jwillman

I got the car put back together yesterday and it started right up and no more noise when clutch pedal is depressed.

I reinstalled the air filter housing and closed her up and this morning she turns over strong but no hint of ignition/ fire.

I can hear the fuel pump and tried a different fuel pump relay as well as putting in the jumper.

I have the car alarm by passed at the CE panel.

Green wire is new.

Whats the best troubleshooting procedure / common failure points, i.e ignition control unit, coil, resistors etc?

Wisconsin Joe

Do you have spark? Timing light, spare plug in a plug wire or starting fluid into the intake will tell you.

Are you getting fuel? A 79 is going to be CIS, and I have no clue on troubleshooting that system. But can you smell gas coming out the exhaust when you crank it?

jwillman

I used a timing gun and got no light during cranking. I did smell fuel.

Time to start troubleshooting the other ignition parts!

Mrmerlin

retrace your path its something you touched

jwillman

I did check the ballast resistors and both are about .26 ohms which is out of tolerance listed in the WSM.

The coil is also showing out. I have 8.75 ohms between pin one (center output to distributor) and pin 4 which is good. I have the same reading on pin1 one and pin 15. It should be .33 to .46 ohms. .

Thoughts?

Not sure the local auto stores can test the coil. I will give that a try tomorrow.

jwillman

Only thing I did after starting the car and testing the clutch was to replace the heat shields above the exhaust and install the air filter housing and tubes.

I pulled the filter housing out and looked for something a miss but don't see something like the green wire pulled loose.

Mrmerlin

is your O2 sensor wire pinched between a heat shield?
could installing the air cleaner have pulled a sensor wire off?

jwillman

no O2 sensor on my year car that I am aware of.

I will double check all the wires.

GregBBRD

There's two "small wires" going to the starter. They go on separate posts. One is for the solenoid and the other is the "bypass wire" for the ballast resistors. Make sure they are correctly connected. I've seen solenoids with places to hook 3 wires....

Regular power for the ballast resistors comes from the C/D unit, through both ballast resistors, and to the coil. The problem is that under cranking conditions the voltage drops below 12 volts and there sometimes isn't enough voltage to supply the coil. That wire from the starter bypasses the first ballast resistor and supplies voltage only to the final ballast resistor, increasing the voltage at the coil.

Checking the voltage is the best way to test the system. Hook up to the 15 post and monitor what is happening, with the key in the run position and the key in the start position.

If you decide you cooked the coil....beware that an American coil will not work. You need the correct coil, which operates on a lower voltage than even an American coil with a ballast resistor.

BTW...the two ballast resistors have different resistance. They should not/can not have the same ohm reading. Be careful around the ballast resistors when they have had power hooked to them. They get so hot that they will remove your fingerprints....ask me why I know.

Dave928S

I have a similar caution ... never wear rings, metal watch bands, or metal watch cases, when working in areas where you have to squeeeze your hand in to a space between potentially live terminals, such as under the dash or in tight areas of the engine compartment.

I shorted a terminal to earth, through a metal watch band I was wearing, and left a perfect 3rd degree burn impression of the band links and watch case on my wrist ... ouch!! The pattern was visible for about twenty years.

jwillman

Thanks Greg

When I disconnected the starter the two small wire posts were different sizes as were the connectors on the wires so only went on one way. I will double check.

Are you saying to ignore the OHM checks and rely on the voltage checks?

When you say American coil are you talking about a coil spec'd for some other type of vehicle? I assume if I find a Bosch coil for a 928 I will be good?

I will also double check the ballast resistors ohm's today. The are marked 4k and 6K so the right part.

jwillman

Damn it. Got the new coil and ballast resistors today and upon testing the new parts they are outside the ranges specified in the WSM using a brand new multi-meter.

On top of that the darn WSM has an error in the troubleshooting text versus the illustrations which I caught today after the new coil arrived.

WSM verbiage says to check resistance between 1 and 15 and 1 and 4( center pin out to distributor). The illustration shows going from 1 to 4 and 15 to 4 which lead me to believe the coil was bad.

Net is I still have a car that doesn't start and not much confidence in the WSM troubleshooting tree.

Guess I know what I am doing with my weekend.

GregBBRD

Yes. Forget tracing ohms until you know if that is the source of your problem. Hook up your voltmeter to the 15 post and watch the voltage sitting there with the key on and then with the car cranking. The correct coil will make spark all the way down to 2 volts.

Know that nothing you measure will an ohm meter will be correct.

Those silly ballast resistors should be marked "~4K +/-1K" and "~6K +/-1K".

Very frustrating to check and decide if they are good or bad.

Here's the "real troubleshooting" technique....especially useful when anyone is out on the road and doesn't have a trusty volt/ohm meter handy. Turn the key on for 5 minutes. Reach down and touch each ballast resistor with your finger.

If you aren't screaming in pain, you have a problem!

If the skin from the end of your finger is now transferred to both of the ballast resistors and they are sitting there smoking from your 'skin donation", they are working and the coil is "accepting" their current. If the "first" ballast resistor is smoking and the "second" one is cold, then you have a short in the wire to the starter or a short in the starter solenoid. If neither is hot, then you either have no voltage from the C/D unit to the first ballast resistor, the first ballast resistor is bad, or the coil is bad. There's no scenario for the first ballast resistor to be cold and the second one hot, unless you have a car that starts and runs only when cranking, but dies when you go to the "run" position.

jwillman

I will try Greg's burning skin test with an IR thermometer - I am a *****.

Yesterday I did the next test in the WSM which had me check for voltage to pin 15 of the old coil with ignition on. I got above 3 volts at the coil and showed battery voltage at the jump post which is acceptable according to the WSM. Looking at the wiring diagram that indicates voltage flowing through resistors to the coil.

Not sure what that really tells me. More to come tomorrow.

jwillman

I discovered that the resistors were wired opposite, i.e. the 6 ohm where the 4 ohnm should have been according to the wiring diagram (assuming it is correct). They were also backwards against the illustration in the WSM ignition troubleshooting. I have never messed with them so done by a PO!

I replaced them with new as well as the coil and tried the ignition switch on test. Both resistors went from 71F to 118F in a couple of minutes based on my IR temp gun.

Unfortunately that did not fix the no start!!