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Discussion Starter #1 (Edited)
Here's a fun one

1978 450SL with K-Jet and Bosch Reluctor-Triggered Ignition.

Out through the Valley of Ashes, 90 miles from home.

High operating temps-- OAT 85F, 3 hour drive at 3000 RPM, engine temps just below 200. Car was idling for a few minutes on black asphalt, electric aux fan operational.

Car sat for 20 minutes with motor OFF. Attempted restart, fast cranking, NO START.

First guess was fuel, vapor lock in lines caused by reformulated panther pee sold to unsuspecting consumers as gasoline. Removed air cleaner, ignition ON, depressed airflow meter disc, heard injectors chirp, crank, nothing.

"Most problems you think are fuel are in fact ignition" -Old Porsche Race Mechanic, 25 years ago.

12.3V present at ballast resistors. Removed distributor cap, contacts normal. Reluctor normal. 5.3KOhm measured between rotor center terminal and wiper. Green coaxial wire normal, no chafing, no apparent issues.

Using tach feature of Bosch Digital Multi-meter (FIX 7677), 8-Zyl setting, no RPM observed between coil 1 terminal (also known as coil NEGATIVE) and ground.

#5 spark plug (most accessible) removed, re-inserted in #5 plug wire, grounded to valve cover, rubber glove for safety, no sparks observed in gap.

*** Diagnosis: No Spark * * *

Waited a few minutes and cranked it again with tach connected.

All of a sudden, RPM indication, engine sprang to life!

Not waiting around for engraved invitation, replaced air cleaner, connected breather hoses, car ran great. Took her to the ton, flat out between pine barrens and beach, pulled like a DB Taurus till closure rate with econobox and prudence took over. Drove it home, no issues. Restart no problem.

Now what?

Elektronische Zündanlage= 0 227 100 001 This is stock, in good condition.

Never had any issues with this box.

Ordinarily would suspect the Los Cheapos Brazilian-Made Coil-- in the Porsche SC Community (Bosch CIS) these things are regularly thrown into the nearest lake or stream for a "Float Test." If they float, they are good and should be re-used. But what I actually saw was no RPM indication between 1 and Ground, which suggests that the EZL decided to throw up its hands.

I have been thinking of replacing the aluminum Brazil coil with a proper blue TCI coil, used ones are not that hard to find. Along the same lines, could use a Bosch Red. Does anyone happen to have the primary resistance, secondary resistance, inductance (mH) and turns ratio for the blue TCI? I could buy one and measure it I guess.

What to do?

1) New EZL Box. $$$ and old tech.

2) Huco ignition? $29, you could carry a spare at that price.

But will this work for a 450SL?

They are listed for the 380SL, 1981-1985, same motor, same firing order.

Do they do variable dwell? There is no vacuum connection so they don't have another map for load.

Has anyone used one of these Huco boxes, with appropriate heat sink compound, on an earlier car?

3) Pertronix? I think this might require a different (D-Jet) distributor. I have not read of anyone replacing the Bosch reluctor-triggered ignition with a Pertronix, only the earlier D-Jet folks. I am a big fan of high-amperage hall effect switching devices and very low primary resistance coils. Lots of flux at the first time constant and good ignition energy, even at high RPM. Downside is you have to carry a DVOM to diagnose (which I do, supra.)

Bottom line: I am no big fan of getting stranded. . . what do you gents think is the best solution?

Thanks in advance for any advice here.
 

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Here's a fun one

1978 450SL with K-Jet and Bosch Reluctor-Triggered Ignition.

Out through the Valley of Ashes, 90 miles from home.

High operating temps-- OAT 85F, 3 hour drive at 3000 RPM, engine temps just below 200. Car was idling for a few minutes on black asphalt, electric aux fan operational.

Car sat for 20 minutes with motor OFF. Attempted restart, fast cranking, NO START.

First guess was fuel, vapor lock in lines caused by reformulated panther pee sold to unsuspecting consumers as gasoline. Removed air cleaner, ignition ON, depressed airflow meter disc, heard injectors chirp, crank, nothing.

"Most problems you think are fuel are in fact ignition" -Old Porsche Race Mechanic, 25 years ago.

12.3V present at ballast resistors. Removed distributor cap, contacts normal. Reluctor normal. 5.3KOhm measured between rotor center terminal and wiper. Green coaxial wire normal, no chafing, no apparent issues.

Using tach feature of Bosch Digital Multi-meter (FIX 7677), 8-Zyl setting, no RPM observed between coil 1 terminal (also known as coil NEGATIVE) and ground.

#5 spark plug (most accessible) removed, re-inserted in #5 plug wire, grounded to valve cover, rubber glove for safety, no sparks observed in gap.

*** Diagnosis: No Spark * * *

Waited a few minutes and cranked it again with tach connected.

All of a sudden, RPM indication, engine sprang to life!

Not waiting around for engraved invitation, replaced air cleaner, connected breather hoses, car ran great. Took her to the ton, flat out between pine barrens and beach, pulled like a DB Taurus till closure rate with econobox and prudence took over. Drove it home, no issues. Restart no problem.

Now what?

Elektronische Zündanlage= 0 227 100 001 This is stock, in good condition.

Never had any issues with this box.

Ordinarily would suspect the Los Cheapos Brazilian-Made Coil-- in the Porsche SC Community (Bosch CIS) these things are regularly thrown into the nearest lake or stream for a "Float Test." If they float, they are good and should be re-used. But what I actually saw was no RPM indication between 1 and Ground, which suggests that the EZL decided to throw up its hands.

I have been thinking of replacing the aluminum Brazil coil with a proper blue TCI coil, used ones are not that hard to find. Along the same lines, could use a Bosch Red. Does anyone happen to have the primary resistance, secondary resistance, inductance (mH) and turns ratio for the blue TCI? I could buy one and measure it I guess.

What to do?

1) New EZL Box. $$$ and old tech.

2) Huco ignition? $29, you could carry a spare at that price.

But will this work for a 450SL?

They are listed for the 380SL, 1981-1985, same motor, same firing order.

Do they do variable dwell? There is no vacuum connection so they don't have another map for load.

Has anyone used one of these Huco boxes, with appropriate heat sink compound, on an earlier car?

3) Pertronix? I think this might require a different (D-Jet) distributor. I have not read of anyone replacing the Bosch reluctor-triggered ignition with a Pertronix, only the earlier D-Jet folks. I am a big fan of high-amperage hall effect switching devices and very low primary resistance coils. Lots of flux at the first time constant and good ignition energy, even at high RPM. Downside is you have to carry a DVOM to diagnose (which I do, supra.)

Bottom line: I am no big fan of getting stranded. . . what do you gents think is the best solution?

Thanks in advance for any advice here.
Informative post, at least for me researching the topic.

I hope you may want to share your post fact experience in the last 4 months and what fixed your car.
Thermal shut down is often the ignition module, or at least this is what "the internet" suggests. Was this in your case too?

I have 380 ignition box in a cast aluminium box with cast aluminium lid and plug-in test was positive (when my car was running). Nothing obviously changed in the way the engine sounded. Hence, the HUCO is likely to work, at least as a spare one to get you home (a thick interface aluminium back plate would be highly beneficial as a heat sink). Alas, I have 3x original 380 ignition boxes and 1 more original-like 0 227 051 024A which I believe it is from a 350SE so keeping a spare 'original' is an easy task.
 

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Discussion Starter #5
I suppose an epilogue is in order.

I went home and dug out the manuals for the 1984 380SL and looked at the wiring diagram and concluded that the Factory eliminated the two ballast resistors with the later box, used a different rotor with lower resistance and a different coil along with the HUCO box.

So I bought a HUCO, a coil, and a rotor, and studied the wiring diagram and figured out a way to "upgrade" the 1978 harness to the 1984 wiring while maintaining the ability to revert back to original.

And then the car never did it again. Not once. Not a hesitation, a stumble, nothing. Started and turned over without a hiccup.

Good cars are HAUNTED and from time to time, they demand our attention. I keep the new parts in the trunk as a talisman against future misbehavior.
 

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I suppose an epilogue is in order.

I went home and dug out the manuals for the 1984 380SL and looked at the wiring diagram and concluded that the Factory eliminated the two ballast resistors with the later box, used a different rotor with lower resistance and a different coil along with the HUCO box.

So I bought a HUCO, a coil, and a rotor, and studied the wiring diagram and figured out a way to "upgrade" the 1978 harness to the 1984 wiring while maintaining the ability to revert back to original.

And then the car never did it again. Not once. Not a hesitation, a stumble, nothing. Started and turned over without a hiccup.

Good cars are HAUNTED and from time to time, they demand our attention. I keep the new parts in the trunk as a talisman against future misbehavior.
For what it's worth, my 84 didn't have the huco box from factory but the massive brick that used to live in there.

Regardless, these cars are ornery. Best to leave the spares in the trunk as a potential punishment for future bad behavior !
 
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