Diagnose engine Problems from Spark Plugs

[onlyfaith]

By looking at the spark plugs we can have a knowledge about the inside of an engine.just by looking at the used spark plugs we ca get an idea of the spark plug heat range, the engine condition and whther or not the carburetor or igntion timing is correct. These guidelines have been derived from NGK hand book 1977. However their Hot but OK range may not be acceptable today..

Enjoy the information..

Normal
Even plugs that seem normal ie fro 6-24 can be the cause of misfiring due to lead deposits.

Wet plugs
Wet plugs firing such as those in fig 1-2 are normally due to one of the following causes..
1. Excessive choking
2. trouble within the ignition system.
3.oil pumping past worn out rings and valve guides.

sooty plugs
sooty plugs like those in fig 3-4 are usually the result of
1. a plug with too high heat rating is used and the plug firing end does not reach its self cleaning temperature ( above 400-450 c) due to light load conditions
2.use of a too rich air to fuel mixture (8:1 to 10 :1)
3. troubled ignition system
4. improper cooling system resulting in exess cooling.

Firing end Burns
The firing end Burns as shown in fig 25,26,27 may be the result of
1.too low heat rating permitting the plug to exeed the highest limit of permitted temperture ie over 850-1000 c due to exessive heavy load operation.
2. A too lean air to fuel mixture
3. ignition timing is too advanced.
4. Abnormal combustion such as knocking
5. cooing system malfunction causing engine over heating.

Over Heating
Over heating condition such as in fig 28 & 29 are due to intense knocking and pre ignition following situations similar to fig 25,26, and 27 where increased temperature of spark plug firing ring results in melting of electrode.

[onlyfaith]

[isi0000]

thanks for sharing......

[vyrus]

Thanks bro! Learned some new stuff

[atif11]

very nice share !!

[Xulfiqar]

reading the plug off - requires a loupe - thats the easy bit - getting the heat range correct is the hard part.

e.g. classic Pakistani case.

Kawasaki KH1xx 100,110, 125 - it originally comes with B8ES - this plug is a regular tip cold plug, if the engine is tuned accordingly, it will never knock at high rpms and perform nicely and evenly on pulls.

Nearly all Pakistani mechanics use BP6ES - add too much fuel to compensate the supposedly lean condition. The engine usually knocks at high rpm and damages the piston/cylinder and conrod too.

If you put a BP6ES in a correctly tuned KH100 engine - it would show as super super lean. Install B8ES back, and it will show correct.

similarly, the daihatsu CB35 engine is a lean burn emmissions engine with higher CR than the CB23 (regular pakistan model charade engine)

It uses an NGK plug - with 7 heat range but extra projected twin electrodes to start the flame ball effectively because the charge is lean and messed with EGR. Using a BP6ES from the shop makes you think its perfectly tuned as it shows whitish electrodes - but infact the engine loses power as it knocks on high rpm and sometimes diesels while shutting down.

e.g. taking into consideration the mitsu galant 4G93 GDI engine, most high perf speed shops made a fortune from selling their owners platinum and iridium spark plugs again and again in the name of engine performance.

NOPES.

That engine is inherently prone to coking itself because of its very high CR - it produces carbon particulates like a diesel engine. When it cokes up it combustion chamber ball cavity in the piston - the plug cannot ignite the fuel mixture, as the compression ball is not centred as required. The original platinum plugs are good for 200,000 kms. but owners replaced them again and again. for the sake of speed shop placebo effect.

My remedy for the Galant GDI was replacement with a 6A12 or 6A13 from a similar Galant/Legnum - very simple engines, very smooth and very reliable - those engines are V6 - but use 3 platinum plugs for the rear bank and 3 copper ones for the front.. (which according to our PW members would be stupid)

[SpoonMotorSports]

Couldn't have said better +1

[Elien]

This is very very helpful for self tuners thanks for sharing..

[Sharo53]

@xulfiqar
sir which plug you recommend for cb-23, EGR system not connected...

[Xulfiqar]

CB23 never had EGR - unless you are referring to the JDM models which had CB33, 35 and 37 engines

[wasay_ahmed]

though its a repost but stil worth posting

[isi0000]

reading the plug off - requires a loupe - thats the easy bit - getting the heat range correct is the hard part.

e.g. classic Pakistani case.

Kawasaki KH1xx 100,110, 125 - it originally comes with B8ES - this plug is a regular tip cold plug, if the engine is tuned accordingly, it will never knock at high rpms and perform nicely and evenly on pulls.

Nearly all Pakistani mechanics use BP6ES - add too much fuel to compensate the supposedly lean condition. The engine usually knocks at high rpm and damages the piston/cylinder and conrod too.

If you put a BP6ES in a correctly tuned KH100 engine - it would show as super super lean. Install B8ES back, and it will show correct.

similarly, the daihatsu CB35 engine is a lean burn emmissions engine with higher CR than the CB23 (regular pakistan model charade engine)

It uses an NGK plug - with 7 heat range but extra projected twin electrodes to start the flame ball effectively because the charge is lean and messed with EGR. Using a BP6ES from the shop makes you think its perfectly tuned as it shows whitish electrodes - but infact the engine loses power as it knocks on high rpm and sometimes diesels while shutting down.

e.g. taking into consideration the mitsu galant 4G93 GDI engine, most high perf speed shops made a fortune from selling their owners platinum and iridium spark plugs again and again in the name of engine performance.

NOPES.

That engine is inherently prone to coking itself because of its very high CR - it produces carbon particulates like a diesel engine. When it cokes up it combustion chamber ball cavity in the piston - the plug cannot ignite the fuel mixture, as the compression ball is not centred as required. The original platinum plugs are good for 200,000 kms. but owners replaced them again and again. for the sake of speed shop placebo effect.

My remedy for the Galant GDI was replacement with a 6A12 or 6A13 from a similar Galant/Legnum - very simple engines, very smooth and very reliable - those engines are V6 - but use 3 platinum plugs for the rear bank and 3 copper ones for the front.. (which according to our PW members would be stupid)

xulfiqar bi plz explain bold context a little bit more.......i could not understand it.........

[SpoonMotorSports]

placebo Lol

[Xulfiqar]

the mitsu GDI engine has its 1800 psi fuel injector in the combustion chamber - and can even run on AFR 20:1 in some conditions, vertically swirling air is sucked in from the inlet manifold and a little fuel is sprayed into the air to cool it off, on the compression upstroke, the air is horizontally tumbled into incredible velocity - the piston has a crescent in it which houses this tight air ball, fuel is again injected into the airball - which literally becomes a bomb, and the plug ignites it. Carbonising (coking) of this engine causes stumbling and loss of running as ignition (fire) cannot happen if that airball is not centred correctly.

[isi0000]

pardon me for my illiterateness .....
@xulfiqar bi
if i consider that the ball phenomenon is also happening in my khyber and by advancing the dizzy i m making sure that before that ball of air become more and more dense by addition of gas..........plugs fire the spark and ignite that ball of fuel and newly coming gas gets sparked by the ongoing blast........is it the reason that we need to advance the dizzy for cng.....if not so the air pressure developed by the fuel ball will not allow the spark to overcome that dense air and jump it to ground electrode......and because it is more dense than petrol and require more powerful spark to blast that ball.........isnt it????

[Xulfiqar]

your khyber is not having this airball phenomenon happening - it only occurs in GDI engines. Your engine is compressing air on a flat piston top.

[Sharo53]

sir im talking about this engine which i swapped recently..

[jz]

nice informative thread

[isi0000]

your khyber is not having this airball phenomenon happening - it only occurs in GDI engines. Your engine is compressing air on a flat piston top.

why we advance the dizzy then????
and this also means that which type of plug i use no effect..........matlab k engine ka koe nakhra he nahi..........no ball phenomenon........no perfectly tuned spark........

[onlyfaith]

I need an advise..

My travelling these days is to very hot desert type areas.

The recommended spark plugs are BKR6E

can i use BKR7E in my car, to minimimize the heat.
ie a bit colder plugs..
stock engine G13B..

Reason i am asking..

I was amazed to see the spark plugs, they looked like burnt this time, around the ceramic insulator area , while the tips were like 25 as in the OP picture,....when i did tuning this time a month back...

thanking in advance for the reply..