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Ignition Coil test
Greetings All ~
I was planning on a day working on little issues with my dad's 84 380SL, but it died before I could get it out of the garage and it won't restart. It appears to have fuel, but no spark. In searching forums, I'm trying to rule out the coil, distributor, ignition module, etc. But I have a real simple question. One of the first tests was to ensure we had current into the + side of the coil. Interestingly enough, we also have 12V when we test the - side of the coil. Does this indicate our coil is shorted out internally? Thanks! Brad |
#2
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Does this indicate our coil is shorted out internally?
Thanks! Brad[/QUOTE] no, it means that the ground signal from the ignition control unit hasn't been applied. this needs to be checked while cranking to start. this way the distributor is turning and signaling the icu. use a scope-if you have 1-or a digital volt meter. no analog meters and no test lights. they allow too much current flow through the tool and WILL short out the transistors in the icu. places to look for problems, the pickup coil in the dist., the green wire from the dist to the icu breaks, especially behind the p/s pump and the icu itself. if it's a huco brand, very likely it's dead. they last about a year or 2. if you need an icu, get a new or rebuilt bosch from someone and not another huco. yes, they're cheap, but you get what you pay for. good luck, chuck. |
#3
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Thanks for the advice Chuck. We tested the distributor pickup and it doesn't show any shorts, but I'm not sure if I am doing this right. We also spun the engine in the dark tonight just to see if we could register any fire. We seem to get a weak spark from the coil wire to ground but that's it.
Bosch ICU unit and I can't tell about the make of the pickup. How do you change these out? For what its worth, this car has run pretty well, started having stalling fits, and now this. After looking under the hood and seeing the crankshaft position sensor disconnected from where ever it goes, I think the shadetree mechanic has really set us up for some frustration. |
#4
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best way to test the pickup is with a scope. you need to see if the waveforms are crisp or ragged. to change the pickup, CAREFULLY lever the reluctor wheel-8 legged star thing-off the dist. shaft. there's a small pin to lock it in place. do not twist it, it can spin on it's center hub if forced. below that is a snap ring holding the pickup in place.
weak spark can be a weak coil, the green wire coming apart, poor signal from the pickup to the icu, less than 12v at the coil and icu or a tired icu. just 'cause it's bosch doesn't mean it won't wear out. a bad ignition sw could drop voltage to the coil and icu. the icu is exspensive and the reluctor is a pain to change, you want to be right. good luck, chuck. |
#5
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I know nothing about that car, but I would think anything disconnected could be a problem. Chuck seems to know about this car but did not mention the disconnected part you stated.
__________________
1998 C230 330,000 miles (currently dead of second failed EIS, yours will fail too, turning you into the dealer's personal human cash machine) 1988 F150 144,000 miles (leaks all the colors of the rainbow) Previous stars: 1981 Brava 210,000 miles, 1978 128 150,000 miles, 1977 B200 Van 175,000 miles, 1972 Vega (great, if rusty, car), 1972 Celica, 1986.5 Supra |
#6
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the crank position sensor mentioned is for the factory tool used at the dealer for timing checks, nothing else. my problem is, i tend to ignore things that aren't relevant. hence, no mention. i'm better under your hood than online. good luck, chuck.
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