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Old 07-07-2009, 11:13 PM
Travsuw Travsuw is offline
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Voltage at coil but no spark at plug

76' F-250 4wd 390

Had the truck running fine until today, cranks just fine but won't fire at all. I've got 12V at the coil and at the end of the plug wire running from the coil to the distributor cap. When i pull a plug out and try to see a spark out of it I get nothing. I also don't think its the ignition because I'm alone and when i try and start it to look at the plug I have to turn it to run and jump it at the solenoid. I also don't have a test light. What do you think I should check using the multi-meter I have?

-Thanks
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Old 07-08-2009, 12:10 AM
montana_highboy montana_highboy is offline
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Sounds like the pickup coil or ignition module, fmc should be around shortly to tell you how to check.
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Old 07-08-2009, 12:18 AM
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joshjones.thewelder
Quote:
Originally Posted by Travsuw View Post
I've got 12V at the coil and at the end of the plug wire running from the coil to the distributor cap.

Clarify this part a little more... you have voltage to the coil, that part is clear, but you state you have voltage coming out of the coil at the post as well?

How did you check that?

Now, to substitute the DMM for the test light, turn the DMM to DC volts, hook your positive to the TACH side of the coil and the negative to ground. Now try and start the engine, the DMM should pulse between 0 and 12 telling you whether the module and pick-up are good or bad.

Also in the meantime you can test for OHMS on the distributor leads, the wires should be orange and purple and the scale is 500-800 ohms.

Post back the results.

Josh
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Old 07-08-2009, 12:18 AM
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It's a little hard to do by yourself without a test light, but if you have alligator clips for your multimeter, you can do it. Set your meter to read DC volts. With the coil connected, connect the multimeter between the TACH TEST terminal of the coil horseshoe connector and engine ground (clean unpainted metal on the block). Use the key to crank the motor over, and the meter should flash between 12 volts and zero.

This is equivalent to connecting a test light in place of the multimeter and watching for it to blink. If your multimeter doesn't have clips, you're going to have to have a friend crank the engine over from the cab while you hold the meter in place. To do this test, you have to use the key to crank the engine over. You can't jump it at the solenoid because you need the ignition switch to power the ignition module for this test.

EDIT: looks like Josh and I posted at the same time.
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Old 07-08-2009, 12:19 AM
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joshjones.thewelder
Also, look inside the distributor and see what the condition of the rotor is. Any moisture in there will cause havoc as well.

EDIT: Dang, we posted at the exact same time!


Josh
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Old 07-08-2009, 12:28 AM
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It actually ended up being a loose connection on the coil bracket. Thanks to anyone who looked at this
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Old 07-08-2009, 12:36 AM
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joshjones.thewelder
??? what was hooked-up to the bracket?

Josh
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Old 07-08-2009, 02:34 AM
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I'm assuming he's refering to the horseshoe connector and not the actual mounting bracket
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Old 07-08-2009, 09:53 AM
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That would be my guess to, hey great explanation you two!


PS: Was going to give you both rep points, but it says I have to spread them around first.

I feel if you deserve them you should get them!!
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