Welcome to the DoItYourself Forums!

To post questions, help other DIYers and reduce advertising (like the one on your left), join our DIY community. It's free!

Spark Check


marunr's Avatar
Member

Join Date: Mar 2003
Posts: 59
OK

08-05-04, 05:10 AM   #1  
Spark Check

Hi,
Is there a way to check the output from the spark plug wire to see if it's correct? I have a 2.3l ford engine in my boat (carburetor, points, condenser). I've developed a bad miss since changing the points, condenser and plugs, though not immediately...maybe after it ran for 4 to 6 hours. I really think it's ignition and I've checked the timing, it just seems to me to have a weak spark and I don't know what would be correct?

Thanks for any advice.

 
Sponsored Links
carguyinva's Avatar
Member

Join Date: Nov 2003
Posts: 1,147
VA

08-05-04, 05:26 AM   #2  
buy a spark tester...

...at the local parts store.

just curious...how did you set the point gap?

 
marunr's Avatar
Member

Join Date: Mar 2003
Posts: 59
OK

08-05-04, 06:48 AM   #3  
Initially I set it by cranking the motor until the cam on the distributor opened them up. Later I removed the distributor and set them, but no change in the way it runs. I also changed the coil, then put the old one back on to see if it fixed it, but no.

Thanks for the reply!

 
marunr's Avatar
Member

Join Date: Mar 2003
Posts: 59
OK

08-05-04, 06:58 AM   #4  
By the way, will a spark tester check the ouput of the wire or just check the plug?

 
carguyinva's Avatar
Member

Join Date: Nov 2003
Posts: 1,147
VA

08-05-04, 07:19 AM   #5  
Sparky

the spark tester will test the availability of spark coming from the coil thru the wire...altho now thinking about it, i'm not sure a conventional breakerless ignition coil will produce enough spark to jump a spark tester. the old time method was to put a screw driver in the end of the wire and hold it 1/4 to 3/8 of an inch from ground. if it will jump a gap like that, the wire and coil would be considered ok. the preferred method back then was by using a coil tester on an ignition scope. i've seen old timers pull wires off while running and just put their thump ober the end of the wire at any rate...

did it run poorly before you worked on it? if not, then it's likely something you did. when i asked how you set the points, i wanted to know if you used a feeler guage, guessed, used a dwell meter...a dwell meter is most accurate and you should set the points to the low side of the dwell spec range because dwell will increase as the rubbing block wears. a cheap dwell meter from a parts store is better than a feeler guage any day. also...did you set the timing with a light? don't time it by ear or feel...do it with a light or a timing meter. is there play side to side in the distributor shaft, if so, the distributor is worn out and should be replaced, this will make it miss. if you changed brands of plugs, double check the heat range. cold plugs will foul quickly and cause misfire. if you do indeed have a coil problem, the plug(s) may be fouled to the point that changing the coil will appear to make no difference

 
marunr's Avatar
Member

Join Date: Mar 2003
Posts: 59
OK

08-05-04, 08:32 AM   #6  
Thanks again. I used a feeler gauge, then a timing light. I've done this on this engine several times in the past and had no problem, so I'm assuming something else is wrong. I wonder if I got a bad set of points or condenser. Unfortunately, because it's a boat, another set costs around $40 so I hate to try it until I've tried some other options.

 
goldstar's Avatar
Forum Topic Moderator

Join Date: Oct 2002
Posts: 4,286
OH

08-05-04, 09:24 AM   #7  
Another old school check is to pull one spark plug wire and start the engine. If it runs worse, turn off the engine, replace that wire, pull the next wire, and start the engine. When you reach a wire that does not make the miss any worse than with all wires attached, you have found the bad wire. Some wires have a carbon fiber conductor which can easily break when the wires are pulled off the plugs. That sounds like what may have happened here.

 
carguyinva's Avatar
Member

Join Date: Nov 2003
Posts: 1,147
VA

08-05-04, 01:08 PM   #8  
that test does not...

...indicate a bad wire, rather a cylinder that's not working. a cylinder not working could be due to many things...mechanical AND electrical.

isolating the cylinder is a good test however

 
Desi501's Avatar
Member

Join Date: Oct 2003
Posts: 2,207

08-05-04, 02:15 PM   #9  
An easy way to test for which cylinder is dead without getting zapped is use a regular bulb testlight. Attach the ground wire to the block, put a little silicone grease on the point of the testlight and slide it under the boot at the dist cap. Do not pierce the wire, just slide it under the boot at the cap. The RPMs should drop on every one. When you get to a cylinder that's not producing power, the RPMs will not drop.

 
marunr's Avatar
Member

Join Date: Mar 2003
Posts: 59
OK

08-06-04, 03:26 AM   #10  
Thanks. If I get to the point of needing to determine if a cylinder is bad I'll try the bulb test. After running a series of checks in the Seloc manual it appears I may have a bad set of points, though they don't look bad. At any rate, went to Napa and found a set for this mallory distrubutor and will try them today. The ones on the motor now were in a tune up kit from the marina and I thought they really looked cheap, but we'll find out. I guess if that turns out to be right i'll check the coil to make sure I didn't burn up the other ones and they were just bad.

 
goldstar's Avatar
Forum Topic Moderator

Join Date: Oct 2002
Posts: 4,286
OH

08-06-04, 08:01 AM   #11  
It still sounds like a bad ignition wire on one cylinder to me. The points open and close for each cylinder. If they provide fire to all but but one cylinder, they are still trying to get spark to the dead cylinder, but something is preventing the spark from reaching the plug. Check the wires going into the distributor cap. Are they all firmly seated. Check each wire from cap to plug. Are any touching metal- the valve cover- a wire loom without a grommet - etc. Check each wire at the plugs. Are they firmly seated or just held on by the rubber boot.
You could also try the water test - spray a little water on each wire in subdued light and look for a spark jumping from wire to engine.

 
marunr's Avatar
Member

Join Date: Mar 2003
Posts: 59
OK

08-09-04, 03:51 AM   #12  
an update: I put in the points from Napa (which were a much better constructed set by the way) but to get it to run we were advanced 20 degrees too much with the timing light.(30 degrees BTDC) Then we developed a backfire. So we went back to the original set of points...apparently the rubbing block was off so slightly that even though it looked the same, it caused too long of a dwell when set at the proper gap. Anyway, I still have a rough running engine but I think I have it narrowed down. I put a kit in the carburetor but it showed little change so the carb may need to be replaced. The fuel filter is a water seperator cannister type, I'm replacing it today. I also suspect an intake manifold leak. I'll let you know. Thanks for the advice so far!

 
Search this Thread