Chrysler Ignition questions.

[pdqford]

I have a 1981 Chrysler 75 HP motor (758H1C) that has run flawlessly for the 30+ years I have owned it.

Last week, out of the blue it wouldn't start. The starter would spin it over but it wouldn't fire up.
Pulled the plugs and grounded each one in turn and no spark!
(We were staying at a small island up in Canada and had to flag down a boater and get a tow to mainland!)

Trailered the boat back home to the States and trying to diagnoses the problem.
I believe the motor has the CD ignition with the breakerless distributor.
With key on I have 12V at the blue wire at the distributor.
I hooked my scope up to the white/blk terminal at the distributor and with the engine cranking I see no pulse signal.
(Does that mean the preamp is bad?)
I disconnected the white/blk wire from distributor and with key on, grounded it and got no spark from the coil tower.
(Does that mean the CD unit is bad?)
I put my DMM across the coil primary terminals and read ~0.4 ohms.
Between the coil primary and secondary it reads 0.527 Kohms.
(Does that mean the coil is bad?)

How do I pinpoint the culprit? Or do the whole ignition systems go at once?

Thanks for any guidance.

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  pdqford
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[Frank Acampora]

While relatively trouble free, the Motorola CD unit does occasionally fail. Same story with the electronic distributor. According to the manual there is no way to test an electronic eye. The only diagnostic test is to replace with a known good one.

Grounding the black/white will show nothing because the blue wire supplies power to a light and when the shutter opens, a photoelectric cell generates a pulse of low voltage to signal the CD box to dump the capacitors into the coil.

 

[pdqford]

Grounding the black/white will show nothing because the blue wire supplies power to a light and when the shutter opens, a photoelectric cell generates a pulse of low voltage to signal the CD box to dump the capacitors into the coil.

Thanks Frank. Could I supply a low voltage to the "trigger" wire if I disconnect it from the distributor and connect a test light to a 12 volt source and touch the test light to the "trigger" wire? with a spark tester inserted into the coil tower? (I'd have to check to see how many volts my test light would drop across the test lamp bulb so the white/black wire didn't get over what? 1.5 V ?)

With the key "on" each touch should throw a spark if the CD box is good ?????

 

[Frank Acampora]

UMMM-- I never measured output from an electric eye so I can't tell you much. In theory, yes, each touch should cause a spark if the CD box is good.

Interestingly enough. as I understand it, the same box is used for electric eye and points distributors BUT--the electric eye uses a make signal to dump the capacitors while the points uses a break signal..

 

[Nordin]

The CD box is the same for points and electrice eye.
You can test the box by feeding the blue wire that goes to the CD box (not the one that goes to the distributer) with 12VDC. Disconnect the blue wire and the black/white at distributer, turn flywheel to TDC the curve at the pully should line up with the rimm of the flywheel. Pull out the #1 plug (top) ground it and then touch the black/white wire to ground. Each touch should give a spark at the plug if the CD box is working.

 

[Glastron_V210]

Oops wrong thread.

Chay

 

[pdqford]

The CD box is the same for points and electrice eye.
You can test the box by feeding the blue wire that goes to the CD box (not the one that goes to the distributer) with 12VDC. Disconnect the blue wire and the black/white at distributer, turn flywheel to TDC the curve at the pully should line up with the rimm of the flywheel. Pull out the #1 plug (top) and then touch the black/white wire to ground. Each touch should give a spark at the plug if the CD box is working.

Hello Nordin,
Thanks for the response.
Is the procedure you described for testing the CD box functionally any different than the procedure I described in my first post?

The reason I ask is because if she no spark with #1 on top dead center, we wouldn't know if the issue was with the CD box, or the coil, or with the coil high tension lead, or with the distributor rotor, or with the distributor cap, or with the #1 spark plug wire. At least it would take the preamp in the distributor out of the equation.

I haven't pulled the distributor yet to examine the preamp, but I can see that it is a black one, not the red one. I haven't been able to see an "electric eye" in there (would I see a little lamp and some light in there?). With three wires on the preamp I'm guessing it is a totally electronic distributor with it Hall effect sensor? Anyone know what kind of a signal it generates on the white/blk sire?

 

[Nordin]

No there seems to be the same procedure you describe in the first post as mine.
The value of your coil measurement also looks good. BUT you maybe get cheated about the primeside value.
The primeside resistance is so low so you can not know if the measurment value is right or if there is a shortcircuit. The VOM is not so exact, but you can figuer out by crossing the tip of the testleads and see if the value gets lower then 0,4 Ohm.

To eliminate the rotor and distcap, hook the plug right up on the coil hightension lead and check for spark and you can also eliminate the coil hightension lead by change it. They are oldschool copperwire.

For information I have a 75Hp 3 cyl. with Motorola CD box and distributer. When I bought it it had no spark. The CD box was bad and after change of the box to a new one it got spark BUT irregularly.
The preamp was bad.
Soo it can be more then one issue.

About the preamp I do not know what kind of signal it is. BUT if as you mension you hooked up a scop (osilloscop) and got no kind of signal........sounds like a bad preamp.