Low voltage at coil and no spark

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Sedanman

Sedanman

67-9 Valiant specialist
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We just broke in my new engine and it ran great then we shut it off to let the smoke clear. It wouldn't start so I hooked up the plug spark checker and no spark. We put a different ballast on,same thing, tested the coil voltage and it's at 4v. The ignition set up is a MP kit I bought in the 90's. I don't have a spare ECU to test if that is the issue. It is grounded good and we can't figure out what happened. It cranks but won't start. We still need to set the initial timing and such. Thoughts?
 
Disconnect the coil - from the wiring harness, take a jumper lead, ground one end, and, with the ignition in RUN, touch the other end momentarily to the coil - and then remove it, and when you remove it, you should get a spark from the coil spark tower wire. If this works, then the ECU or the reluctor coil is bad. (Just don't be touching the wire jumper end when you remove it from coil -!

And you can ohm out the reluctor coil to see if it is likely god or bad. I think the good ohms value is 150 to 500 ohms but maybe some one who has that info will chime in.
 
A pickup coil is typically 300 Ohms, but an Ohms test is inconclusive, because a shorted turn renders them broke. A turn short cannot be measured with VOM.

More important is to measure the (-) coil lead, and the supply side of the ballast. 4V seems low, since the coil primary resistance is about the same as the ballast, and the transistor that pulls the coil low may drop a volt there, the coil (+) should be about 7V with coil energized. Reading the supply side of ballast measures switched battery voltage. It might be low.

Also check reluctor to pickup gap with brass feeler. The gap is critical for starting, since the VR signal increases with RPM. That might be the reason it ran, but is unable to restart.
Three things can make the (-) coil lead always low (when it goes high spark happens). The VR signal is too low due to failure, poor 2 wire connection, or output transistor is shorted. The output transistor can be checked by disconnecting harness, and use VOM to measure resistance at transistor body to ground. Good is high resistance, bad is several Ohms.
 
Start by running a jumper direct from coil+ to a 12V source. Don't leave that hooked up any longer than needed for testing

Make absolutely certain the ECU is grounded

Coil + with key on and engine stopped should be somewhere +/- 6--10V, coil NEG should be very low, perhaps 1/2--2 volts

With key on or jumper in place remove the dist. connector and take up the connector going to the ECU (not the distributor) Ground the bare terminal, and this should produce a single spark each time.

Wiggle/ work all connectors in/ out.

Probe the coil + and the ballast. What you say, sounds like supply voltage is low. On the "key" side of the ballast, voltage should be "same as battery"
 
What they say above.... Grounds and bulkhead connections at the firewall or bad ignition switch. Any chance you had a wire get on exhaust and melt to ground?
 
No,all wires are away from hot areas. I didn't get a chance to mess with it last night but I went out this am and just for the hell of it checked to see if it is getting spark and it is. We are going to try firing it up again and see what happens. My whole MP ignition system is new,I did put in the blaster coil instead of the stock one. I installed an NOS switch. I will keep you updated
 
It turned out that the reluctor on the distributor wasn't gapped correctly. It was at 0.30. It's all good now. Thanks for the input
 
[ame="https://www.youtube.com/watch?v=Tlcinz9X54M"]Picture 3086 - YouTube[/ame]
 
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