Baffling ignition problem

I continue to have ignition problems with my '74 cj5. Here is my current one. My jeep ran just fine until after I put it to bed one night a few days ago. The next morning I changed the oil and because speedometer stopped working I fiddled around behind the dash and discovered that my Speedo cable was not screwed in so I screwed it in. Now it wont start. Insert look of bafflement. With the key to acc I get about 12v, at start I get about 10.5v. I thought that maybe after having washed the engine bay after a wet trail ride maybe there were some corroded contacts. To test I jumpered from the relay to the coil. Nothing. From the dist to a good ground. Nothing. Replaced the pertronix with points. Nothing. Briefly jumpered from the + coil to the + pole on the battery nothing. Swapped out the coil with a known good coil. Nothing. Swapped out the rotor. Nothing. The cap is recent so I presume that its good. Help please.

Karl

 

Could you have dislodged something under the dash? Might be a shorting wire or a partial ground... the underside of most dashes are a mess.

Replace the cap... to presume is dangerous at this stage and it only is a couple bucks.

 

Karl, I presume the engine cranks but won't start? The standard thing is to check for fuel and spark.

Assuming you look down the carb and see a squirt of fuel when you pump the throttle, and you have no spark (remove the coil wire from the dist cap and hold near a grounded surface). If you have no spark, you have points ignition, and you see 9 or 10 V at the coil, either the points aren't opening, the condensor is open or shorted, or the coil has a short. Both coil terminals will show ~10V if the engine is off and the key is on, regardless of the position of the points. The cap and rotor are irrelevant if you have no spark from the coil wire to ground.

I can explain more about the coil-points-condensor circuit if needed. hth Tim

 

Timgr,
There is fuel. I have a fancy spark checker; plug it in and ground and it lights up when there is spark. I prefer the spark checker because there less potential for getting shocked, starting a fire... I only get one spark that comes as soon as the ignition system is energized (right when the key is turned and not after). I had a pertronix ign. but I took it out and put in a tested (nearly new and known to work) points set. I have not tested the points, if you measure resistance on a capacitor they take a charge and show increasing resistance, but I am reasonably sure its OK. I will check to be sure though. I get 12v from the + pole to gnd key on. WIth the starter rolling it drops to 10.5v. Originally I thought this meant that the high voltage bypass that is wired to the relay, that is, according to the tsm, the blue wire, that bypasses the green resistance wire from the ignition switch that is energized while running, was corroded. It turns out that this is not the case though because I jumpered across it with no effect. The only other thing I can think of is a wire under the dash, but I cant think of anything that would have the effect of preventing starting if I am getting voltage to the coil.

Karl

 

Karl, from your description, it seems you understand what should be going on with the points circuit. The one blink from your spark checker probably comes from the initial energizing of the coil when you turn the key on. You could try removing the distributor cap, moving the engine to where the points are closed, turning the key on, and moving the points open and closed with a stick or something. Each time the points close, you will make a spark ... may not work with your spark checker, since you need a complete HT circuit for the detector to be triggered. I'd suggest that you put a plug wire on the coil and connect it to a spark plug resting on the fenderwell if you are concerned about a shock.

JMHO - I'd forget about the dash until I was sure that I could make a spark with the points circuit. If you have 9-12V at the coil, there's nothing else that the dash circuit does except turn that 9-12V on or off. Your findings of 12V running and 10V starting is backwards, but that shouldn't keep you from getting a spark.

 

I am off to a work related geology field trip and wont be able to work ont the Jeep for a few days. I will post updates when I get back.

Karl

 

Back from my geology field trip. Mmmm, turbidites. I had a little bit of time to work on the Jeep. I think I have narrowed the problem down to the starter solenoid and the voltage regulator. WIth the ignition key in the start position I get 12v to the solenoid small post labelled start (blue wire). on the other small post labelled ign. and no other wires connected I get 0v. When I hook up my voltaeg regulator I get 10.5v measured from the post to the - post on the bat. From what I can figure I should be getting 12v from the small ign post, but I am not too confident in this because I cant imagine only that part of the solenoid not working. I checked my points and originally they were good, but in the process of jumpering things let all the smoke out and it was too late to get a new one and check my latest notion about the solenoid. Any thoughts?

Karl

 

Oops. Re pics of the Jamboree. I got em. Just reducing the size of em and posting. I should have some up tonight or tomorrow. I will post a message in the ot forum.

 

I have solved the ignition problems I was having. I had two problems. The first was a couple of corroded contacts. I cleaned everything up and used plenty of dielectric grease. I put the points back in and it fired right up first try. I then reinstalled my pertronix ignition and it would not start. I checked the wiring and added a ground from the dist. to the -ve bat post. It would not start. I tested everything I could think of and came to the conclusion that the Pertronix has failed. I read a couple of other threads on this board that discuss the same thing: put the jeep away come back no start. I contacted pertronix and they suggested a few tesets which seem silly to me given that it runs with points. Nevertheless I will try them to make sure, but I am jaded from what I have read about the durablity of the pertronix. Has anyone else had problems? Do any of you run the MSD ignition? What do you think of it?

Karl

 

Good to hear that you were able to figger it out. Sorry, but I can't offer any good insight...