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Reliability of modern transistor module builds
https://www.slantsix.org/forum/viewtopic.php?t=16837		 Page 1 of 2
Author:  ZacharyB [ Sat Apr 01, 2006 5:58 pm ]
Post subject:  Reliability of modern transistor module builds
Hey,

This past winter I posted about having no spark. I checked everything and was only getting 6 V to the coil. Then I replaced the transistor module and the car finally ran.

The ignition stopped working again tonight! No spark. I am only getting something like 45 mV at the coil now. Did my transistor fail again so quickly? The other one supposedly lasted 30 years... The ond one has 5 pins, but this newly manufactured one has 4 pins (what was the fifth pin for, oxygen sensor programming? This car is from 1973)

Another thing that confuses me is that I am only getting 45-250 mV at the coil, but output of the coil is 12V (to the distributor). I know output should be something like 15,000V, so my coil is working correctly (upping the voltage it is receiving) and 12V is just a coincidental number trying to confuse me... right? :?:

Thanks for any help
Author:  SlantSixDan [ Sat Apr 01, 2006 6:10 pm ]
Post subject: 
It's far too easy to get a piece-of-cràp module these days. Even the "genuine" Mopar ones are Taiwanese garbage.
Author:  ZacharyB [ Sat Apr 01, 2006 6:23 pm ]
Post subject: 
Can you recommend a good place to buy from, or a good elec. ignition transistor manufacturer? Don't want to have to buy another from the same parts store (Parts Authority) just to have it fail again in 3 months!!
Author:  CStryker [ Sat Apr 01, 2006 6:36 pm ]
Post subject: 
I've had good luck with Borg Warner parts. Both their standard and "select" lines carry lifetime warranties. Just make sure that they are adequatly grounded.
Author:  Charrlie_S [ Sat Apr 01, 2006 6:58 pm ]
Post subject: 
The coil does not get 12 volts from the module. The coil gets 12 volts, direct from the ign switch, in the start position. The coil will get somewhere around 8-10 volts from the ballast resistor, when in the run position. The module switches ground on and off, on the coil negative. If you have less voltage on the positive coil terminal, check for a bad connection.
Author:  ZacharyB [ Sun Apr 02, 2006 12:01 am ]
Post subject: 
Do you guys mean the ground from the battery to the engine block (near the water pump)? Are there any others I should be aware of on this circuit?
Author:  Charrlie_S [ Sun Apr 02, 2006 4:43 am ]
Post subject: 
You must have a good ground from the engine to the battery, and the chassis. But the switched ground I an refering to is the small wire from the negative terminal of the coil, to the ignition module. The module should have a good ground from the case to the body, and the module connects and disconnets this small wire, to ground. It triggers the coil, just like a set of points would.
Author:  ZacharyB [ Mon Apr 03, 2006 2:56 am ]
Post subject: 
Interesting... I'll clean the bolt and mating surface that is used to attach it to the fender.
Author:  Charrlie_S [ Mon Apr 03, 2006 5:38 am ]
Post subject: 
You will still need to find out, why you do not have 12 volts to the coil. Disconnect the wire from the neg (-) coil terminal. Turn the ign switch to "run", and check the volatge on the positive (+) coil terminal. It should be 12 volts. If not, get a wiring diagram, and trace this circuit back, and find out where you have you are losing it.
Author:  ZacharyB [ Mon Apr 03, 2006 6:35 am ]
Post subject: 
Sorry about that, I do appear to be getting 12V to the coil. I must have measured it incorrectly last time (across coil posts, not power with ground). I'm still kind of new to electrical work

I got a couple of chugs out of the engine after cleaning the contact points and threads of the attaching bolts for the module, but sheared a bolt off for one of the grounds near the battery, so now I have to drill out and retap with a new bolt. Will update.
Author:  ZacharyB [ Tue Apr 04, 2006 5:36 am ]
Post subject: 
I cleaned the engine->battery ground and drilled a new hole for the other ground on the bulkhead near the driver's side headlamp (the bolt that sheared. It proved too slippery and hard to drill through). I don't know if it was either of these two things but the car now runs. Thanks to everyone who responded and took the time to help me out. :)
Author:  Charrlie_S [ Tue Apr 04, 2006 6:28 am ]
Post subject: 
Glad I could help. You know, it is nice, when someone responds with a "thank you", and the results of their endevors.
Author:  ZacharyB [ Wed Apr 05, 2006 12:25 pm ]
Post subject: 
Hmm, scratch that, something changed and now the car won't start again. I'll have to do some more experimenting. Perhaps replace my corroded-looking negative battery cable somehow...
Author:  Jeb [ Wed Apr 05, 2006 7:59 pm ]
Post subject: 
Check to see if the magnetic pickup in your distributor is getting any power. A multimeter comes in handy for this. Just test the leads coming from the ignition unit.

If it is getting power, now see if it works. Pop off the distributor cap and turn the ignition switch to the "on" position. Take a screwdriver and hold it close to the magnetic pickup. the electromagnet in the pickup (follow the wires) should pull the screwdriver towards it. Post back to us with your results.
Author:  ZacharyB [ Sat Apr 08, 2006 12:18 pm ]
Post subject: 
Jeb, thanks! Beforehand, tell me if the current to the magnetic pickup is governed by the transistor module or not, so I know what to suspect when I do the testing.

(I can't do it now, the car is parked 30 blocks away from me where it died)

My father already made me order a new module because they're cheap (he ordered it before your reply). So if replacing it doesn't fix it I'll know where to look next
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