I belive that with an O2 sensor unpluged a chip will not do anything at all. Open loop with a modified chip should be open loop without a modified chip. Please enlighten me if I am wrong.

John Roncallo

You might be right. I have not taken the time to delve into the MB manuals/software system. My dad does have a diagnostic star something laptop that plugs into the car + absolutely horrid UNIX to NT port computer program from MB that was ungodly expensive so I would hope it is in there somewhere. All I know is from trial and error so far and little tidbits of info that I have gathered from the web. I think that there are open loop maps and closed loop maps. The closed loop primarily just adds/removes fuel depending on engine load and either throttle position or RPM. Timing is also retarded/advanced I think based on these maps and the knock sensor(s). Open loop should just be a predetermined map that no longer attempts to maintain 14.7 under load. Thus adjusting that map to the optimal fuel ratio ~12.5 (can be different for different engines/setups) + increased timing + better air flow + high octane fuel + cool climate if it is not already so should provide decidedly increased power. Again I would say around 30-50 hp. The O2 sensor is only accurate around 14.7. Above or below that it is not accurate at all. The problem with closed loop is that even if you do inject more fuel when the computer gets a reading that the A/F ratio is lower than 14.7 it leans it out. The only way to change that is to either fool the O2 sensor (inline resistor or something) so that the new 14.7 is actually 12.5 or to disconnect it completely and add fuel some other way either by an open loop map or additional injectors in the air intake or something. This would be great for power but really bad for economy. The best scenario is that under say 50% throttle the computer starts increasing timing and starts moving towards a ~12.5 or so ratio. In cars that are capable of open loop I imagine that it is probably pretty close to the optimal ratio under full throttle. So the best bet is probably just getting a 92 computer for the 500E to enable open loop. To do this properly would require a dyno, wideband A/F ratio meter, and a completely different computer system or being able to modify the amount of fuel + timing using the stock ECU. My car has auxillary fuel injectors + computer and the stock computer will still maintain 14.7 under normal acceleration no matter how much I inject using the extra fuel injectors. Unplug the O2 sensor and I can as rich as I would like.

It would probably be easier to make an entire replacement box. I know as fact that Ford used Motorola microprocessors with undocumented, Ford-only instruction sets in the 80/90's, and that Bosch also used Motorola/Siemens (second source) microcontrollers in that era (no idea what they use now).

The processors and programming tools have never been better or cheaper than they are now. PCB software is available on the 'net for free and PCB companies on the internet can get your artwork and make boards in just a few days. BUT...the engineering required is considerable, you can forget about ever getting EPA approval, market is so small, etc...it would be a labor of love to do this sort of work. Furthermore, two guys in a garage, no matter how smart they are, are not going to beat even average Bosch/MB engineering with their $$$$$$$ of dollars of test /dyno equipment to play with. I'd guess there would be no hope of "optimizing"...either you give up engine temperature, emissions, gas mileage, drivablility, or some or even all four characteristics for any even vaguely discernable performance improvement. Replacing a chip and knocking off a second in a 1/4 mile on a 16 second car is probably a pipe dream or urban legend. MAYBE... a reasonable goal would be to "NOP" ("no-op" or do-nothing) the code setting rev limiter characteristics, but then you have to wonder if this would be a good idea (BTW, in an "analog" system in a car such as my 86 560, I think that this is done with a resistor in the fuel pump relay module-a lot easier!).

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86 560SL
With homebrew first gear start!
85 380SL
Daily Driver Project

http://juliepalooza.8m.com/sl/mercedes.htm

Climate, altitude, amount of air in the intake, and quality of fuel are the variables that you can tune for with a completely programmable system. Switching from a stock computer to the Tec3 I think that someone got around 50 hp over a stock C36. I assume there were other mods such as air intake, exhaust manifolds, etc.

We will do quite a bit of the design of a simple microprocessor this semester and create our own next semester. I am a CS major and have mainly focused on high level programming but it seems that here they expect you to do a lot of CE and some EE in the 3rd and 4th years. I should be able to program the Motorola processor with the accompanying buses/storage devices now but I haven't ever seen any info on what you need to 1. upload code (I assume flash into an EEPROM or some such) if that is even possible (it may have code stored in ROM or have a lot of hardware that perform functions) and 2. where and how the values for timing and injection are stored. We went over I think the MC68000, SPARC something, and others briefly in computer architecture. I haven't researched it at all so if you have any basic and introductory resources and tutorials for the Bosch ECU/how to edit maps/what board to plug the ECU into etc. I would love to see it. If I can get the assembly I could figure it out over time but would probably never take that much time. From the little that I did read about a bosch ECU setup it appears that they have fixed memory element (s) i.e. blocks of physical memory that you dump the values for fuel injection into. That should be simple enough and is what I assume what "performance chips" do. If that is all that is done then it is no wonder that they don't work. If you have code/hardware that uses but overrides the map based on other input then the map is useless if you are trying to do something that is contrary to the hardcoded/wired algorithm that uses the other input. I imagine that newer ECUs lend themselves more readily to tweaking for performance gains because a lot of hardware now is being replaced by software (which can be changed) and is more modular and behavior oriented instead of functionally oriented. Well it has been that way for quite a while but it is used more widely and improved every couple of years.

I owned a 400E for 4 years until some moron in a jeep rear ended me and totaled the car. Thank goodness his insurance paid off well. Anyhow........

I researched performance mods for this car ad nauseum, and there are two things I will agree with on the thread so far: 1) If you wanted cheap upgrades, you bought the wrong car! Most Mercedes car nuts would tell you that normally aspirated motors will not see much, if any gain from chip upgrades, and a substantial potential for serious problems, IF they get it wrong. Why risk it?!

2) The rear dif on the 400E is the absolute FIRST thing you should do! I bought mine from Bergwerks, which is unfortunately out of business now, but find a source for a 2.82, and you will absolutely think you bought a new car! It will take .5 - .7 secs off your 0-60. The motor has plenty of go, it's just geared for crap. Your mileage will suffer about 2 MPG on average, but it REALLY transforms the car from a sedate family sedan that can do 155 on teh Autobahn, to a quick sport sedan. Plan on $1000-ish for the dif and 5 hours labor. You also have to do a different gear for the speedo, or you will get lots of tickets. ("Honest officer, my speedometer said I was only going 55!")

You will obviously need more rubber. I had 215/55 16" wheels and they were just about right for the motor and rear dif. In a straight line on dry pavement, I couldn't spin them. Any kind of turn, or dicey traction, and they would light pretty easily.

I also lowered the car with H&R springs. Cheap at $269, but an hour per wheel. And plan on scraping speed bumps.

One CHEAP mod is to remove the resonator, but it doesn't do much to performance, only adds a (Much needed!) bit of edge to the exhaust.

Or - you can go find a C32 like I did and go REALLY fast!

Mike

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Mike in Denver
'93 400E Now DEAD - Rear ended and totalled.
Replaced by '02 C32 AMG - FAST!

I aggree with the diff mod on the 400E, From everything I read, It's well worth it! A 3.40ish to a 3.83 is a big jump! I changed the diff in my 300E from 3.07 to 3.27 and noticed a substantial difference in acceleration. The only bummer is higher RPM's at highway speeds.
Good Luck!
Adam

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Current Stable:
01 ML55 AMG
92 500E (a few mods)
87 300E (lots of mods)
00 Chevy 3500HD Diesel Box Truck
68 18' Donzi Marine
06 GT i-Drive7 1.0 Mountain Bike (with GPS!)

PREVIOUSLY OWNED:83 300SD, 87 420SEL, 88 420SEL, 90 420SEL, 86 560SEL, 86 190E 2.3-16V AMG, 94 E320