Replacing Bosch jetronic with MegaSquirt EFI - Mercedes-Benz Forum
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#1 (permalink) Old 05-05-2007, 07:56 AM
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Replacing Bosch jetronic with MegaSquirt EFI

A popular thread in this forum called "Performance Upgrades"
http://www.benzworld.org/forums/vint...-upgrades.html
discusses such modifications as turbocharging, supercharging, header and exhaust upgrades, transmission swaps, cool air induction and other power increases. It also explored the idea of replacing the Bosch D or K jetronic with the MegaSquirt EFI controller and several users (myself included) had done the conversion or were in the process of doing so and there seems to be some interest from others in this specific MegaSquirt project.

In the interest of keeping the original thread on topic about the many possible performance upgrades to vintage Mercedes I'm starting this new thread to discuss specifically the MegaSquirt conversion. I will post to the other thread only when my MS project is completed and can comment on its merits as a "performance upgrade" or when I finally get around to fabricating headers and completing other non MS modifications.


MegaSquirt is a stand alone user-programmable control (via laptop) for spark and fuel and can be adapted to any spark controlled engine with the right choice of components. The conversion can be seperated into two phases (fuel and spark) and each phase can be done completely independently of the other while maintaining vehicle driveability. Here's a summary (vastly simplified) of the conversion from the Bosch K-jetronic CIS to MegaSquirt EFI in my 1978 450 SEL:


Phase 1. FUEL

-- Remove the Bosch CIS components consisting of mechanical fuel injectors, fuel distributor, air flow sensor assembly and miscellaneous warmup and enrichment devices; they will no longer be used.

-- Acquire MegaSquirt II v3, relay board, wiring harness bundle, wideband O2 sensor and controller, set of 8 Bosch 19 lb/hr fuel injectors and fuel pressure regulator (used from Ford Mustang), fuel rail from earlier Mercedes EFI, coolant temp sensor, intake air temp sensor and throttle position sensor (all cheap, stock GM parts).

-- Install all of the above (there will need to be some fabricating of brackets and other "adaptive engineering" to accomplish this) and use the MS software with a laptop to load the default fuel maps to get the engine runnning and then drive around to datalog. Software will revise fuel maps to optimise for peak power at or near WOT and for maximum fuel economy at other times.

Phase 2. SPARK

-- Remove distributor, coil and ignition control module; they will no longer be used.

-- Acquire EDIS 8 module plus coils and wires (used from Ford Mustang), 36-1 trigger wheel and sensor and the necessary wiring.

-- Install all of the above (also requiring "adaptive engineering") and use the MS software to load timing tables. Datalog and revise map for optimal performance.



User 'oughtsix' has succesfully done phase 1 of this conversion and I invite him to post a summary here on this thread. He's done a lot of pioneering work for this particualar setup and has extensive and very useful pictures. I've been documenting extensively as well, and as soon as I can set up a place to host, I'll post pictures, too. Others who are now doing or are interested in doing the MegaSquirt conversion should start posting their projects.

note: MegaSquirt has a large support community and forums for many applications. MegaSquirt EFI :: Index

I have no affiliation or relationship whatsoever with MegaSquirt.
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#2 (permalink) Old 05-05-2007, 08:29 PM
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Megasquirt may be the way to go for W126 owners as well now that Bosch no longer supplies the throttle position sensor for the CIS-E unit.

Near Manassas Va. '65 220S, 2006 Ford Crown Victoria Police Interceptor, '99 Volvo V70, '72 350SL 4 speed

Not part of the in-crowd since 1952. It's BRAKES not breaks. You break a bone, use brakes to stop your car. /rant

http://www.megamanual.com/index.html
http://www.bgsoflex.com/megasquirt.html
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#3 (permalink) Old 05-06-2007, 09:17 PM
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Hi Guys,

Well I was in the junk yard this weekend and worked out how to do the TPS.

Take one MB Throttle Body with the idle control switch and add a small plate. Then add the tps off a mid eithies ford (Crown Vic) and you have a working TPS for the benz. I will fab it this week and report back with pictures ect.

By the way I have finished my Megasquirt and it seems to work fine.

More later

Jon White
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#4 (permalink) Old 05-08-2007, 02:51 PM
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Hello Hbar and Jon, (and anyone else that would like to comment!)

Have you guys had any luck with a TPS solution? I keep looking at the 65mm ford throttle bodies on E-Bay but haven't made the jump yet. I like the look of the Mustang throttle bodies with the integrated IAC (idle air control) valve but I wonder if the idle air control valve is to big to fit into the Mercedes intake. I have also looked at the throttle bodies on the 4.6 ford trucks on ebay. It looks like these throttle bodies have the IAC implemented on an elbow that sits underneith the throttle body. I am thinking about ebaying one of the mustang 65m throttle bodies with a IAC and TPS and removing the IAC valve and covering the holes in the TB with a small scrap metal plate if the IAC valve proves to be too big.

I am open to any TPS suggestions. I have my whole intake apart and don't really want to put it back together only to take it apart again.

Thank you for the PM to the new Megasquirt thread!
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#5 (permalink) Old 05-09-2007, 08:11 AM
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At this point I've decided NOT to get the whole throttle body unit from a different application but to use the existing TB and adapt a different TPS to it (or somewhere on the throttle linkage). I've acquired several used TPS's and am now mocking up a few variations along these lines to see what will work the best.

It looks as if 'jon' in post #3 is thinking the same thing.

I will (I swear) post pictures this weekend.
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#6 (permalink) Old 05-09-2007, 08:13 AM
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Jon, how does the MegaSquirt power and mileage compare to the stock Bosch?
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#7 (permalink) Old 05-09-2007, 10:21 AM
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I think Jon was refering to finishing soldering and assembeling the megasquirt board and has it working on the bench with the stimulator which is quite an accomplishment (I hated soldering those 4 little transistors). Congratulations! If he has a runing car this would be too much for me to bear as I have over a year into mine

I have a big hump on my throttle body behind the throttle switch which interfears with trying to adapt another TPS.

Can I ask why you decided to abandon the Ford throttle body? For me the cost of the Mustang throttle body and not knowing it is going to work is prohibitive.

While you guys are working on TPS's remember that the actual range of movement and the start and stop points of the TPS are not signifigant to megasquirt. Megatune has a real nice TPS range adjustment feature where you sit in your car with the gas pedal out and you just hit a button in megatune telling it that the TPS is at idle. Then you put the gas pedal to the floor and hit another button telling megatune that you are at WOT (wide open throttle) it then figures out everything from this. You can even have the wiring on the TPS backwards and megatune will work.

If you decide to go with a off the shelf potentiometer (variable resistor) the only thing you need to look out for is that the potentiometer is "linear taper" and not "audio taper". "Audio Taper" potentiometers change resistance exponentially with the movement of the shaft and a linear tapper potentiometer changes resistance linearly. I had a radioshack 10K potentiometer working but the cheap stamped sheet metal nut proved to be too flimsey. Maybe I will try e-bay'ing a quality built potentiometer.

Don't get too hung up on the TPS issue. My engine was running very nicely without any TPS enrichment at all. The TPS enrichment "fine" tunes the AFR for maximum power during acceleration. Without TPS (acceleration) enrichment you will still be miles ahead of the CIS injection system which could never get in the same ballpark of this type of fine AFR tuning. We are talking about tuning a few tenths of a point of AFR. CIS would be real lucky to get with in 4 or 5 points of stoich (14.7AFR). The main variables for tuning megasquirt are manafold vacuum (MAP) and RPM. TPS is is a very minor variable in comparison.

Making the fuel rails is just a matter of drilling holes in the right place and not breaking a drill bit off in the process. If you guys get stuck on the fuel rails let me know. I would be happy to drill a set of rails for you if you wanted to send me the fuel rail stock and pay for shipping both ways. The only cravet is I could make no guarentee that they would work on your vehicle. I would like to see you guys progress so you can tell me where to mount the relay board in the engine bay

Hbar, I would really like to see your pictures but don't sweat getting them up. There are only so many hours in the week and personally I would rather spend them working on my install than messing around with trying to figure out where to host the pictures.

Last edited by oughtsix; 05-09-2007 at 11:01 AM.
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#8 (permalink) Old 05-10-2007, 10:22 AM
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Hi Guys,

I so far have only just finished building the megasquirt. I still have to modify it for PWM Idle Control as that is what is used on the later Mercedes which has the idle control box next to the abs brain that keeps breaking ( my father is on his third one on a car that has down less than 50,000 miles from new). I have got all the bits to the tps on the stock throttle body, tps from an 86 Crown Vic the throttle body shaft from the Crown Vic and the original Mercedes throttle body with a tps switch on ( W126 is where mine came from, I also picked up a complete inlet manifold so I can check clearance with pulling my car to bits). Just need to mount ford tps using Ali plate some screws and the cut down shaft to provide the correct key for the ford tps.

The ilde control is foxing me a bit at the moment as the later car uses feed from manifold and base of cis injectors to do idle.

Still waiting for the fuel rails and the very expensive drill bit that drilss the correct hole. SO fuel rails still need to be built but the plus piont is that all the cis heads seem to have the same injector spacing (not all the same but some offset).

Anyway enough rambling, hopefully will have time Friday and Saturday to work on fabing the tps stuff. As I have to replumb my pool this weekend too.

See you all later

Jon White

PS oughtsix where are you located ?
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#9 (permalink) Old 05-10-2007, 04:03 PM
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Hello Jon,

I live in Redmond Oregon (Outside of Bend OR) and fortunately it isn't pool weather here yet. There is always something broken on our above ground pool every year but fortunately I have a week or two before I have to figure out what the problem and expense will be this year.

My first IAC valve was a 5 foot piece of vinyl tubing, a plastic barbed T fitting and a 1/2" ball valve that sat in the passenger compartment with me. They were all extra parts I had lying around. I adjusted the ballvalve by hand while I was trying to get the engine to turn over and stay running for the first time. (Truthfully the ball valve was a later refinement for my first trip around the block as I just put my thumb over the tubing the first time I got the engine to stay running to lower the idle RPM.)

Basically my approach was to rig things to get the engine running then come back to figure out the finer points of the engineering later. By taking this approach I could get my engine running without worrying about wether my IAC solution was working and I was able to get my IAC working without worrying about whether the rest of the engine was running smoothly or not. I tried to isolate the variables and work on one problem at a time instead of trying to get everything to work together the first turn of the ignition key. Kind of like not doing the fuel and timing at the same time.

I still don't have an airfilter solution yet.

My intake has two ports on it for Idle control. Both of these fed through tubing from the mechanically tempature controlled IAC valve and an extra small aluminum manifold that also carried the cold start injector for my CIS system. I am still using this stock idle controll system with the cold start injector still in there but disconnected from fuel.

P.S. Cool aquisition of the fuel injector pocket reamer. I found out about them after I built my rail and wish I had one. They are spendy but I am sure it will be worth it!

Last edited by oughtsix; 05-10-2007 at 04:18 PM.
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#10 (permalink) Old 05-12-2007, 10:09 PM
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LINKS TO PICTURES

Top of engine torn down:
http://s209.photobucket.com/albums/b...h_IMG_0008.jpg

CIS components. You can see the auxilliary air bypass valve on top of the water passage on the front of the intake:
http://s209.photobucket.com/albums/b..._MBIntake1.jpg

These are the fuel rails that I'll be using from an early 70's Mercedes with the Bosch D-jetronic EFI:
http://s209.photobucket.com/albums/b...FuelRails1.jpg

An injector and rail boss; I'll need to make a tight connection between these two with a short section of hi-pressure fuel line: http://s209.photobucket.com/albums/b...dRailBoss1.jpg

The stock mechanical fuel injector with its sleeve and o-ring from the Bosch CIS K-jetronic:
http://s209.photobucket.com/albums/b...echFuelInj.jpg

New Bosch fuel pump and filter with assorted bracketry (same as stock pump and filter but it needed replacing anyway): http://s209.photobucket.com/albums/b...PmpwFilter.jpg

The MegaSquirt2 with relay board and wiring: http://s209.photobucket.com/albums/b...Q2nRLYnWIR.jpg

Innovate WB O2 sensor and controller:
http://s209.photobucket.com/albums/b...AndControl.jpg
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