Truck won't start! Ignition help needed

[ginter]

I got no spark! 72 Cheyenne 350/350

The truck was running like crap, cutting out pretty bad. It started out slowly, but over the course of a week it got progressively worse. Acted like a fuel or vacuum issue. I went out Sunday and started the truck, still ran like crap but it did run. Checked vacuum and replaced very short carb bolts (recent engine swap) and couldn't find any leaks. Went out and bought tune up parts, and changed the plugs. THAT'S ALL! Plugs that came out were mint, normal to a tad lean. Obviously they were all firing OK. At this point the truck wouldn't start at all. No spark. Not even trying to fire. I have 12 volts at the coil during cranking, the hot wire to the coil itself has power. A new coil tests exactly the same as the old one on the bench with a meter. Primary 1.5 ohms and secondary 11k ohms. Installed the new coil with the same result. Pull the swcondary coil wire off the dizzy and check it for spark against ground while cranking, nothin'. I pulled the tach wire (I think that's what is) from the negative postof the coil, and pulled the external condensor (radio suppression) from the positive pole. Nothin on the coil now but secondary wire to the dizzy, positive wire for power, and negative wire to the dizzy. Still won't start.

Any ideas?

[Gordo]

Assuming it still has points, I would replace the points and condenser and set the gap with a dwell meter (30 degrees) if possible, if not a feeler gauge will do. If memory serves me right it was .019 for new points or .017 for used ones.

[ginter]

Thanks Gordo. That is the next step as soon as the rain stops.

But why do I not have any spark from the coil secondary to the distributor cap? It just doesn't make sense/

[Gordo]

That's what the points control.

[ginter]

OK, it stopped raining. New cap/rotor/points/condensor. Still no spark. 7 VDC across the coil primary with the key on, 11.5 VDC while cranking over. I even put a jumper wire from the starter (you know, that post that bypasses ballast while cranking) to the coil primary positive just to make certain it had 12 VDC when cranking. Same problem.

Anybody have any idea where to go from here? Please? Troubleshooting steps?

[lngbed71]

Ignition switch?

Have you tried the voltage regulater? I dont mean to make it sound like you're dumb, but have you tried the fuses, starter? I've had alot of problems with mine, until one day I got sick of messing with it, and bought all new HEI, wiring, starter, alternator, everything that could have been the problem. It was needed big time..

[72K10]

The wrong plug wires might cause enough resistance so that spark doesn't make it to the plugs.

But it sounds like something very simple that you're overlooking out of frustration. I'd recheck how you have the coil, starter, and distributor wired. If I recall correctly, there's a (green?) wire off the starter that runs to the points-style distributor / coil. That may have something to do with it. Or you might have the coil wired backwards??

It's gotta be in the wiring somewhere, if all the components test OK

[ginter]

Thanks for the replies guys. If any of my assumptions here are wrong, please feel free to correct me. I don't claim to be a genius. Live and learn.

lngbed71 Ignition switch?

Well, I have no voltage at the coil with the switch off, 7VDC with the switch in the run position, and 12VDC with the switch in the start postion and the starter cranks away. It would appear as if the ignition switch is doing it's job.

Have you tried the voltage regulater? I dont mean to make it sound like you're dumb, but have you tried the fuses, starter? I've had alot of problems with mine, until one day I got sick of messing with it, and bought all new HEI, wiring, starter, alternator, everything that could have been the problem. It was needed big time..

Hmmm... I checked the fuses, re-seated a lot of the connections (especially anything labeled ignition or looking like it might be). I'm not sure, but shouldn't one of these trucks start without an alternator installed and just a battery? I mean all of the requirements for spark are there at the coil. I don't really want to do a wholsale swap of electrical parts trying to fix an ignition problem.

The wrong plug wires might cause enough resistance so that spark doesn't make it to the plugs.
But it sounds like something very simple that you're overlooking out of frustration. I'd recheck how you have the coil, starter, and distributor wired. If I recall correctly, there's a (green?) wire off the starter that runs to the points-style distributor / coil. That may have something to do with it. Or you might have the coil wired backwards??

But I never changed the plug wires. It ran, an hour and a half later after changing *JUST* plugs, it wouldn't start. I didn't do any wire swapping or changing. All of the plug wires test good, including the coil wire (4.5 ohms). They're also in pretty nice shape. They're obviously not that old. As for the green wire you speak of, mine is yellow, but I know the one your talking about. I even ran a jumper wire from that post on the starter to the positive coil primary so it had constant 12VDC - no joy. The voltage at the coil positive primary also goes to 12VDC when cranking indicating that the function of that wire (bypassing the ballast resistor) is working properly. I would tend to agree that based on the circumstances it's likely something very simple, but I can't find it, and the truck had no spark before I ever touched a wire.

Could this problem be caused by a faulty Vreg or alternator?

Is there some voltage that I'm missing or check to see if I'm missing?

It seems to me that all the requirements for ignition spark are there, but there is still no spark.

Help?

[Lippyp]

I had a problem a little while back with crappy running and then dying on me with a refusal to start with no spark. It turned out to be a short inside the distributor where the connection for the condensor to the points was. It was making intermittant contact and also shorting out against the baseplate of the distributor. Took ages to find as it looked like it was making contact. Fried the condensor too. Just check all the wires again and make sure this isn't happening. This was on an aftermarket Mallory twin point dizzy though not stock GM.

[old Rusty C10]

how about checking to see if theres any wired near or touching the exhaust i had a ford that did that and it blew out a fuseable link took it to two mechanics and i checked it and rechecked it until one dayi was good and annoyed after it stalled on the bridge and found it bypassed the wire to get it home and reinstalled the fuseable link and it was good

[ginter]

I think I have a possible cause figured out. Lippyp is very close. This truck has stock points dizzy, although it appears to be a reman. Looks almost like new. I've owned the truck for just a month or so, and I don't have a ton of history. Anywho...

The standard dwell meter hookup (red wire on negative coil primary and black wire to ground) produces NO movement of the gauge in either tach or dwell mode. Hhmmm... The old and the new coils produce no spark. The coil has voltage supplied to it, and it's good, but it's not doing it's job. Where's the ground path for the coil? Well, it's the wire that goes to the dizzy. That wire connects to the points. Old points/cap/rotor/condensor as well as new were no help either. The points when closed (if grounded to the base plate properly), and the wire from them provide the ground path to the coil. Perhaps the dizzy wire is bad? Stranger things have happened.

I'm going to jumper wire the points to the negative coil primary after work and see what happens.

Question: I'm used to seeing a ground wire in a dizzy that grounds the points plate to the distributor base. Do these dizzys have anything like that? Or is the base directly grounded to the housing?? If so, that could be the cause as well.

[ginter]

Lippyp is the winner!

The stupid little spring clip on the bottom of the points had come off and was shorting the points to the base plate. Trucks running again. Thanks for the replies guys!

[cableguy0]

well if it was me i would end all future frustration and go get yourself an hei and be done with the points nightmare

[ginter]

That's the plan. I didn't want to try to do an upgrade though when the truck wouldn't run. I like to know everything is solid before doing upgrades. I could have ended up chasing wierd stuff and not knowing whether it was the new parts or the something that was causing it not to run in the first place.