Im just digging into this, but would be interested in any simple mods anyone has accomplished that work, but which are safe. I dont want to burn up an engine. I had an 88 300E back in 97 and absolutely loved that car, but the mileage was never that great. Ive read some of you are reaching near 30 MPG highway, thats what I would like to aim if at all possible. So to start I have several questions.

If I want to alter fuel mixture, what kind of duty cycle am I looking for, and is un-plugging the O2 sensor enough to put the system in open loop? Is it safe? I have a rattle under the car in the exhaust, thinking the cat might be toast anyway, might gut it out then I wont have to worry about it. Its got pre-cats too and I see all the later cars appear to have lost them?

I know about pulling the ignition resistor to advance timing, save that for later?

I am not so much interested in gaining HP as I am improving mileage/efficiency, but the two often go hand in hand. I am not interested in internal mods, porting or the like, unless it physically would improve economy, like port matching for example. To that end (economy), what is the thought on exhaust flow/backpressure? I'm going to have the motor out so anything simple that could be done to that end while its out, including altered valve timing, would be considered.

Ive wrenched for over 40 years, and years ago I actually had a pretty good handle on CIS, but never from a performance standpoint, and its really been a while. I need to dust off the brain and get the books out and dig into this.

There are a few mods you can do to a 103. I underdrive my alternator and p/s pulleys. I cut an alternator pulley on the lathe and use the diesel p/s pulley. Doubt you could measure an improvement in MPGs but every bit helps.

I also run the cam advanced to move the powerband down a smidge. The stock cam gear is capable of 0, +3, -3 degrees. I don't rev my turbo motor hard so the loss of top end is a non issue for me. Nor would it be for one driving for MPGs.

Leaning out the CIS will get you a measurable gain of MPG. When I was running CIS I built a controller to intercept the O2 sensor signal and allow me to modify it +- 300MV in real time. I picked up 3 MPG averaged over 1 tankful by running it leaner. Keep in mind this is the heavy AWD wagon which at the time had 3.29:1 gearing, a 3.07:1 sedan should do a little better.

Lightweight wheels are another place to gain efficiency, and while you're at it put the whole car on a diet too.

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90 300TE 4-M
Turbo 103, T3/T04E 50 trim
T04B cover .60 AR
Stage 3 turbine .63 AR
A2W I/C, 40 LB/HR
MS2E, 60-2 Direct Coil Control
3" Exh, AEM W/B O2
Underdrive Alt. and P/S Pulleys,
Vented Rear Discs, .034 Booster.
3.07 diffs 1st Gear Start

90 300CE 104.980
Milled & ported head, 10.3:1 compression
197° intake cam w/20° advancer
Tuned CIS ECU
4° ignition advance
PCS TCM2000, built 722.6
600W networked suction fan
Sportline sway bars
V8 rear subframe, Quaife ATB 3.06 diff

If you have a air temp sensor a G Force Chip will deliever more mileage,but no power.You can't have both.I will mail you mine for mail at cost. X2 on timing but thats what G Force does

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1999 w140, quit voting to old, and to old to fight, a god damned veteran

Before you even think about any mods then start with basics.

Do a compression and leak down test...if you're not within factory spec then you'll never achieve anything.

The M103's are notorious for vacuum leaks, so do a smoke test and correct any leaks.

Finally "tune" to factory spec which includes both the fuel and ignition systems.

If your cat is plugged then that doesn't help performance...

Even then 30MPG will be a far reach as you're running a 3.07 rear gear...
You can change the rear gear but is it worth it as you may loss MPG trying to accelerate....

I've owned my 1988 300CE from new in May of 1988 and low 20's are about as good as it gets...

__________________
http://i19.photobucket.com/albums/b1...c/GOWIDE-1.jpg
1971 280SL ROADSTER
1988 300CE TWIN TURBO WIDEBODY
1994 E320 CABRIOLET
1999 C43 AMG
2005 G55K AMG
2008 CLK63 AMG BLACK SERIES

PM sent, thank you. Does the chip go inside the Lambda computer, or somewhere external? Your saying the chip alters the ignition similar to removing the resistor?

Okay, I think I recall the cam sprocket, it mounts in different positions valve timing rather than the offset keys used on the older engines? I think I saw that in one of my books. I believe I have a 103 service manual, a genuine paper one, but dang if I can put my hands on it.

Just to be clear though, I am not necessarily looking for more power, im more than satisfied with its performance. I am primarily interested in changes to improve fuel mileage and overall economy. And as the roots of better economy are basically cost savings, having to buy higher octane fuel defeats the whole purpose if the goal is to save money. Like simultaneously getting the car to run on 89 octane while making it burn less fuel would be the goal.

Kitty-less, the O2 sensor could be retained to more closely manage fuel mixture than running open loop, correct? Allowing me to lean it out a bit further without fears of burning it up? To be accurate do I need an exhaust gas analyzer, or can I get close enough by watching duty cycle and reading plug colors?

Any other controls in the CIS system that can be bypassed or deleted?

Possibly different driving characteristics/terrain/elevation, but our 87 300E was always high teens in town, mid 20's highway rolling 75 plus.

This motors coming out and another ones going in. Everything will be checked before its dropped in. And yes, vacuum leaks can raise total hell, not only with economy, but in the right spot can lean a cylinder and burn it down.

The 1988 M103 does not have an air temp sensor and there is nothing in the EZL or CIS control that is "chippable"..

Don't believe everything you read as there is not much one can do to drastically alter inputs to the CIS-E or EZL...
Remember there are two distinct systems one for fuel and the other for ignition...no combined control.

You should be able to run 89 octane as your CR is only 9.2:1

__________________
http://i19.photobucket.com/albums/b1...c/GOWIDE-1.jpg
1971 280SL ROADSTER
1988 300CE TWIN TURBO WIDEBODY
1994 E320 CABRIOLET
1999 C43 AMG
2005 G55K AMG
2008 CLK63 AMG BLACK SERIES

If you are high teens to mid 20's then you're spot on...
My "low 20's' is average over the 25 years of ownership...
The only thing that will improve highway mileage would be a higher ratio rear gear...

__________________
http://i19.photobucket.com/albums/b1...c/GOWIDE-1.jpg
1971 280SL ROADSTER
1988 300CE TWIN TURBO WIDEBODY
1994 E320 CABRIOLET
1999 C43 AMG
2005 G55K AMG
2008 CLK63 AMG BLACK SERIES

There is also fuel quality and chemical makeup to consider. I dont know about Delaware, but Minnesota was screwing with it all the time and too often everyones cars ran like total crap. If you bought gas outside the metro, in the rural areas, the gas was much better and you got significantly better mileage. MTBE was nasty, but I think most areas have stopped using it now. Ethanol up to 10% wasn't a big problem, but sometimes it was more like 15% or more and could destroy older carbed engines, boat motors and snowmobiles especially, if they weren't jetted rich enough.

Running the engine lean is about the only thing you can really do. Make it a point to never peg the economy gauge in the red.

Reducing weight would help. Lightweight rims, keeping an empty trunk, etc.

The only BIG game changer is adding a 5 speed manual trans. People report close to 30mpg on the freeway with the stick.

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Eugene

10 E63 AMG
93 300te 4matic
07 BMW X3
14 Ford F-150 Fx2

Sorry been talking the Chip tells the ECU to advance timing,and mellow out the air fuel ratio.
It does not increase it my 1/4 mile times proved it.I went slower buy mileage was high
I hate to see it going to waste I paid $69. for it. I know a new BMW owner with a GForce he got it for mileage.
Now that I use Nitrous I'm looking for lower timing

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1999 w140, quit voting to old, and to old to fight, a god damned veteran

The M103-12V doesn't have an ECU...
EZL for ignition and CIS-E for fuel, two separate control systems with minimal inputs...not even an air temp sensor on the 1988.

__________________
http://i19.photobucket.com/albums/b1...c/GOWIDE-1.jpg
1971 280SL ROADSTER
1988 300CE TWIN TURBO WIDEBODY
1994 E320 CABRIOLET
1999 C43 AMG
2005 G55K AMG
2008 CLK63 AMG BLACK SERIES

That would make it a real sweet car.

If its leaned out (normal 14.7:1 ratio) you say not to run the economy gauge into the red. I thought I had read the CIS richens the mixture at WOT, and the O2 Lambda went into open loop???

Ed's right on the money here.

The CIS in 1988 wasn't wideband, it was narrowband, so really it could only tune to 14.7 effectively.

If you're keeping with CIS, ed's pretty much right. Those of us who've switched to EFI will really only see a gain in mileage at cruise over a well tuned CIS machine. The only reason why this happens is that I have my engine tuned to lean out quite a bit. I went until I got knock or lean misfire under very light load and high advance. I think my M104 squeaks out 25-26 on the highway, during the summer, if I baby it and a member on 190Rev got 32 out of his bone stock, pretty much stripped 2.6 190e. FWIW We're both running 5sp manuals and a 2.87 rear diff.

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1993 190E 2.6 Sportline

Bob, may I assume you guys are running cats?

I've read the O2 goes open loop at WOT, and was sure I read the CIS went rich at WOT too, but havnt confirmed. Anyone know?

Just to be clear, mines an 89, if it makes any difference.