No Fire

Ok guy's here is what happened. I bought a 1977 CJ5 Jeep this past friday, 304 3 speed. When I got the jeep home I parked it in my building. Then saturday I decided to go out and tinker with it. I noticed that the factory tach and factory clock was not working. I thought maybe the fuses was were bad. I went to the auto parts store and bought all new fuses and replaced them. Then I removed the tach. Before I treplaced the fuses and removed the tach the jeep was starting and running like a charm. After replacing the fuses and removing the tach the jeep is getting no fire. So I replaced the coil and the ignition box. Still not firing. So I ask some friends and they told me that when I removed the tach I borke a connection, so I replaced the old tach and still nothing. They also said to make sure that the ACC fuse was not blown, checked that still looks good (but not sure what amp the fuses needs to be, would that make a difference)Then I removed the tach again and just tied the wires together that were on the tach. No understand this is a factory tach and clock.

does anyone have any idea's on what I should do.

Also I was told to try and hot wire the jeep by running a wire from the positive side of the battery to the positive side of the coil, he said that should give it fire, did that and still nothing.

Lost in Tennessee Please help

 

I am assuming you have the original Duraspark ign. Chances are...it had nothing to do with anything you did, rather just a coincidence. The box probably died (common). If you wish to keep everything stock, replace the box. If you want to improve your ignition system ten fold...then replace the distributor with an HEI and get rid of the box. These work so well, you will think you changed your engine.
http://store.summitracing.com/partdetail.asp?autofilter=1&part=MAA%2D8560001&N=700+115&autoview=sku

 

A '77 will be Prestolite ('75-77), not Duraspark ('78-on).

You need to be systematic. Randomly changing parts is the wrong approach.

Do you have a meter? With the key on, see if you have power to the coil. Next, see if you get any spark when you try to start the engine. Take the coil wire out of the cap, hold it close to a metal surface, and crank the engine. You should see a 1/4" long blue-white spark. Don't get shocked - I have a pair of long plastic pliers (I think they are actually fuse pullers) I use for this. Taping the wire to the end of a stick also works.

No juice? Look at the ignition switch (a common failure) and the wiring between the ignition switch and the coil.

No spark but you have juice? Then there's something wrong with the ignition, either the module or the parts in the distributor. Test that you have power to the module with the key on.

Got spark? Look for no fuel. If you have spark plus fuel, it's going to fire.

JMO - don't spend a lot of money to fix Prestolite ignition - there are better alternatives (see McG post above - A Duraspark from a '78-on is another possibility).

Welcome from Boston!

<edit> If you have no power to the coil, a hot wire won't help. You need power to the coil and to the ignition module. A hot wire only works with points ignition.

 

He said he hooked power direct to the coil, so I figured it would not be the switch. I guess we should ask...How do you know that is has no fire?

 

Maybe you posted before I added this? AFAIK a hot wire won't work with electronic ignition. The switch would disable both the coil feed and the feed to the module.

 

Does the prestolite get power to the box first? I thought it went from ign switch, to the coil, then to the box. But, I do not have one, so I was not sure.

 

I don't think that's possible, since the box has to interrupt that connection to make a spark - if the box opens that circuit to make a spark, then there's no power to the box. Seems to me all modules would need a separate power feed. I could check the diagram at home.

 

This is what I always thought the Prestolite was like. One feed wire to the coil, to the mod, and to the alt. All comes hot with the ign switch turned on. Is this incorrect?
http://www.jeepforum.com/forum/showthread.php?p=5200340

 

That's the HEI module driven by a Duraspark distributor. The HEI module has a feed from the ignition, and the coil is fed from the module. The Prestolite is set up just like the Duraspark, with an external coil and a module sitting on the fenderwell (they use different principles to trigger, but the packaging is very similar). The Duraspark or Prestolite could be like the HEI and send power to the coil from the module, or there could be a separate wire from the ignition to the coil and from the ignition to the module.

Either way, there needs to be power to the module in addition to power to the coil. The module can't depend on the coil feed for power, since it needs to be turned on and off - there's no physical way to do that and still have power to the module at all times. You cannot hotwire an electronic ignition by putting a wire from the battery to the coil - it just won't work. You may be able to hotwire it by feeding power to the module, which then sends power to the coil (ala GM HEI), or by feeding power to the coil and module both ... it depends on the design of the circuit.

Clear?

 

I am going to have to disagree with you here. And I'll tell you why. My Brother's box stock 1976 CJ7 is sitting in my shop right now. It has a 304 with the stock prestolite. It has a one big red wire coming from the ign that branches into three. One goes to the positive side of the coil, one goes to the ign mod and the other goes to the reg.
So, in this case. If the ign switch was bad, and not giving power to the mod or the coil, seems reasonable to me that it would start..
You will see in this first diagram that the factory has it just like my Brother's. A wire to the positive terminal and to the ign mod off the same wire.
http://www.junkyardgenius.com/ignition/jeep/jeep04.html
My feeling...(not being an expert on the presolite system) is that the mod is triggered by the dizzy, which then tells the coil to fire from the info it gets to the dizzy, switching the negative side of the coil, making it fire.

 

Oh...also, with other types of ign systems, the positive terminal does not switch off or on, it just stays hot when you turn on the ign, the negative side is what switches off and on. So a mod could be powered by the positive terminal since it's a steady on. Just could not be powered by the negative side.

 

I made a drawing of what I understand here -



This should be self-explanatory. In example B, a hot wire to the coil will only work if +12V can backfeed to the module through the switch. Don't know if this can happen, or what other effects it might have. If the module feeds the coil, like example C, then a hot wire to the coil will not work under any circumstances.

 

This is how this works.
A hot wire from your ign system goes to the positive side of the coil. That same wire goes to power the module. The negative side of the coil (the one that triggers the coil to fire) goes into the module.
One single wire comes off of the distributor that turns into two wires via a plug but still on the same wire. They both go into the module as well.
The distributor sends a signal to the mod, the mod sends a signal to the negative side of the coil, the coil fires. The red wire off of the ignition to the positive side of the coil, does NOT fluctuate and is used to power the mod. The negative side is what fluctuates. It's pretty much a fancy set of points, just using a different way to signal the coil to fire. So, jumping the power to the positive terminal (on this ignition) will make this start if that was what was missing.