Alright everyone, bear with me on this, I'm a bit frustrated with this right now. I recently decided to remove all of the wiring/sensors relating to the Spark Control computer on my truck, and convert the ignition to a gm 4-pin module and a coil from a late 90's chevy truck, part # for the coil is IC58 at napa, and the module is TP45. I swapped in a dist. from another small block that has a vacuum advance. Here's where my research gets a little cloudy. I know that one side of the module is the two wires from the dist. The other side is hooked to 12V source with ign on, and the negative of the coil. The coil also gets 12V with ign on, and for right now I have the middle wire of the coil (tach) disconnected. Originally, I had a relay which would give me battery voltage to both coil + and module with key on, decided to simplify it even further after it wouldn't start, just to be sure the relay wasn't the issue. I have checked my grounds at least 50 times, all parts are brand new, and the module even pulses the coil neg. when I turn it over. So why, for the life of me, is my spark from the coil so weak I can hold the wire with my hand while I crank? I've seen this done on a slant six and from what everyone says, it's literally plug-n-play, no additional wiring needed. I want to think it's the pickup in the distributor, since it's the only part that isn't new, but then why would the module give off a pulse? I know the pickup sends an AC signal, but I've gotten mixed answers as to how many volts, and what the pickup should ohm out to. If anyone can help, please, I'm ripping my hair out over this.

 

Can't help you with cheby parts. Vehicle info would be helpful! I am assuming it has/had the lean burn system. Positive 12v needs to go to the coil and the ground trigger from the module will fire the coil. At least that's the way most work. Compare the stock(previous to the lean burn system) ignition to the gm module you should be able to figure it out.

 

The truck is an 87 d150 with a stock 318, holley 2 barrel and an a904 trans. Only modifications done so far are adding a tach, a complete dual exhaust, and I'm in the process of swapping the bulbs in the cab and cluster to LED. This truck ran perfectly up until I pulled the SCC/ESA computer and wiring out. I could swap it back in and it would start right back up, but I wanted a simpler ignition for when I start upgrading the engine for more performance. I like the GM setup because it's really compact and straightforward. Now, on to what I've done so far. I have verified good ground to the module, and it and the coil get 12V with the key in run AND cranking. It currently will throw spark intermittently, but when it does spark it's clean blue. I have one of those adjustable spark testers and it will not jump the gap at the 30k setting, but will do so when set just wider than for points. If I set it to the gap for small engines, it will fire more frequently but it's still intermittent. I had the distributor out turning it by hand and also did it in the truck, no difference to the spark frequency. I have a new distributor on the way to rule it out, but I feel like it still won't fix it. I'll draw a wiring diagram and attach a picture of the GM assembly I'm using so you can see what I'm working with.

 

I forgot to mention, this truck has no ballast resistor, the computer performed that function. I'm also wondering if the starter perhaps is turning too slowly to fire the coil strong enough, but I doubt it because the old ignition system fired the truck cold in around a second, two if it was below 40F. The starter doesn't seem sluggish at all. I've been meaning to get a newer style starter because I'm told they spin the motor faster, and it would help clear those headers I put on there.

 

What coil pick up are you using? I know they are different from the old 70's style(like the diagram) and what they used in the late 80's early 90's. It may not be compatible with the gm module. If you are looking for an upgrade with better performance get a MSD6A. It's a simple install and will out perform most ignitions.

 

I've looked at that MSD box and while I'll agree it's definitely better, I want this truck to just be simple, cost effective, and reliable. I'm not going crazy with it, I get my speed kicks with my old camaro. If you're asking about the pickup in the distributor, it's the standard reluctor/magnetic style pickup that all the mopar electronic distributors use. I know it should work because every diagram I look at uses a stock vacuum adv electronic distributor, the 4-pin module, and either the IC58 or IC29 coil. In fact, I've watched both coils running a vehicle on youtube. I'm just not sure what I'm missing. I put the new distributor in today and it's still intermittent spark, so in my mind, the only thing left can be that module. I suppose it could be bad out the box, but what are the odds that all the parts I bought were defective? I know the first coil was bad, it tested way off when I ohm'd it, confirmed now that I at least have a little spark instead of none. I had run some basic tests on the module but I don't have the fancy stuff to do it properly. At the urging of one of my friends at Napa, I attempted to have the module tested at my local Advance Auto today, but nobody in there had a clue how to hook it up and test it. I almost lost my patience with them but getting mad doesn't get anybody anywhere. I will try swapping the modules tomorrow and just see what happens, it's still well under warranty anyways.

 

I think I just need to give up. I feel like I've been lied to, so many posts discussing this conversion saying it works when it just doesn't. There is just no way that all of these parts I keep returning for new ones are bad. There is NOTHING different between my wiring and everyone else's, and it just will not fire. I am at a loss for words at this point.

 

Intermittent spark would lead me to the pickup coil.......

 

I finally have the truck running. As it turns out, the module was dead. It figures with my luck I'd have all my new parts have defects out of the box, but that wasn't my only issue. The new module also didn't work, but after tinkering, I learned that although the module was well grounded through the screw-hole, the metal base of it wasn't grounded at all. These modules have two points that need grounding, the metal plate on the bottom and the ring around one of the mount holes. I discovered that the plate and screw hole, while they have a brass? sleeve in them, are not connected to each other. After sanding the mounting bracket heavily under the heat sink, I reassembled the bracket and put it on. It fired right up. I'm not sure why the extra step wasn't taken to simply connect the two areas internally, but that also makes me wonder if all the people who have had issues with the modules dying have a bad ground on the module plate. This truck runs far better now though. The old ignition, while all of the parts were almost new as I'd replaced them over the past few years, simply couldn't provide any power. Now, I have to be careful not to burn rubber under even light acceleration. I'd like to thank everyone who offered advice, and I hope my experiences will help anyone who does this in the future. It really is a simple swap, I just missed a detail in my efforts.