How does one verify health of various ignition components in early car?
 

Long weekend in the car and on the ride home while cruising at about 3100 rpm the tach suddenly 'shut off' (along with the motor!) and almost as suddenly everything was back to normal. Wife was behind me and didn't even notice it but it had me paranoid the rest of the trip home (was 2 1/2 hrs from home at the time).

I feel like it must be electrical based on the tach needle dropping like it did (rev's certainly didn't drop that much in the brief moment that it happened) but i really don't know my way around the ignition system beyond points gap and timing. condensors and the like are foreign to me.

The car has had a slight stumble when cruising around 3k rpm (very slight) which i assumed to be a carb cleaning coming up....but now i'm not so sure. When checking the plug wires i was able to push one of them slightly better onto the cap (had recently reset gap and timing so maybe i knocked it loose) and driving after tells me i MIGHT have resolved the stumble....

but maybe the stumble isn't related to the sudden loss of power?

thoughts?

motor is a 2.4 with webers...no gimicky modern stuff currently attached to it.

this has not happened before although another time i was coming home from ax'ing the car had a bad stumble the entire way home between 2500 and 3500 which somehow resolved itself and may very well have been due to plug wires being loose where they attach to the plug boots.

odd.

Start with the haynes manual. Gives decent trouble shooting for a lot of the components.

If you're still running points, check those first...the tach is triggered by the points. My guess is you'll find a wayyy too small points gap.

JUST reset the gap a couple weeks ago after the car started wanting to quit at stoplights (yay me for not just bumping the idle speed:) ). Verified two days ago at .012 but will check again.

Had the same problem on my '76 and it was a bad points gap. The points were wearing down really quickly because I had improperly lubed the points/distro shaft contact - so points that measured good were out of spec a week later.

I've also had similar symptoms caused by dirt/dust floating around inside the cap and fouling up the points - so make sure everything is clean.

If all checks out there, check your grounds, especially around the coil, CDI, and distributor.

ah, dtw did you use the Bosch dizzy lube?

Nah, I've got some Wurth (I think) di-electric grease that my wrench sold me. When I bought it I splooged some out of the tube and put it on the distributor. At the time I thought "gee, this is kinda runny...oh well". Idiot me...turns out it was just some runny goo at the top of the tube, and the real grease (much heavier) had yet to squeeze out of the tube.

For all these reasons a good early investment is a Pertronix or, even better, a Crane optical ignition. Set it once and forget it.

Agreed, but there are complaints out there about each of these systems, too. I had just about given up on my points and had a new Crane system on the shelf ready to go. Then on my last round of troubleshooting I finally got it right. The car's been running like a top ever since, so I am leaving the Crane on the shelf for the time being.

I had trouble with my first and only Pertronix, though most of that was self inflicted. Most of the Crane complaints I've heard have to do with setting it up, using it with an MSD, getting the tach to work, all of which can be trying. BUt once in place, it's pretty much bullet proof.

The big problem with hall-effect or optical ignitions like the Allison/Crane or the Pertronix is this: when they fail, you can't diagnose the problem at the side of the road. (Unless you carry a handheld oscilloscope in the car!)

Whereas with points, it's pretty easy to get out a flashlight and the toolkit screwdriver and reset the gap or change the points set entirely, in the dark, in freezing rain, at the side of a highway with semi tractors blowing by at 80 mph, 300 miles from New York City. . . not that I've done that or anything. . . :)

Anyway. . . how to tell the "Health" of various systems:

1) CDI Box-- do you hear a "whine" when the unit is powered up? That's the oscillator inside generating an AC which steps up +12V to +460V to charge the cap-- it makes the coil windings vibrate hence the whine. . . are all the connections clean? That's decent roadside troubleshooting.

2) Plug wires-- check with ohm meter for continuity and resistance.

3) Points-- check gap, dwell (dwell's not that important with CDI)-- the points current is only 420mA so points wear is negligible over tens of thousands of miles

4) Rotor, cap visual inspection, check resistance

5) Distributor- check advance with dial back timing light, create map of advance curve and compare to factory specs . . . over time. Manually rotate rotor to verify that centrifugal advance working/not seized

6) every connection in the electrical system must be checked to be free of corrosion-- including the grounds.

thanks John, that is exactly what i was looking for.

what about the cap? those go bad right?

yes they do - check each button carefully

I had a fine looking cap that wouldn't fire once... the center button was damaged.

also run a business card in between the points - in the gap - to clean the surfaces periodically

I got my money on insufficient point gap.

I had this problem with my 912. The rotor got sloppy and the tac would drop for a moment. New rotor and it is rock solid. Simple solution

An easy thing to check is the ground strap between the battery and the chassis. Mine came loose for a second and behave just as you described. Of course, it also fried my CDI...

I have pertronix and love it. I had a problem a couple of months after installing it and found your CAN troubleshoot it. I have a cheap voltmeter and a 12volt light tester too in the car and I just checked to see if I had 12vdc going in to the Pertronix. I did not and it was a prblem in the 12 pin connector.

I also carry a spare pertronix......what does it cost? $100? I also have a spare set of points......so i am covered for roadside repairs.

Bottom line is I love the Pertronix and will not do without it.

Many good suggestions for a points car above. My checklist at every oil change (3k miles):

1-Look at inside of distributor cap and wipe the back stuff that seems to accumulate inside.
2-Put a dab of Bosch Distributor grease (a single tube will last you a lifetime) on the the lobe (do not use anything else)
3-Use an ignition file and burnish the points contacts to clean them up
4-Check dwell and/or gap and adjust as needed.

If the rotor or contacts inside the cap look burned, replace both. Keep old one as spare.

There is an old adage .. If you are having ignition problems, points will get you home.

Harry with the ignition file are talking like one or two swipes or more than that?

2 swipes with a good contact file should do it, depending on how "bad" they're worn....mush better than a business card,,......

Best,

Doyle