Sooty spark plug

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Awkward

Awkward

Member
Posts
60
Hi, Iv just recently fixed the EFI system only for a new gremlin to start... Any one got any ideas on why one of the spark plugs has started to become sooty...? The other 7 spark plugs are perfect in colour, the injectors have just been cleaned and tested and are ok, all the spark plugs are new....
Andy
 
For the others to be ok i'd say the Plug is not firing.

Check over the ignition system..

HT lead

Dizzy cap etc etc.
 
Spark plug is faulty, not getting hot enough to burn off the deposits. Try swapping the sooty plug into another cylinder and see if it still gets sooty. If the changed plug in the "sooty" cylinder gets sooty, plugs are ok.
 
My additions to the list of theory’s:
1. It appears that this particular cylinder is over fuelling, and the only way that can happen is the injector is allowing more fuel into the cylinders combustion chamber than it should.

2. It’s very doubtful and not impossible I suppose, but the spark plug could be the wrong grade and incorrectly labelled in manufacturing.
 
discool said:
It appears that this particular cylinder is over fuelling, and the only way that can happen is the injector is allowing more fuel into the cylinders combustion chamber than it should.
Click to expand...
I agree that is the most likely cause but the OP wrote that all injectors have been cleaned and tested. Should be able to check by swapping a couple of injectors and see if the problem moves to a different cylinder. I'm assuming the injectors are basic and don't need programming individually.
 
On these the fuelling system is very basic.
They don't need programming.
The injector doesn't inject directly into the cylinder but into the inlet manifold so it's not really one injector per cylinder although there are 8 of them.

OP Is there actually an issue with the running or is it just that one plug is sooty?
That said, I have had a couple of issues over the years with a misfire on LPG which on both occasions were down to one plug although it was fine on petrol.
 
kermit_rr said:
Turned out to be a worn exhaust cam on that cylinder. It wasn't opening enough to let all the gases out
Click to expand...
Thats logical. Suppose the same would happen if there is any fault stopping the valve opening fully - such as bent push rod, stuck hydraulic lifter, badly adjusted valve clearance.
 
Sorry missed all your posts, normally I get an email to give me the heads up...? In the end I swapped good firing HT leads and spark plugs that made no difference and then moved the injector from the suspect No. 5 cylinder to No1 that then fixed the problem....!!! I think there was an air leak some where that was cured when I put everything back together.
 
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