What's the best way of checking for a misfiring plug - Hot Rod Forum : Hotrodders Bulletin Board
Hotrodders.com -- Hot Rod Forum



Register FAQ Search Today's Posts Unanswered Posts Auto Escrow Insurance Auto Loans
Hot Rod Forum : Hotrodders Bulletin Board > Tech Help> Engine
User Name
Password
lost password?   |   register now

Reply
 
LinkBack Thread Tools
  #1 (permalink)  
Old 07-12-2003, 12:19 AM
Jag Daddy's Avatar
British Style with USA Muscle
 
Last photo:
Join Date: Mar 2003
Location: Valencia, California
Age: 57
Posts: 1,078
Wiki Edits: 0

Thanks: 7
Thanked 0 Times in 0 Posts
What's the best way of checking for a misfiring plug

I have an intermittant problem on my SBC, sometimes when I run the engine it seems like I have a plug not firing. Whats the best way of checking it while the engines running?

Regards
Mark

    Advertisement
Reply With Quote Quick reply to this message
Sponsored Links
Advertisement
 
  #2 (permalink)  
Old 07-12-2003, 12:54 AM
mstngjoe's Avatar
Member
 
Last photo:
Join Date: Jan 2003
Location: Oregon
Age: 63
Posts: 593
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
If it's not constant, it might be tough to spot.

If it was missing at idle for instance, you could disconnect one plug wire at a time. If it got worse, that plug & wire would not be the culprit. Only if it didn't get worse when you pulled a wire would you be able to id the bad one.

You could pull all the plugs and see if one sticks out as having a misfire as compared to the others.

You could also put a tester to the wires and check their resistance. Could be a bad wire there too.
Reply With Quote Quick reply to this message
  #3 (permalink)  
Old 07-12-2003, 01:44 AM
Member
 
Last photo:
Join Date: May 2003
Location: Shreveport LA
Age: 64
Posts: 5,103
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
If you have HEI, I wouldn't pull a plug wire. Not again, anyway. Shocked the he!! out of me, & blew the module to boot. When they said High Energy Ignition, they weren't kidding. I'd pull one wire at a time with the engine off, then put it on an old plug that was grounded to the engine. Then check rpm on a tach for comparison.
Reply With Quote Quick reply to this message
  #4 (permalink)  
Old 07-12-2003, 02:07 AM
malc's Avatar
Living At The Speed Of Life
 
Last photo:
Join Date: Jun 2003
Location: Espaņa Right Coast
Posts: 3,263
Wiki Edits: 0

Thanks: 90
Thanked 94 Times in 80 Posts
I got me a little tester,it is a cylinder with a groove cut at right angles.In this you put the plug lead and when earthed to the car body the cylinder has a light in it that flickers to let you know the plug is working.So far so good,I found the plugs were all working, but visible evidence showed nš7 was fouled,if itīs a Chevy check nš7 first.
Reply With Quote Quick reply to this message
  #5 (permalink)  
Old 07-12-2003, 03:22 AM
Member
 
Last photo:
Join Date: Jul 2003
Location: Sydney, AU
Posts: 44
Wiki Edits: 0

Thanks: 1
Thanked 0 Times in 0 Posts
You think that's bad, ever been zapped by a MSD? Your whole arm goes numb for a while!

Jim's right though, you don't want to just pull leads off with no where for the ignition energy to go as damage may result.

malc, thanks, you just reminded my that I have one of those tools somewhere. I will have to find it now.

Lots of potential problems. Coil, leads, plugs, cap, rotor. Could also be mechanical, valve etc.
Reply With Quote Quick reply to this message
  #6 (permalink)  
Old 07-12-2003, 11:19 AM
Member
 
Last photo:
Join Date: Jul 2002
Location: seattle
Posts: 182
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
try your timing light on each wire first dont pull wires it hurts like hell trust me if all lights up pull out one plug and ground it to somthing and spin motor look for spark
Reply With Quote Quick reply to this message
  #7 (permalink)  
Old 07-12-2003, 11:57 AM
mstngjoe's Avatar
Member
 
Last photo:
Join Date: Jan 2003
Location: Oregon
Age: 63
Posts: 593
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Yeah, I'll admit you guys are correct on that HEI stuff.

My bad on that.
Reply With Quote Quick reply to this message
  #8 (permalink)  
Old 07-12-2003, 12:37 PM
Gas Guzzling Democrat
 
Join Date: Jul 2002
Location: Brooklyn, NY
Posts: 79
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Quote:
Originally posted by malc
I found the plugs were all working, but visible evidence showed nš7 was fouled,if itīs a Chevy check nš7 first.
my #7 plug is really bad too, from a 350. Is this a known chevy problem?
Reply With Quote Quick reply to this message
  #9 (permalink)  
Old 07-12-2003, 01:45 PM
malc's Avatar
Living At The Speed Of Life
 
Last photo:
Join Date: Jun 2003
Location: Espaņa Right Coast
Posts: 3,263
Wiki Edits: 0

Thanks: 90
Thanked 94 Times in 80 Posts
I think itīs to do with coolant flow,that cylinder is furthest away
and runs hotter.That is why they reversed the flow of coolant,
to the heads first.
Someone will put me right!
Reply With Quote Quick reply to this message
  #10 (permalink)  
Old 07-12-2003, 01:58 PM
kiaserknife's Avatar
Member
 
Join Date: Jan 2003
Location: kansas
Posts: 60
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
just fire the engine cold let it run about 10 seconds, then dip your finger in water and touch it to the exhaust manifold by each plug.
the one that is dead or misfiring will be the coldest one, just listen for the hiss.
Reply With Quote Quick reply to this message
  #11 (permalink)  
Old 07-12-2003, 03:03 PM
malc's Avatar
Living At The Speed Of Life
 
Last photo:
Join Date: Jun 2003
Location: Espaņa Right Coast
Posts: 3,263
Wiki Edits: 0

Thanks: 90
Thanked 94 Times in 80 Posts
First find an "innocent" to do that one!
My father gave the plug lead on his Triumph motorcycle to my mother to hold,the"innocent".Then spun the magneto.
Test positive.
Reply With Quote Quick reply to this message
  #12 (permalink)  
Old 07-12-2003, 08:19 PM
lakecityg's Avatar
Member
 
Join Date: Jun 2003
Location: Lake Charles, Louisiana
Age: 35
Posts: 94
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
start your engine and let it run for a minute. then remove your oil dipstick and touch it aganist each header pipe. do that to each one. they will all smoke except for the one which is not firing. hope this helps
Reply With Quote Quick reply to this message
  #13 (permalink)  
Old 07-12-2003, 09:23 PM
BstMech's Avatar
NYOFP4RJ3CHRIS
 
Join Date: Sep 2002
Location: TN. In the corporate states of America
Age: 41
Posts: 1,552
Wiki Edits: 0

Thanks: 0
Thanked 1 Time in 1 Post
Quote:
Originally posted by kiaserknife
just fire the engine cold let it run about 10 seconds, then dip your finger in water and touch it to the exhaust manifold by each plug.
the one that is dead or misfiring will be the coldest one, just listen for the hiss.
I usually use a little spit on my fingertip when checking the header temps, the spit turns gooey and sticks a little longer. Especially after drinking a little soda or eating a candy bar.
Reply With Quote Quick reply to this message
  #14 (permalink)  
Old 07-13-2003, 04:21 AM
Member
 
Last photo:
Join Date: May 2003
Location: Shreveport LA
Age: 64
Posts: 5,103
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
You can also spray WD40 on the exhaust manifold/header by the exhaust port. It will smoke away on the ones that are firing, but not one the dead one. Might not do to well on the siamesed ones though. Works on a big-block.
Reply With Quote Quick reply to this message
  #15 (permalink)  
Old 07-13-2003, 12:08 PM
johnsongrass1's Avatar
Race it, Don't rice it!
 
Last photo:
Join Date: Jul 2002
Location: Columbia, Mo
Age: 38
Posts: 4,080
Wiki Edits: 0

Thanks: 0
Thanked 10 Times in 10 Posts
Why not just spray water from a bottle onto the header tube near the head? No one gets hurt this way.
Reply With Quote Quick reply to this message

Recent Engine posts with photos

Quick Reply
Message:
Options

Register Now

In order to be able to post messages on the Hot Rod Forum : Hotrodders Bulletin Board forums, you must first register.
Please enter your desired user name (usually not your first and last name), your email address and other required details in the form below.
User Name:
If you do not want to register, fill this field only and the name will be used as user name for your post.
Password
Please enter a password for your user account. Note that passwords are case-sensitive.
Password:
Confirm Password:
Email Address
Please enter a valid email address for yourself.
Email Address:

Log-in

Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.




Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools

Posting Rules
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On



All times are GMT -6. The time now is 03:07 AM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2014, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0 PL2
Copyright Hotrodders.com 1999 - 2012. All Rights Reserved.