Hey all, I hope I can describe my problem.

I recently rebuilt a 1979 302, some machining and high compression pistons, cam, gt40 heads, wieand intake, Holley 1850 manual choke and vacuum secondaries.

We put it in the truck, fired right away. Started with 10 reg advance and that seems to be where it wanted it. Timing light showed about 35 deg at 2500 rpm. We did the cam break in, it ran pretty good, not great, but pretty good without fine tuning. That was last weekend. This weekend I finished brakes and such so I could run it under load and seat the rings, this is where it gets problematic.

It developed a come and go intermittent miss that wasn't linked to any one cylinder (I pulled plug wires off one at a time). Looses about 100rpm and misses for about 1.5-2 seconds then clears up and runs fine for 8-10 seconds at all engine speeds. I had already put on a new coil, plug wires, plugs etc.... decided that maybe the 40 year old distributor was causing me headaches, so I replaced it, now...

It won't start at all. Funny part is you can bump the starter, or crank for 10 seconds, doesn't matter, as soon as you let go of the key it hits on 1 or 2 cylinders but will not take off.

Yes, the distributor is stabbed correctly, yes the firing order is correct, static timed at 10 deg. New vacuum hoses on everything. I'm stumped and frustrated.

Thoughts?

 

New does not necessarily mean good these days. If you still have the old distributor, put it back in. If not or want to troubleshoot what you have try using this Duraspark II troubleshooting guide: Duraspark II T/S Guide

 

Thanks, I was looking for something like that, must not have been using the right terminology for Uncle Google to understand it

And, no, I left the old distributor as a core when I picked up the new one

 

What about the DS module itself? Is it also 40 years old?

Did you try to see if it was actually generating spark? Like pull one of the plug wires, hold it near a ground spot and crank, and see if a spark jumps?

The symptom you're describing, a sputter when stopping the crank, sounds similar to something I ran into when I installed a MSD ignition box onto my old points distributor. I was powering it with a switched source, which gets turned off while cranking, so the box was not getting power. By chance, the engine backfired during one of my attempts, so it kept turning when I released the key, and the box got power, and it lit a spark, and the engine suddenly came to life. It took me a while to figure out and re-wire the power cable to the key switch terminal that supplied power during crank.

 

Flat tappet cam I think I'd be be looking at a wiped cam lobe or lobes too. Any of the rockers loose ?

 

Okay I don't know why I didn't check for spark. Simplest things first right. My brain went straight to worst case I guess.

No spark. Except once in a while as we stopped cranking.

So then I went through the duraspark troubleshooting guide linked above. Here are my results let me know what you're thinking.

Battery voltage is 12.7, mid 10's cranking

Battery and starter sides of solenoid is the same

+Terminal on coil only shows 8.8-9.3, potential problem?

Resistance on coil is 2.2ohms

No readings on the parallel distributor terminals, nor between either of the verticles and the horizontal terminal - bad pickup coil on the remanned distributor???

"S" terminal on solenoid shows 9.5-9.8 v cranking, slight drop in voltage.

White into module has 0 volts reading while cranking - what does this mean? Is the white wire a signal from the module or is it supposed to be receiving voltage on the white while cranking?

Red into module has 12.4-12.7 v

Black at module to black at distributor harness has 0.3 ohms resistance.

So, it looks like I have a small loss in voltage to + side of coil while cranking, a small loss through solenoid to the S terminal that could be compounding. A white wire at the module that, what I understand, should have voltage while cranking, but has nothing - I don't know what this means. And a bad pickup coil...

Would this jive with those of you that have more experience with the system then me?

 

I haven't had a cover off yet, but I would doubt it's the cam. Its only run long enough to do the cam break in. . Used a cam lobe EP grease, engine fired and ran almost immediately after assembly, ran it up to 2000 ish rpm right away for about 30 minutes, No fillings in the filter after the cam break-in run. That's where we quit for the weekend. Finished up my brakes the following weekend so I could get it on the road under load to seat rings but it never lit up again, and now here I am. But I'll definitely be looking if we can't find anything electrical.

 

The two failures I had happened during breakin. Just sayin...… And if you ran it then with the valve covers on, you wouldn't know what was going on during breakin.

 

The wires for the DS2 module:

Red - power supply. This needs to be connected to a source that is on whenever the key is on, even when cranking; a constant on source. Some people connect it to the same wire that goes to the coil + terminal. That will work, as that wire is the constant source through a resistor for the coil. During cranking, that resistor is shorted out so the coil gets full voltage, and so would the DS2 module. During run, they both get voltage dropped from the resistor, which is why you measure about 9V on that wire. But for higher performance, the DS2 should be connected directly to a constant on 12V source.

White - cranking sensor. This is connected to the S terminal on the starter relay, and the DS2 module senses it to retard timing during cranking to make that easier. So it should measure nothing when not cranking, and 12V when crankinig.

On the distributor:

Black - ground. This goes to the single horizontal slot on the connector. The DS2 module uses this for its power return.

Orange/Purple - the pickup coil. They go to the vertical slots on the connector. The DS2 module gets the magnetic trigger from these. You should measure a low resistance across them. If not, this may be your problem. Just by deduction, if this was the only item you changed in the ignition, and now the engine won't start, it is highly suspect. Can you take it back to the store for an exchange? Better yet, take your DMM with you to the store and measure those 2 slots on another distributor, and compare it with what you measure on yours.

 

Thanks, good info XLT

To clarify, the voltage of 9ish at the coil+ is normal during 'run', but what about cranking? Is the the low 9volts normal during cranking?

White to the module has 0 volts during cranking. I haven't opened up harnesses yet, does it come straight from the 'S' terminal or does it come from the ignition switch? And the Red to module is good, 12v run or crank.

Reason I ask : I may have found an issue with the switch while testing last night - there was one instance when turning the key from run to crank where the starter cranked but stopped as I hit the end of the key turn, but as I backed off from the end of the keys stroke it would hit the starter again.

Wondering if that's causing some trouble too.

 

It should have 12v + while cranking and if it doesn't, you've got a wire loose somewhere. I believe the coil should also go to the S terminal on the relay to get the 12v during cranking.

Funny that it worked before though. Sounds to me like you had something short and/or melt. Have you traced all your wires around? Did you ground something you shouldn't have or pinch it?

 

Yes, the coil + should get full 12v when cranking. This is done within the starter switch by shorting out the resistor that the coil + normally gets its power through during run. If you're seeing intermittent starter engagement that's somehow affected by the key switch, you should check, clean, or replace the switch.

You can try another test. Disconnect the normal wire going to the coil and connect a wire directly from the battery + to it, then try to start the engine. Don't leave that connection for too long, as that can burn out the coil.

 

I'll give some of these suggestions a try. I have a new ignition switch and solenoid coming. Probably won't get to anything immediatly.

As far as pinch or shorting from damage, I highly doubt it. There's no external damage to any harnesses or connectors, no corrosion. Under the hood anyway. I haven't gotten under the dash yet, but if there was something hot enough to have caused damage in the cab, we would have noticed. Having said that, I'll be going thru the whole thing. Starting with the switch. Who knows what's been lurking in there for the last 40 years.

 

I thought I should follow up on this, as it bothers me to see questions asked, potential answers supplied, and then no follow up to it or outcomes.

So a lot of problems seemed to compound here

2 pooched new distributors. One with a faulty pickup, and one with an incorrect shaft installed, causing the timing to be way out. Third was good

Ignition switch contacts were burnt and corroded.

Original DS Module had also failed, I replaced it with one from Napa, and still couldn't make anything work. Did some testing on the module and found that the new one was bad.

Traced all the wiring in the truck to make sure there wasn't something on the truck shorting causing it to fail. All was well. NAPA wouldn't warranty it, thanks.

Replaced everything with an MSD setup. Problems almost solved, for a short run, a few minutes, it ran "ok". Then it all went to hell again. Wouldn't idle, missing, then couldn't start it. Back firing bad thru the carb when cranking. Turns out it there was a scrubbed cam lobe on #2 intake.

What an adventure lol. I'm glad it's just a toy.

The cam shaft really pissed me off, mostly the excuses I got from the machine shop who supplied parts for the build and Mellings. Somehow it was my fault, or the oil, or valve spring tension or any number of other reasons. Confounds me that 1 lobe would fail when there are 15 others that are fine. This is a hardening failure of either the cam lobe or the lifter.

Anyways, there's my findings. She runs like a top now. It's been a long road.

 

All those problems will certainly make diagnosis difficult. Glad you got it all sorted out.