How to check for bad COPs with multimeter

evolucion311 · Mar 30, 2009

Hey guys,

Can anyone explain how one would check to see if a COP is bad? I have an 02 GT that is hesitating and stumbling at low RPMs under high load in low gears but not WOT.

Specifically, what range of resistance or voltage is normal for a healthy COP, unhealthy?

COramprat · Mar 30, 2009

When mine went out it was for good. Threw a code and missed entire rpm range. But to answer the question you should attach an ohmmeter between the coil primary terminal (prongs inside connector ). It should read 0.55 ohms. Connect between secondaries (inside boot and connector). Should read 5.5K ohms.

evolucion311 · Apr 7, 2009

Update:

I tested my COPs with a multimeter. Testing at the two pin connectors resulted in a 0.9-1.2ohm resistance. Testing impedance between a pin and the bottom of the COP resulted in a 5300ohm resistance. Testing of the COP spring itself resulted in a 4ohm impedance.

The result was the same for all COPs.

The middle two COPs on the passenger side were a bit difficult to obtain a reading for when measuring the pin-spark plug impedance. The reading danced around wildly until I was able to get the usual 5300ohm reading. I suspect these two may have some problem to them but I cannot say for sure. Again, its just a guess not founded on anything solid.

I pulled the spark plugs and they look normal with a slight grey/brown color to them.

Is there another test I can perform to try and find the source of this low RPM miss?

trinity_gt · Apr 7, 2009

Keep in mind that the ohmmeter test of a COP only tests one aspect of it. The winding resistance, primary and secondary, can be tested with the ohmmeter. However, the insulation quality cannot. That is, there is insulation internal to the COP separating these windings. If the insulation has been punched through or is otherwise weak but still somewhat intact, you may get a normal resistance reading on an ohmmeter but the insulation breaks down at a few kilovolts, it can limit the spark energy available.

If you suspect a bad COP and have misfire codes for a given cylinder, check the resistance with the ohmmeter as you've done. If it checks out, swap the COP with another cylinder and see if the misfire follows the COP or stays with the cylinder. Replace any COP(s) that have a misfire following them around...

jonesy watson · Apr 7, 2009

i had the same problem on my 02, I pulled the driver side valve cover off and my timing chain was loose, the tensioner arms were wore down to nothing, changed them out and the car is alive again, also i had replaced the COP's, for that price you can get new timing set. good luck

evolucion311 · Apr 8, 2009

I have no CEL codes showing. I previously replaced my O2 sensors, again with go code, and the stumbling disappeared for a few weeks. I am thinking EGR at this point.

hotcobra03 · Apr 8, 2009

if no codes ..look into a bad spark plug also...wrong gap ,broken insulator.....bad gas can cause this issuse also... like the other guy said,,cop`s normally spit codes..good luck

evolucion311 · Apr 8, 2009

I replaced the cop boots six months ago, pulled all plugs and checked gap, no joy

evolucion311 · Apr 10, 2009

ForPointSex · Apr 11, 2009

There is no way to check if a COP is bad without a COP tester. When I had a bad COP, it OHM'ed out correct. I bought 1 COP at Autozone and swapped it out 1 by 1 until I found the bad one. It never threw any codes either.

evolucion311 · Apr 13, 2009

So did you swap the COPs one at a time and then take it for a drive each time, noting the drive quality?

98blackstallion · May 12, 2009

I just converted my 98 GT to COP and I'm having the same problem as the OP

Brute03 · May 13, 2009

ForPointSex said:
There is no way to check if a COP is bad without a COP tester. When I had a bad COP, it OHM'ed out correct. I bought 1 COP at Autozone and swapped it out 1 by 1 until I found the bad one. It never threw any codes either.

i did exactly the same thing and my faulty coil tested within spec also, so the resistance test is pretty useless if you ask me

cougar694u · Aug 17, 2009

Not a super old post, but bringin it back to get some info.

Was the issue resolved? I'm having the same issue, so I may go pick up 1 or 2 coils and start swapping them down to find the problem.

Bullitt5339 · Aug 18, 2009

I tried the swapping route, and after about a week of swapping, and not getting anywhere, I gave up and did what I should have done from the beginning. Take it to ford, and have them run a load test on the COPS. 10 minutes at the dealer, $75 later, and I knew exactly which 4 were weak. Replaced those, put new boots and springs on the others, and life was good again.

cougar694u · Aug 18, 2009

Thanks for the reply, think I'll go this route to try and figure out my issues.

How to check for bad COPs with multimeter

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