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MB 450SE 1973 Ignition waveform
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MaxClassic
- Newbie
- Posts: 1
- Joined: Wed Apr 01, 2020 7:46 am
MB 450SE 1973 Ignition waveform
Hello guys,
I've been busy on an old W110 with 450SE engine (1973 D-jetronic).
I will tell you in short what happened to the car in the past:
The car didnt run on Petrol, but did run on LPG. On petrol the car was trying to run, but it would die out when playing with the throttle.
- Fuel pressure was non existant, pressure regulator connected the right way! (it was pressurizing the fuel tank lines)
- Fuel Injectors tested, one was always fully open
- Fuel injection image checked, they werent spraying, but hosing > ECU replaced > Injectors sprayed again
- All injection system parts checked including the wiring loom.
Car can on Petrol again, but isnt running nicely on all 8 cyilinders.
It wil run and drive, but when you put the engine under load it is stuttering and dropping in RPM.
On LPG however, the car has enough power to go along without any real stuttering.
Next I Pulled a spark plug to check the spart visually while starting the engine. It is sparking, but not real powerfull. Since LPG is transferred into the engine in gas-substance, and petrol needs to mix with air in the cilinder, I thought this could be the problem.
Next ive replaced the spark plug leads including the ignition coil lead (king lead) together with the rotor and distributor. I've set the points and ignition timing to factory spec and replaced the vacuum advance (leak).
After that the car sat for about a year.
Yesterday I picked up the project again, the car started on LPG, drove it into the shop and started diagnosting using the bought Picoscope.
As you can see the primary voltage isnt steady, and the current on the ignition coil doesnt come above 4A.
The ignition coil values:
Pr: 2.5 ohm
Sc: 8.1k ohm
What is causing this disturbance on the primary voltage? Could that be that the condenser is in bad shape?
And comparing the ignition coil current to that of other vehicles, it is low on amperage. Is it possible the previous mechanic put a wrong ignition coil on the car?
I would really appreciate the help!
Greetings, Max
EDIT: last attachment the - wasnt connected, so the primary voltage was below 0V
I've been busy on an old W110 with 450SE engine (1973 D-jetronic).
I will tell you in short what happened to the car in the past:
The car didnt run on Petrol, but did run on LPG. On petrol the car was trying to run, but it would die out when playing with the throttle.
- Fuel pressure was non existant, pressure regulator connected the right way! (it was pressurizing the fuel tank lines)
- Fuel Injectors tested, one was always fully open
- Fuel injection image checked, they werent spraying, but hosing > ECU replaced > Injectors sprayed again
- All injection system parts checked including the wiring loom.
Car can on Petrol again, but isnt running nicely on all 8 cyilinders.
It wil run and drive, but when you put the engine under load it is stuttering and dropping in RPM.
On LPG however, the car has enough power to go along without any real stuttering.
Next I Pulled a spark plug to check the spart visually while starting the engine. It is sparking, but not real powerfull. Since LPG is transferred into the engine in gas-substance, and petrol needs to mix with air in the cilinder, I thought this could be the problem.
Next ive replaced the spark plug leads including the ignition coil lead (king lead) together with the rotor and distributor. I've set the points and ignition timing to factory spec and replaced the vacuum advance (leak).
After that the car sat for about a year.
Yesterday I picked up the project again, the car started on LPG, drove it into the shop and started diagnosting using the bought Picoscope.
As you can see the primary voltage isnt steady, and the current on the ignition coil doesnt come above 4A.
The ignition coil values:
Pr: 2.5 ohm
Sc: 8.1k ohm
What is causing this disturbance on the primary voltage? Could that be that the condenser is in bad shape?
And comparing the ignition coil current to that of other vehicles, it is low on amperage. Is it possible the previous mechanic put a wrong ignition coil on the car?
I would really appreciate the help!
Greetings, Max
EDIT: last attachment the - wasnt connected, so the primary voltage was below 0V
- Attachments
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- Mercedes-Benz_S-Class_Petrol_20200331-0006.psdata
- (13.88 MiB) Downloaded 316 times
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- Mercedes-Benz_S-Class_Petrol_20200331-0005.psdata
- (14.74 MiB) Downloaded 321 times
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- Mercedes-Benz_S-Class_Petrol_20200331-0003.psdata
- (8.34 MiB) Downloaded 335 times
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- Mercedes-Benz_S-Class_Petrol_20200331-0002.psdata
- (12.54 MiB) Downloaded 293 times
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Grant_Baker
- OneWave
- Posts: 47
- Joined: Tue Feb 07, 2017 10:58 pm
Re: MB 450SE 1973 Ignition waveform
Wikipedia Google service information says the 73 450SE was a W116, not a W110. Just thought you might be interested or unaware.
The 3.5A current peak does seem low by today's standards.
Your file 0002 shows there is likely a rotor air gap problem. See my attached annotated image.
Your file 0005 shows a possible coil trigger turn off problem and possible voltage drop on primary problem. There should be an abrupt change when the circuit is opened. Since there is not an abrupt change, spark will be weak. See my attached annotated file. Perhaps the coil trigger turn off problem is actually caused by the rotor air gap. I would solve the rotor air gap problem first. Your file 0006 doesn't seem to have the same voltage drop on primary problem that I see in 0005.
The 3.5A current peak does seem low by today's standards.
Your file 0002 shows there is likely a rotor air gap problem. See my attached annotated image.
- Rotor air gap
- Attachments
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- Coil trigger turn off problem