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One oily/sooty plug


plumster
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Can any of you folks explain why the spark plug just in number 1 cylinder regularly get sooty?

It cause the odd miss & is disconcerting, its stopping me from going on any long runs, once cleaned car is smooth & revvy but after a few miles seems to do it again.

Any suggestions welcome, cheers.

Edited by plumster
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Hi Sam, the best way to check your engine is a compression test with a hot engine. When you discover that cilinder has got a lower compression do it again with some engine oil sprayed into that cilinder so you can find out if it are worn piston rings. Keep us posted.

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Compression is first to try as Herman says as that low CR would highlight an issue. 
 

Try moving that plug to another cylinder, see what happens.

Couple of other things; Is the engine breathing heavy ? If not then it could be pulling a little oil down the inlet valve stem too. It’s not much at this stage as it’s burning it in the cylinder. You could look for a very feint blue in the exhaust gas, but it’s not likely to be visible  at this stage. 

Usually if it was a restriction to air abi e the carb (air filter etc) you see the sooting on all plugs, so think we can rule that out.

Edited by Jessopia74
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+1 for oil bypassing a valve stem seal. I had this exact issue...car would run sort of OK, but kept oiling up one plug. No blue smoke or anything visible.

Stem seal was broken...changed that and no issues since.

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i would have thought that any valve seal / issues would cause an oiled up fouled plug.very common for the valve stem oil seals to do this as they harden with the heat BUT this wouldnt cause a sooty plug.a single sooty plug would indicate a rich mixture on that particular cylinder. possible with injection but not with a carb?. are you on a carb ?

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4 hours ago, cam.in.head said:

i would have thought that any valve seal / issues would cause an oiled up fouled plug.very common for the valve stem oil seals to do this as they harden with the heat BUT this wouldnt cause a sooty plug.a single sooty plug would indicate a rich mixture on that particular cylinder. possible with injection but not with a carb?. are you on a carb ?

It will burn small amounts of oil just like a fuel/additive. 

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21 hours ago, cam.in.head said:

i would have thought that any valve seal / issues would cause an oiled up fouled plug.very common for the valve stem oil seals to do this as they harden with the heat BUT this wouldnt cause a sooty plug.a single sooty plug would indicate a rich mixture on that particular cylinder. possible with injection but not with a carb?. are you on a carb ?

Yeah on Weber carb with K & N filter, I am going to get a new set of plugs 1st & monitor the performance.

I don't have access to a compression tester so that will have to go on the back burner for the mo.

 

Cheers chaps, will let you know how it goes (or splutters).......😆

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as a very basic compression test .disable the coil power supply and just crank the engine. an obvious low compression cylinder will show as a faster section instead of 4 equal strokes.a slight issue wont show up but a major loss will .

and again,just to clarify. you are saying sooty ? not oily and with a build up of crusty deposits .

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I would say sooty, more than oily, tomorrow afternoon I will whip the offending article out & have a proper look, maybe even post a pic for ya.

 

Cheers chaps.

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I’ve just been reading some guff on my Rover V8 engine and thought a leaky injector may be your problem. See described below;

 

To check the fuel pressure, a gauge is fitted to the supply line immediately after the fuel filter. The ignition is powered up, and the gauge is read. The pressure reading should be between 34.0-38.0psi (2.390-2.672 kgf/cm2). Next, turn the ignition switch off and observe the pressure drop in the system. After one minute, pressure should drop no more than 10psi (0.7 kgf/cm2). To check for a leaking injector, first check the spark plugs! (A leaking injector will typically result in a sooted-up spark plug.) Range Rover advises that all eight injectors can be removed from the manifold without being disconnected from the fuel rail (which is presumably still full of fuel.) If you can manage to get them out and inspect them for leakage, you should observe no more than two drops of fuel per minute from any injector. 

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theoretically then seeing as you have a carb.there is no way you can get that cylinder to be sootier than the others mixture wise at least.so a compression test ( even if the basic one i mentioned) may show up some issues or another thing to check is,,early 2 litres had a realy soft cam that tended to wear down usually on one cylinder rather than equally.if you have a worn lobe or two that could affect whats going in or coming out of a particular cylinder.easiest way to check is with rocker cover removed.spinning on starter( ignition disabled again) should show any obvious lift problems / differences.

if not and all seems well then its probably the start of a failing inlet valve stem seal on that cylinder.a common and well known issue.this small amount of oil will burn off as jess mentioned and may not manifest itself as oil burning and fouling until it gets worse.seal can be changed without taking head off with various methods.

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  • 2 weeks later...

After the trauma of not being able to open the bonnet was sorted...

Took out all 4 plugs & sod's law they were quite clean, certainly none of them blackened.

So changed all 4 for a new set of Bosch plugs & pottered off to the seaside, 80+ miles & it never missed a beat.

Thanks all for advice, I will keep an eye on it over the next few ride outs before I feel confident to go on any really long runs.

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On 12/04/2022 at 18:42, ®evo03 said:

Would it be a ht lead issue, maybe not seated right, or loose plug? Might have been a easy fix issue,  maybe even I failed plug,

 

Possible, but I have had the HT leads on & off quite a bit, maybe I should replace them all anyway, ticks another box.

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