How to Test Spark Plug Wires

Testing spark plug wires and diagnosing bad spark plug wires. Learn how to test spark plug wires with a multimeter. If your car is stalling, idling poorly, hesitating, getting bad fuel economy, misfiring, or you have a check engine light, you should check your spark plug wires. This will also show you How To Fix P0300 random misfire codes in your car.

There are 3 main tests I go over
1. Water spray at night (look for sparks)
2. Visual inspection (cracks, burns, etc)
3. Using a multimeter (ohm meter resistance test)

How to gap a spark plug:
How to replace spark plug wires:
BMW Spark Plug Replacement:
Spark Plug Wire Looms out of Zip Ties:

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Author: phillyfinestnews


39 thoughts on “How to Test Spark Plug Wires

  1. Huge help with my 1997 Mercedes Benz. Was misfiring, traced it back to the spark plug wires! This video taught me a lot! Thank you!

  2. Hey Chris,
    Let me tell you a story lol
    My engine purs. Happy little 1.6 petrol. Got my timing belt changed and it suddenly idles like a bag of crap. There's a tick coming from the carb. The engine makes light pops, sometimes the whole car shakes. The rpm bounces around 800-900 on this ~1 second rhythm. During this time, I noticed when I change gear the rpm lingers a second before it drops. I took one lead out at a time to see if the idle changed at all, no such luck.
    Rest of the rpm range is pretty smooth, car feels roughly as powerful as it was.

    So I drive it for a few days when it starts idling at 2,000 rpm. The exhaust gases are way hot, temp is above normal. Possible hint of petrol on the exhaust too, hard to tell.

    Sometimes, I can use the clutch, slow it down and it stays down, sometimes only letting it go cold stops it.

    Now, I'm of the impression this guy screwed up the timing belt. He tells me it's the leads and the injectors.

    Any thoughts?

  3. Testing spark plug wires

    1: water mist test (at night or in the dark) spray each wire look for sparks, replace sparking wire.

    2: remove spark plug wire, and visually inspect it for cracks, burns, and corrosion, replace bad wire.

    3: using a multi meter, put it on ohms set it to 20000, test each wire you should have around 1000-10000 ohms. (Move wire and take different readings while Bending the wire if it loses a significant amount of ohms while Bending replace the wire

    Weird idle
    Radio interface
    Bad gas mileage

  4. a tried and true method ive used for decades if you have a miss is if you are afraid of getting zapped put on a leather glove and pull off each wire from the distributor to see if there is a bad wire/plug. if you pull it off if its bad it will not make a change and a consistent miss on a cylinder. now swap over a wire and see if it comes to life. if it does not- change the one plug. if it comes to life replace the plug or all of them.

    checking ohms on wires does not mean much since the resistance varies greatly even on different brands. unless you spot a wire that is WAY different than the others. many types of wires have very high resistance so the voltage has to build up to give a hotter spark–same as resistance spark plugs.

    if you have truly wild random misses also take off cap and check for moisture or conductive dust. but wires is always a top suspicion and they can and will be bad out of the box–ive had it happen and got my money back and put on odd brand and problem was gone. In the southwest the dust has iron and other stuff in it and is VERY conductive.

    if you find bad wire or plug should you replace them all? NO–not unless you are rich and you know they are old or if they LOOK old. remember the other plugs and wires are CONFIRMED good. that being said if they look old and car has issues by all means replace all plugs and wires as a start such as after buying used car.

  5. Awesome video. Worked on cars throughout the 80's into the early 90's. Carburetors, distributors, etc. Then I lost my garage due to divorce. Didn't open a hood for 20 years. When I finally did I didn't even know what I was looking at. Went to work and learned these ECM controlled engines. Now I'm doing my own work again. Thanks a lot for your awesome content!! New sub here!!

  6. Great video as always but what was the point of the tape measure? I understand greater resistance on longer wire but did I miss some equation or calculation process?

  7. Thank you so much Chris, I had a very rough idle and bucking at 70mph.
    Troubleshooted and replaced parts after parts for 3 full days with no luck.
    Just a hour ago I did your spray water test and discovered one lead was burned by the exhaust with no insulation left, and was grounding out!

    Thank you so much!!!!!

  8. Thanks a bunch. Super video. My boat engine (2 cycle) has old plug wires that have "tarnish" on the terminals. I have replaced two of them. It seemed to help my engine run a bit smoother but there is an occasional miss or rough idling. I believe I'll replace the other four wires as well.

  9. @chrisfix would add spark plug wires cause engine stalling? I spray tested my spark plug wires and they're was some pretty crazy sparking.

  10. Fantastic how-to. Thorough explanation, great demonstration of concepts and techniques. You aren't just showing how to do these tests, you are showing how to show things.

  11. Chris this is Steve from Annapolis you're outstanding I wish I was as smart as you and I was younger keep up the good work thank you for the videos it really helps me out I got to swallow my pride even though I think I know a lot mechanically

  12. I have a 1994 GMC 5.7L, the old wires had about 4500 ohms per ft (one was broke and bad) . The new wires ( all 8) had about 1500 ohms per ft. Good right?! Wrong, the new wires have only 7 mm diameter which lead to arcing at cylinder #2 right thru the new wire! ( I found the arcing like Chris Fix suggested in the dark). I had to install one of the old wires to get it to run correctly and not miss. What is also critical, is to get at least the same diameter of insulation (in my case at least 7.5 mm).

  13. Hi Chris. I have 2013 MDX. It has s misfire in cylinder 5. My error code is P0305.

    So I have done the following
    1) Swapped Coil and Plug from cylinder 5 to 6, code remained P0305
    2) Tried Seafoam, Redline S1 and Mystery Motor Oil treatment in fuel tank and Engine, issue did not resolve.
    3) I got compression test done and it showed low compression in Cylinder 5 120 PSI vs 170 PSI in cylinder 4. Then I got an auto body shop to do all 6 comparative compression test and it came compression is only 25% in cylinder 5 and approximately 75% in cylinder 6. Cylinder 1,4,2 were 100%, cylinder 3 was 92%
    4. I took it to Acura and got valve adjustment done, they said it was loose intake valve. It made engine sound alot better and I felt it got power but misfire still shows in p0305.

    I watched your video and have read forums. Now I am not sure what to try or do next. Any advice and help will be great.
    What do I try next?

  14. How could a spark plug wire have 1000 ohm to 10000 ohm and work I am not sure but it should have no or very little resistance to work

  15. Chris, what model vehicle are these plug wires for? I'm looking for a set with that type connector at the distributor for a project i'm working on. Thanks

  16. Hi Chris. I have two new sets of plug wires. One set gives me values for 2k and 20k ohms, while the other set only gives me readings for 20k ohms. What does that mean that I do not get a reading for 2k on the secondary nd set? Thks..jc

  17. Why is it that people seem to change their wires much less than the spark plugs themselves? It seems like if you need to replace your plugs then you might as well replace their wires too, no??

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