Important info about LH Injection Controllers
12-08-2003, 08:44 PM
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Important info about LH Injection Controllers
Dear 928 Porsche friends,
I’ve read much about the topic of injection controllers and their repair in this forum. Unfortunately, I must state that some information provided is incorrect due to a misunderstanding of how the LH controller works or perhaps is simply wrong by intention. You will be very surprised at the many “secret tips” that follow.
Circuit diagrams of the LH are posted in the internet, however, they contain elementary errors so please use them with caution. Someone once suggested adding a 12 Volt Zenerdiode to protect the LH module. Given that the nominal electrical system volage of a German automobile is 13.8 Volts and all the electronic elements of the system are designed to function at that voltage, there is no need for such a diode. Forthermore, a protection diode is already present in the controller!
How might I know these facts? We repair controllers. For 13 years we created for our internal use innumerable circuit diagrams, test software and two controller diagnostic stations. The controller which we best understand is the 928 LH controller.
The main cause of failure in the LH is the hybrid circuit. To understand the function of the hybrid, please envision it as a type of interface that converts the 5 Volt signals of the microprocessor to 12 Volts, or 12Volt signals of the controller to the level lower 5 Volts for the microprocessor. Additional functions such as Lambda regulation, resets and reference voltages are also integrated. The hybrid circuit contains two integrated circuits (ICs) and several descrete components which provide these functions. The ICs are protected by a silicone covering. Over the course of the time, oxygen and water molecules diffuse through the silicone covering and cause oxidation at the chip which eventually leads to a loss in functionality. Unfortunately, the loss of the hybrid circuit functions can lead to the complete loss of controller functionality and thus the engine stops running.
When asked how the failure occurred and how it affects the car, nearly 95 % ot the time the answer is: "it worked properly when turned off, afterwards the engine would no longer start."
Beyond "oxidation" and “turning off your engine"you need to understand these two facts.
1. The age of the controller is the main enemy here, not the actual hours of operation
2. The controller will fail mostly after turning the off the engine. As Murphy’s law dictates, it will fail most often at the place where it will cause you the highest possible inconvenience.
From these facts it follows:
a) It is it your "Karma" that will get you!
b) If your controller fails, never buy a used or repaired controller that contains an old hybrid chip because then “it will get you again.” The record that one customer holds is three successive failures when purchasing used controllers, each failure came approximately 6 months apart.
c) as a precaution, have the controller tested – or - better yet have it rebuilt – or – buy a new one (that hasn’t been sitting on a shelf for 10 years!). Some functions of the hybrid can fail without becoming noticeable to the driver. The loss of some functions is, however, already a clear indication for that the "remainder" of failures will soon follow.
d) Don’t give in to your Karma, but rather you should be like a customer of ours who always carried a used replacement controller in the glove compartment. So, when his module actually went out on him, he simply swapped them. But he was lucky, since his replacement controller could have also died of “oxidation” in the glove compartment during this time.
If you should decide to have your controller a repaired or rebuild, then you should contract with someone who COMPLETLY replaces the hybrid circuit. Our hybrid circuit replacement, in contrast to the original, possesses substantially improved characteristics such as lower power consumption (therefore it does not become so hot) and most importantly incorporates fail-safe functions thus making it practically impossible for the complete failure of the controller. This becomes possible by a coprocessor function incorporated into our hybrid replacement. However, do not fear. There is a hardware function that takes over this failsafe too. But that has never happened before. Moreover, as part of our rebuild process, where it is necessarily other elements of the controller are brought up to date with the newest state-of-the-art components.
The good news is that other than the hybrid circuit, the LH controller is a durable and very reliable controller.
If you desire further information about us, our repairs, or the LH module please contact our North American business partner, Richard Andrade at electronikrepair@earthlink.net
Achim Müller
ACM Elektronik
Wilhelm-Busch-Str.8
74747 Ravenstein/Oberwittstadt
Tel +49 (0)6297/929462
I’ve read much about the topic of injection controllers and their repair in this forum. Unfortunately, I must state that some information provided is incorrect due to a misunderstanding of how the LH controller works or perhaps is simply wrong by intention. You will be very surprised at the many “secret tips” that follow.
Circuit diagrams of the LH are posted in the internet, however, they contain elementary errors so please use them with caution. Someone once suggested adding a 12 Volt Zenerdiode to protect the LH module. Given that the nominal electrical system volage of a German automobile is 13.8 Volts and all the electronic elements of the system are designed to function at that voltage, there is no need for such a diode. Forthermore, a protection diode is already present in the controller!
How might I know these facts? We repair controllers. For 13 years we created for our internal use innumerable circuit diagrams, test software and two controller diagnostic stations. The controller which we best understand is the 928 LH controller.
The main cause of failure in the LH is the hybrid circuit. To understand the function of the hybrid, please envision it as a type of interface that converts the 5 Volt signals of the microprocessor to 12 Volts, or 12Volt signals of the controller to the level lower 5 Volts for the microprocessor. Additional functions such as Lambda regulation, resets and reference voltages are also integrated. The hybrid circuit contains two integrated circuits (ICs) and several descrete components which provide these functions. The ICs are protected by a silicone covering. Over the course of the time, oxygen and water molecules diffuse through the silicone covering and cause oxidation at the chip which eventually leads to a loss in functionality. Unfortunately, the loss of the hybrid circuit functions can lead to the complete loss of controller functionality and thus the engine stops running.
When asked how the failure occurred and how it affects the car, nearly 95 % ot the time the answer is: "it worked properly when turned off, afterwards the engine would no longer start."
Beyond "oxidation" and “turning off your engine"you need to understand these two facts.
1. The age of the controller is the main enemy here, not the actual hours of operation
2. The controller will fail mostly after turning the off the engine. As Murphy’s law dictates, it will fail most often at the place where it will cause you the highest possible inconvenience.
From these facts it follows:
a) It is it your "Karma" that will get you!
b) If your controller fails, never buy a used or repaired controller that contains an old hybrid chip because then “it will get you again.” The record that one customer holds is three successive failures when purchasing used controllers, each failure came approximately 6 months apart.
c) as a precaution, have the controller tested – or - better yet have it rebuilt – or – buy a new one (that hasn’t been sitting on a shelf for 10 years!). Some functions of the hybrid can fail without becoming noticeable to the driver. The loss of some functions is, however, already a clear indication for that the "remainder" of failures will soon follow.
d) Don’t give in to your Karma, but rather you should be like a customer of ours who always carried a used replacement controller in the glove compartment. So, when his module actually went out on him, he simply swapped them. But he was lucky, since his replacement controller could have also died of “oxidation” in the glove compartment during this time.
If you should decide to have your controller a repaired or rebuild, then you should contract with someone who COMPLETLY replaces the hybrid circuit. Our hybrid circuit replacement, in contrast to the original, possesses substantially improved characteristics such as lower power consumption (therefore it does not become so hot) and most importantly incorporates fail-safe functions thus making it practically impossible for the complete failure of the controller. This becomes possible by a coprocessor function incorporated into our hybrid replacement. However, do not fear. There is a hardware function that takes over this failsafe too. But that has never happened before. Moreover, as part of our rebuild process, where it is necessarily other elements of the controller are brought up to date with the newest state-of-the-art components.
The good news is that other than the hybrid circuit, the LH controller is a durable and very reliable controller.
If you desire further information about us, our repairs, or the LH module please contact our North American business partner, Richard Andrade at electronikrepair@earthlink.net
Achim Müller
ACM Elektronik
Wilhelm-Busch-Str.8
74747 Ravenstein/Oberwittstadt
Tel +49 (0)6297/929462
12-08-2003, 08:53 PM
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Very interesting! 
Did you ever notice that these guys with the plethora of information and orders-of-magnitude improvements NEVER manage to mention the PRICE of their magic elixer in their initial message?
Did you ever notice that these guys with the plethora of information and orders-of-magnitude improvements NEVER manage to mention the PRICE of their magic elixer in their initial message?
12-08-2003, 09:07 PM
#3
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Sounds like you have taken the 'black science' out of this unit and replaced it with good ol' engineering.
Richard Andrade, eh - that name sounds familiar.
I'm sure that as your agent, utilizing rennlist as a marketing venue, he is a rennlist site sponsor?
Richard Andrade, eh - that name sounds familiar.
I'm sure that as your agent, utilizing rennlist as a marketing venue, he is a rennlist site sponsor?
12-08-2003, 09:57 PM
#4
Nordschleife Master
Rich had mentioned he was into a new business venture. If rich says its the ****, I believe him. Hes a good man. and BTW - He can drive a race car pretty good. He took me for a ride not too long ago and the Arizona Motosport Park in the Phoenix west Valley.
He's always been fair and honest and true 928 gentleman.
As a matter of fact, I place a call into him tonight telling him about my "Knock on wood - cross my fingers" soon to be addition an 85 S2.
God, I love this forum!.
Peace -Take it to the red!
He's always been fair and honest and true 928 gentleman.
As a matter of fact, I place a call into him tonight telling him about my "Knock on wood - cross my fingers" soon to be addition an 85 S2.
God, I love this forum!.
Peace -Take it to the red!
12-09-2003, 11:00 PM
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Viribus,
What kind of hints are you looking for?
The L-Jet doesn't have the "infamous" hybrid, so it doesn't have the time-dependent failure mode of the LH-Jet. Failures are the normal "damaged by over voltage" or random component failure types of thing.
In terms of functionality, the L-Jet is an analog-computing machine, there are no digital microcontrollers in it. So there is no "tweaking" or changing chips for tuning. It is what it is.
If you're looking to get more fuel to the engine for more power, larger injectors and more fuel pressure are about all that can be done at the ECU level.
If you look at the challenge Porsche and Bosch had in the mid-70s to engineer a reliable system to meet smog requirements, they did a pretty damn good job. The problem for us was once that was done for MY '80, Porsche didn't do anything more for the US except bump up the displacement to 4.7-liters through MY '84. It was just too much work to change anything for the relative low manufacturing volumes. Besides, the US-trim 928s of the day still kicked *** on most of what Detroit was putting out in those days.
We missed the "S-2" 300 - 310 HP "S" monsters delivered to Europe and ROW.
By the time the S4 came around, the digital processing and 32-valve engine were suitable as a world engine. The LH + EZK were good enough to meet all the smog requirements and pump out good HP in smog trim.
What kind of hints are you looking for?
The L-Jet doesn't have the "infamous" hybrid, so it doesn't have the time-dependent failure mode of the LH-Jet. Failures are the normal "damaged by over voltage" or random component failure types of thing.
In terms of functionality, the L-Jet is an analog-computing machine, there are no digital microcontrollers in it. So there is no "tweaking" or changing chips for tuning. It is what it is.
If you're looking to get more fuel to the engine for more power, larger injectors and more fuel pressure are about all that can be done at the ECU level.
If you look at the challenge Porsche and Bosch had in the mid-70s to engineer a reliable system to meet smog requirements, they did a pretty damn good job. The problem for us was once that was done for MY '80, Porsche didn't do anything more for the US except bump up the displacement to 4.7-liters through MY '84. It was just too much work to change anything for the relative low manufacturing volumes. Besides, the US-trim 928s of the day still kicked *** on most of what Detroit was putting out in those days.
We missed the "S-2" 300 - 310 HP "S" monsters delivered to Europe and ROW.
By the time the S4 came around, the digital processing and 32-valve engine were suitable as a world engine. The LH + EZK were good enough to meet all the smog requirements and pump out good HP in smog trim.
12-09-2003, 11:34 PM
#7
Nordschleife Master
Is there any "mapping" in the L-jet ECU?
The reason I ask is best I can tell, all the ECUs are the same, even between diffrent engines on diffrent cars. It seems like Bosch tuned the AFM and the injectors to the car, and left the ECU and other sensors pretty much common.
I think the 928 got a special ECU because it goes up to 8 volts for some reason, but it seems like other Bosch L-jet cars almost have the same ECU, weighter it's a 914, or a 924, or a VW bug, or a Ford pick up, or a MB. Turbo or not, it doesn't seem to matter.
Oh, and would you know what the max duty cycle of the injectors is? Not for the injectors, but that the ECU will command the injectors to do.
Thanks.
The reason I ask is best I can tell, all the ECUs are the same, even between diffrent engines on diffrent cars. It seems like Bosch tuned the AFM and the injectors to the car, and left the ECU and other sensors pretty much common.
I think the 928 got a special ECU because it goes up to 8 volts for some reason, but it seems like other Bosch L-jet cars almost have the same ECU, weighter it's a 914, or a 924, or a VW bug, or a Ford pick up, or a MB. Turbo or not, it doesn't seem to matter.
Oh, and would you know what the max duty cycle of the injectors is? Not for the injectors, but that the ECU will command the injectors to do.
Thanks.
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12-10-2003, 12:19 AM
#8
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if you are referring to the three dimensional chart of often pictured by ECU tuners, there is no such "map" in the L-Jetronic controller.
If you are interested to understand the L-Jetronic system in more detail, Bosch publishes a book called "Gasoline Fuel-Injected System L-Jetronic" edition 95/96. You'll find it at the big three. It goes into as deep of an explanation of the L and LH system as the layperson might care to understand.
On page 19 of the Bosch book there is a figure that shows how the different L-Jetronic controller stages work to create the output voltage to the injectors.
The engine speed goes into a pulse shaper and frequency divider. This and the voltage signal from the MAF go into a Division control multivibrator. The output of that block is basically the "ideal" fuel quantity for the RPM and that signal goes into a multiplier stage. The multiplier stage looks at engine temp, air temp, vehicle voltage and load range to create the signal for the injectors that takes into account other variables needed for differing fuel mixtures and drivability.
If you are interested to understand the L-Jetronic system in more detail, Bosch publishes a book called "Gasoline Fuel-Injected System L-Jetronic" edition 95/96. You'll find it at the big three. It goes into as deep of an explanation of the L and LH system as the layperson might care to understand.
On page 19 of the Bosch book there is a figure that shows how the different L-Jetronic controller stages work to create the output voltage to the injectors.
The engine speed goes into a pulse shaper and frequency divider. This and the voltage signal from the MAF go into a Division control multivibrator. The output of that block is basically the "ideal" fuel quantity for the RPM and that signal goes into a multiplier stage. The multiplier stage looks at engine temp, air temp, vehicle voltage and load range to create the signal for the injectors that takes into account other variables needed for differing fuel mixtures and drivability.
