[Diy_efi] Jetronic

Tue Feb 28 22:15:24 UTC 2006

I would like to say that the LE systems NEVER have closed loop. When a 
such system has closed loop, then it is called LU even if the car was 
intended for the european market.
Here in Sweden, catalyzers and closed loop lambda control became 
mandatory from '89. However, '87 and '88 cars with catalyzer were 
granted a sales tax rebate so many of those also have closed loop.

The main difference between LE1 and LE2 systems is that the LE1 uses a 
separate cold start injector while LE2 has additional circuitry in the 
ECU to give the cold start enrichment with the main injectors.

I only have studied LE2 and LU2 ECUs in detail. Many years ago, i began 
reverse engineering them and drawing up schematics, but the work is not 
yet finished. It seems like only two different PCBs are used, one for 
LE2 with only leaded components (although densely packed, all resistors 
are 1/8 W for example) and another for LU2, where most resistors are 
surface mounted Mini-MELF parts. The main functionality of LE2 is 
located in one custom IC and a hybrid circuit. The hybrid contains two 
ICs that were separately mounted in the older L-jetronic ECUs.
The custom IC mainly contains a divider stage that is triggered by the 
ignition pulses, it divides by two for a 4-cylinder engine, by three for 
a 6-cylinder engine and so on, then a monostable stage that creates an 
impulse whose length ("basic time") depends on the voltage from the air 
flow meter. Also, some circuitry for full load enrichment is within that IC.
The hybrid contains circuitry that adds time to the impulse for cold 
running enrichment, acceleration enrichment and so on.
Besides that, there is a lot of quad OP's that are used for various 
functions that depend on each engine manufacturer's ideas. This may be 
various idle corrections, the cold starting circuitry, additional full 
load enrichment for turbo engines etc. The PCB is so flexible that just 
about any idea from the engine manufacturer can be implemented.
On the LU2 ECUs, there is an additional hybrid circuit which contains 
the lambda control circuitry. Basically, an amplifier/comparator for the 
O2 sensor signal, and an integrator for determining the control 
characteristics.

The most common faults on LE and LU ECUs relate to bad solder joints and 
moisture damage. The PCB is not of very good quality and it does not 
have plated-through holes. Also, it has no protective coating and in 
many cases it is not washed after the wave soldering. Those ECUs may be 
produced in either Germany or Spain, the German ones seem to be somewhat 
better quality. Another common fault is the power transistor controlling 
the injectors. It often has a strange marking but it is in fact a BDX53F 
(NPN darlington). It usually fails open (probably, it first gets shorted 
and then the bonding wires burn off) if someone tries to use 
low-resistance injectors without a ballast resistor. Sometime, in case 
of moisture damage, corrosion between the transistor and heat sink can 
bend the package so that the silicon chip cracks.

LE2 and LU2 ECUs are notorious for bad RF immunity. In cars where the 
ECU is located in the passenger compartment, it is common that the 
engine dies when someone is using a cell phone or portable radio 
transmitter in the car. This is not surprising, due to the design of the 
ECU. A 2-side PCB with no ground plane and very little decoupling of 
incoming signals, and additionally a case with a plastic bottom.
On the other hand, due to the analog design, those ECUs do not create 
any nasty RF emissions.

Best regards

Torbj?rn Forsman

Bill Washington wrote:
> One minor addition to Torbj?rn's information:
>     In the analog systems from mid 80s on there were also LE2 and LU2 - 
> (LE refers to European spec and LU refers to USA spec) and LE2 and LU2 
> both have closed loop lambda control. The Bosch part number on my LE2 is 
> 0 280 000 344.
>     For years I have been trying to obtain a circuit of the Pinted 
> circuit board in the ECU to repair, and modify a faulty one I have, but 
> these schematic appear to have been printed on a very rare material 
> called 'unobtanium'.
>     These later LE2 Jetronic ECUs use a single printed circuit board 
> with leaded components on one side (including a couple of hybrid 
> modules) and very dense surface mount components on the other and a 25 
> pin connector to the wiring loom.
>     I have found one early LE Jetronic ECU schematic for a BMW on the web
> (0 280 001 310) but it is significantly different from my ECU, and is 
> therefore of little assistance....
> 
> Regards
> Bill
> 
>>
>> Subject:
>> Re: [Diy_efi] Motronic hacking...
>> From:
>> Torbj?rn Forsman <torbjorn.forsman at gengas.nu>
>> Date:
>> Sun, 26 Feb 2006 23:55:41 +0100
>> To:
>> diy_efi at diy-efi.org
>>
>> To:
>> diy_efi at diy-efi.org
>>
>>
>> It is not very precise to call an injection system "Jetronic". This is 
>> a brand name that Bosch uses for all systems that only deal with fuel 
>> injection, not ignition.
>>
>> Analog systems are D-jetronic (manufactured from about 1969 to 1974), 
>> L-jetronic (1974 to mid-80's), most LE-jetronic (1981 to early 90's) 
>> and all LU-jetronic (the same as LE but with closed-loop lambda control).
>>
>> Digital systems are LH-jetronic (from early 80's to mid 90's, most of 
>> them but not all have closed-loop, LH 2.4 and later have adaptive 
>> lambda correction and some diagnostic features), LE3-jetronic (the 
>> last non-closed loop system, the ecu is integrated in the air flow 
>> meter) and Mono-jetronic (a TBI system, only used with closed-loop and 
>> adaptive lambda correction).
>>
>> The K-jetronic, an all-mechanical system should also be mentioned. It 
>> may have a closed-loop add-on and is then called K-lambda-jetronic. A 
>> similar but newer variant is called KE-jetronic, it exists both 
>> without and with closed-loop. Most KE systems are analog but the KE3 
>> is digital (and then uses an ecu that is very similar to the 
>> Mono-jetronic ecu).
>>
>> Most digital Jetronic systems use an Intel MCS-51 CPU. Either a 
>> standard  8051/8031 with a separate A/D converter, or an 80535/80C535. 
>> In some cases, mask programmed 8051's may be found but they more 
>> commonly have an external eprom. Anyway, all PCBs are designed for 
>> external eprom so it is a simple task to solder an eprom socket and 
>> the address latch in place, and change the jumper for the CPU's EA 
>> signal.
>> The eprom may be socketed or soldered in place depending on 
>> requirements from each car manufacturer.
>>
>> Some older LH-jetronic (in particular, LH 2.2) use instead an 8049 
>> CPU. The very earliest LH systems might have an RCA 1802, like the 
>> early Motronic systems.
>>
>> The simplest way to identify a Jetronic system is to look at the Bosch 
>> part number of the ECU.
>> I.e. 0 280 000 561. The first six digits tell just that it is a 
>> Jetronic CPU. The seventh digit indicates the number of cylinders, 0 
>> means 4 cylinders, 1 means 6 cylinders and 2 means 8 cylinders. The 
>> eighth digit indicates the variant. 0 means D-jetronic, 1 and 2 means 
>> L-jetronic, 3 means LE- and LU-jetronic, 5 and 9 means LH-jetronic, 7 
>> means Mono-jetronic and 8 means K-lambda and KE. The two last digits 
>> are a leap number.
>>
>> So, when asking about a "Jetronic" system, be sure to include the 
>> variant of the system. I.e. mention that you have an LH 2.4 with 
>> closed-loop.
>>
>> Best regards
>>
>> Torbj?rn Forsman
>>
> 
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