reading Spark Plugs. How accurate?
Thread Starter
Le Mans Master
Joined: Feb 1999
Posts: 9,935
Likes: 38
From: South Carolina
St. Jude Donor '03 & '05
reading Spark Plugs. How accurate?
I have been doing allot of datalogging, with a wideband (right side pipe only)and a TTS datasmaster program. Well, I added fuel, and removed fuel , did VEMAster etc just to see what changes. Well the Wideband was usually around 14.2 cruising, and at WOT around 13.1-13.2 ish, depending on my playing with the fuel etc. I did get it down to 12.7-12.9 though eventually, but my injectors are at 93%ish.
But after all these trials etc I noticed the plugs look good, with slightly tan to dark tan on all of them. But the datalogs say its pulling fuel on the engine, on the left side. But, like I said, plugs are good.
So, if you arent datalogging, are your plugs telling you everything is okay if there the right color?
I know I had an IAC issue and some other little possible issues to mess with the left side, but the plugs are the end result, correct?
But after all these trials etc I noticed the plugs look good, with slightly tan to dark tan on all of them. But the datalogs say its pulling fuel on the engine, on the left side. But, like I said, plugs are good.
So, if you arent datalogging, are your plugs telling you everything is okay if there the right color?
I know I had an IAC issue and some other little possible issues to mess with the left side, but the plugs are the end result, correct?
Le Mans Master
Joined: Feb 2005
Posts: 5,146
Likes: 3
From: The Motor City
The plugs are a good reference point for idle, mid range etc. For WOT, the motor would really need to be shut down right after it is run, and then inspect the plug's insulater down below the threads. There are other considerations on spark plug reading inc. ground strap, flat spot on top of threads etc. this is a decent description:
http://www.4secondsflat.com/Spark_plug_reading.html
when you say "pulling fuel away" I guess you mean the INT. (short term counts) ...but where is the BLM currently?
To me 95% DC at WOT doesn't bother me on mine because it is only there for a brief time (less than a sec.) at around 6-62k.
http://www.4secondsflat.com/Spark_plug_reading.html
when you say "pulling fuel away" I guess you mean the INT. (short term counts) ...but where is the BLM currently?
To me 95% DC at WOT doesn't bother me on mine because it is only there for a brief time (less than a sec.) at around 6-62k.
Last edited by mseven; Nov 1, 2007 at 10:01 AM.
Melting Slicks
Joined: Feb 2006
Posts: 2,753
Likes: 15
From: backwoods upstate ny
B/s
this is a decent description:http://www.4secondsflat.com/Spark_plug_reading.html
truth;
plugs are a ''sample'' of what ''went on'' in the combustion chamber for the last few seconds prior to shut-down, except for serious detonation damage (black ''pepper'' specks on the center porcelain) which will show longer.
if your ''unleaded gas'' motor colors the center porcelain tan in a short time, you are either running extremely rich or getting a small oil burn.
''burn line'' on the ground leg will move with changes of fuel mixture, or spark lead, or operating condition.
would need a book to fully explain ''plug reading'', can't do here...short version -- look at your plugs for ''danger'' signs (''pepper specks'' or ''second ring'' in porcelain around center electrode)... look to o2 sensor reads, exh temps, elapsed times, for tuning.
Thread Starter
Le Mans Master
Joined: Feb 1999
Posts: 9,935
Likes: 38
From: South Carolina
St. Jude Donor '03 & '05
The plugs are a good reference point for idle, mid range etc. For WOT, the motor would really need to be shut down right after it is run, and then inspect the plug's insulater down below the threads. There are other considerations on spark plug reading inc. ground strap, flat spot on top of threads etc. this is a decent description:
http://www.4secondsflat.com/Spark_plug_reading.html
when you say "pulling fuel away" I guess you mean the INT. (short term counts) ...but where is the BLM currently?
To me 95% DC at WOT doesn't bother me on mine because it is only there for a brief time (less than a sec.) at around 6-62k.
http://www.4secondsflat.com/Spark_plug_reading.html
when you say "pulling fuel away" I guess you mean the INT. (short term counts) ...but where is the BLM currently?
To me 95% DC at WOT doesn't bother me on mine because it is only there for a brief time (less than a sec.) at around 6-62k.
I guess I can doa WOT and shut her down and see what the plugs look like.
Thread Starter
Le Mans Master
Joined: Feb 1999
Posts: 9,935
Likes: 38
From: South Carolina
St. Jude Donor '03 & '05
''4 sec'' descript is indecent, sprinkles a few truths amongst a load of fertilizer...note that the article shows plug coloring when using LEADED race gas, unleaded street fuels do not color the plugs as those pics show....pics of the cooked ''hemi'' are of a blown alky engine that may have died from poor cooling, wrong plug heat range, lean-out due to undersized fuel lines, etc/etc/etc--only applicable to street in very broadest terms.
truth;
plugs are a ''sample'' of what ''went on'' in the combustion chamber for the last few seconds prior to shut-down, except for serious detonation damage (black ''pepper'' specks on the center porcelain) which will show longer.
if your ''unleaded gas'' motor colors the center porcelain tan in a short time, you are either running extremely rich or getting a small oil burn.
''burn line'' on the ground leg will move with changes of fuel mixture, or spark lead, or operating condition.
would need a book to fully explain ''plug reading'', can't do here...short version -- look at your plugs for ''danger'' signs (''pepper specks'' or ''second ring'' in porcelain around center electrode)... look to o2 sensor reads, exh temps, elapsed times, for tuning.
truth;
plugs are a ''sample'' of what ''went on'' in the combustion chamber for the last few seconds prior to shut-down, except for serious detonation damage (black ''pepper'' specks on the center porcelain) which will show longer.
if your ''unleaded gas'' motor colors the center porcelain tan in a short time, you are either running extremely rich or getting a small oil burn.
''burn line'' on the ground leg will move with changes of fuel mixture, or spark lead, or operating condition.
would need a book to fully explain ''plug reading'', can't do here...short version -- look at your plugs for ''danger'' signs (''pepper specks'' or ''second ring'' in porcelain around center electrode)... look to o2 sensor reads, exh temps, elapsed times, for tuning.
Safety Car
Joined: May 2002
Posts: 4,659
Likes: 82
From: Toronto ontario
[QUOTE=mseven;1562562972]The plugs are a good reference point for idle, mid range etc. For WOT, the motor would really need to be shut down right after it is run..QUOTE]
I couldn't have said it better. Remember that after a wot run if you idle the mixture may color the plugs to look like it's running better.
Take your tools with you , grab a coffee and go for a nice wot run and shut her off asap. Pull over wait till it cools and then read the plugs. I've done it and I was surprised as hell how different they looked than even idling for 20 seconds after a wot run.
I couldn't have said it better. Remember that after a wot run if you idle the mixture may color the plugs to look like it's running better.
Take your tools with you , grab a coffee and go for a nice wot run and shut her off asap. Pull over wait till it cools and then read the plugs. I've done it and I was surprised as hell how different they looked than even idling for 20 seconds after a wot run.
Le Mans Master
Joined: Feb 2005
Posts: 5,146
Likes: 3
From: The Motor City
Steve, from the blm you've shown I would methodically find the richer areas and continue tweaking the tune. Is the DC hitting 95%+ before 6k at wot ?
Thread Starter
Le Mans Master
Joined: Feb 1999
Posts: 9,935
Likes: 38
From: South Carolina
St. Jude Donor '03 & '05
I don't find this to always be the case. What I've found in tuning is that extremely rich will black soot the insulater and flat above the threads. Somewhat on the rich side (blm 124ish) will create tan, and with additional tuning and attaining 128 blm, it will usually becomes a light gray.
Steve, from the blm you've shown I would methodically find the richer areas and continue tweaking the tune. Is the DC hitting 95%+ before 6k at wot ?
Steve, from the blm you've shown I would methodically find the richer areas and continue tweaking the tune. Is the DC hitting 95%+ before 6k at wot ?
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Melting Slicks
Joined: Feb 2006
Posts: 2,753
Likes: 15
From: backwoods upstate ny
I don't find this to always be the case. What I've found in tuning is that extremely rich will black soot the insulater and flat above the threads. Somewhat on the rich side (blm 124ish) will create tan, and with additional tuning and attaining 128 blm, it will usually becomes a light gray.
''semantics'' issue of ''extremely''....''pouring'' gas in WILL coat the whole plug in soot, richer than desireable will color up tan...light grey is satisfactory...''snow white'' is suspect of lean, check frequently.when in doubt, as when starting tune, rich side is safer for the engine, but not excessively rich which will ''wash'' the cylinder walls and cause premature ring wear.
Le Mans Master
Joined: Feb 2005
Posts: 5,146
Likes: 3
From: The Motor City
''semantics'' issue of ''extremely''....''pouring'' gas in WILL coat the whole plug in soot, richer than desirable will color up tan...light grey is satisfactory...''snow white'' is suspect of lean, check frequently.
when in doubt, as when starting tune, rich side is safer for the engine, but not excessively rich which will ''wash'' the cylinder walls and cause premature ring wear.
when in doubt, as when starting tune, rich side is safer for the engine, but not excessively rich which will ''wash'' the cylinder walls and cause premature ring wear.
It is true the whole plug reading can take up volumes, but the above insulator visual you stated is a good place to start, as it particularly shows off idle to midrange operation. Additionally I look at the g. strap, and top thread surface for a general understanding that the software data (bpw, timing, blm, int., 02 etc.etc.) matches what I see as a product (to some degree) of combustion, and that there are no big problems that I cannot seeing in scans.
Upgrading the inj. size to around 40+ or changing fp. would help lowering the DC. If your plan is to do either, only downside is that you will end up going through the tune again to get the bl's back in-line.
