Need a bit of help getting this thing firing

B

big_b16

New member
79 Scout w/345. Cannot get it to fire. Have checked and replaced wires. Am getting 12vdc at the positive side of the coil. Originally had points but bought new pertronix unit. Don't think it works since I am not getting an intermittent 12v signal at the negative side of coil when I rotate the distributor past a lobe or two. Have also installed points (0.016" gap). After a few days of working on it, realized we had a **edited** prestolite cap and a Holley rotor (banged on the head of cap when rotating). We've timed the bugger off of #8 more times than I care to remember. At one point we had it running very rough but timing light showed it 50 degrees retarded (like I feel now). Tried to re-time it and it never ran again. I've got intermittent signal on each plug wire as tested with inductor lead of timing light. New ground wire to block from battery. Tried 12v direct from battery to pos side of coil (actually resistor since we're trying with points). When I pull a plug and check the spark, there's a very weak spark. When I put a plug in the coil wire, there's several small sparks, not very easily seen. I am of the impression that if you're running a plug out of the coil, that baby should pop pretty good. I'm at wits end on what the issue is. Is it possible the wrong coil is being used...if so, what coil should be bought in order to use the Holley cap/rotor with points. If the pertronix unit is working properly by not cycling while the distributor shaft is spinning, can the same coil be used with it. Thanks for any thoughts. I'm at wits end on this one. Almost time to make some deep lake structure with this thing. One more thing, is it alright to install the condenser in the bracket along with the coil and connect it to the negative side of coil there, the wire connecting it to the points is a short, the ballast is simply on the other end of the wire?
 
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Welcome to the forum dude, but I gotta say...for an initial post...ya got a big pile of crap ta deal with! So I'll be gentle with ya so ya will come back and visit agin!

First off, take about two hours and read every post in this ignition sub-forum...because you will see this same theme repeated over and over again! You are/were not alone...ya just don't know stuff, that's why us old farts exist...for training purposes only.

Since you still have the original stuff, put the ignition system all back stock and let's start from there, you are bouncin' all over the place with the shotgun approach to diagnostics. And ya ain't told us which distributor you have!!! I ain't got distributor esp! Same for which part number p-tron, there are only about 47 different numbers available and many folks have the wrong ones!

The oem coil works just fine for pertronix conversion, absolutely no reason to change that if it's functioning properly.

And no need to change the "feed" to the coil positive from the switched source, breaker points require the ballasted feed, the pertronix don't give a shit, it'll work either way.

The condenser that is mounted on the coil has nothing to do with ignition system operation, that is only used for rfi suppression to reduce cracklin' on the radio! Throw it away, it's useless.

Just put the points and condenser back in the distributor, set the dwell, and fire it up. If it won't fire, then we'll make it fire. Once it's running right, then we'll install the p-tron, setting the air gap on it during the process with the "special tool" that was packed with it (depending upon which p-tron and which distributor you have!).

I don't think you have a "pertronix cap"...you have a prestolite cap (if it has male terminals) and you are right it won't work correctly onna Holley distributor. But we must know which distributor you have, if you don't know, then your educational process will take an additional hour of time while ya read the thread that tells ya how to tell! See tha sticky at the top of this sub-forum? Read it!

Get busy, ya gotta lotta homework to do tonite before ya go wrench! You will find coil specs for nearly any application along with source part numbers.
 
Thanks. I guess I forgot to mention that there's a Holley cap and from what I can decipher it's a Holley distributor. I'm basing that off the fact the distributor shaft is round with a notch. I was of the impression the prestolite had a d shaped shaft. I also did a little comparison of the pics you posted regarding the different types of distributors. I've got the curved Holley points installed. I checked the clearance of the gear and the housing as per one of the threads you had some other time...it's at .030". I also dis-assembled the distributor to ensure the weights were working properly and there were no scorch marks on the plates from a spark grounding out somewhere.

The condensor on the coil is the one that would usually go in the distributor, I just put it on the coil for ease of access. I'll bury it back in the distributor once she's ready to run. Unless it's imperative it's connected directly to the points versus on the end of a 12" piece of wire connected to the points.
 
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So the distributor has been removed from the engine????

That adds to the deal...go here and make certain ya got it stabbed correctly:

http://www.forums.IHPartsAmerica.com/ignition-tech/640-new-guy-clueless-about-ignition.html

The ez way to verify tdc on #8 compression stroke is remove the passenger side valve cover and watch the rocker arms with yore left eye, and watch the timing Mark with yore right eye. If yore gotcheyed like me, that's a real advantage in doing so.

And, verify that the ground strap tying the breaker plate to the distributor body ground is in place, that must be used no matter which guts ya got in the distributor.
 
I read that thread a couple days ago. We've sometimes rotated the oil pump so that that when I stab the distributor it'll line up on the correct wire...sometimes it's quicker than pulling all the plug wires to try and move them one way or another. Either way, I'm fairly certain the distributor has been stabbed properly. I've seen the shiny bushing/washer just above the oil pump drive slot. The cam gears looked intact while I was in there too.

The ground wire is connected to both plates in the distributor with shiny clean screws. No dirt in the distributor whatsoever.

We haven't pulled the valve covers to verify tdc, but I've used a compression tester (and a finger after a while). As well as observing the piston height using a wire. I stopped rotating the engine at about 5 degrees below so I knew I hadn't bypassed the point where the exhaust valve opens. Had the rotor pointed exactly at #8 and have rotated it a lobe either way in an attempt to get it to fire. When that didn't work, went so far as to pull distributor and rotate it 180. Once that didn't work, we put it back. We've set the wires starting with 1 and going around clockwise through the firing order.
 
big_b16 said:
thanks.
The condensor on the coil is the one that would usually go in the distributor, I just put it on the coil for ease of access. I'll bury it back in the distributor once she's ready to run. Unless it's imperative it's connected directly to the points versus on the end of a 12" piece of wire connected to the points.
Click to expand...

The condenser wired out side of the dizzy May make a difference. When it is shunting the back emf from the coil the current spike is relatively high. The loss in coil field collapse rate due the the small resistance the extension wire adds to the primary system will have an effect. Really dunno how much. But sure thing if it was more effective out side of the dizzy they would have put it there. Try it where it belongs. One unknown eliminated is going to be one question answered.

Robert
 
Here's a couple pics of what is there.

picture146a.jpg


picture147a.jpg
 
big_b16 said:
.

We haven't pulled the valve covers to verify tdc, but I've used a compression tester (and a finger after a while). As well as observing the piston height using a wire. I stopped rotating the engine at about 5 degrees below so I knew I hadn't bypassed the point where the exhaust valve opens. Had the rotor pointed exactly at #8 and have rotated it a lobe either way in an attempt to get it to fire. When that didn't work, went so far as to pull distributor and rotate it 180. Once that didn't work, we put it back. We've set the wires starting with 1 and going around clockwise through the firing order.
Click to expand...

You time on tdc #8 on the compression stroke. That is no where near to when the exhaust valve opens. Like 180 degrees away. You need to re check the dizzy instal point.

Turn the motor by hand (clockwise from the front) with your compression gauge or finger (my preferance) in #8 plug hole. As soon as you begin to feel air pressure continue turning the engine less than (180* more) untill the balancer Mark and the "0" Mark on the front cover line up. That is the tdc you want to use when verifying proper dizzy clocking.
Rk
 
Robert kenney said:
Turn the motor by hand (clockwise from the front) with your compression gauge or finger (my preferance) in #8 plug hole. As soon as you begin to feel air pressure continue turning the engine less than (180* more) untill the balancer Mark and the "0" Mark on the front cover line up. That is the tdc you want to use when verifying proper dizzy clocking.
Rk
Click to expand...

That's exactly what we've been doing. When I stop it after feeling air blow past, it's usually about 50* low, then I slowly rotate it up to right about 0*. Does it matter if it's a couple degrees below, the coil will line up just right when it comes to 0* or 4* above which is think is right. My gut instinct is that I'm not getting a strong enough spark. I think the timing is right.
 
Now that we have pictures. How are the coil and the condenser grounded? Ground the condenser to the dizzy body first. Looks like there could be a source of bad grounding.

Robert
 
That's possible, however if the condensor is grounded through it's body, it is grounded through the strap into the block with the bolt holding the coil bracket down. I'd imagine the same bracket is what is grounding the coil. We can easily put the condensor back into the distributor, but when it was there the engine had the exact same symptoms.

Dizzy body should be grounded through it's securing bracket and bolt as well as body into the recess in the block. Plates in block are grounded through the two screws that hold it in place in the dizzy. I could do an ohm check on all grounds but don't think the potentials will waver from the block.
 
Any easy tests to verify the output of the coil. I hooked it up to an auto ranging multimeter, but once I kicked it over, it didn't auto range fast enough. Every crystal on the screen illuminated...craftsman almost had to do a return for a faulty dvm.
 
Try 12v+ to the + side of the coil not the resistor. Depending on which side of the resistor you put it on you May not have been supplying the coil with straight 12v power.

Rk
 
With a '79 I was informed they came with electronic ignitions, so we added a 1.8 ohm ballast resistor to the + side of the coil. Is this correct?
 
Robert kenney said:
try 12v+ to the + side of the coil not the resistor. Depending on which side of the resistor you put it on you May not have been supplying the coil with straight 12v power.

Rk
Click to expand...

Yes.

What color in the spark. Should be blue - blue white. Not yellow. Also the gap that the spark will jump is directly related to the voltage. Should be able to jump 1/8 - 1/4 inch minimum.

Verify primary voltage: with the ignition switch on run and the points closed, you should have 7-9 volts between ground and the + coil terminal. You should see approximately the same voltage across the + and - coil terminals. Do the test quick so you don't over heat the coil.
 
Robert, I should mention that "beastud" is the other guy who is working this project with me.

We've tried the direct wire to the coil and the points didn't care for it much. We tried it with the resistor inline direct from the battery and same thing. I've used the dvm to measure battery voltage at the coil both through the ignition switch and with the direct wire (obviously). We used 16ga wire for the 12v source so I don't think we're adding any unnecessary voltage drop due to the small added resistance.

With the resistor on I think it was right near **edited** 4v. Too low.

The spark was very weak, pretty hard to tell the color. We have all plugs gapped to .035" and I doubt very much if it would jump a 1/4" gap. I used a gap tester that was about 1/4" from the end to the ground and it never would jump. I tried a different kind of spark tester and the sparks were orange...which might be a product of the tester (the ones you wire inline with the plug still in the block and the plug wire from the dizzy).
 
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beastud said:
with a '79 I was informed they came with electronic ignitions, so we added a 1.8 ohm ballast resistor to the + side of the coil. Is this correct?
Click to expand...

With the coil you have the system needs a full 12 volts while cranking as the starter draws the battery voltage down to low to make a strong spark, during teh run phase the balast just about halfs the voltage.

For this testing go direct to the coil with 12 volts.

Rk
 
Should the spark be strong enough that you can hear it pop when you've got the plug out and grounded? I know on my boat motors and others it usually does, I've never had so many problems timing a car that I've had to remove them to troubleshoot.
 
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