Coil Questions

[Doc308]

I've been trying to track down a miss and I discovered a crack in the boot of one of my coils ( refer to photo). I presume that this would cause an arcing of the spark(?)

I have all of the coils out of the car and when I tested using a multimeter, the needlle on the Ohms gauge pegs in the direction of "0 " . The temp in the garage was around 50-60 degrees ( F). The manual states that a reading of between .9 and 1.1 should occur when the coil temp is 77 degrees.

Q-I presume that I should expect the readings to rise when the coils are warmer. How important is it that they be exactly 77 degrees ? I brought all of the coils into the house for another reading once they warm up a bit.

 

[Briank]

I would say you need one new coil.

Yes the resistance will go up as they get warmer. The needle on the ohm meter will not go as far to the left. You are using the 1X setting and are "Zeroing" the meter before measuring?

EDIT: Change 10x to 1X

 

[Sudesh]

You should also replace the seals on the coil covers and check if you have the collor in place, 2 per side.

Seals, no 22 and 20

Collor's

 

[Doc308]

Thanks for the replys so far. Yes, my seals and collars are there and are good.

Regarding the rip in the boot, would taping it up real good be an OK temporary fix until I get a new coil installed ?

 

[ftuhy]

The temperature coefficient of resistance of copper is approximately .004 per degree C. So, if the temperature drops 10C (18F), the resistance will drop by 4%. So, that .9 to 1.1 Ohms at room temperature would be 0.864 to 1.056 Ohms at 54 F vs 72 F.

That's hardly an effect you'll see on anything but a precision, calibrated, Ohmmeter.

When high voltage (20,000 volts and more on ignition systems) finds a leakage path, it usually leaves a carbon trail behind. I'm not sure a that even a good high dielectric electrical tape would help much as a temporary fix, but it couldn't hurt. As BrianK noted, order that new coil pack.

 

[Doc308]

I just bought cheap digital multimeter and , using this at indoor room temperarature, I get a "0" reading on all of my coils. What gives? Is this just a function of a not-so-sensitive multimeter ? What would a lower-than-expected reading indicate? I would guess that a higher reading, i.e. more resistance than expected, would be of greater concern (?)

 

[ftuhy]

What is the lowest resistance scale on your DMM?
Even on my good DMM, the lowest scale is 199.9 Ohms full scale. Meters are rated at accuracy of full scale, and then usually +/- one or two digits. So, with even 0.5% accuracy (1 Ohm on a 200 Ohm scale), 1.0 Ohm could read between 0.0 to 2.1 Ohms -- not much help.

Set your meter to the lowest scale possible. (For example, if it has a 200K Ohm and a 200 Ohm scale, use the 200 Ohm scale. If its auto-ranging, you get whatever range the meter decides.) Make sure your meter reads full scale - something like 1999 or all 9's - with the leads open circuit, then short the leads to each other and make sure the meter reads zero. If it reads some small residual value, that can be due to accuracy/calibration or some resisitance in the test leads. Subtract that value from the actual reading when you measure the coils.

I you had the world's most accurate meter, a resistance that is lower than specified could mean some of the windings are shorted out or shorted to ground, resulting in a reduced output voltage.

A higher than specified reading could mean a degraded internal connection or damage to the coil wire that increased its resistance - from corrosion, for example.

 

[Briank]

I get a "0" reading on all of my coils. What gives? Is this just a function of a not-so-sensitive multimeter

Yes

 

[Doc308]

OK--I set the meter to the lowest ohm-reading setting , which is 200 on this instrument. When doing this , I can't get a test reading lower than .5 when I cross the two probes together--i.e. I can't attain the 0 reading which is recommended before testing the coil. Then, in testing the coils at this setting, they all read 1.5.

So, is it reasonable to assume that the .5 test reading ( which may represent a .5 error in the instrument) may be used as a constant number in testing the coils? If so, my actual coil readings ( minus the .5 error) would then read 1.0 , which would be in specifications (.9--1.1).

(By the way, the multimeter is a $9 Cen_Tech model, which is sold at Harbour Freight )

Thanks for this on-going guidance. I really appreciate it!

 

[ftuhy]

Way to go. Of course you still have that one pack with the crack to replace.

A few more lessons and we can make you really dangerous! :biggrin::biggrin:

 

[docjohn]

Ok all together now ,sitting in lotus position .....Ooooohmmmmmm.......:biggrin:

 

[Briank]

(By the way, the multimeter is a $9 Cen_Tech model, which is sold at Harbour Freight )

I work with 480 VAC and 600 DC, people have been badlly injured using meters like that.

 

[ralph cerbone]

Way to go. Of course you still have that one pack with the crack to replace.

A few more lessons and we can make you really dangerous! :biggrin::biggrin:

Frank, tell him he is reading the res. of the leads ,

 

[ftuhy]

Ralph,

I did that in my "tutorial" (post #7) & that's what he did. He got 0.5 for the leads, 1.5 for leads + coil => 1.0 for the coil.

:biggrin:

 

[ralph cerbone]

oops ,sorry Frank,stand corrected , i still working with only one eye, haven't got my new glasses yet ,:smile:

 

[Doc308]

Thank you again, Ralph and Brian--very informative.

 

[NSXclear]

FYI
The coil packs are the same for the fronts and rears. The only difference is the FR and RR stamped on them.

I had one ripped RR coil pack boot also, after letting my nephew remove them for me. My friend had a good used one, but it had the FR written on it. It worked just the same.

Others on prime have confirmed that they are inter-changable.