I also took a look at the other posts you recomended and they look pretty good!!! Thanks a lot for the extra info.
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| How do I bench test a coil? https://slantsix.org/forum/viewtopic.php?t=49802 |
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| Author: | 74A1Swinger [ Fri Sep 14, 2012 5:53 pm ] |
| Post subject: | How do I bench test a coil? |
Hi I'm having coil problems and have used a test from aa1car.com to bench test 2 new coils and they both have shown to be shorted out internally. I not sure how this could be and am wondering if I'm doing something wrong or if I really have 2 bad coils in a row. Any help would be great at this point! |
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| Author: | SlantSixDan [ Fri Sep 14, 2012 6:37 pm ] |
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You almost certainly don't have two bad coils in a row -- sounds like you have faulty information from the site you've been looking at. What kind of test does that site prescribe, and what have you been doing? Back up a step; coils seldom give trouble. What kind of problems are you experiencing? Get the books described in this thread as quickly as you can and start reading. Tune-up parts and technique suggestions in this thread. |
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| Author: | 74A1Swinger [ Fri Sep 14, 2012 7:41 pm ] |
| Post subject: | |
Well I'm going to answer first and go back and read the info you posted. The test is a bench test for a coil using a digital 10 megaohm impedance ohmmeter (I've got a 20M, which I thought should work). Next refer to the vehicle manufacturers service information for the coil test specifications because the values can vary depending on the application (my specs are: Primary resistance 1.41 to 1.55 ohms and Secoundary resistance 9,200 to 10,600 ohms). To test the coil connect the ohmeter's two test leads to the coils primary terminals (+ and -). Most coils should read between 0.4 and 2 ohms. Zero resistance would indicate a shorted coil while a high resistance reading would indicate and open coil. Secondary resistance is measured between the positive (+) terminal and high voltage output terminal. Newer coils with segmented core construction typically read 6,000 to 8,000 ohms, while others can read as high as 15,000 ohms. http://www.aa1car.com/library/ignition_coils.htm Now I've been doing a tune up to pass emissions which I failed this time. This includes the following: Plugs, plug wires, cap, rotor, pick-up coil assembly w/lead wires, air filter, (PCV valve and filter only six months old w/low miles), fuel filter. After replacing everything I started the car up and it ran very well concidering I didn't time it or adjust the fuel just yet. While switch over to do that I noticed the negative coil wire casing had a tiny crack where it connected to the connector so I tried to tape it up, but in the process of reinstalling the wire connector I tightened it just a tad to much and the terminal cracked, so I needed a new coil. I purchased a new one and installed it without testing it and the car turned over, but absolutely did not get any where near starting, I tried a couple more times, and it was getting plenty of gas, so I looked up that test and performed it and it was 0 ohms on both primary and secondary resistance. When I got the second coil I tested it before I put it in and it failed the same way. They were BWD Select #E30 coils. |
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| Author: | 74A1Swinger [ Fri Sep 14, 2012 7:57 pm ] |
| Post subject: | |
I also took a look at the other posts you recomended and they look pretty good!!! Thanks a lot for the extra info.
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| Author: | Slanted Opinion [ Sat Sep 15, 2012 4:02 am ] |
| Post subject: | |
It is indeed possible to get two new parts in a row that are defective. It's rare as heck, but when it happens it will drive you crazy! Put in a known good coil, one from a friend's car that is running. If your engine runs, then swap in one of your new coils. If it doesn't run, well... There you go. Was your DMM set to the lowest scale of measurement when you tested these coils for resistance? - Mac |
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| Author: | 74A1Swinger [ Sat Sep 15, 2012 7:59 pm ] |
| Post subject: | |
Sorry for the long delay in getting back to you both, but it turned out to be a hectic day and in the afternoon I started back on the car because of the light bulb that went off in my head at about 11:30pm last night. Mac, I realized exactly what you brought up about having the multimeter on the right scale. I feel like a complete dufiss  , because when I read it I took it as meaning that the meter should be on the megaohm scale and that's why it came up zeros. Anyway the secound one turned out good after all and the first one was probably good as well (Dan you were right about the coils ... "You almost certainly don't have two bad coils in a row"! ). After I went back over the ignition system I found the real culprit, which as it turns out was the rotor. It had some how popped up on the distributor shaft just hi enough to come out of the keyway or slot in the distributor shaft and was spinning on top of the shaft making it stationary while turning over the engine. So no spark. The symptoms made it seem exactly like a bad coil. I've never ran across or heard of a rotor doing that before now. Any way, I learned a good lesson and got a new story to add to the book. Thanks for the help you guys! |
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| Author: | SlantSixDan [ Sat Sep 15, 2012 8:55 pm ] |
| Post subject: | |
Glad to help out! Do get those three linked books and don't be a stranger, now, y'hear? 
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| Author: | KBB_of_TMC [ Tue Sep 18, 2012 2:59 pm ] |
| Post subject: | |
IMHO, while resistance tests may definitely show a coil bad, it doesn't prove it good. In my experience, a coils with more than about 1 (US) billion sparks on them often have give problems and I replace them. An oscilloscope test is pretty good, but still may not catch all flaky coils. I've also seen a brand new Accel yellow coil that apparently would arc internally sometimes and burn out ignition modules... |
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| Author: | Slanted Opinion [ Wed Sep 19, 2012 3:23 am ] |
| Post subject: | |
Very true... coils can operate at 40,000 volts (on the secondary). An ohmmeter (driven by a 9 volt battery) can give only the most basic insight into how well the coil will function in real working conditions. Grabbing a poorly insulated coil wire though, can give you immediate feedback as to whether spark is present!  - Mac |
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