Can I ask for more troubleshooting? I've narrowed it down a bit

[TimQ]

A few months ago I posted a long description of an intermittent stalling and starting problem I've been having with my 1986 C-10 (V6, 4.3, auto). The long description can be found here.

I've narrowed it down now to a clear intermittent spark issue. Last week I replaced the entire distributor unit which included a new module, coils, cap, rotor, etc. and I even did the plugs and wires too. So, everything between the wire from the ignition all the way to the plugs is new.

After I got it running again (originally missed the part in the book about noting the configuration of the old dizzy before pulling it so getting the time on was a bit fun) I changed the oil (a first for me) and took off to test her out. Drove about 10 miles to a gas station and filled her up while getting a drink. Came back out and the damn thing wouldn't start. This time I had some tools with me so I could check for spark and there was nothing. No spark at all. I tinkered with it for 20 minutes or so and then got pulled home by some nice fellows driving a Ford (yeah, they gave me grief but were fun about it).

Anyhow, here's the best part...when they got me home and the chains were unhooked, I tried starting it again and she turned right over. WTF!!!

Anyhow, at this point I assume I must have a broken/loose wire somewhere (already checked to see if the dizzy was a bit loose...it's not). I assume it would have to be between the ignition and the dizzy. What I'm looking for is some advice on where to look, what other wires there might be, etc.

For example, coming out the back of the dizzy I know there is a harness with a few wires that seem to run over towards the passenger side somewhere. What are those for? Basically, I'm just looking for some ideas on where wires go, etc. so I can begin testing with some sense of what things do and where they go. I've checked the various wiring diagrams I have and they aren't too clear at this level of detail.

Any and all suggestions are welcome and appreciated.

Thanks in advance,
TimQ

[Hottrucks]

next time it poops out ( because you can't fix something thats not broken??) check the wire going into the bottom of the Dizzy cap for power...it sounds like it could be a bad ingnition switch????

[68 TT]

Originally Posted by TimQ

... Anyhow, here's the best part...when they got me home and the chains were unhooked, I tried starting it again and she turned right over. WTF!!!

Are you saying it doesn't crank over or that it cranks over but doesn't fire?

[TimQ]

When it isn't starting, it cranks over just fine...just doesn't fire. And, when I check the plugs for spark, there's none. And I also checked fuel...that part is fine.

Of course if I wait some random amount of time and come back (or get the thing towed) it sparks just fine. Totally random.

[TimQ]

Hottrucks...thanks for the tip. Just went out to try it and she started just fine. Just a matter of time..then I'll check it.

[68 TT]

Originally Posted by TimQ

When it isn't starting, it cranks over just fine...just doesn't fire. And, when I check the plugs for spark, there's none. And I also checked fuel...that part is fine.

Of course if I wait some random amount of time and come back (or get the thing towed) it sparks just fine. Totally random.

Check the condition of the primary power wire into the HEI. I had one that the female terminal inside the plastic connector somehow got loose and another that the wire was heavily corroded. Both made intermittent contact.

[TimQ]

Well, it conked out in the driveway tonight (just had her running while I was cleaning up the garage) giving me a good shot at trouble shooting.

I checked the power coming into the "bat" terminal on the distributor cap. That was fine the entire time. I took apart the dizzy cap, router, and all that. It seemed fine. Put it all back together and still nothing.

Any other thoughts?

[PugDad]

Originally Posted by TimQ

Well, it conked out in the driveway tonight (just had her running while I was cleaning up the garage) giving me a good shot at trouble shooting.

I checked the power coming into the "bat" terminal on the distributor cap. That was fine the entire time. I took apart the dizzy cap, router, and all that. It seemed fine. Put it all back together and still nothing.

Any other thoughts?

How did you check the power? A light, or a meter?

[TimQ]

Ran a a meter from the wire to a ground on the frame. showed 12+ volts. Also checked the connecter and all seemed in order.

[TimQ]

This might be a stupid question...but reading the manual for this thing, it says the following:

"Either a voltmeter or a test light may be used for this test. Connect the test light wire to ground and the probe end to the BAT terminal at the distributor. If the light comes on, you have voltage to the distributor. If the light fails to come on, this indicates an open circuit in the ignition primary wiring leading to the distributor."

Now, I tested it by disconnecting the wire the connects to the "BAT" terminal and probing between the wire and ground. Should I be probing between the BAT terminal and ground? Or is the manual assuming I can get to that terminal somehow with the wire still attached (which I don't really think I can)?

[PugDad]

Originally Posted by TimQ

This might be a stupid question...but reading the manual for this thing, it says the following:

"Either a voltmeter or a test light may be used for this test. Connect the test light wire to ground and the probe end to the BAT terminal at the distributor. If the light comes on, you have voltage to the distributor. If the light fails to come on, this indicates an open circuit in the ignition primary wiring leading to the distributor."

Now, I tested it by disconnecting the wire the connects to the "BAT" terminal and probing between the wire and ground. Should I be probing between the BAT terminal and ground? Or is the manual assuming I can get to that terminal somehow with the wire still attached (which I don't really think I can)?

No, you are ok. You have verified the integrity of the primary wire going to the distributor.
If you were an electron, and you traveled back down the wire from the distributor, what would be the next thing you would run into? Ignition switch? Relay? Terminal block?

[TimQ]

I'm prety green at this, but I would assume that main wire goes back through the firewall and to the ignition switch. But, since I have good voltage I assume the problem isn't in that direction???

THe other way is the distributor and I replaced the entire thing. Out the other size of the distributor there's a connector with 4 wires. According to my wiring diagram this goes into the "Engine Control Module" which I assume is some sort of computer. Could the problem be coming from that side? Heck, I'm not even sure this truck has any real comptuter as it has a carb.

[tucsonjwt]

Just curious - when your truck would not start months ago before you started working on it, was it also a "crank, but no start" condition back then also? Or, did you have a "click, but no crank" condition back then?
It seems to me that if you always had a "crank, but no start" condition through this whole process, then your ignition switch and starter/solenoid are good - so you would be correct in looking into the spark distribution/control system.
I went through 7 years and countless $$$ of intermittent "click, no start" condition. As I mentioned in the previous thread, unless you find a mechanic who will guarantee to track down and fix this, you (and/or mechanics) will just be throwing parts at it like I did. Not all old squares are easy to fix.

[TimQ]

It's a crank but no start. And, after a late night of searching around, I think I've found the issue. My guess is that it is the ECM or ESC or whatever the thing is called. basically, on this 86 there is a little computer that detects knock and adjusts accordingly. This thread describes my problem exactly...

http://67-72chevytrucks.com/vboard/s...d.php?t=305283

and this link at the bottom of the thread talks about it some more.

http://www.73-87.com/7387garage/drivetrain/escrepl.htm

I'm going all in that this is the issue.

[PugDad]

Originally Posted by TimQ

I'm prety green at this, but I would assume that main wire goes back through the firewall and to the ignition switch. But, since I have good voltage I assume the problem isn't in that direction???

THe other way is the distributor and I replaced the entire thing. Out the other size of the distributor there's a connector with 4 wires. According to my wiring diagram this goes into the "Engine Control Module" which I assume is some sort of computer. Could the problem be coming from that side? Heck, I'm not even sure this truck has any real comptuter as it has a carb.

I was troubleshooting a circuit once. I zeroed in on a switch. But, voltage was good through it, it ohmed out great, and it actuated great--break the circuit, make the circuit. I poked around in other directions, but they didn't seem to make sense. I replaced the switch, and the problem went away.

I read your other post about the ECM. Sounds like you found a good lead. If you follow that, and it doesn't fix the problem, you might want to consider replacing the ignition switch.

[TimQ]

I bypassed the ESC and she started right up. Go figure. Engine sounded like crap when trying to accelerate but it's now at the shop and someone else's problem for a few days.

Thanks for all the tips.