no current from distributor to spark plugs only!

[hahaitzskippy]

Hello everyone

1985 318i
car died while driving and did not fire up again.

fuel pump works (smell a lot of fuel when trying a lot)
compression in each piston is at 150psi
there is current/voltage to the coil.
there is current/voltage from the coil to the distributor

i took out the spark plugs and tested it, no spark

this is where my problem is.
the current/voltage goes to the distributor but i get no current/voltage from the distributor through the leads to my spark plugs.

spark plugs and leads have 1000 miles on them.
already bought and tested new cap & rotor

is this just a simple distributor issue? or might there be something else that could be the problem.

a new dizzy is about $150

any input?

-------------------------------------------------------------
problem solved

if you run into any spark issue. start the most obvious beginning, ignition coil then to the dizzy then other components.

if the primary & secondary resistance on the ignition coil is out of spec, it is bad. get a new one. the specs should be in the bentley

primary resistance
TCI system (which was my car) .82 ohms
motronic .50 ohms

secondary resistance
TCI system 8250 ohms
motronic 5000-6000 ohm

my ignition coil was the culprit.

put a spark plug in a plug line that is connected only to the ignition coil. ground the spark plug and crank the car. if no spark, then proceed to test the ignition coil's resistance. if out of spec, need to be replaced.

hope this helps cheers

[Andy.B]

http://auto.howstuffworks.com/ignition-system.htm

The distributor directs 'bursts' of high voltage to one lead at a time. There isn't a constant voltage to each plug.

Did you mean continuity?

I'm not familiar with the particulars of the m10 ignition system, but basically, you aren't checking for current to the plugs, at least in a traditional sense. You want to check that the coil is firing, and the distributor is properly sending that voltage through the cap and rotor, down a spark plug lead, and through a spark plug, causing it to arc.
Disconnect a spark plug wire from a plug, remove the plug from the cylinder head, and then reconnect the plug wire to the plug with the plug not threaded into the head. Lay the plug somewhere on the engine where metal on the plug is touching metal on the engine (but don't hold onto it with your hands) while a helper cranks the engine.
If the spark plug is arcing with the engine spinning, then the issue is either timing related, or unrelated to the ignition system altogether.

[hahaitzskippy]

http://auto.howstuffworks.com/ignition-system.htm

The distributor directs 'bursts' of high voltage to one lead at a time. There isn't a constant voltage to each plug.

Did you mean continuity?

I'm not familiar with the particulars of the m10 ignition system, but basically, you aren't checking for current to the plugs, at least in a traditional sense. You want to check that the coil is firing, and the distributor is properly sending that voltage through the cap and rotor, down a spark plug lead, and through a spark plug, causing it to arc.
Disconnect a spark plug wire from a plug, remove the plug from the cylinder head, and then reconnect the plug wire to the plug with the plug not threaded into the head. Lay the plug somewhere on the engine where metal on the plug is touching metal on the engine (but don't hold onto it with your hands) while a helper cranks the engine.
If the spark plug is arcing with the engine spinning, then the issue is either timing related, or unrelated to the ignition system altogether.

I am also having a friend who is an electrical & mechanical engineer help me. we have a tool that can check for current & voltage running through the lines.

in the referenced link above, LINE D has current & voltage going through it, however, LINE A gets nothing meaning the spark plugs produce no spark.

hopefully that made more sense.

i am guessing something is wrong with my distributor and isnt "distributing" anything to my spark plugs

[Andy.B]

Does line D have surges of current/voltage going through it, or constant voltage?

[hahaitzskippy]

Does line D have surges of current/voltage going through it, or constant voltage?

from what i remember, it surges. i will have to check again.

there is only something running through the lines when i crank the engine of course.

does it make a difference?

[Andy.B]

Essentially, the distributor ignition system is a crazy Rube Goldberg device, especially compared to modern coil on plug systems.

There are basically two different circuits in the ignition system:

The coil is fed by a constant 12 volts when the ignition is on. The 12v circuit runs through an electromagnet in the coil, and out to some method of ground. In the earliest systems, the ground was controlled by the points inside the distributor, which are cam actuated by the distributor shaft. Quite literally, it works just like one of the engines valves opening and closing when pushed by lobes on a cam. Points were later replaced by sensors inside the distributor, and in later versions, instead of a device in the distributor body, the ground is switched by the ecu, which gets its signal from a crank position sensor. Basically, that is the extent of the circuit. 12 volts is fed to the coil, passes through an electromagnet, and the ground is flipped on and off by the points inside the distributor, or by the ecu. This first circuit is the primary circuit.
The magic is that the electromagnet in the coil emits an electomagnetic field on a separate circuit that runs through the coil. When the electromagnetic field collapses as the primary circuit is triggered by the ecu, it causes the electrons in the second circuit to surge down the wire, and through the thick lead from the coil to the distributor cap. This is where the distributor is performing a second job. Basically, it act like a traffic conductor. As the distributor turns with the engine, the rotor inside the distributor connects a circuit between the incoming coil lead (that is being repeatedly fed by high voltage bursts of electricity) and whatever spark plug wire it is pointing at during its rotation, sending the burst of high voltage electricity down that spark plug wire, and to the plug, where the only path to ground is by 'arcing' across the gap from the electrode to the prong that sticks out above it. That arcing is the spark. The spark plug itself is also pretty basic. Its only job is to provide that little gap that the electricity can jump across on its path to ground, creating a spark. Just like when you get a shock from static electricity touching a doorknob.

So it sounds like you have confirmed that the primary circuit to the coil is being fed 12 volts, just like it should, and that the triggering of the ground is working, causing the secondary circuit (the thicker lead to the distributor cap) to get pulses of high voltage. That means most of the system is working.

The next step is to make sure that the electric pulse is being routed properly from the coil lead at the cap, through the rotor, and back to one of the spark plug leads at the cap, then down the lead, and to a spark plug. The easiest (and lowest tech) way to do this is to do what I posted above. Pull a plug from the motor, and have it resting somewhere on the engine so the threads are grounded, and turn it over. It will be doing the same thing it does when it is threaded into the head, but now that you can see the electrode, you will hopefully be able to see the spark occur. If there isn't a spark happening.

If there IS a spark occurring, then the issue is timing related. Either the spark plug wires are in the wrong order (just put them in the right order), the rotor isn't pointing to the correct spot in the cap (the ignition timing needs to be set), or the issue isn't spark related.

If there ISN'T a spark occurring, then the surge of electricity isn't making it from the distributor lead to the spark plug lead, and the problem is either in the wires, or the cap or rotor (or both) are worn out, and need to be replaced.

I would:
-check the spark plug wire order
-pull a plug to check for spark
-pull the cap and rotor and look for pitting/corrosion/cracks/damage
-and only once everything above checks out OK, and you are getting a spark to the plugs, would I break out the timing light and the Bentley and set the ignition timing.

[Andy.B]

If you haven't done it, or don't know when it was last done, I would recommend replacing the plugs, wires, cap and rotor, all at once. They are all wear items, and pretty cheap to replace, and provide cheap insurance and peace of mind.
As a rule, any car I get, that is the thing I do, along with oil change, and new filters for everything.

[Todd Black 88]

Pull the cap off the rotor, and bump the starter. Make sure the rotor is actually spinning. If it died while driving, and won't start now, you may very well have lost your timing chain.

[Andy.B]

That is possible, but he said he had good compression, which makes me assume the cam is still spinning and doing its job. I figure the chain is still there, and since 'spark' is getting to the distributor from the coil, the problem is either in the distributor, or the timing is way off.

Its all just air/fuel/spark:

If we have compression, but it isn't even starting, then we can pretty much rule out air.

And spark is a pretty basic test. Just pull a plug.

If the spark looks good, then its either ignition timing or fuel related.

But lets get the basics ruled out first.

[hahaitzskippy]

i already replaced the cap and rotor.

the spark plugs are new, less than 1000 miles on them

i will definitely check the voltage and current again to make sure we have all that.

[Andy.B]

Have you pulled a spark plug to verify that you are or are not getting a spark?

[Todd Black 88]

Missed that he tested compression.

How are the engine grounding straps?

[hahaitzskippy]

Have you pulled a spark plug to verify that you are or are not getting a spark?

yes i did verify that i had no spark by pulling the spark plugs out, grounding it, and cranking the engine.

no spark :(

[Andy.B]

But you are getting a 'spark' voltage out of the coil?

[hahaitzskippy]

But you are getting a 'spark' voltage out of the coil?

yes for sure out of the coil