Weak Spark off Coil!?? - 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> Electrical
User Name
Password
lost password?   |   register now

Reply
 
LinkBack Thread Tools
  #1 (permalink)  
Old 02-28-2009, 12:29 PM
11echo's Avatar
Old Guys Rule!...EVERYTHING!
 
Last photo:
Join Date: Jun 2003
Location: Bakersfield, CA
Age: 64
Posts: 467
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Weak Spark off Coil!??

I'm trying to get my 64 1/2 ton truck started, it has a 235 6 cyl and has been sitting for some time. It turns over but doesn't attempt to start. I checked the carb. and its getting gas. So I check the spark at the plugs ...and I'm getting spark but it's real weak (yellow). So I check it of the high tension wire off the coil and it's weak there also. I got out my voltmeter and I'm getting 12V to the positive side of the coil. And then checked the Neg. to a ground and getting 12V there. I thought it was a bad coil so I had afew extras in my shop, but after trade it out 3 times, they all have the same weak spark. FYI checked timing too and it's ok. I'm not real good with the electrical side of things, so if there are any "Pro's" out there at can give me an idea I'd appreciate it!!

    Advertisement
Reply With Quote Quick reply to this message
Sponsored Links
Advertisement
 
  #2 (permalink)  
Old 02-28-2009, 01:25 PM
Will I ever get it done?
 

Last journal entry: Rear Armrests
Last photo:
Join Date: Oct 2004
Location: Tulsa, OK
Age: 57
Posts: 1,049
Wiki Edits: 0

Thanks: 1
Thanked 3 Times in 3 Posts
It's normal to have 12 v on the neg. side of the coil if and only if the points are open. If the points are closed, the voltage from the neg. terminal to the ground should be zero.

Check the points (or better yet replace them). Same with the condenser. Make sure your dwell is set correctly. Make sure your coil wire is in good condition (might be a good time to replace all the plug wires). Make sure the pos. side of the coil is getting 9 - 10 volts while cranking.

Is the fuel stale. If so, drain it out and get some fresh gas to the carb.
Reply With Quote Quick reply to this message
  #3 (permalink)  
Old 02-28-2009, 01:51 PM
buggmann's Avatar
build it like you like them
 

Last journal entry: buggmann stilling looking
Last photo:
Join Date: Oct 2007
Location: ?????
Age: 35
Posts: 274
Wiki Edits: 2

Thanks: 0
Thanked 1 Time in 1 Post
buggmann

MY 1953 CHEVY HAD THE SAME PROB
I HAD TO CHANGE THE WIRE OFF THE
SIDE OF THE DISTRIBUTOR AND WE
HAD TO CHANGE OUT THE CONDENSER
AND THE POINTS YOU MAY WANT TO TRY
SOME OF THEES THINGS
Reply With Quote Quick reply to this message
  #4 (permalink)  
Old 02-28-2009, 02:44 PM
T-bucket23's Avatar
Hotrodders.com Moderator
 
Last wiki edit: Engine basic condition - how to check Last photo:
Join Date: Aug 2005
Location: Massachusetts
Age: 56
Posts: 5,090
Wiki Edits: 26

Thanks: 7
Thanked 102 Times in 87 Posts
If the point gap is to wide it can cause weak spark as the coil does not have enough time to build a charge.
I wrote a wiki article on ignition troubleshooting. You may want to check the steps there.
A fresh set of point and a new condenser may help but before I changed anything I would recheck your voltages and make sure the distributor is grounded well. Make sure when the points are closed the negative side is at 0 volts. Check the voltage at the coil with your meter again but use the distributor housing as the ground for your meter.
You could also disconnect the negative side of the coil and attach one end of a wire to a good ground and the other end to the negative terminal, pull it back off while watching the spark at the coil to see if it is nice and blue. This will prove the coil is capable of making a good spark.
__________________
Artificial Intelligence is no match for Natural Stupidity



Chet
Reply With Quote Quick reply to this message
  #5 (permalink)  
Old 02-28-2009, 03:00 PM
11echo's Avatar
Old Guys Rule!...EVERYTHING!
 
Last photo:
Join Date: Jun 2003
Location: Bakersfield, CA
Age: 64
Posts: 467
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
I'm getting 12.4V on the POS side and 12.4V on the NEG side of the coil (Ing. on but not cranking)...I did a continuity check thru the coil primary to secondary wiring and am getting 12.4V thru the coil. I checked at the points and am getting 12.4V there also. I replaced the high tension wire between the coil and dist. and shorted it out to check the spark ...same weak spark. AND this after I replaced the condenser and points with new ones.
I'll double check the pt. gap that could be something!??
Reply With Quote Quick reply to this message
  #6 (permalink)  
Old 02-28-2009, 04:01 PM
Member
 
Last photo:
Join Date: Jun 2007
Location: murfreesboro tn.
Posts: 731
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Quote:
Originally Posted by 11echo
I'm getting 12.4V on the POS side and 12.4V on the NEG side of the coil (Ing. on but not cranking)...I did a continuity check thru the coil primary to secondary wiring and am getting 12.4V thru the coil. I checked at the points and am getting 12.4V there also. I replaced the high tension wire between the coil and dist. and shorted it out to check the spark ...same weak spark. AND this after I replaced the condenser and points with new ones.
I'll double check the pt. gap that could be something!??
to much volts at coil , you need close to 9 or points will burn up and or stick
only should have the 12 volt while cranking , the yellow wire from starter aids in that 12 volt only when cranking .
your resistor bad or resistor wire is bad .
Reply With Quote Quick reply to this message
  #7 (permalink)  
Old 02-28-2009, 04:12 PM
Member
 
Last photo:
Join Date: Nov 2004
Location: Lakeland FL
Age: 65
Posts: 4,110
Wiki Edits: 0

Thanks: 0
Thanked 3 Times in 3 Posts
you need to check the voltage at the coil "while cranking"....

all that reading the 12.4 no load told you is the batt surface charge is good and the wiring is ok...

the starter motor does pull a gazzillion amps...
a worn starter or bad starter grounds and cables can pull the voltage to the dist down to <9V and that will make a weak spark
(also why points cars do need a parallel volts wire supply from the solonoid while cranking)

a cheat test:
hook up a 2k rpms running car with batt jumpers to yours,,,that puts full 14V and alot more amps to your starter motor and ign....

if it does start (likely it will), the next test is just hook a batt jumper from batt neg post to the starter body or close to it....
if it starts you need to improve the grounds cables and have the starter load tested at a parts store for free...

ps:
sounds like you have no ballast resistor
(ign on should read 6-9V)
that does ruin points contacts and add resistance,,,,
steal one of your wife's emory boards and sand the points contacts surfaces...

a points system is limited to only about 2-3amps input so a volts supply wire direct from the batt neg to the aluminum body of the dist can help,,,
Reply With Quote Quick reply to this message
  #8 (permalink)  
Old 02-28-2009, 04:51 PM
buggmann's Avatar
build it like you like them
 

Last journal entry: buggmann stilling looking
Last photo:
Join Date: Oct 2007
Location: ?????
Age: 35
Posts: 274
Wiki Edits: 2

Thanks: 0
Thanked 1 Time in 1 Post
buggmann

HEY MY 53 DOES HAVE A GROUND
FROM THE DISTRIBUTOR TO THE
COIL

I HAVE SEEN ON WITH A GROUND FROM
THE DISTRIBUTOR TO THE BLOCK DOES IT
HAVE TO HAVE ONE LIKE THIS
JUST ASKING THANKS BUGGMANN
Reply With Quote Quick reply to this message
  #9 (permalink)  
Old 02-28-2009, 05:22 PM
11echo's Avatar
Old Guys Rule!...EVERYTHING!
 
Last photo:
Join Date: Jun 2003
Location: Bakersfield, CA
Age: 64
Posts: 467
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
OK got her going ...but I ain't sure which of the two fixes did it!?? I looked up the point gap and it said 0.010" ...which I had it set too, but looking at data for the same engine 2 years younger it was listing 0.019" ...so I set it to this number. Then I got to thinking about the gas ...accelerator pump was working on the carb. ...I could see the gas squirting down into the throat, but I thought adding some fresh stuff wouldn't hurt. After those two fixes she fired right off.
AFTER ACTION REPORT: ...The 12.4V was the reading I was getting cold (not cranking) ...But I did check during cranking and was getting 9.8V ...so resistor wire is good ...FYI

THANKS for all the good input here guys! ...Mark
Reply With Quote Quick reply to this message
  #10 (permalink)  
Old 02-28-2009, 06:31 PM
T-bucket23's Avatar
Hotrodders.com Moderator
 
Last wiki edit: Engine basic condition - how to check Last photo:
Join Date: Aug 2005
Location: Massachusetts
Age: 56
Posts: 5,090
Wiki Edits: 26

Thanks: 7
Thanked 102 Times in 87 Posts
Point gap should be .017 to .019 or the thickness of a matchbook cover if you ever did road repairs. .010 is way to close and the points wont be open long enough to allow the field in the coil to completely collapse to generate spark.
Glad you got it running and thanks for posting back, a lot dont.
__________________
Artificial Intelligence is no match for Natural Stupidity



Chet
Reply With Quote Quick reply to this message
  #11 (permalink)  
Old 02-28-2009, 06:34 PM
T-bucket23's Avatar
Hotrodders.com Moderator
 
Last wiki edit: Engine basic condition - how to check Last photo:
Join Date: Aug 2005
Location: Massachusetts
Age: 56
Posts: 5,090
Wiki Edits: 26

Thanks: 7
Thanked 102 Times in 87 Posts
Quote:
Originally Posted by 11echo
OK got her going ...but I ain't sure which of the two fixes did it!?? I looked up the point gap and it said 0.010" ...which I had it set too, but looking at data for the same engine 2 years younger it was listing 0.019" ...so I set it to this number. Then I got to thinking about the gas ...accelerator pump was working on the carb. ...I could see the gas squirting down into the throat, but I thought adding some fresh stuff wouldn't hurt. After those two fixes she fired right off.
AFTER ACTION REPORT: ...The 12.4V was the reading I was getting cold (not cranking) ...But I did check during cranking and was getting 9.8V ...so resistor wire is good ...FYI

THANKS for all the good input here guys! ...Mark
You actually should have more voltage while cranking and less while running. The higher voltage gives a stronger spark while cranking and the lower run voltage will help keep your point healthy.
__________________
Artificial Intelligence is no match for Natural Stupidity



Chet
Reply With Quote Quick reply to this message
  #12 (permalink)  
Old 02-28-2009, 07:16 PM
1947 Chevy Coupe
 
Last photo:
Join Date: Jun 2008
Location: Las Vegas
Posts: 208
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Also, Make sure the negative terminal goes to the points and the + terminal goes to the ballast resistor. This will definitely cause weak spark if backwards.
Reply With Quote Quick reply to this message
  #13 (permalink)  
Old 02-28-2009, 07:25 PM
Will I ever get it done?
 

Last journal entry: Rear Armrests
Last photo:
Join Date: Oct 2004
Location: Tulsa, OK
Age: 57
Posts: 1,049
Wiki Edits: 0

Thanks: 1
Thanked 3 Times in 3 Posts
Quote:
Originally Posted by burnt olds
to much volts at coil , you need close to 9 or points will burn up and or stick
only should have the 12 volt while cranking , the yellow wire from starter aids in that 12 volt only when cranking .
your resistor bad or resistor wire is bad .
If you have 12 at both the positive and negative terminals, the points aren't closed. If the points aren't closed, there is no load on the resistance wire or resister, so the voltage will be full battery. When the points are closed. The negative should be zero. The coil will be a load in the circuit and the resister or resistance wire will cut the voltage at the positive terminal to about 8 - 9. This assumes key to run position without cranking.
When cranking, the voltage will still only be about 10 as the battery voltage drops during cranking.
Reply With Quote Quick reply to this message
  #14 (permalink)  
Old 03-01-2009, 09:55 AM
Member
 
Last photo:
Join Date: Nov 2004
Location: Lakeland FL
Age: 65
Posts: 4,110
Wiki Edits: 0

Thanks: 0
Thanked 3 Times in 3 Posts
LOL, a third version for the same info...

the 9.8V while cranking with the key in the start position tells you how hard the starter motor is working and/or the condition of the starter/batt/cables system...
(that's on the low side but need details {batt age, etc} other than tell you to do some PM on all the connects and add another ground cable batt neg to the starter body or close to it so it will work as long as possible and crank faster when hot)

with the motor running at idle there should be 6-9V at the coil if the ballast resistor or resistor wire and/or coil primary resistance is working to prevent prolonged arcing damaging the contacts at idle because they are moving to slow...
rev the motor to around 2500+ and the volts should climb to 11+V,,,the alternator or generator amps output over powers the resistor if it is working so you do have a intense spark while driving.....
(approx 10Kv at .032 gap)

most points systems were set up with approx/roughly 3ohms total resistance to knock down the idle volts....
most common is 1.5ohms resistance in the "ign on" supply wire and 1.5ohms resistance additional in the coil primary...
not likely your coil is original,,,you can measure the primary resistance with a meter per the attached pic'

Buggman,
you can "think of" a DC negative ground system circuit as the positive terminal is "pulling" the energy from the negative terminal to/thru the device and what's left goes onto the positive terminal...
so you want "0" ohms resistance on the negative energy supply side to the device for no voltage drop,,,,easy to do with just a copper wire from the device ground connect direct to the batt neg post....
(rather than go thru the neg cable to the motor and body and plug connects and whatever to get to the device)

doesn't really matter if the wires are in series or parallel connects or a spider web of connects from the devices,,,just as long as there is a all copper path to the batt neg post to add more grounds fields sources to everything....

on a points system, the condensor/capacitor and points ground connect is the dist body so a ground wire batt direct to the dist can only help....

headlights/heater blower/brake lights/whatever operation will often improve with a ground wire added,,,
make a long jumper and test connecting batt neg to their ground...

if nothing else, the grounds wires will help the devices last longer...
Attached Thumbnails
Click image for larger version

Name:	coil testing.JPG
Views:	416
Size:	12.4 KB
ID:	36621  
Reply With Quote Quick reply to this message
  #15 (permalink)  
Old 03-01-2009, 12:16 PM
Member
 
Last photo:
Join Date: Jan 2003
Location: tennessee
Posts: 5,909
Wiki Edits: 0

Thanks: 0
Thanked 7 Times in 7 Posts
Actually you should never see a full 12 volts at the coil as it is designed to run on about 9 volts, if you are showing 12 volts with the ignition on/engine off then you apparently do not have the proper resistance in the circuit. There is a GOOD reason for this but it is probably one of the most mis-understood functions of an ignition system. If the coil was designed to run on 12 volts it would not work very well at start-up because the starter motor load causes the circuit voltage to fall to about 8-9volts which would cause a very weak spark just when you need a strong spark the most. Fortunately the auto designers noticed this little problem , they installed a coil that would operate at peak efficiency at the 8-9 volts of the start-up load and then used a resistance circuit in the form of a resister wire or ceramic resister to drop primary voltage to the coil while the engine is running. This resister circuit is then by-passed while cranking (that's the purpose of the second ignition wire) to provide full voltage while the system is under the starter motor load. This second wire (without resistance) will also have only 8-9 volts during cranking because of starter load but would jump to full 12-13 volts when the starter is released so at that point it is then removed from the circuit when the key is released from the start position.



To sum it up a properly wired ignition will have a full time resister circuit at 8-9 volts that is hot with the key in "run" and a second non-resistance ignition wire (usually from the solenoid) that is hot ONLY during cranking to provide the proper 8-9 volts during start up. The bottom line is if you are showing a 12-13 volts with the key "on" before cranking then the resistance circuit is either not working properly or has been by-passed. This, by itself, should not cause a weak spark unless the coil has been damaged from excessive voltage. A good way to think of it is that the coil is actually only a 9 volt coil and not a 12 volt coil as it should never see 12 volts in a properly wired system.
Reply With Quote Quick reply to this message

Recent Electrical 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


Similar Threads
Thread Thread Starter Forum Replies Last Post
1991 olds 88 3800 engine coil pack fumplet Engine 28 07-19-2007 12:39 AM
No spark on 91 Buick LeSabre awg1011 Engine 7 07-05-2007 05:33 AM
No Spark While Cranking rperryman Electrical 5 06-04-2006 05:28 PM
Can't restart engine Weak spark? Ratchet Engine 4 06-19-2005 06:00 PM
Ignition Coil resistance Question Old School Nut Engine 3 06-11-2005 03:36 PM


All times are GMT -6. The time now is 07:45 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.