder if anyone still knows the correct way to test using the plugs ? I read it many years ago in Vizards excellent 'Tuning for Performance' book

I suppose its too 'old hat' nowadays ......

 

[tref]

Yep, I look at the plugs... not sure about the "correct method", but have played the "kill the engine at the point of the problem, coast to a halt and whip out a plug" game before now if that is the one?
In fact - the plugs were the give-away that enabled me to get the 924T Cab running again.

 

[peanut]

ORIGINAL: tref

Yep, I look at the plugs... not sure about the "correct method", but have played the "kill the engine at the point of the problem, coast to a halt and whip out a plug" game before now if that is the one?
In fact - the plugs were the give-away that enabled me to get the 924T Cab running again.

yep thats the method Tref . Never forget the first time i tried it at speed and suddenly found I not only had no power steering or brakes but the steering column lock applied too ! gulp []

 

[tref]

Er, um... yeah... forgot about that, er... "incident"! One quickly learns to just turn the ignition just one notch!

 

[sawood12]

Yes, it is an important indicator as to the health and running condition of your engine. I used to use it regularly on my first car - an Escort MK3 with twin webbers, to make sure the carbs were set up right. However with modern ECU's and fuel injection systems this check is largely redundant because the AFR is usually always spot on and if not you'll easily tell from other indicators like poor running or warning lights coming up in the dashboard. But they can still tell you about the health of your cyl head valve guides, piston rings and can help diagnose other problems.

Another indicator is the colour of the coating that builds up on the inside of your exhaust tail pipe. If it is too sooty and black then you're running rich or have oil in your exhaust, if it is too yellow then you're running lean, it should be a nice light brown to indicate a healthy AFR. However the 944 turbo was the first car I had that was black and sooty, which concerned me for a time until I realised this was normal and is due to the fact that they do run rich while on boost on purpose so is normal. I guess if you drove around off boost all the time you'd get the nice light brown coating.

I service the Focus myself and have got out of the habit of checking spark plug gaps though. I havn't had a problem with running at all yet but I should blow the dust off the feeler gauges next time I do a service.

 

[Neil Haughey]

Thats a relief I thought I was the only one that did this. Its one of the reasons I haven't got round to refitting the metal cover on the 968 that fits over the fuel rail etc. Takes literally 5 mins to check the plugs.

 

[zcacogp]

Looking for a biscuitty-brown (fawn) colour ... yes. A great idea, and a good post Peanut.

One question I have wondered is how long it takes for the colour of the spark plugs to change? For instance, if you find the plugs are black and damp, and thus adjust the fuelling to make it leaner, how long does it take for the spark plug colours to reflect this lean-ness? A couple of seconds of running? A few minutes? An hour or so? More?


Oli.

 

[DivineE]

Those who check plugs of 944 turbos do you typically find the rear two plugs darker/more sooty than the front two when the car has been on choke? It's not important and I wasn't expecting so but just wanted to confirm something on a car I looked at and didn't buy.

 

[peanut]

ORIGINAL: zcacogp

Looking for a biscuitty-brown (fawn) colour ... yes. A great idea, and a good post Peanut.

One question I have wondered is how long it takes for the colour of the spark plugs to change? For instance, if you find the plugs are black and damp, and thus adjust the fuelling to make it leaner, how long does it take for the spark plug colours to reflect this lean-ness? A couple of seconds of running? A few minutes? An hour or so? More?


Oli.

well according to Vizard you should warm the engine up to operating temperature the run the car at the rev band you are interested in say 4000rpm in top for few miles .
Find a straight clear stretch of road and turn the ignition off at 4000rpm and coast to a stop. Then you read the plugs . Otherwise you'll just be reading the coating from an overfueled starting mixture with the engin e cold.

If the plugs are really sooted up and heavily carbonised to start with it might be best to clean the loose stuff off with a toothbrush and petrol first .

The bit you 'read' is the ceramic part covering the electrode not what is on the electodes obviously

There is a guide to reading plugs in the back of most Haynes manuals

 

[zcacogp]

Hmmmm. Interesting, thanks Peanut.

Hadn't heard the bit about coasting to a standstill with the engine turned off before, but it makes sense.


Oli.

 

[Copperman05]

I dont regularly check my spark plugs for any colour change but I'm happy to see the light brown end of the plug when changing them. I guess its more of an issue for carburetted engines as at least you can adjust them, not sure if its possible with FI.

Edd

 

[peanut]

ORIGINAL: zcacogp

Hmmmm. Interesting, thanks Peanut.

Hadn't heard the bit about coasting to a standstill with the engine turned off before, but it makes sense.


Oli.

yes the important thing is that the throttle has to be wide open when you kill the engine so that the plugs give you a 'snapshot' of the fuel and ignition characteristics at that rev band you are testing .