12a tach dies and car losses spark?
 

It's just like the title says. I'm getting intermittent spark and the tach dies right before. Any ideas? I'd rathe not replace ignitors and coils if there's another issue. I wa plauing with my dizzy just now and got a mild spark when I retarded it a little... then the engine died again. Pls help!

Quick update. I replaced my coils with what I thought were known good ones and took it for a 10 m8nute industrial area run. All seemed well so I headed out on the street and the tach goes to zero again right before the engine died 2 minutes later. Now I'm stranded at a gas station.

Sooo,problem not likely ignition coils. A VERY common failure pattern of an igniter is loss of spark when warm(hot) and when cooled down will run normally til heat soak duplicates the problem again.
The tach signal is generated by trailing ignition and while your car will run without trailing ignition,it won't for long as trailing also triggers fuel pump circuit and when float bowls in carb empty the car will shut off.

There could be other problems with wiring,personally suspect failing igniter is at the heart of this complaint. Suggest obtaining a known good used one or a new one and replacing it and retest.Even if this is not the cause of the problem,having a spare igniter in your possession is never a waste of money. Own this car long enough and you will have need of it.

Don't neglect scraping off old thermal paste and coating back of replacement igniter with fresh thermal paste,omitting this step guarantees a short life of the replacement. Post back your findings/results.

Since J109s are pricey I will be looking for a few GM HEI 4 pin ignition modules and working on a dlidfis setup tomorrow. First thing will be to wire an hei in place of the trailing J109. If that goes well, it will be time to go dlidfis hei on the leading side. I will definitely post results when the issue is resolved. You are the best! Plus one on the thermal paste, I would have missed that for sure! Plus one on the trailing ignitor running the fuel pump relay too!

Update: I tossed the trailing j109 and swapped in the leading one. I wired in a 4 pin gm hei look alike that I found on kijiji that was intended for a 79-85 fiat spider. The tach is back and the car fired up reluctantly after advancing the timing as far as the dizzy would turn (the bracket hit the alternator). It runs. No spark on the leading though so I have to do a proper job of that. I'm done for tonight as its 1am and raining and I'm parked outside. GSLSEforme you were right on the money about the trailing igniter. The engine bay temps are very hot. I assume that's due to incomplete combustion from no leading spark. The engine is idling at 600rpm when it was set for 1000 prior. I have no idea what the actual timing advance/regard is as I don't have a light or pulley marks and I just earball it for power with my butt dyno and phone GPS 0-60 app. I will update further when my car works properly. I have a new coil and Delphi ignition control module on the way for Monday pickup. This is long

Running it like that will be hard on the Apex seals with the timing so far off. Fix the leading ignitor and time it correctly before you start applying load. Turning the distributor to its max to get trailing to run the engine is a recipe for disaster. You could have bypassed current to the fuel pump to get it running, as well. Something to consider as a fuel cut switch, aka anti-theft device.

Thanks for the input. I agree. I won't be driving it until I have at least two working ignitors and coils. I'm glad to have solved the mystery of the tach dying prior to the engine. I won't do the fuel pump switch as yet since its an outdoor car and it's raining and the priority is the leading spark anyways. The car is just asking me to learn and install direct fire, So I'll do it up with a GM HEI to leading coil to dizzy and once that works I'll go dlidfis. It's a good experience to see how spark and timing controls temps, stability and power. I'm surprised how much power it still has on trailing only. I'd guess its lost about 30% on the butt dyno. It isn't knocking so I should be ok for a few more starts. I will keep the thread updated.

In the interest of keeping that engine alive,i would run it only once in that condition-to limp it home. Fix it right before running it anymore.

I thought full advance was ok but you should never go full retard. :)

I wired the HEI in place of the leading J109 that I binned. With the hei plugged into the leading there's a bit of a tick like an arc. If i put my finger across B and C on the HEI I get a very minor shock. The idle stabilized to 900 rpm when I advance the trailing vacuum pot and the motor still likes full advance but it'll run at halfway with less power. I drove it home now at basically full leading and trailing advance. I laid into it a bit and it has a vicious amount of power. it's just above freezing here in Toronto, so that's a plus for power. It sounds very angry. I'm going to mess with it some more tomorrow. Any insights would be much appreciated.

My advice is on par with the above. Set the timing to spec and NEVER run the engine on the leading or trailing ignition alone. Personally, I would have just picked up a set of J109's and left the ignition system alone. They are built well and are reliable. There are plenty of people here on the forum that have sets that they would have sold you.

Keep that dead J109, you can gut the interior circuitry and straight-through wire it to use it as an adapter to get the signal off the dizzy when you do your direct fire setup.

You can not go wrong with the HEI/TFI coil setup. Makes a world of difference.

Also, you can run just leading alone with no issues. The trailing just helps to reduce the stink. I did it for a a few years when I did my HEI conversion, always started well and ran well.

Pre-81 Thermal Reactor setups do exactly that (lead spark only) during normal acceleration from idle to around 3K rpm, to provide a rich-enough exhaust feed for the TR to get hot enough to do it's job.

Running leading and trailing is more thermally efficient, but running lead alone is not unsafe for the engine. Might make your cats get pretty hot, though, if you still have them; rich exhaust will do that.