# 3 sparkplug black sout
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Professional
Joined: Nov 2006
Posts: 108
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From: NC
# 3 sparkplug black sout
Hi
I went to dealer to check misfire.
They recommend new pcm
replace pcm and still black sout on plug #3
smell gas on plug but still misfire
new plugs on engine new air filter
could it be injector.
no error code
No check engine light on
Thanks
I went to dealer to check misfire.
They recommend new pcm
replace pcm and still black sout on plug #3
smell gas on plug but still misfire
new plugs on engine new air filter
could it be injector.
no error code
No check engine light on
Thanks
Former Vendor
Joined: Nov 2012
Posts: 309
Likes: 0
1. Not enough air.
2. Weak Spark. Failed spark plug(s).
3. Too much petrol.
4. Ignition timing retarded / not advancing.
The main thing to establish is the soot on all plugs or just one or a number. If all, then 1,2,3 & 4. If just one or two, or a bank if multi carbed, then focus on that bank. Dry fouling is not caused by failed valves.
1 Not enough air.
Usual suspect is blocked air filter element. Renew, clean plugs (gentle wire brush, use emery paper to clean electrode faces, re-gap and rinse in solvent/brake cleaner, dry on a clean rag.) Replace, but do not over tighten; if threads are clean, hand tight plus a quarter turn is usually enough.
2 Too much petrol.
On carburettor cars, floats too high (most can be checked/adjusted), worn main jets. On Fuel injection cars, dirt or worn injectors. Try a cleaner such as BG 44k.
3 Weak Spark.
Often, just a bad connection; check HT leads are securely connected, and if all plugs affected, check and then double check coil to distributor lead. Check coil earth is good. If leads are looking ugly consider replacing. Modern coils very reliable, but if everything else (inc timing) is good and all plugs are affected, it is a suspect.
4 Ignition timing advanced.
If mechanical distributor, at higher revs, the advance mechanism might be seized preventing the ignition timing not to advance as it should under load and at higher eves. Remove cap, check rotor arm springs back after rotating it slightly. Using timing gun, make marks, check firing is before top dead centre, and when revved, the timing advances more.
2. Weak Spark. Failed spark plug(s).
3. Too much petrol.
4. Ignition timing retarded / not advancing.
The main thing to establish is the soot on all plugs or just one or a number. If all, then 1,2,3 & 4. If just one or two, or a bank if multi carbed, then focus on that bank. Dry fouling is not caused by failed valves.
1 Not enough air.
Usual suspect is blocked air filter element. Renew, clean plugs (gentle wire brush, use emery paper to clean electrode faces, re-gap and rinse in solvent/brake cleaner, dry on a clean rag.) Replace, but do not over tighten; if threads are clean, hand tight plus a quarter turn is usually enough.
2 Too much petrol.
On carburettor cars, floats too high (most can be checked/adjusted), worn main jets. On Fuel injection cars, dirt or worn injectors. Try a cleaner such as BG 44k.
3 Weak Spark.
Often, just a bad connection; check HT leads are securely connected, and if all plugs affected, check and then double check coil to distributor lead. Check coil earth is good. If leads are looking ugly consider replacing. Modern coils very reliable, but if everything else (inc timing) is good and all plugs are affected, it is a suspect.
4 Ignition timing advanced.
If mechanical distributor, at higher revs, the advance mechanism might be seized preventing the ignition timing not to advance as it should under load and at higher eves. Remove cap, check rotor arm springs back after rotating it slightly. Using timing gun, make marks, check firing is before top dead centre, and when revved, the timing advances more.