Ignition impulse/pickup coil woes

[todd1561]

About 6 months ago I pulled the engine on my car for some frame repairs and general resealing of a leaky PRV. All is good there, but during the removal the one item I forgot to disconnect was the ignition pickup coil connector. It got cracked and pulled apart by lifting the engine, see below. At first I didn't think too much of it, figured I'd just crimp on a new connection at some point. The connector is intact enough that it's stayed together for some test drives now that the engine is reinstalled. However, I'm finding I have a slight misfire when doing moderate acceleration, especially when in 1st or 2nd gears, I'll even see the tach jump, jitter or freeze during these moments. This only seem to happen when at full running temperature. I had spare plugs, cap, rotor and coil so I swapped those out to no effect. Plugs are gapped properly and the ones I've had in there for the last 20 years show even coloring, nothing out of the ordinary.

The car idles fine and runs generally great when going, other than that occasional stumble under load. I'd think that connection would either work or not, but maybe it's more sensitive that I'm thinking. I read elsewhere on this forum from Dave that this cable is shielded as it's very noise sensitive. Do we think this broken connector could be the source of my problem? Can a new connector just be crimped on? I see D-Go sells (https://www.deloreango.com/us/2-pin-male-sensor-connector.html) a replacement connector that would seem to work (even listed under the same part # as the entire pickup coil harness), but I'm not sure if there's more going on with this connector than a simple crimp. As you can see in the picture there seems to be some kind of additional braiding over one of the pins. I ohm'd out my pickup coil and I'm reading 740 ohms, which from what I'm reading elsewhere is a little high (should be around 600?)

Anyway, would appreciate anyones thoughts, unfortunately a new pickup coil/harness is pretty expensive to buy on a hunch.

Thanks!

https://toddnelson.net/misc/3474751.jpg

[Bitsyncmaster]

That braiding is the shield. You can solder the wires (one wire and one shield) to those exiting pins and should be good to go. When working with shielded wires you "comb" the shield strands and then twist them into a wire.

[todd1561]

To make it a little clearer what I'm dealing with I removed the rest of the crumbling plastic on the plug. The electrical contact pins are still intact and connected to the wiring. It appears to be a standard 2-conductor wire where the ground is unsheathed and just wrapped around the other wire. To replace the plug I'd need to cut this off including whatever that yellow, braided looking sleeve is. Unlike the other connectors on this car which are just push in terminals, this one was molded with the wires in place. I think that yellow sleeve is effectively like heat shrink tubing keeping the two pins from shorting out and not something that's otherwise significant.

I think what has me more concerned right now is my earlier resistance measurement of ~740 Ohms, that was when the car was still pretty warm. Now that it's cooled off a little it's down to 665 Ohms. The figure I've seen mentioned is the value should be between 550-600 Ohms. I'm not too far outside of that range when hot, but the fact that it gets worse as things heat up dovetails nicely with my stumbling issues only presenting once the car is warmed up. Does anyone have any real world experience with testing these impulse coils to know if mine is in a problematic range?

https://toddnelson.net/misc/4781326.jpg

[Bitsyncmaster]

When the copper wire heats up, the resistance goes up. It's quite a lot of change. Your resistance sounds normal to me.

[iflights]

I used to have a "stall while hot" condition where I would just be driving on a hot day, and the engine would shut off. No sputter, it would just die. So I put together a list of all potential culprits and started knocking them out one by one. The impulse coil was on my list of something to potentially replace as it was noted within various posts in the forum it could be a contributing factor.

Never did replace the coil as I solved my issue before I got to it.

It's only money, but the results of having a reliable car were worth it.

[82DMC12]

I think the cable is fine even if it's ugly. I'm sure you can find a way to solder it and insulate it , but if it were me I would just replace the cable. It's expensive but I'd sleep better!

[David T]

The impulse coil is a common failure point. It can show up as an intermittent or just affect the quality of the idle. Because it is probably an original part and is over 46 years old, the best course of action is to just replace it. It gives you a chance to also service the distributor (probably could use some cleaning, lubrication, and adjustment anyway). It is possible you strained the cable and have other problems besides the connectors you can see.

[todd1561]

Thanks guys, for now I'll at least pick up one of those replacement connectors from D-Go and fix the broken connector. New impulse coil prices range from $350-665 depending on the vendor. And the separate cable runs $238 for a genuine Bosch from Houston. So kinda spendy to just replace on a hunch especially considering mine seems to pass the normal resistance tests.

It's pretty clear at this point my issue only presents itself when the car is hot (like driving for 20+ minutes hot). I think I'll try to take some measurements of the impulse coil with an oscilloscope while driving to see if I can detect a dropout during the stumbling. Then move my way up the ignition system from there if it looks normal.

I did find a slightly loose ground ring terminal on the lambda ECU yesterday, I haven't had a chance to drive the car since fixing that. I also applied Deoxit on all the connectors in that compartment. Maybe I'll get lucky!

[82DMC12]

Thanks guys, for now I'll at least pick up one of those replacement connectors from D-Go and fix the broken connector. New impulse coil prices range from $350-665 depending on the vendor. And the separate cable runs $238 for a genuine Bosch from Houston. So kinda spendy to just replace on a hunch especially considering mine seems to pass the normal resistance tests.

It's pretty clear at this point my issue only presents itself when the car is hot (like driving for 20+ minutes hot). I think I'll try to take some measurements of the impulse coil with an oscilloscope while driving to see if I can detect a dropout during the stumbling. Then move my way up the ignition system from there if it looks normal.

I did find a slightly loose ground ring terminal on the lambda ECU yesterday, I haven't had a chance to drive the car since fixing that. I also applied Deoxit on all the connectors in that compartment. Maybe I'll get lucky!

If you buy an impulse coil, try to get an OEM one. It is a yellow-ish plastic body and it says AB on it. That's genuine Bosch. The newer ones are white and I've heard about strange behavior from them. I had one in my car, I replaced it "while I was in there" and immediately had all kinds of weird behavior from my tach. I swapped the old one back in and the glitchy behavior went away. I don't know for sure it was the coil but sure seemed like it.

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