Teach Me About Spark Plugs

[martyn]

Ok, so I have a bit of a misfire that has got progressively worse.  It’s time to do something about it and I think changing the spark plugs is a good start.

Having never needed to deal with spark plugs before (tin top gets serviced in a garage each year) I need educating on the subject.

How do I know which type to buy?  The NGK product finder lists some Caterhams, but not the Sigma (let alone 150).  I can find something listed under 2008 Focus 1.6 but will this be suitable or not?

Are performance (iridium?) plugs worth buying? Or are these simply marketing placebos?

Anything else I need to know?    The car is a 2008 Superlight 150

Thanks.

[Jonathan Kay]

Have you got the Guide for the 150? I think that gives the part number.

You can almost certainly find a part number on your current ones, and that will help you find the equivalent of whatever make you choose.

Please can someone advise: does that engine have a lost spark system? If so there's a subtlety about identifying replacement plugs. (The manufacturers use different original plugs on the cylinders that have the extra sparks.)

There is a surprising number of problems with people, plugs and tools. I'd recommend using a clever tool with a rubber insert and being very careful as you engage the thread.

You'll be fine.

Jonathan 

PS: No comment on whether this is the cause of a misfire... but check your lead connections first.

[Terry Field]

Martyn

Good for you for having a go. I am sure you will get good advice about plugs on BC.

Don't forget the importance of good plug leads as well. I don't know how old the car is, but leads do break down over time and the first you know about it is when the car stops or runs badly. A new set of leads would at least remove that as a possible source of the missfire and help you in tracking it down

Terry

[Bone Rat]

Hi,

Just serviced my Roadsport 150 Sigma - as far as I could find out they were NGK TR5B-13. Seems to run fine after change from the original Ford plugs

Andy

[ChrisC]

With the 150, there is also obvious checks to carry out, are the TB's balanced and TPS set?   If it's been running fine on the original plugs, why not remove them and get a set from your local ford dealer?

[martyn]

Thanks for all the help guys.  However, please don't get distracted by my mention of a misfire.  I'll start another thread for that if necessary.  For now I'm just looking for advice on spark plugs.  I'm confident that replacing them will resolve the misfire having seen the state of the carbon build up on them!

So, what to buy..?  The current ones are NGK TR5B-13.  I guess the easy option is a straight swap for another set of those.  Is it worth considering the more expensive iridium ones?

Another question...  What torque should I use when fitting the plugs?

[martyn]

Jonathan, I'm not sure what guide you are referring to. Presumably some workshop manual?  The only guide I have is the Assembly Guide and that doesn't mention spark plugs (and neither would I expect it to).

[Jonathan Kay]

Yes, I meant that, but for recent cars there's also an Owner's Handbook. I can't check until I get home on Sunday...

On posher plugs: i'd normally say that for most modern engines in most uses there's no advantage in going above the manufacturer's spec... but yours don't sound happy. So until that problem is resolved I suppose there might be...

Jonathan

[CharlesElliott]

25Nm is the torque on the K series, I assume it is a fairly universal tightness.....

[RS2000]

So POBC if the plugs have a lot of carbon on them, is that perhaps a sign that they are not a hot enough plug?

[martyn]

I’m sorry but what does POBC mean!?

Yes the carbon build up may indicate that the plug is too cool, however the engine does run rather rich in my opinion.  That could also account for the carbon build-up.  It’s difficult to know if the plugs are the symptom or the cause.

Given that I have only owned the car for 4 months and don't know much of it's history, I'll just go with a straight swap and see what difference that makes.  If I find myself in the same position 6-12 months down the line then I'll know there is some other problem that needs addressing.

[Jonathan Kay]

I think it's used for both "People of BlatChat" and "Power of BlatChat" with the lovely idea that the latter is almost supernaturally effective.

:-)

Jonathan

PS: I'd prefer "PoBC".

[Smithy77]

Regarding torque, I have always (rightly or wrongly) used the rule of thumb of tightening to figer/pinch tight, then another 1/4 turn. Done this on every engine without any problems

[revilla]

I always torque to 25Nm but never liked the feel of it - because the washers on the plug crush to form a seal, it always feels like the thread is starting to strip as it yields as you approach the final torque value. Never have actually damaged one and now I know why it feels like that, but always gives me an unbeasy feeling all the same!

[mikecocker]

The sigma spark plugs have a small taper to seal them, rather than a crush washer. Torque is 15 Nm. I use the FoMoCo AYFS22CB plugs in my 140 and they run perfectly with no carbon build up. I think a check of the mixture would be more helpful than changing the heat range.

[Q Catcher]

Yep, taper seat spark plugs don't follow the old 1/4 turn rule.

Probably best to stick with the original spec plugs, but it may be worth noting that on some Ford engines from the noughties there were updates that recommended changing from a '5' heat grade to a '6' (that's the number in the middle of the code) and using a 0.8mm gap (as opposed to the originally recommended 1mm) if there was a problem with misfiring.

[SteveA]

I went to buy some plugs from Ford the other day and apparently FoMoCo AYFS220CB have been replaced by FoMoCo CYFS-12VN4. Ive bought a set but not tried them on my Sigma 140 yet.

[Jonathan Kay]

Spec or part number aren't in either the Assemby Guide or Owner's Handbook.

Do you need any more on identifying them or finding equivalents?

Jonathan

[martyn]

Thanks Jonathan.

I've identified the plugs currently in the car and I'm going to replace with the same ones for now. I'm almost certain that will fix the misfire, but I suspect that the car is running rich and that is what caused the plugs to get in such a state.  While diagnosing the problem I'm being careful to only change one thing at a time.  Hence the reason for not changing the type of plugs.   Fix one thing then review for a period and see what further problems come up.

[Jonathan Kay]

Wise approach.

Good luck

Jonathan

[bigdog]

It's been my experience that spark plugs are very, very rarely the cause of a running issue. They are however a very reliable indication of other issues. Fluffy black carbon=too rich, Gooey black carbon=oil from bad valve guides.