Found something interesting when I changed plugs
Thread Starter
Melting Slicks
Joined: May 2000
Posts: 2,498
Likes: 4
From: Brentwood TN
Found something interesting when I changed plugs
My toy has 93K on it and had the original 41-953 platinum plugs that were gapped at 0.060" when new. The old plugs had gaps ranging from 0.072" to 0.080" (the car was running fine - 31mpg interstate). Is this 20 - 33% larger than specified gap typical or unusual?
All the plugs except #8 were the expected blackish dark brown color. Number 8 was slightly tannish almost white color. I think #8 cylinder is running lean, maybe due to an injector on the way to failing.'
Is there a home-garage way to check the injector for partial plugging?
A final question about the plug -
Afterd swappin out plugs the engine seems to want to hunt around idle speed and idles roughly for a few seconds after coming off the throttle. Is the pulg gap enough of a firing and performance issue that the ECM needs to relearn the spark plug firing and timing since the smaller gap means the engine may be firing a few degrees sooner now than before and effedtively putting in more timing. I'm hoping it learns its way out of this in 25 miles or so.
Charlie
All the plugs except #8 were the expected blackish dark brown color. Number 8 was slightly tannish almost white color. I think #8 cylinder is running lean, maybe due to an injector on the way to failing.'
Is there a home-garage way to check the injector for partial plugging?
A final question about the plug -
Afterd swappin out plugs the engine seems to want to hunt around idle speed and idles roughly for a few seconds after coming off the throttle. Is the pulg gap enough of a firing and performance issue that the ECM needs to relearn the spark plug firing and timing since the smaller gap means the engine may be firing a few degrees sooner now than before and effedtively putting in more timing. I'm hoping it learns its way out of this in 25 miles or so.
Charlie
Le Mans Master
Joined: Feb 2002
Posts: 6,937
Likes: 21
From: Waldorf MD
Did you notice the platinum "pucks" on the plugs? It is usual for some of those to fall off, that would give you an high gap.
With the voltage available, I am not surprised you noticed no difference.
Make sure you have not broken any wires. I had no problems after replacing my plugs at about 85,000 miles.
Run a can of Techron through it, will help clogged injector.
With the voltage available, I am not surprised you noticed no difference.
Make sure you have not broken any wires. I had no problems after replacing my plugs at about 85,000 miles.
Run a can of Techron through it, will help clogged injector.
Thread Starter
Melting Slicks
Joined: May 2000
Posts: 2,498
Likes: 4
From: Brentwood TN
Did you notice the platinum "pucks" on the plugs? It is usual for some of those to fall off, that would give you an high gap.
With the voltage available, I am not surprised you noticed no difference.
Make sure you have not broken any wires. I had no problems after replacing my plugs at about 85,000 miles.
Run a can of Techron through it, will help clogged injector.
With the voltage available, I am not surprised you noticed no difference.
Make sure you have not broken any wires. I had no problems after replacing my plugs at about 85,000 miles.
Run a can of Techron through it, will help clogged injector.
There were no pucks on the plugs. Curiously, the tips were pointed much like the iridium plug, not cylindrical.
The car idled smoothly before swapping the plugs and levels out after a few seconds of hunting between maybe 600 and 900 rpm. I had pulled the small diameter tube vacuum line that goes into the air bridge just in front of the throttle body but it is solid. While I'm on it, what is that vacuum line for or what does it do?
I'll take the car out tomorrow for a 30 minute trip or so and see if that makes any difference.
Charlie
Safety Car
Joined: Aug 2000
Posts: 4,933
Likes: 30
From: San Rafael CA
Which plugs, and at what gap, did you install ?????
The PCM does control a number of issues concerning the firing of the plugs ... dwell time being a big part of it, along with when it "fires the plug" by cutting off the voltage to the primary circuit in the coil.
The PCM (Powertrain Control Module) can be forced to do an idle relearn .... that may be what you need.
The PCM does control a number of issues concerning the firing of the plugs ... dwell time being a big part of it, along with when it "fires the plug" by cutting off the voltage to the primary circuit in the coil.
The PCM (Powertrain Control Module) can be forced to do an idle relearn .... that may be what you need.
Team Owner
Joined: Mar 2001
Posts: 21,325
Likes: 3,841
From: small town in S.E Pa. PA
St. Jude Donor '03-'04
More than likely as my good friend Oldvetter has said...some of the pucks or maybe all have fallen off... as time goes on the ECM makes slight adjustments as the engine conditions change... You shocked the system with new plugs and wires...it will correct itself on its own, or you can do an idle relearn...
No reason for me to be here Chuck.. seems you have it all covered.
No reason for me to be here Chuck.. seems you have it all covered.
Thread Starter
Melting Slicks
Joined: May 2000
Posts: 2,498
Likes: 4
From: Brentwood TN
AC iridium 43-985 plugs gapped .040", checked and verified on all eight. A couple were .042 and a light tap on the handle of my ratchet closed it up to .040.
I'm thinking a gap that is nearly half that of the plugs that were in the engine have to be firing a milisecond or three sooner than they were before. I'll post what the result of driving it is.
Charlie
I'm thinking a gap that is nearly half that of the plugs that were in the engine have to be firing a milisecond or three sooner than they were before. I'll post what the result of driving it is.
Charlie
Tech Contributor
Joined: Dec 2006
Posts: 10,962
Likes: 29
From: Van Buren Arkansas
Wounded Warrior Escort '11
I know there is a PCM update for the plugs...its supposed to allow for differences in the plugs along with lots of other things.
Last edited by dgrant3830; Jan 12, 2008 at 11:12 PM.
Safety Car
Joined: Aug 2000
Posts: 4,933
Likes: 30
From: San Rafael CA
This is the engine "Idle Learn Procedure" from the 2001 Service Manual ... can't hurt to try ... First step for either transmission is disconnect battery for 5 minutes (remove negative cable (ground) from battery), then re-connect ... then ....
Automatic ....
Turn OFF the ignition
Turn OFF the A/C controls
Set Parking brake and block wheels
Start engine
Ensure engine coolant temperature is 176 degrees or higher
Shift transmission to DRIVE
Allow engine to idle for at least 5 minutes
Shift transmission to PARK
Allow engine to idle for at least 5 minutes
Turn OFF the engine for more than 30 seconds ...
Manual ...
Turn OFF the ignition
Turn OFF the A/C controls
Set Parking brake and block wheels
Place transmission in NEUTRAL
Start engine
Ensure engine coolant temperature is 176 degrees or higher
Allow engine to idle for at least 5 minutes
Turn OFF the engine for more than 30 seconds ...
Automatic ....
Turn OFF the ignition
Turn OFF the A/C controls
Set Parking brake and block wheels
Start engine
Ensure engine coolant temperature is 176 degrees or higher
Shift transmission to DRIVE
Allow engine to idle for at least 5 minutes
Shift transmission to PARK
Allow engine to idle for at least 5 minutes
Turn OFF the engine for more than 30 seconds ...
Manual ...
Turn OFF the ignition
Turn OFF the A/C controls
Set Parking brake and block wheels
Place transmission in NEUTRAL
Start engine
Ensure engine coolant temperature is 176 degrees or higher
Allow engine to idle for at least 5 minutes
Turn OFF the engine for more than 30 seconds ...
Last edited by BlackZ06; Jan 12, 2008 at 11:49 PM.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Top 10 Most Expensive Corvettes Ever Sold on Bring A Trailer
Brett Foote
10 Things Every Corvette Owner Needs (2026 Edition)
Michael S. Palmer
8 Most "Only Corvette Owners Understand" Quirks and Problems
Pouria Savadkouei
10 Reasons the C6 Z06 is Still A Performance Benchmark After 20 Years
Joe Kucinski
How Much Horsepower Every Corvette Engine "LOST" in 1972
Joe Kucinski
Top 10 DOs and DON'Ts for Protecting Your Convertible Top!
Michael S. Palmer
Top 10 Most Explosive Corvettes Ever Made: Power-to-Weight Ratio Ranked!
Joe Kucinski
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Thread Starter
Melting Slicks
Joined: May 2000
Posts: 2,498
Likes: 4
From: Brentwood TN
Iridiums come gapped at 0.040 out of the box. Two were gapped at 0.042 and I tapped them lightly to close up to 0.040 because I'm ****. 
Hadn't heard about a firmware update. I'll call a dealer to see if they can provide the parts.
Charlie
Hadn't heard about a firmware update. I'll call a dealer to see if they can provide the parts.
Charlie
Le Mans Master
Joined: Mar 2002
Posts: 5,955
Likes: 161
From: PNW
If the other end of that line goes to a nipple on the RH valve cover, then you're talking about the fresh air make-up line for the PCV system.
Tech Contributor
Joined: Dec 2006
Posts: 10,962
Likes: 29
From: Van Buren Arkansas
Wounded Warrior Escort '11
It isn't a part for the firmware update rather them connecting the Tech2 to the car and performing the updates. Before going to that, chances are more that you have a bad wire or just need the idle relearn to be done. A quick and simple method for bad wires is to turn on the AM radio and dial to a frequency where there is no station then listen for spark noise that matches the RPM of the engine. If you hear it, you need wires.
Thread Starter
Melting Slicks
Joined: May 2000
Posts: 2,498
Likes: 4
From: Brentwood TN
Le Mans Master
Joined: Aug 2005
Posts: 5,375
Likes: 328
From: CA.
St. Jude Donor '13-'14-'15
The small vacuum line on the air bridge is used to make adjustments to your fuel presuure-it should go to your pressure regulator on the other end-It adds pressure with increased airflow or load--shouldn't affect the idle issue--
Thread Starter
Melting Slicks
Joined: May 2000
Posts: 2,498
Likes: 4
From: Brentwood TN
Found the problem. It turns out if the MAF is loose from the bridge enough to allow unmetered air to flow to the engine the ECM gets confused. Stupid computer. Reattached the MAF to the bridge and it works just fine.
Charlie
Charlie
Thread Starter
Melting Slicks
Joined: May 2000
Posts: 2,498
Likes: 4
From: Brentwood TN