I need help troubleshooting an installation of a DSII ignition. I'm installing a DS II ignition on a '69 model 351w engine. I've looked at all of the diagrams I can find, and I'm wired up just like they all show. The engine won't start, and here's what I"m finding.

I've got 12 volts going to a ballast resistor which then feeds the coil. I've got 12 volts going to the DS Module. I've also got 12 volts from the "I" terminal on the solenoid going to the white wire on the DS module. When I check voltage at the coil, I only show about 4.8 volts. If I unplug the DS Module, the voltage jumps to about 8 volts. Same thing if I check the voltage anywhere along the wire that feeds it. I took the igition module to the parts store where they checked it and said it's fine.

So what's going on? Why the voltage drop when the module is powered up? I'm so confused.

Steve

 

The "I" terminal on the solenoid should go straight to the coil +, bypassing the resistor in start mode giving the coil full battery voltage during cranking. The white wire on the module goes to the red/blue wire on the solenoid that hooks to the "s" terminal.

If it still won't start, hook a testlight to the negative of the coil, and hook the other part of the testlight to a good engine block ground. When you crank the engine, the testlight should blink(the module is turning the coil on and off to fire the coil).

 

That's the way I have it hooked up. And I've tried a test light on the tach side of the coil... it does flash, but not brightly.

I did more testing last night and am still confused. Basically, plugging in the power leads to the Duraspark box AND the harness to the distributor drops the voltage to the coil by about 5 volts. In other words, without the DS module hooked up, I get 12 volts at the coil. Once I plug in BOTH of the harnesses to the DS module, the voltage to the coil drops to about 7 volts. I checked it every way I can think of, but it's always the same result.

I'm thinking now that there's something messed up in the distributor. It's a brand new one, but it'd been moved from shop to shop for a number of years, so I'm guessing something is wrong with it.

I'll get a new one tomorrow and let you know what happens.

Steve

 

Way cool problem… I had to put my thinking cap on for this one.

Short answer is I still think you have a bad DS2 module.
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The voltage drop at the coil + only will happen when there is current flow, the voltage is dropping across the ballast resistor. When you pull the plugs on the DS2 module you open the circuit, thus no current flow.
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The normal current flow for the coil is from the coil neg. ,, then into and out of the 4 pin connector and then it finds a ground in the dist. under the cap were the harness clamping screw is.
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If the module is bolted to metal frame the current flow could be… DS 2 module to case ground, unbolt it from any metal and see if this changes the voltage drop. Put your test light on the module case to engine ground, it should NOT glow. The DS 2 module does not use case ground as it is mounted on plastic in my truck. The part store test most likely did not ground the case so it might have looked good to them.

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Let me know what you find.

Jim

 

Hmmm. Interesting theory. I've seen the same voltage issues with this box, (which was new and retested) and with another new DS box. Doesn't mean that I didn't do something to screw it up while I was checking everything.

It is mounted with metal to the fender, so I'll un-ground it and see what happens. I'll also check the current flow.

Not that it makes any difference, but I've removed the ballast resistor from the line for now. With the resistor in line, the voltage to the coil dropped to about 4.5 volts.

 

4.5 volts is pretty low, are you sure there wasn’t already a ballast resistor in the system? That low of voltage could be caused by 2 ballast resistor in series.

Without any ballast resistors in the circuit you would/should get full battery voltage (12 volts) at the coil + with the key on, you should also get 12 volts on the coil neg if there is no current flow,,, which is how it should be with the key ON and engine not running or cranking,,, same as when the points are open in a point style Dist. If you are getting a voltage drop across the coil you have current flow through the coil. You can measure the voltage drop directly by putting the meter leads across the coil.
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To test for the existence of another ballast resistor in the system, ground the neg side of the coil to induce a current flow, if the voltage at the coil + drops a lot, like from 12v to 8 or 9 volts then there is another ballast resistor in the system still. If the voltage stays at 12v then there isn’t another ballast resistor in the circuit.

 

That's true. He didn't say what vehicle the engine is installed, but most did already have a resistance wire in the harness.

 

I'm sure there isn't another resistor or resistor wire in the system. This is a 351w that's installed in a '78 Toyota Landcruiser. It's been running in this vehicle for many years. We pulled it completely apart this year for a complete rebuild... sandblasting the body, etc. Most of the wiring I did myself either originally, or re-did it this time.

When the engine was originally installed, we used the old points type ignition, with a ballast resistor, and everything ran perfect. A number of years ago we purchased the parts to change to the Duraspark, but never made the swap. So when the rebuild happened, so did the new ignition... and that's where we are now.

My new wiring ties into the stock Toyota wire coming from the ignition switch at the firewall. I've got 12 volts there. And I've been through the entire harness (while it was out of the vehicle) and am sure there's not a resistor wire in the bundle.

Like I said, one thing that confuses me is even when I take the ballast resistor out of the line and am feeding 12 volts to the coil, the moment I plug in the DS module, the voltage drops. So, since I've tried a couple of brand new DS boxes and they make no difference, and I've run all new wire to the coil and the DS box, I'm guessing its the distrib. But we'll see.

It's enough to make my head hurt. We didn't get a chance to mess with it last night, but plan to tonight. We'll install the new distributor and see what happens.

Thanks for all the input.

Steve

 

Well, you learn something new every day. We installed the new distributor last night and all is right with the world. The voltages check out like they should. Current flow is good. And THE ENGINE STARTED! I still don't know what is wrong with the other dist. and at this point I don't know that I care. (actually, I'll probably pull it apart and try to figure out what's messed up and try to salvage it)

Thanks to all for your advice and suggestions. This is a great forum!

Steve

 

More then likely you have a bad pick-up coil in the old distributor.