Fixing 'Shudder/Miss' After Tune Up...
TeamRush
Active Jeeper
I am SWAMPED with 'Shudder/Miss' complaints every spring,
This spring is no exception.
*IF* You refuse to buy a good set of plug wires,
Good distributor cap/rotor,
Some reasonable spark plugs,
There is NOTHING I CAN DO FOR YOU.
The discount store $30 wires simply WILL NOT do the job you are looking to get done.
Aluminum terminals in the distributor cap WILL NOT do the job.
*IF* You want your engine to run good, then you are going to have to fork out about $100 for plug wires,
About $35 - $40 for a good quality BRASS TERMINAL cap and rotor.
Most of you don't remember, but these things shook, shuddered, missed occasionally when they were BRAND NEW,
30+ years and 100,000+ miles of engine wear later,
They are going to be LESS likely to idle/run smooth as a kitten.
Have REASONABLE expectations,
This is NOT a computer controlled, fuel injected engine with modern camshaft and machining...
-------
*IF*...
You have reasonable plug wires, which is CRITICAL to these old single coil engines,
And you have a brass terminal cap, good rotor, ect.
Then you are down mostly to 'Ground' issues,
And 'Bad' spark plugs...
GET YOUR IGNITION MODULE 'GROUNDED'!
That is the 'Black' wire from the module in '78 newer factory ignitions,
It's the 'Black' wire bolted to the fender (RUSTED/CORRODED) on '75 to '77 CJs.
GET YOUR CYLINDER HEADS 'GROUNDED'.
Bolting to the engine block and HOPING those rusted, corroded, thread sealer caked head bolts, deposit caked head gaskets are making a solid electrical contact is just a pipe dream...
Mechanical connections ARE NOT electrical connections.
Make proper electrical connections to the head and ignition module for the 'Ground' circuit back to the battery negative...
------
Then check your SPARK PLUGS!
CLEAN AND CLOSELY INSPECT THE SPARK PLUGS!
Center electrode in the cylinder end rounded over dramatically, time to replace.
Gouges in the 'Ground' electrode, especially on the sides, time to replace.
Any chipped or cracked ceramic around the center electrode, time to replace...
ANY rust in the cylinder end, around the center electrode, between electrode/ceramic and body, TIME TO REPLACE!
----
Break out the Multi-Meter,
Set it to RESISTANCE, and check the spark plugs.
No one ever tells you what the resistance SHOULD BE,
So you check all and average, look for super high or low readings.
First,
Top electrical connection (where the spark plug wires connects) to the CENTER ELECTRODE at the bottom of the spark plug,
The part that goes into the cylinder.
Do ALL your spark plugs,
Since you have 'Resistor' plugs, the 'Resistance' should be about the same, more or less about 10%
If one is MUCH HIGHER, or MUCH LOWER than the rest,
It's JUNK.
------
Second,
Check from top electrical connection, where the spark plug wire attaches,
To the plug main body, the part that screws into the engine head.
This should be ZERO, NOTHING AT ALL.
Open Circuit.
If your meter shows ANY electrical continuity between core and body,
THE SPARK PLUG IS JUNK!
-----------
WHEN YOU BUY PLUGS AT THE STORE,
DO NOT ACCEPT BOXES THAT HAVE BEEN DROPPED!
Crushed corners are a dead give away!
-----
Then GAP your plugs properly...
THIRD,
NEVER, EVER, UNDER ANY CIRCUMSTANCES,
PRY ON THE CENTER ELECTRODE TO GAP PLUGS,
Or for any other reason!
'Resistor' plugs have a VERY DELICATE carbon 'Pile' resistor built into the body, directly attached to the center electrode,
And prying WILL crack that carbon pile!
Once cracked, it will burn the crack gap wider with use,
And you wind up with misfire, weak fire, shaking, shuddering, outright missing of the engine.
IF YOU DROP A SPARK PLUG ON THE GROUND,
SCRAP IT!
It's not worth $1.99 to install an INTERNALLY cracked plug into your engine,
Just replace it and move on.
The crack WILL NOT show up on resistance tests when it's fresh,
But it WILL BURN WIDER as you use the plug,
And it will do so quickly...
Your fresh 'Tune Up' turns to
in about 500 to 1,000 miles and the engine starts shuddering/shaking at idle, starts dropping mileage, and looses power as the crack burns wider.
Just not worth the $1.99 an undamaged spark plug will cost you replace the one that got dropped...
USE needle nose pliers or dedicated gapping tool that DOES NOT pry on the center electrode to gap the plugs.
DO NOT HAMMER ON THE 'GROUND' ELECTRODE TO CLOSE UP SPARK GAP!
Hammering on the 'Ground' electrode is the same as dropping the plug on the ground, or prying on the center electrode!
I don't care how you saw your 'Mechanic' do things,
JUST DON'T DO IT...
--------
Two more things,
When you reinstall the cleaned, checked, gapped plugs,
USE COPPER 'NEVER-SEIZE' on the threads!
(zinc is OK if you can't find copper, but copper is better)
The 'GREASE' in the Never-Sieze keep the heads/plug body from RUSTING,
This makes for a more SOLID 'GROUND' contact with the head.
It also makes for an environmental seal in the plug threads, helping keep moisture/corrosives out of the threads.
MAKE SURE THE PLUG WIRES 'SNAPS' or PUSHES SOLIDLY onto the plugs when you reconnect the plug wires!
A dab of dielectric grease in the BOOT,
Both sides! Plug and Wires sides, will help keep moisture out of the electrical connection, and you won't have corrosion problems,
Pulling the boot back slightly, making sure you have a SOLID electrical contact,
Then slipping the boot down into place will often guarantee you have a solid plug connection.
Giving plug wire terminals a 'Pinch' to tighten them up BEFORE you install on the plug will help keep a good tight electrical connection.
------
*IF*...
You do these things,
The IGNITION shudder, occasional miss will be SERIOUSLY minimized or eliminated...
Then you can start looking for 'Issues' other places,
Sloppy timing chains, (a HUGE cause of 'Shudder' issues),
Fuel metering issues, stuff like that...
This is all SIMPLE stuff,
Real basics that for some reason get overlooked...
So I hope this helps someone chasing a 'Shudder'!
This spring is no exception.
*IF* You refuse to buy a good set of plug wires,
Good distributor cap/rotor,
Some reasonable spark plugs,
There is NOTHING I CAN DO FOR YOU.
The discount store $30 wires simply WILL NOT do the job you are looking to get done.
Aluminum terminals in the distributor cap WILL NOT do the job.
*IF* You want your engine to run good, then you are going to have to fork out about $100 for plug wires,
About $35 - $40 for a good quality BRASS TERMINAL cap and rotor.
Most of you don't remember, but these things shook, shuddered, missed occasionally when they were BRAND NEW,
30+ years and 100,000+ miles of engine wear later,
They are going to be LESS likely to idle/run smooth as a kitten.
Have REASONABLE expectations,
This is NOT a computer controlled, fuel injected engine with modern camshaft and machining...
-------
*IF*...
You have reasonable plug wires, which is CRITICAL to these old single coil engines,
And you have a brass terminal cap, good rotor, ect.
Then you are down mostly to 'Ground' issues,
And 'Bad' spark plugs...
GET YOUR IGNITION MODULE 'GROUNDED'!
That is the 'Black' wire from the module in '78 newer factory ignitions,
It's the 'Black' wire bolted to the fender (RUSTED/CORRODED) on '75 to '77 CJs.
GET YOUR CYLINDER HEADS 'GROUNDED'.
Bolting to the engine block and HOPING those rusted, corroded, thread sealer caked head bolts, deposit caked head gaskets are making a solid electrical contact is just a pipe dream...
Mechanical connections ARE NOT electrical connections.
Make proper electrical connections to the head and ignition module for the 'Ground' circuit back to the battery negative...
------
Then check your SPARK PLUGS!
CLEAN AND CLOSELY INSPECT THE SPARK PLUGS!
Center electrode in the cylinder end rounded over dramatically, time to replace.
Gouges in the 'Ground' electrode, especially on the sides, time to replace.
Any chipped or cracked ceramic around the center electrode, time to replace...
ANY rust in the cylinder end, around the center electrode, between electrode/ceramic and body, TIME TO REPLACE!
----
Break out the Multi-Meter,
Set it to RESISTANCE, and check the spark plugs.
No one ever tells you what the resistance SHOULD BE,
So you check all and average, look for super high or low readings.
First,
Top electrical connection (where the spark plug wires connects) to the CENTER ELECTRODE at the bottom of the spark plug,
The part that goes into the cylinder.
Do ALL your spark plugs,
Since you have 'Resistor' plugs, the 'Resistance' should be about the same, more or less about 10%
If one is MUCH HIGHER, or MUCH LOWER than the rest,
It's JUNK.
------
Second,
Check from top electrical connection, where the spark plug wire attaches,
To the plug main body, the part that screws into the engine head.
This should be ZERO, NOTHING AT ALL.
Open Circuit.
If your meter shows ANY electrical continuity between core and body,
THE SPARK PLUG IS JUNK!
-----------
WHEN YOU BUY PLUGS AT THE STORE,
DO NOT ACCEPT BOXES THAT HAVE BEEN DROPPED!
Crushed corners are a dead give away!
-----
Then GAP your plugs properly...
THIRD,
NEVER, EVER, UNDER ANY CIRCUMSTANCES,
PRY ON THE CENTER ELECTRODE TO GAP PLUGS,
Or for any other reason!
'Resistor' plugs have a VERY DELICATE carbon 'Pile' resistor built into the body, directly attached to the center electrode,
And prying WILL crack that carbon pile!
Once cracked, it will burn the crack gap wider with use,
And you wind up with misfire, weak fire, shaking, shuddering, outright missing of the engine.
IF YOU DROP A SPARK PLUG ON THE GROUND,
SCRAP IT!
It's not worth $1.99 to install an INTERNALLY cracked plug into your engine,
Just replace it and move on.
The crack WILL NOT show up on resistance tests when it's fresh,
But it WILL BURN WIDER as you use the plug,
And it will do so quickly...
Your fresh 'Tune Up' turns to
in about 500 to 1,000 miles and the engine starts shuddering/shaking at idle, starts dropping mileage, and looses power as the crack burns wider.Just not worth the $1.99 an undamaged spark plug will cost you replace the one that got dropped...
USE needle nose pliers or dedicated gapping tool that DOES NOT pry on the center electrode to gap the plugs.
DO NOT HAMMER ON THE 'GROUND' ELECTRODE TO CLOSE UP SPARK GAP!
Hammering on the 'Ground' electrode is the same as dropping the plug on the ground, or prying on the center electrode!
I don't care how you saw your 'Mechanic' do things,
JUST DON'T DO IT...
--------
Two more things,
When you reinstall the cleaned, checked, gapped plugs,
USE COPPER 'NEVER-SEIZE' on the threads!
(zinc is OK if you can't find copper, but copper is better)
The 'GREASE' in the Never-Sieze keep the heads/plug body from RUSTING,
This makes for a more SOLID 'GROUND' contact with the head.
It also makes for an environmental seal in the plug threads, helping keep moisture/corrosives out of the threads.
MAKE SURE THE PLUG WIRES 'SNAPS' or PUSHES SOLIDLY onto the plugs when you reconnect the plug wires!
A dab of dielectric grease in the BOOT,
Both sides! Plug and Wires sides, will help keep moisture out of the electrical connection, and you won't have corrosion problems,
Pulling the boot back slightly, making sure you have a SOLID electrical contact,
Then slipping the boot down into place will often guarantee you have a solid plug connection.
Giving plug wire terminals a 'Pinch' to tighten them up BEFORE you install on the plug will help keep a good tight electrical connection.
------
*IF*...
You do these things,
The IGNITION shudder, occasional miss will be SERIOUSLY minimized or eliminated...
Then you can start looking for 'Issues' other places,
Sloppy timing chains, (a HUGE cause of 'Shudder' issues),
Fuel metering issues, stuff like that...
This is all SIMPLE stuff,
Real basics that for some reason get overlooked...
So I hope this helps someone chasing a 'Shudder'!
Last edited:
