Classic MB Streetfighters
HFM ECU Tuning
Custom ECU tuning solutions that deliver more horsepower and torque for Bosch HFM ECUs originally installed on Mercedes M104 and M111 engines
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Select your ECU version below to see the tuning options available :
Motronic 3.4
Early Version
The early ECU is found in 09/1992 through 02/1994 vehicles. It can be immediately identified when removing the case cover. If there are two boards connected by a ribbon cable, it is an early version ECU
Motronic 3.42
Later Version
The later version was phased into production 05/1994 and was used through 1997. It can be easily identified. When removing the cover, if it is a single board, it is the later version ECU.
Other Classic MB ECUs
We also provide tuning for KE Jetronic ECUs installed with the 104.981 engine.
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If you have another classic MB ECU you are interested in tuning, contact us. We may be able to develop a solution.
Why HFM?
With the availibility of modern standalone options, why should you choose to tune your HFM? While some may think a 30 year old ECU is a relic, the HFM ECU is a very powerful and capable ECU. The HFM module utilizes two 16 bit coprocessors. The majority of the mapping is 8 bit so there is plenty of processing power. The HFM also has phenomenally good knock sensing. Utilizing 2 knock sensors it provides individual cylinder knock retard in 0.35 degree increments.  The HFM is already seamlessly intergrated into the vehicle so there is no re-engineering of peripheral systems.  Electronic throttle control, ASR, cruise control, and idle control are designed to work with the HFM. Not to mention everything else an ECU is expected to do... cold start, warmup, decel fuel cut, fuel safety shutoff, fault monitoring, live data... all still work perfectly as Mercedes intended. Preserving the integrity of these systems preserves the value of the vehicle.
Is my HFM re-flashable?
The EPROM used in the HFM modules, both early and late, are one time programmable. The EPROM must be removed and replaced to alter the tuning in the ECU. As a unit, the HFM can not be re-flashed. Some variants have a socketed eprom, making chip swapping simple. Others have a 44 pin plcc EPROM chip soldered directly to the circuit board. These require the chip be carefully de-soldered and a replacement tuned chip soldered back in place.
What tuning is possible with the HFM ECU?
We have worked extensively with the HFM binary files, both early and late versions. We are able to tune Ignition maps, Fuel maps, Camshaft switchpoint maps, and the Intake manifold switchpoint map. Additional functions such as EGR, Purge Valve, and fuel injection timing maps can be tuned if needed. Coolant temp timing retard and Intake Air temp timing retard maps are defined for tuning as well, if needed. The AMG 3.6L engine is commonly swapped into HFM equipped vehicles and it is possible to remap the stock 2.8 or 3.2 ECU to the 3.6 base mapping. Performance tunes are also available for better than base line results.
What about checksums?
Our test mule, a 1993 320CE, Japanese delivery LHD, with a 3.6 swap experienced several unexplained running hiccups with an uncorrected checksum binary file. Developing the binary for tuning, the checksum algorithm was calculated and no hiccups have been duplicated with checksum corrected binaries. We are not certain correlation is causation, however all of our tuned binary files are checksum corrected before writing to EPROM .
Can you tune VDO HFM ECUs?
No, we curently do not tune VDO HFM ECUs. The VDO is assembled with the eprom on a daughter card with a 72 pin header and no access. It is exceptionally difficult to remove without significant risk of damage to the board.
About Us
As a Mercedes Technician of 3 decades, the love of the brand is ingrained. The tuning journey began with a personal car, 1990 300CE. After doing some engine mods, the KE Jetronic ECU wasn't up to the task of fueling properly. Disappointed at the lack of tuning options, the binary file was pulled and studied up, down, left, and right until I could remap the WOT enrichments and keep them from being turned off at operating temps. Code was also added to the binary to alter data being sent over CAN to the EZL ignition module. Fast forward past some EGS52 TCU tuning, and EDC16 CDI tuning. The current test mule was acquired, A 1993 320CE, LHD Japanese delivery, with the 3.6 AMG engine swapped in. Wanting to tune the car for maximum performance, every available HFM ECU binary has been studied and tested until it was possible to take the car to the dyno and tune the original HFM ECU. Now that the secrets of these ECUs have been unlocked, we are offering tuning for all models equipped with HFM.
Coming soon
This summer we are working of tuning the HFM to run E85. Due to the higher compression of the 3.6 engine, power is essentially limited by the knock tendency of the engine. Higher octane fuel allows more timing and we are expecting E85 to have impressive results.
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The next project car will be an attempt to turbocharge an HFM equipped car. We are expecting the HFM will handle boost well after ironing out a few fueling kinks.
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Stay Tuned!
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Questions or comments?