Checking spark plug wire ohms

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Checking spark plug wire ohms

Post  f250mike on August 11th 2010, 4:12 pm

Last Wednesday night at the track my truck was missing. So I changed spark plugs, cleaned out the carb, and checked the ohms of the plug wires.
I don't know what is a good or bad reading. Can someone let me know if these Ohms are ok?
cyl# Ohms
1 - 99
2 - 114
3 - 139
4 - 131
5 - 126
6 - 124
7 - 126
8 - 134
The wires are MSD 8.5mm super conductors.
mike

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Re: Checking spark plug wire ohms

Post  Lem Evans on August 11th 2010, 5:06 pm

MSD says 50 ohms per foot.

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Re: Checking spark plug wire ohms

Post  bbf-falcon on August 11th 2010, 5:23 pm

The guy's at Firecore50.com has alot of info on this subject

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Re: Checking spark plug wire ohms

Post  kjett on August 11th 2010, 9:40 pm

Like Lem said, 50 ohms per foot, so figure the length of each wire and mutiply by 50. For example, a 2' wire should read around 100ohms, 3' should be 150 ohms, and so on.

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Re: Checking spark plug wire ohms

Post  G-Code on August 11th 2010, 11:14 pm

I forget the readings but some years ago my engine was down on R's (150-200) and felt sluggish. Two trips to the river and a bunch of changes. Decided to the check the ohms and three wires were 45-60% off from the other 5. Got a new wire set and back to normal.

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Re: Checking spark plug wire ohms

Post  Frank Kramer on August 12th 2010, 3:37 pm

From MSD Promag site:


6. How often should spark plug wires be replaced?

Spark plug wires are a consumable item like oil in the engine, they should be changed on a frequent schedule that is determined by how often they run. A routine schedule of cleaning, inspecting and checking the resistance of the wires should be done as a routine maintenance program of the car. Some teams even keep a logbook of the resistance of when the wires were built to compare after running.

Some of the most common problems can come for the actual wire crimps that can be resolved by re-crimping the terminals or replacing the terminal. The terminals are designed as a conductor crimp so the conductor does not have to be bent over which can fracture or damage the conductor making it read a higher resistance than normal.






The resistance should be 40 to 50 ohms per foot once the measurement is noted that value should not change. The only other facture that can not be checked is the outside jacket, other than cleaning and a visual inspection looking for abrasion, cuts and pinholes, the jacket will deteriorate in time due to the amount of energy being transferred through the wires.

The coil wire should be replaced often as it gets hit 8 times more than the other wires. Big budget teams replace wire set about every third race while most others would replace them every 6th to7th race. There really is no gauge as to how often to replace wire set. Remember the wires are the actual delivery system of the spark energy to the spark plug that will affect a performance of the engine if not up to par.



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Re: Checking spark plug wire ohms

Post  f250mike on August 12th 2010, 7:12 pm

Thanks guys.
I'll have to go measure the wires and do the math.
It may be time for new wires.

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Re: Checking spark plug wire ohms

Post  Diggindeeper on August 15th 2010, 12:16 pm

G-Code wrote:I forget the readings but some years ago my engine was down on R's (150-200) and felt sluggish. Two trips to the river and a bunch of changes. Decided to the check the ohms and three wires were 45-60% off from the other 5. Got a new wire set and back to normal.

G-

higher ohms are not a good thing. ohms are opposition to current flow.

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