I swapped cylinder 7 and 8 ignition cables and the engine started right away.....it idled much higher, started hunting...so I went out turning the idle air screw down.... suddenly the engine stopped... didn't start again.....
No way to get the thing started...nothing. I tried everything... I even changed the fuel pressure gauge... I T-ed it into the fuel rail in order to have the cold start injector active in case that engine has not enough fuel....still nothing.
crazy.
I could smell unburned fuel...so fuel seems to be available. Then I pulled a spark plug and had my wife starting while I connected the thread of the plug to battery minus.....no Spark!
crazy...why can the spark stop from one moment to another?
Assumption: If the plug doesn't show spark during starting if connected to the ignition cable and the plug thread conneted to Ground then ignition is not working ...is this correct?

Can someone help me trouble shoot ignition?

First things first. Use a voltmeter to check for voltage at the coil "+" and "-" terminals. Should be between 6-12 volts depending on which type of ballast resistor is installed.

Double check your distributor cap and rotor because it seems to me you had some fitting problems with it earlier.

The problem could be as simple as the cap being not correctly in place.

Check the voltage FIRST!

__________________
“Whatever story you're telling, it will be more interesting if, at the end you add, "and then everything burst into flames.”
― Brian P. Cleary, You Oughta Know By Now

Thanks Mike

I tried to turn key to position 2 (this is where the fuel pimp kicks in for 2 seconds) but no voltage at the coil(should there be voltage in position 2??)

Then at position 3 (engine is turning over now)....I saw some voltage. I did pull the center wire off the distributor and it had sparks against the steering pump housing... I tried the same a second time and NO SPARKS...third time NO SPARKS... is there something really crazy going on?

This is similar to what I experienced before.. suddenly no sparks and engine died all of a sudden.

can we go step by step so I can understand.
Again the question: should there be voltage at the coil (+ and - wire) when key is in position 2 (this is when the fuel pump kicks in for a second or two)?
Or is there voltage only when the engine is turning...key position 3?

Position #2 (run) should have voltage to the coil. Check your fuses. I don't know which fuse (if any) should be the one for your car. Maybe Graham or someone more familiar with your model can chime in.

You have two ignition circuits to your car. One (position #2) is for normal operation (always "live" in the "run" position) and the second (position #3 or "start") is active only when the starter is engaged.

Quite possibly when you pulled the heads you either didn't reconnect a wire or it broke.

__________________
“Whatever story you're telling, it will be more interesting if, at the end you add, "and then everything burst into flames.”
― Brian P. Cleary, You Oughta Know By Now

Why do you think I had sparks (center distributor high voltage cable) at one point and then nothing at the next moment? This is some intermittent?

If all wires are there (well the car was running since I changed heads) and it was running today for a short while until it died... It started firing again after lots of cranking for a few seconds, then immediately died again, never started again.
Then later I tested the sparks and I had sparks for a few moments then nothing.

If no voltage at coil..+ is coming from switch gear (transistorized ignition switch unit?)
Is the switchgear faulty? How can the switchgear be tested?

Would a Pertronix unit (Pertronix point replacement kit..Ignitor 1... plus new coil)solve the issue?

Martin,
I have arrived in SC, kind of tied up, but had a thought about your "new" problem

From what you wrote, considering engine had been running previously, it sounded like there might be a possibility that you lost the 12V connection to the 0.4ohm resistor(2) from the ignition switch (1).

When you turn the ignition sw to posn 2, you should get 12V on one side of the 0.4ohm resistor where (red/black?) wire connects. Easy to check by measuring one side of resistor to ground. In the diagram below, when you turn the key to posn 3 to engage starter, you will get power fed from the starter circuit (16). This feeds the full 12v to the ignition system during cranking because it bypasses the 0.4ohm resistor. If you had spark only when cranking but no spark after key goes back to posn 2. then it might be worth first checking connection at resistor and if no voltage there, then continuity back to ignition switch. Also double check all fuses & main relay (no wiring diagram here, so not sure if power to ignition switch is via fuse or relay) If you have 12v at resistor with key in posn 2, then problem is elsewhere.

ADDED: Maybe remove condenser in case it shorted (it isn't needed) and make sure points are set to 0.014" and clean. Because everything WAS working,, I would look for something simple first!

Re Pertronix. You would need model 1885. It would be a good addition. It could just replace the points/condenser. Or with Flamethrower coil it could replace switchgear too. Lot's of Djet guys have done this. But maybe try and find out what is wrong first and do that later as upgrade (unless switchgear is definitely bad)

I am interested to hear how you make out. You are certainly getting a lot of advice!

__________________
Graham
85 300D,72 350SL, 98 E320, Outback 2.5

Read the other thread. This section from engine manual might also help:

http://handbook.w116.org/Engine%5C107%5CM117_45%5C075-520.pdf

Gives methods of testing ignition components for w116, 107 but should be same for your car.

__________________
Graham
85 300D,72 350SL, 98 E320, Outback 2.5

hope you are well.
Great diagram!...Graham, thanks.
Didn't know that the starter motor (key pos.#3) give 12V to #15 of switch gear.
There seems to be no relay or fuse between terminal #16 of starter motor and #15 of switchgear! I can't find anything in my diagram I have. cable is a 1.5 rt/vi (red/lilac). I found the resistance 0.4Ohm in the engine bay.
I can measure the 0.4Ohm on the meter and it has one cable on one side and 2 on the other side...the second one must come from the starter then. okay. I can find 12V in Key position 2 and 3 at the resistor...I think.
I am on my way here. I think the pulse cable to the distributor is faulty.
I'll check next.


Good news for the new bung position: much better AFR results from the few moments I had the pleasure to run the engine.
Hope I am back soon.

Pertronix: I agree that I should solve problems first before starting a new issue. If just replacing the point in distr (and no flame thrower) would then be also the problem of frying the unit when key is in Pos.2 for a while. I heard that the Pertonix is in danger when you leave the key in position #2 (drive) without driving.

great, I am becoming an ignition specialist

I had that cable short out against exhaust manifold once. Even at the distributor I suppose it could ground. It can just be a plain wire. Some early cars had a shielded wire. And check if condenser is shorted out.

There is always that possibilitybut only IF distributor stops with contacts closed. I have never had a problem with mine and when working on car it is easy enough to disconnect the power to the Pertronix. I was going to install a heavy duty fuse in the red wire to Pertronix just as a disconnect (maybe 15A?) But we are getting ahead ourselves here

__________________
Graham
85 300D,72 350SL, 98 E320, Outback 2.5

Wow, I have her going!... didn't drive yet but the engine sounds really nice now.
When hot I was checking dwell (was 30 degrees - good) then I pulled the vacuum at distr. looking for best vacuum- was around 19/20" then I backed off to 17.5",
then connected the vacuum hose... vacuum went down to 15".
Ended up at 2 degrees ATDC (w/vacuum) and roughly 10 degrees BTDC w/o vacuum... nice clean idle of 800 rpm.
Now I was looking for AFR: was at 12.2- sounds better (fuel pressure at steady 32psi). I think you said 13 is the target (ECU screw... but later in the game.
Was late and I shut the car down and heard air noise from the right rear wheel.... climbed down-air bellow leaking....didn't believe it. This lady is stubborn...doesn't want to hit the streets of Oman. I need to get a new bellow. ( I have 2 old ones still..they look awful but they keep air since over 40 years, well did....How do I get an air bellow to Oman?
However the joy of a healthy engine is just uplifting I have to say (and I forget about the air leak for a while).

Note, PertronixII does not fry if ignition is left on.

I have it on mine with the flamethrower and its been great so far.
I removed OE switchgear.

__________________
1972 W108 280SE 4.5
1977 W116 450SEL
1981 E12 528i BMW

Interesting that it works for you. Hard to argue with success!

Pertronix always recommended the Ignitor 1 for Mercedes V-8s. (Model 1885) even although the Ignitor II was available. Reason apparently being that Ignitor II was not recommended for use with solid core wires that our early cars have.

There is a lot of stuff in Peachparts forums on Pertronix and Arthur Dalton is the local guru

This is from one thread:
Ignitor II
This post could be very useful if Martin decides to install a Pertronix.
Pertronix upgrade

__________________
Graham
85 300D,72 350SL, 98 E320, Outback 2.5

So the problem was the distributor wire? (I see that in other thread!). Something simple, as usual!

The AFR will change once car is fully warmed up, so don't worry about it until then. It looks about right.

Congratulations on getting this far!

Can't help you with your other problem, but I am sure you will get it sorted out!

__________________
Graham
85 300D,72 350SL, 98 E320, Outback 2.5

Just to complement the information:
Pert II comes with a 9 before (Model 91885)
Correct, can't be used with solid wires.
* I'm not using solid core wires. I'm using Bosch wires.
Note my car is a 4.5L

__________________
1972 W108 280SE 4.5
1977 W116 450SEL
1981 E12 528i BMW