plugs

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stevemarl
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plugs

Post by stevemarl » Wed Oct 09, 2019 2:34 pm

Just wondering if anyone has any ideas why I would havr 3 plugs which are spot on and one, No4, which is totally sooted up? Not capri but same idea, single carb into manifold, 4 equal length inlet branches. Runs perfectly, no visible smoke. (The LH one looks whiter in pic, it`s actually correct pale coffee colour)

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Re: plugs

Post by D366Y » Wed Oct 09, 2019 3:06 pm

I know the Haynes has pictures of different spark plugs and what different colours mean, in the meantime I found this link which will hopefully be of help - https://e3sparkplugs.com/blog/are-your- ... something/

To save you clicking, here's what it says about the plug you've described;

A black, feathery carbon deposit on your spark plugs can be an indication of a weak spark or an overly rich fuel mixture. Causes may include a stuck choke, misadjusted or heavy carburetor float, a leaky injector or carburetor needle valve, low coil output or high resistance in your spark plug wires.

If it's only one I'd only guess that maybe the spark isn't strong enough, maybe a dodgy lead and/or plug?

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Re: plugs

Post by Paul G » Wed Oct 09, 2019 4:05 pm

The centre electrode on the blackened plug looks to be shorter and the gap wider than on the "normal" plug. I'd try a new set of properly gapped plugs before condemning anything else.

If the new plugs don't do the trick then look into new leads, doing a compression test on the engine or looking for an air leak on the inlet manifold around the affected cylinder.

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Re: plugs

Post by Caprigear » Wed Oct 09, 2019 6:29 pm

I would start with a compression test before anything else.
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Re: plugs

Post by stevemarl » Wed Oct 09, 2019 6:31 pm

Just to clarify, the first 3 plugs were spot on the correct beigey colour, the 4th is absolutely black with soot. Very observant Paul - you`re right, when I came to check the gap it was way, WAY wider then spec (all the others had hardly any erosion at all; they were all new and correctly gapped 6k ago at last service along with new leads.) Just weird, I`ve never known one plug be SO badly fouled. I have now put a new cap and rotor in, as the old one was q bit grubby and it is the only other thing that could be causing misfire. Strangely, it was running great. Suppose I might as well do a comp. test while they`re out, hope to God it`s not a crack in manifold, although that would weaken one cylinder wouldn`t it? or could it be over- compensating for a leak elsewhere?

Martin, will do a test tomorrow, fingers crossed.

Can you do a compression test ccold? I could do that now ?

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Re: plugs

Post by stevemarl » Wed Oct 09, 2019 7:03 pm

Just done a test on 3 & 4 (1,2 & 3 are the same) both are giving 200 psi, and that`s stone cold so that looks OK. Just see how I go on with the new cap. Otherwise it looks like manifold`s cracked.

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Re: plugs

Post by Mc Tool » Wed Oct 09, 2019 9:49 pm

A cracked manifold ? Must be Sherlock's day off :roll: :xd: A cold comp test is great for finding out how things are when the engine is cold :) but you really need to do it hot. As a rule (there are exceptions )if you have only one pot acting the goat it's likely that it's not something common to all cylinders ....like a carb or a coil, more likely to be something like a plug or a lead . You could try swapping the plug and then the lead but not both at once......to see if the fault follows the part.
In some engines the coolant flow around the block/head can result in the rear cylinder always running hotter than the rest and thusly they usually show signs of age or failure before the rest. This is why you need to do a hot comp test . You may find that a cylinder starts to oil up or loose compression when it gets hot. If you zoom in on that black plug you can see black deposits in the last thread and the surface adjacent to that .....this is completely burnt oil .What sort of engine is it ?
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Re: plugs

Post by stevemarl » Wed Oct 09, 2019 11:42 pm

It`s a little Fiat sohc transverse thingy, F.I.R.E. as they`re known.
I couldn`t check hot due to the absence of wheels etc , as I`m still giving a bit of tlc to its calipers (a proper service)` I`ll put it back together tomorrow and give it a run round then get hot figures. TBH though I`ll be vrery surprised if they`re lower, generally the pistons, rings etc improve seal as they expand. I always thought you did comp. tests hot as all the components expand at working temp and cold would give a misleadingly low low result? My money would be (is) on the distributor cap as the internal metal looked a bit `oxidised` and everything else is pretty new.

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Re: plugs

Post by Mc Tool » Thu Oct 10, 2019 4:18 am

Even letting it idle up to temp is ok . I guess there would have to be a heap of different theories re piston wear/damage: temp : bla bla bla ,and all of them probly happened to some poor bastards (bastii ? ) somewhere. I had an outboard motor that chundered big time and the fuckest piston came out of the one cylinder that I thought might be ok after initial inspection :roll:
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Re: plugs

Post by stevemarl » Thu Oct 10, 2019 9:14 am

Mc Tool wrote:
Thu Oct 10, 2019 4:18 am
Even letting it idle up to temp is ok
Not if your in a small lock up on a cold, wet Manchester night it`s not!

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Re: plugs

Post by Paul G » Thu Oct 10, 2019 9:32 am

The little Fiat "FIRE" engines usually have bullit-proof bottom ends but are prone to head and head gasket failure. You need to have this in mind if the other things don't fix the blackening plug. Good little engines though, rev like hell and quite powerful for their size.

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Re: plugs

Post by Mc Tool » Thu Oct 10, 2019 10:10 am

stevemarl wrote:
Thu Oct 10, 2019 9:14 am


Not if your in a small lock up on a cold, wet Manchester night it`s not!
If I was stuck in a small lock up on a cold wet Manchester night.........yeah ,I'd probly start the car and slip away :lol:
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Re: plugs

Post by D366Y » Thu Oct 10, 2019 10:37 am

stevemarl wrote:
Thu Oct 10, 2019 9:14 am
Mc Tool wrote:
Thu Oct 10, 2019 4:18 am
Even letting it idle up to temp is ok
Not if your in a small lock up on a cold, wet Manchester night it`s not!
If you ran it up to temperature it might start warming you up! :lol:

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Re: plugs

Post by stevemarl » Thu Oct 10, 2019 11:13 am

D366Y wrote:
Thu Oct 10, 2019 10:37 am
f you ran it up to temperature it might start warming you up!
Depends though whether you got warm before you go into a coma `cos of the CO ;)

Just been out for a run up the motorway to B&Q, everything seems fine, compression (Mr McTool was right) HAS come down... to 190psi - so I`m really happy with that, plus the plug looks like this: Image
So it does seem it was the cap after all. I still would`ve thoughtif a plug was misfiring it would be wet; soot suggests it IS burning the fuel but why woud it be rich? (Again, the flash makes the deposits look whiter than they are)

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Re: plugs

Post by pbar » Thu Oct 10, 2019 11:18 am

Mc Tool wrote:
Thu Oct 10, 2019 10:10 am
stevemarl wrote:
Thu Oct 10, 2019 9:14 am


Not if your in a small lock up on a cold, wet Manchester night it`s not!
If I was stuck in a small lock up on a cold wet Manchester night.........yeah ,I'd probly start the car and slip away :lol:
There are far worse places to be in Manchester, whatever the weather!

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Re: plugs

Post by stevemarl » Thu Oct 10, 2019 11:30 am

Paul G wrote:
Thu Oct 10, 2019 9:32 am
The little Fiat "FIRE" engines usually have bullit-proof bottom ends but are prone to head and head gasket failure. You need to have this in mind if the other things don't fix the blackening plug. Good little engines though, rev like hell and quite powerful for their size.
Yep, coildn`t agree more, they`re great little engines apart from HGF they have no other issues. Been in the family from new, now on I think its 3rd head gasket (probably why the Compression`s so good - I`ve always had the head skimmed after failure just to be safe - God knows what the C.R.is now!) My brother replaced this with a Punto: that too has had 2 head gaskets I`m sure. Having said that it`s a couple of hours work to replace it, I can get it back on the road next day, very simple. I mean it`s 31 years old, flys through the emissions (HC = 120) runs great and still has 190psi across all cylinders
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Last edited by stevemarl on Thu Oct 10, 2019 11:53 am, edited 1 time in total.

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Re: plugs

Post by stevemarl » Thu Oct 10, 2019 11:41 am

pbar wrote:
Thu Oct 10, 2019 11:18 am
There are far worse places to be in Manchester, whatever the weather!
Oh, I`m well aware of that Paul! TBH, I spent the afternoon /evening in there just going round everything for it`s 6k service: brakes, steering, suspension checks, oil change, plus antifreeze and brake fluid change. Absolutely happy as a pig in shit, almost Emporium levels of contentment! Little `in joke` there ;) I really do need a project.

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Re: plugs

Post by Paul G » Thu Oct 10, 2019 1:11 pm

Having almost 250,000 miles on the clock says how good those engines are. I doubt many Fiestas have done that on an original engine.

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