No-fun ignition puzzle.

[1968 Falcon]

This forum is always the place I come to when I am just completely stumped. My butt has been saved when I'm thousands of miles from home by the advice I've found here, so I'm really grateful to all of you.

With that said, here's the problem I'm having: my 1968 Falcon with a 200 I6 is acting really erratic. It will run very smoothly with good power for random distances, from half a block to several miles, but then it will suddenly cut out quickly a few times and then just stop. Usually if I come back a few hours to a few days later it is in the same condition and won't even stay running with the accelerator pressed, though it occasionally just comes back to life like nothing happened and runs like I described above.

I've had my timing light hooked up to the primary coil wire when its doing this so I can see if it's firing, and it looks like it just stops sparking consistantly when the stumbling starts. The spark goes away and then the rpm's drop. The exhaust also smells really strongly of unburned gas when this happens. I could be perceiving wrong, but that made it look like an ignition problem. Since this problem started I've replaced the condenser, rotor, points, cap, and spark plug wires with quality NAPA replacements. I found that the ignition circuit had slightly too much resistance, so I replaced a bunch of sketchy wiring at the ignition switch and replaced the resistor wire between the ignition switch and the coil with regular wire and a balast resistor so the whole system has exactly the right resistance. I've replaced the grounding wire inside of the distributer, and completely taken apart the top two plates of the distributer and thoroughly cleaned all possible electrical contact points. The air filter is also good.

I always set the timing to 10º BTDC and the dwell to 37º. I've messed with the initial timing between 6º and 12º and it has no effect on the sudden stumbling.

I also rebuilt my carburetor about a year ago, which made the car run better when I did it and didn't seem to cause any problems. So I don't think it's carburetor related, but there's a possibility it is somehow.

Some things I haven't replaced yet that may be suspect:
-Grounding wires from the engine (though they don't look corroded, and I've had no problems with the starter or the alternator charging)
-PCV valve
-The distributer itself is pretty worn and most of the bushings and linkages have a fair amount of play, but I would think that'd make the engine run crappy all the time if it was the cause of this problem.

I've spent probably three weeks trying to figure out what is going wrong, and this is my daily driver. So I'm really frustrated.

Any ideas what I've missed?

 

[bubba22349]

here are a few more things for you to check. First you might check or replace the fuel fitter it might be plugging up and then as it sits many times they will open up again also a deteriated fuel shock on the tank pickup can do the same plugging up the fuel pick up then open again as it sits. If you have a volt / ohm meter use it to check the coil primary and secondary windings for the right resistance readings. Since you mentioned that your distributor show signs of being well worn. Use your dwell meter to check to see if dwell is dropping excessively as you rev the engine some, if it is then the top bushing in the distributor is badly worn. Bad bushings will still let the engine idle good but as the RPM goes up it gets erratic. This also shows up when driving as missing as the point gap begins to close up, progressively getting worse as your speed increases. Good luck

 

[1968 Falcon]

Thanks for the suggestions, I hadn't thought of measuring the dwell while revving the engine. That will definitely let me know if it's just the distributer being too worn out. I forgot to say that the coil is also new, an Accel coil. I also have a fuel tank, sending unit, and fuel filter that are less than two years old. I will definitely check the filter and coil resistance.

 

[bubba22349]

Well then with that new info I would probably focus on the distributor first. Good luck

 

[JackFish]

Check around your carb for vacuum leaks.
I had a similar thing and my carb gasket/spacer was shot.

 

[1968 Falcon]

I did some more work/investigating tonight. I cleaned the ground wire contacts from the engine to the negative battery post and the body of the car, and it had no effect. Currently it is non-running. I tested for spark using my timing light while cranking and it looks like there just isn't any, except for occasional moments where it fires for a few turns. My ballast wire measures 1.3Ω and the primary circuit on the coil measures 1.2Ω (supposed to be 1.4Ω for an Accel?). I can measure the resistance between the ignition wire in the firewall, through the coil and distributer and engine, to the body of the car, and it is only about 2.2Ω. Which would suggest there are no bad connections, unless one only acts up with actual power going through it. The secondary resistance in the coil is right on target. I've switched condensers and it had no effect.

Literally the only part of the ignition system I haven't touched yet is the inside of the ignition switch. Which could be a culprit, although I've measured the voltage from the coil lead wire with the switch "on" and it is 12v (too high if anything, but that would just make my points wear out, not keep it from firing).

I have no ideas left. Maybe I'll try to jump the main engine ground wire tomorrow in case the current one is broken inside or something.

JackFish, I have had a vacuum leak problem before. Took forever to figure out haha. This seems different though since there just isn't spark.

 

[bubba22349]

Is the ignition switch very old? You might try bypassing the switch by using a jumper wire direct from the battery or battery cable side of the solenoid to the coil (hot wired). Then use a remote starter switch on the solenoid to turn it over, if it will start then you know the ignition switch is not making good connections inside it. On your ballast resistor how do you have it wired? Full 12 volts coming from the ignition switches "Run Position" terminal goes to one side of ballast resistor (Input side) the other side of the ballast (Output side) goes to + side of coil. With key in run position you should read around 6 to 8 volts. For starting the I terminal of the starter solenoid should go to the output side of the Ballast Resistor so that it gets full 12 volt to coil when cranking with the key in the starting position. Good luck

 

[JackFish]

JackFish, I have had a vacuum leak problem before. Took forever to figure out haha. This seems different though since there just isn't spark.

Then a DSII upgrade might solve your issues!

Umm, how old is the timing chain?

 

[1968 Falcon]

bubba, jumping the solenoid to the coil will be the next thing I try, thats a good idea. I have the ballast resistor mounted on the firewall, directly replacing the resistor wire I took out. I added it after all of these problems started because the resistor wire did have somewhat high resistance and I thought that might be the problem. (it of course didn't change anything once I replaced it) When the falcon is running for a moment, I've measured the voltage from the + coil wire and it was around 8-9 volts. If I measure when the engine isn't running its something like 12.3 volts, I think it has something to do with how the resistor behaves when there's actual flow through it.

Both the ignition switch and the timing chain predate my ownership of the car, so they're at least 6 years old, could be 45 years old. The odometer says 45,000, so it's probably 145,000, but it could be more, I don't have any good way of knowing. I'm almost positive the engine is the original, it has the factory date tag still from the right year.

JackFish, I was talking to someone else about this and they also said timing chain. If the chain had skipped a tooth or stretched wouldn't the car run awful all the time though? What is so frustrating about what is happening now is that the car runs perfectly, then suddenly stops running for a few minutes or days, then randomly starts running perfectly again for another few feet or few miles. I'm also just scared of it being the timing chain because I'm afraid of the inside of my engine...

All of these suggestions are wonderful.

 

[bubba22349]

Sounds like the ballast resistor is working right, they do have replacement resistor wires that you can splice in. You can get an idea of the condition of the timing chain turning the engine in the correct rotation (as running) until the timing mark is on TDC. With distributor cap off mark the rotor's position with a chock line then turn the engine backwards just until the rotor starts to move. Now read how many degrees of movement there was on the timing tab. A timing chain replacement is not a fun job but it can be changed in the car fairly easy hardest part is to get the crankshaft damper off. Good luck

 

[JackFish]

Chain doesn't have to jump a tooth.
They stretch. So sometimes it's loose, sometimes the slack gets taken up, which throws the timing in and out.
This one should probably be replaced just as a matter of regular maintenance especially if it's original and the engine has never been rebuilt.

 

[thesameguy]

I may have misread, but nowhere did I see that you replaced the coil... it sure sounds like the coil failing!

 

[1968 Falcon]

I think the timing chain will have to be a summer project... I'll check it though. I'm also planning on putting a new oil pump in, I figure it can't hurt to have better oil pressure.

thesameguy, I have replaced the coil actually. I replaced the original coil with two Autozone ones, and then about a month ago with a new Accel coil. The problem has gotten consistently worse over time though, regardless of the coil. I tested the Accel coil the other night and it was on spec other than the primary winding being 0.2Ω lower than normal. And I've switched in one of my old coils and it made no difference. There is the freak possibility that all four coils I've had have been bad.

 

[bubba22349]

To insure accuracy coils should really be tested at about room temperature, also you need to factor in the meters calibration if it's not zeroed out .

 

[jimlj66]

I'm just a pointed head electrician but I don't see how it could be your timing chain. You say you have no spark when the car acts up. An intermittent problem tells me your timing chain is not broken. A loose chain could throw your timing out enough to cause the car problems, even not run if it is bad enough but you would still have spark.

Before replacing any more parts I'd try hot wiring the car as bubba suggested. If that takes care of the intermittent problem look for bad wiring or a bad ignition switch.

 

[thesameguy]

Before replacing any more parts I'd try hot wiring the car as bubba suggested. If that takes care of the intermittent problem look for bad wiring or a bad ignition switch.

If the coil has been replaced, this I think would be the next step - the pink wire off the ignition switch could be damaged. "No spark at all" is an electrical problem - "spark at the wrong time" is a mechanical one.

 

[wsa111]

You have been advised by the best.
Should be an easy problem to diagnosis if you are focused on several areas.
When the condition occurs do you have primary voltage at the + post of the coil?
What is the charging voltage of the alternator at the battery?
Next pull the distributor & check the drive gear for condition?
If you hook up a timing light when the condition occurs do you have a firing pulse?
Do this for every plug wire & see if you get a pulse?
Put in an other distributor & advise.
Does the timing mark jump around or is it steady?
Just checking if you polarity reversed. Good luck.

 

[1968 Falcon]

Okay! Heres what I've done: I tried jumping it like described, and there was still no spark. I replaced the coil with an even nicer MSD coil, because why not. That had no effect. So on a limb, I put in a third condenser, and it started right up. The last one was a month old and was supposedly the "premium" one from NAPA. I'm tired of this now though, I've had several condensers fail quickly in the past year, but they're normally easier to diagnose. I've had condensers I bought from AutoZone, Macs, and now NAPA fail after less than two months. All in the last year. Does anyone else have this problem?

I don't completely trust the car again yet, but it does seem to run nicely.

What wsa111 mentioned: My timing mark does jump a degree or two occasionally. And light acceleration up to 30mph, especially in 2nd gear, is uneven. Sort of lurchy, not bad, but definitely not silky smooth. Is that just a sign of the distributer being worn out and imprecise? Heavier acceleration and any situation with more load is very smooth.

Thank you all for taking time to help me with this.

 

[JackFish]

Some testing with a vacuum guage might provide some clues.

 

[rbohm]

alright, the first thing to check is the rotor in the distributor. if the conductor is damaged, it wont let the spark through. and check the insulator for damage as well, many years ago we had a student in one of my classes steal a rotor from the school i was going to because his had taken a dump. turns out he didnt inspect the rotor he stole very carefully because it was on the school used to demonstrate what happens when the rotor itself goes bad. i suspect you have a crack in the rotor that is letting voltage leak out to the distributor shaft instead of the spark plugs.

if the rotor is good, then with the key on and the points closed, check for voltage through the coil. if good then try replacing the condenser as they sometimes go bad and create a dead short to ground. then check the points, i know you replaced them already but still, for them either being welded together and not opening, or for a ledge or something that is otherwise preventing the circuit from being broken to create a spark. and check the for the proper gap setting, .017" iirc(it has been a long time since i dealt with points).