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1979 chevy c10

looking for ideas on no start
4.1 engine with no spark
I have replaced everything in distributor including plugs and wire
still no spark
rotor is turning when engine cranks so I assume timming chain is good

I have replaced Ignition Coil ,Distributor Capacitor & Terminal Block, pickup coil ,Ignition Control Module,Distributor Rotor, cap , wires

I AM out of ideas and seems like I am just wasting money on parts and still no start
truck only has 50k for miles on it and not driven very much just died going down hwy with out any warning
THANKS FOR ANY HELP

Pull the Distributor cap and have someone crank the engine while you watch. Make sure the rotor is spinning while the engine is cranked… If it’s not turning, you may have a broken timing chain.

Yosemite

This truck should have the GM HEI system and that’s probably the best ignition system that ever existed.

Verify that you have battery voltage at the distributor. If not (and my memory is VERY fuzzy on this) I think there may be a fusible link in that power lead. I’ve got a few factory GM electrical manuals on this era of car and truck. Will take a look at them and determine whether the link theory is correct or if my memory is fuzzier than I think. Will post back later.

Um… coil?

The way these motors produced spark is pretty simple. 12VDC energized a coil wrapped around an iron core. The points, driven by the little cam in the distributor’s shaft, were in series with the coil primary and opened the circuit when the distributor cam opened the points. The magnetic field that had developed in the coil’s coil collapsed when the circuit was opened and induced a voltage spike in the iron core. The induced spike was then directed to the proper sparkplug by the rotor. There are some minor details like the condenser (a capacitor across the points to prevent charges and material transfer), but that’s basically all there was to it.

Since the rotor is turning when you try to start it, you have correctly assumed that the timing chain is good. You’ve also verified that you have no mechanical failure between the camshaft distributor gear and the distributor.

Since the problem seems to be electrical electrical, you’re going to want to start by checking the coil primary for voltage. It’ll be VDC, basically a squarewave. If you’re using a simple voltmeter, you may see it as a low voltage. You’ll actually be reading the average between the full battery voltage and zero. If you’re using a scope, you’ll be able to see the actual wave and check the waveform.

If you have a proper waveform on the primary, and nothing out the core, the coil is fried. The primary is being turned off & on, but you’re getting no induction, probably because the coil windings are shorted.
If you have full battery voltage, than the coil is shorted to ground internally and you’re getting no induction to the primary.
If you have zero voltage, than either you have an open or a short to ground in the wire leading to the coil. Trace back to the starter relay, and to the battery if necessary, from there.

One more thing: be sure your ground straps from the engine to case ground are good. If they aren’t than they might have enough resistance to eat up (“drop”) too much of the voltage to allow the coil to induce sufficient voltage to spark with the added large load of the starter motor, but still allow the starter motor to crank.

Two more thing: be sure the points are opening as the rotor approaches one of the spark plug paths; look at the posts under the cap, turn the crankshaft by hand until the points open, and see if it’s lined up with a sparkplug connection under the cap. That’ll at least give you an idea if things appear normal without pulling the timing chain cover off. The points need to open and induce the spike in synch with a sparkplug connection at the rotor, else the motor won’t fire.

Post back with any questions or with the results.

I have replaced Ignition Coil ,Distributor Capacitor & Terminal Block, pickup coil ,Ignition Control Module,Distributor Rotor, wires

Check voltage at the coil primary. And the engine ground to the body. A simple ohms check should suffice.
Also double check the timing of the points relative to the spark plugs and also to be sure they’re firing the correct cylinder.

Post the results.

The schematic I looked at does not show a fusible link in that power lead. You need to make sure that the main power lead at the distributor cap (red or pink) has battery voltage when the key is in the RUN and START positions.

If there is no power at that lead then one has to suspect a bad ignition switch or a failed fusible link farther on down the electrical chain.
I think the fusible links on this model are run off of the starter motor solenoid connection and resemble short lengths of wire; probably in color.

With the highest respect, are you certain it’s the spark that’s missing? Sometimes someone will say they have no spark. when what they actually mean is that the engine isn’t firing… and they may not be the same thing. I interpret “no spark” as meaning no voltage pulse. An engine can have a properly functioning ignition system and still not fire due to no compression or no fuel.

Just making sure I didn’t misunderstand the post. I’ve done that before. I even overlooked the stuff you said you’d already changed when I wrote my first post… and error for which I humbly apologize.

thanks for all the info when no SPARK I took a spark plug held it to the block while plug in and cranked engine over no spark or anything coming from sparkplug
I will check volts and will let you know THANKS AGAIN

We’ll get 'er done, no worries. Just keep nibbling away at the problem and we’ll keep talking.

I guess lucky sometimes, but OK4450, who has already joined us, is one of the most knowledgeable guys I know, and there are some other extremely knowledgeable and highly experienced guys here too. A no spark condition is always fixable.

Off hand, does anyone know if the 79 used a ballast resistor or ballast wire coming of the coil? The ballast wire burned out on my 71 Buick and it stopped dead. I replaced the wire with a Mopar ballast resistor and it was good to go.

Ed B.

Cool page with chevy wiring diagrams. The pic I attached is the ignition fusible links.
http://forum.73-87chevytrucks.com/smforum/index.php?topic=11766.0

Ed B., neither. 1979 had the HEI distributor. Uses full battery voltage to the distributor/coil assy.

If the ballast resister was the problem, the truck would seem like it was starting, but when the key was returned from “start” to “on”, the engine would immediately die. I don’t get the impression this is the symptom.

I presume this truck has a conventional distributor, with one high voltage wire coming to it from the coil, and individual wires going to the spark plugs. And a separate single ignition coil probably mounted up high on the firewall, and instead of mechanical points, uses some kind of electronic ignition module, timed by a magnet or something on the distributor shaft. Is that right?

The ideas posted above are good, especially to make sure the 12 volts is getting to both the ignition module and to the 12 volt terminal of the coil. And that the ignition module ground is solidly connected to chassis ground somewhere.

I’m assuming you’ve carefully looked for carbon tracks (indicating the spark is jumping to the wrong place) on the inside of the distributor, distributor cap, and spark plug wires. And that the engine is well grounded to the chassis. Likewise, the battery ground is well grounded to the chassis.

Everything still seem ok? Still won’t start? Try starting the engine in complete darkness, with a helper. You might can see a spark jumping somewhere in the engine compartment it shouldn’t, that you can’t see in daylight.

With H.E.I ignition the coil is mounted in a square recess on top of the distributor cap. There is no center coil wire. It’s a direct connection. The module is mounted inside the distributor.

Thanks for the description of HEI technology. Just curious, how is the spark timing determined? Conventional points, i.e. a set of mechanical points that open and close as they rub on a cam on the distributor shaft, and that creates a low voltage signal to trigger the ignition module to produce a spark via the distributor cap mounted coil? Or is there some kind of electronic sensor and it detects the rotation position of the distributor shaft?

The GM HEI of this era used a Hall Effect generator inside the distributor. Do a net search for an explanation of a Hall Effect. It basically involves a timer core, an 8 toothed wheel, and magnetism.

Even the HEI distributors still used a conventional vacuum advance mechanism with centrifugal weights and springs. I forget the exact year but I think electronic spark timing started with GM in 1981 as that is the year when everyone (mostly) was using O2 sensors, ECMs, and so on.
In the mid or late 80s GM revamped the HEI a bit. Again, the year is a hazy memory…