Testing coils on a coil over plug system?

art leong · 09-12-2011, 12:01 PM

I need to check the coils. How should I do it?

NewHemi · 09-12-2011, 01:37 PM

There may be better ways.... But the best way I have found so far, is either heat/temp check on exhaust via EGT readings, or using a touchless thermometer. (bought mine at Harbor Freight for a few bucks) See if one cylinder is cooler than others.

Or if that doesnt work, then it is just brute force... replace (or if you don't have a lot of spares, rotate by putting a spare one in, and if no change, move the removed one into the next position, etc.) each one until you see a difference. No difference, no problem...

When we had problems with a coil pack, it only showed up at load, or higher rpm. At low rpm, it worked just fine.

Good luck Art!

David
The New Hemi Guy

art leong · 09-12-2011, 02:17 PM

I'm having trouble keeping it running when putting the car in gear. Have changed the converter (no help). Checked and recheck all wires and grounds. Changed the fuel filters (no help). Done a leakdown test (2% to 4%), looked at the top end, all cams and running gear look okay. Checked plug wires 27 to 29 ohms resistance, new plugs. Double checked timing.
When I drop it in gear it just gets crappy and stalls. I've data logged it and there is nothing showing that could cause this. What ever it is it seems to have gotten worse, before I could keep it running with the gas pedal but now it is almost impossible to keep running.
It seems to get worse as I work on it. Then get a bit better the next day.
There are no vacuum leaks, when I put my hand over the intake it reacts immediately.
I've played with the tune (richening it or leaning it) and it doesn't seem to change much and doesn't get better

Ed Wright · 09-12-2011, 02:48 PM

Art, good auto parts stores carry adjustable coil checkers. Very simple. If you can't find one, Snap-On used to carry them too. Their's just cost more. Set the adjustable gap to 40,000 volts. Should have a sharp blue spark. Should hear a snap each time it fires. Sounds crude maybe, but will show up a weak coil in a heart beat. Hook it to the spark plug end of the wire, you may also find a leaky plug wire.

buzzinhalfdozen · 09-12-2011, 03:15 PM

Art, if the engine runs when not in gear, how well does it run? does it sound normal, snappy throttle response? Though it is possible that you have an ign. problem, I'd doubt it would start at all with a bad coil, 4 cyl. engines with just 1 hole out tend to just barely run. Assuming you have headers, easiest way to check for dead hole is a spray water bottle, start engine let run a few minutes, then spray header tubes, should be instant sizzle on all. That will at least tell you if you've got a dead one without spending a dime. If you find that you do indeed have a dead cyl. as mentioned before swap coil with another cyl. if misfire follows you've got a bad coil, if not look at the control circuit for that coil. Good luck ans please let us know what you find. Joe

Ed Wright · 09-12-2011, 03:39 PM

A leaky wire, boot or cracked plug can show up in gear and not idling in neutral. A little de-natured alcohol or soap in the water will break the surface tension so the water will cling to the plug wire, boot & plug, instead of bead up and not cover the entire surface. That will find small leaks quicker. I prefer the alky. A jumper wire, one end grounded and the other on a thin screw driver or ice pick will help find leaks too. Run the screw driver (or ice pick) along the coil's body, plug wire, boot and plug. a good digital lab 'scope is good for checking wave forms for the control circuit. If you are used to using them you can pick out a coil with an internal problem also by using the secondary clamp. I have an old Fluke 98A that still does that kind of work really well.

buzzinhalfdozen · 09-12-2011, 04:07 PM

Ed, yes I agree putting engine under load will amplify any ign. system issues. After rereading Arts' post I noticed you said you have 27-29 ohms on the plug wires, how long are they that sure is low resistance their not by chance solid core? Other things I've seen, Engine coolant temp sensors giving incorrect temp reading causing incorrect pulse width. This one sometimes gets overlooked.What kind of fuel press. do you have? Does it put out any smoke, as in excessively rich, can you keep it running by adding fuel...ie. carb cleaner? Need to try to determine if you're dealing with an Ign. or a fuel issue. Joe

art leong · 09-12-2011, 04:16 PM

I just tried to put it in gear with the wheels off the ground. And it goes in okay the wheels turning I can give it throttle slowly and it accepts it (won't crack the throttle on the jackstands though). But when I step on the brake the engine slows down and then dies when the wheels stop, unless I work the throttle hard.
Going to try to raise and lower the fuel pressure by 5 pounds and see what happens.
Another thing I checked was the injectors and the fuel rail and switched to different manifold setups.

It is definetly a lack of power thing. But it seems to be in the lower rpm range. Once it gets up to around 4000 it runs decent.

Ed Wright · 09-12-2011, 07:06 PM

Al, make bigger fuel pressure changes. It doesn't drop cylinders? Just dies? If it does not drop cylinders it sounds rich to me. Like Joe said, the coolant temp sensor may be out of calibration. Usually if one is too lean to idle in gear they will surge some in neutral. If you have an open in the coolant temp sensor or it's circuit the ECU will consider that -40 deg F. If that ECU has a scan function check that out. If it shows -40, take a piece of a paper clip and jumper the 2 pins in the coolant temp connector. You should then see something like 300 + deg F. If you it's the sensor. If not it is a wiring issue.

Mark Ruset · 09-12-2011, 08:05 PM

Art what kind of car are you working on? I copied part of a page from a GM service manual, not sure if this will help.
This ignition system uses individual ignition module/coil assemblies for each cylinder. The engine control module (ECM) controls the spark events by transmitting the timing pulses on the ignition control (IC) circuits to the individual ignition module/coil assemblies in firing order sequence. Each ignition module/coil has the following circuits:

•

An ignition 1 voltage circuit

•

A ground circuit

•

An IC circuit

•

A low reference circuit

09-12-2011, 12:01 PM	#1
art leong VIP Member Join Date: Dec 2001 Location: Richmond Hill, Georgia Posts: 2,003 Likes: 0 Liked 1 Time in 1 Post	Testing coils on a coil over plug system? I need to check the coils. How should I do it? __________________ Art Leong 2095 SS

09-12-2011, 01:37 PM	#2
NewHemi Senior Member Join Date: Dec 2009 Location: Ohio Posts: 472 Likes: 0 Liked 1 Time in 1 Post	Re: Testing coils on a coil over plug system? There may be better ways.... But the best way I have found so far, is either heat/temp check on exhaust via EGT readings, or using a touchless thermometer. (bought mine at Harbor Freight for a few bucks) See if one cylinder is cooler than others. Or if that doesnt work, then it is just brute force... replace (or if you don't have a lot of spares, rotate by putting a spare one in, and if no change, move the removed one into the next position, etc.) each one until you see a difference. No difference, no problem... When we had problems with a coil pack, it only showed up at load, or higher rpm. At low rpm, it worked just fine. Good luck Art! David The New Hemi Guy

09-12-2011, 02:17 PM	#3
art leong VIP Member Join Date: Dec 2001 Location: Richmond Hill, Georgia Posts: 2,003 Likes: 0 Liked 1 Time in 1 Post	Re: Testing coils on a coil over plug system? I'm having trouble keeping it running when putting the car in gear. Have changed the converter (no help). Checked and recheck all wires and grounds. Changed the fuel filters (no help). Done a leakdown test (2% to 4%), looked at the top end, all cams and running gear look okay. Checked plug wires 27 to 29 ohms resistance, new plugs. Double checked timing. When I drop it in gear it just gets crappy and stalls. I've data logged it and there is nothing showing that could cause this. What ever it is it seems to have gotten worse, before I could keep it running with the gas pedal but now it is almost impossible to keep running. It seems to get worse as I work on it. Then get a bit better the next day. There are no vacuum leaks, when I put my hand over the intake it reacts immediately. I've played with the tune (richening it or leaning it) and it doesn't seem to change much and doesn't get better __________________ Art Leong 2095 SS

09-12-2011, 02:48 PM	#4
Ed Wright Veteran Member Join Date: Mar 2005 Location: Sand Springs, OK Posts: 8,132 Likes: 896 Liked 390 Times in 170 Posts	Re: Testing coils on a coil over plug system? Art, good auto parts stores carry adjustable coil checkers. Very simple. If you can't find one, Snap-On used to carry them too. Their's just cost more. Set the adjustable gap to 40,000 volts. Should have a sharp blue spark. Should hear a snap each time it fires. Sounds crude maybe, but will show up a weak coil in a heart beat. Hook it to the spark plug end of the wire, you may also find a leaky plug wire. __________________ Ed Wright 4156 SS/JA

09-12-2011, 03:15 PM	#5
buzzinhalfdozen Senior Member Join Date: Sep 2006 Location: Bellevue Ohio Posts: 984 Likes: 0 Liked 11 Times in 8 Posts	Re: Testing coils on a coil over plug system? Art, if the engine runs when not in gear, how well does it run? does it sound normal, snappy throttle response? Though it is possible that you have an ign. problem, I'd doubt it would start at all with a bad coil, 4 cyl. engines with just 1 hole out tend to just barely run. Assuming you have headers, easiest way to check for dead hole is a spray water bottle, start engine let run a few minutes, then spray header tubes, should be instant sizzle on all. That will at least tell you if you've got a dead one without spending a dime. If you find that you do indeed have a dead cyl. as mentioned before swap coil with another cyl. if misfire follows you've got a bad coil, if not look at the control circuit for that coil. Good luck ans please let us know what you find. Joe __________________ Joe Buchanan SS/BX 3117

09-12-2011, 03:39 PM	#6
Ed Wright Veteran Member Join Date: Mar 2005 Location: Sand Springs, OK Posts: 8,132 Likes: 896 Liked 390 Times in 170 Posts	Re: Testing coils on a coil over plug system? A leaky wire, boot or cracked plug can show up in gear and not idling in neutral. A little de-natured alcohol or soap in the water will break the surface tension so the water will cling to the plug wire, boot & plug, instead of bead up and not cover the entire surface. That will find small leaks quicker. I prefer the alky. A jumper wire, one end grounded and the other on a thin screw driver or ice pick will help find leaks too. Run the screw driver (or ice pick) along the coil's body, plug wire, boot and plug. a good digital lab 'scope is good for checking wave forms for the control circuit. If you are used to using them you can pick out a coil with an internal problem also by using the secondary clamp. I have an old Fluke 98A that still does that kind of work really well. __________________ Ed Wright 4156 SS/JA

09-12-2011, 04:07 PM	#7
buzzinhalfdozen Senior Member Join Date: Sep 2006 Location: Bellevue Ohio Posts: 984 Likes: 0 Liked 11 Times in 8 Posts	Re: Testing coils on a coil over plug system? Ed, yes I agree putting engine under load will amplify any ign. system issues. After rereading Arts' post I noticed you said you have 27-29 ohms on the plug wires, how long are they that sure is low resistance their not by chance solid core? Other things I've seen, Engine coolant temp sensors giving incorrect temp reading causing incorrect pulse width. This one sometimes gets overlooked.What kind of fuel press. do you have? Does it put out any smoke, as in excessively rich, can you keep it running by adding fuel...ie. carb cleaner? Need to try to determine if you're dealing with an Ign. or a fuel issue. Joe __________________ Joe Buchanan SS/BX 3117

09-12-2011, 04:16 PM	#8
art leong VIP Member Join Date: Dec 2001 Location: Richmond Hill, Georgia Posts: 2,003 Likes: 0 Liked 1 Time in 1 Post	Re: Testing coils on a coil over plug system? I just tried to put it in gear with the wheels off the ground. And it goes in okay the wheels turning I can give it throttle slowly and it accepts it (won't crack the throttle on the jackstands though). But when I step on the brake the engine slows down and then dies when the wheels stop, unless I work the throttle hard. Going to try to raise and lower the fuel pressure by 5 pounds and see what happens. Another thing I checked was the injectors and the fuel rail and switched to different manifold setups. It is definetly a lack of power thing. But it seems to be in the lower rpm range. Once it gets up to around 4000 it runs decent. __________________ Art Leong 2095 SS Last edited by art leong; 09-12-2011 at 04:45 PM.

09-12-2011, 07:06 PM	#9
Ed Wright Veteran Member Join Date: Mar 2005 Location: Sand Springs, OK Posts: 8,132 Likes: 896 Liked 390 Times in 170 Posts	Re: Testing coils on a coil over plug system? Al, make bigger fuel pressure changes. It doesn't drop cylinders? Just dies? If it does not drop cylinders it sounds rich to me. Like Joe said, the coolant temp sensor may be out of calibration. Usually if one is too lean to idle in gear they will surge some in neutral. If you have an open in the coolant temp sensor or it's circuit the ECU will consider that -40 deg F. If that ECU has a scan function check that out. If it shows -40, take a piece of a paper clip and jumper the 2 pins in the coolant temp connector. You should then see something like 300 + deg F. If you it's the sensor. If not it is a wiring issue. __________________ Ed Wright 4156 SS/JA

09-12-2011, 08:05 PM	#10
Mark Ruset Member Join Date: May 2006 Location: Southwest Florida Posts: 263 Likes: 35 Liked 43 Times in 29 Posts	Re: Testing coils on a coil over plug system? Art what kind of car are you working on? I copied part of a page from a GM service manual, not sure if this will help. This ignition system uses individual ignition module/coil assemblies for each cylinder. The engine control module (ECM) controls the spark events by transmitting the timing pulses on the ignition control (IC) circuits to the individual ignition module/coil assemblies in firing order sequence. Each ignition module/coil has the following circuits: • An ignition 1 voltage circuit • A ground circuit • An IC circuit • A low reference circuit __________________ Mark Ruset 2048 STK