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  #1  
Old 06-16-2003, 10:16 PM
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Those with M102 & M103 "free power upgrade" must read!

On many discussion forums we have have read of the "free horsepower upgrade" available to those with M102 and M103 motors by way of removing or changing the value of the R16 ignition reference resistor. Many who perform this simple modification (generally removing R16) claim great results using the "seat-of-the-pants meter". It is amazing what we can make ourselves believe if we want to. Well, I have got some bad news for those who have simply removed R16. Read on.

It is generally accepted that maximum power and fuel economy will result from using the maximum amount of ignition advance possible without causing pre-ignition (knocking or pinging) for a fuel of given octane rating. The EZL ignition modules fitted to the M102 (1.8, 2.0 & 2.3) and M103 (2.6 and 3.0) motors follow different advance curves dependant upon a programming resistor known as the R16 reference resistor. Most threads suggest that a higher value resistor results in more advanced ignition timing and thereby deduce that removing the resistor completely will give maximum ignition advance. NOT TRUE. A higher value resistor can give more advance up to a point but an open circuit (resistor removed) is read as a fault condition and sets the most retarded ignition curve. Many falsely believe that R16 can just be a variable resitance that will dial up whatever ignition advance you wish. This is not the case. The ignition module has a finite number of ignition advance curves or maps that are selected by certain fixed resistor values (0, 220, 470, 750, 1300, 2400 ohms).

As an owner of both M102 and M103 powered cars I decided to test the effect of different values of R16. As a temporary arrangement, I removed the plug containing R16 and removed the resistor (220 ohms in my 300TE and 470 ohms in my 190E). I then connected a 2-core cable to the plug of sufficient length to reach into the cabin of the car where I had a box containing a rotary switch with all the above listed resistor values as well as an open circuit position. I then test drove each car (with 98 RON fuel) and noted the effect of different resistor values. Most obvious was how little effect different resistor values had. Only at higher engine speeds at full throttle on long hills was any change noticeable at all and only then by repeatedly switching from one resistor to another. How anyone could notice a change after stopping the car, getting out and removing or changing the resistor, getting back in and driving further, escapes me. Also interesting was that the best performance was not necessarily obtained at the highest resistance setting and certainly not when open circuited.

I then decided to verify my findings with a timing light. As suspected, greatest change occured at higher speeds (> 3000 rpm) and high load (simulated with vacuum hose disconnected from ignition module). R16 has no effect on ignition timing at idle. As also suspected, an open circuit R16 gave the same minimal advance as a short circuit. At the intermediate values different amounts of advance occured and this was dependant upon which motor. For my M103 six, 750 ohms actually gave the greatest advance. In my M102 four, 1300 and 2400 ohms both gave the same result so I went with 1300 ohms. The original lower values were presumably to suit our low octane (92 RON) regular unleaded fuel here in Australia. We also have 95 RON premium unleaded and more recently some suppliers have changed their premium to 98 RON (which I now generally use). In the 300TE (which we use for long journeys) I have fitted the R16 plug with a small switch which is normally set to the 750 ohm position (for premium fuel) with a 220 ohm position available for the situation where only regular fuel may be available (eg. when travelling in country areas).

My reason for posting this is to alert those who are contemplating or have performed this modification to take a measured approach with their car. Ideally a dynanometer would give the most valid readings but at the very least a timing light should be utilised. Without such equipment to verify the effect of any change of the value of R16, I would leave it untouched. I would certainly advise against removing it unless you can measure results different to those obtained with my cars. Possibly, different results may occur with different models delivered in different markets. It comes back to not modifying something unless you fully understand the implications of doing so.
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  #2  
Old 06-16-2003, 10:36 PM
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That is why I reinstalled my r16. I felt nothing spectacular. But strangely, my engine did start to run hot.
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  #3  
Old 06-16-2003, 10:52 PM
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Greg,
Thanks for taking the time to investigate and post these results. Originally, the R16 "mod" was started for the 190E 2.3-16 valve U.S. spec model only...somehow, it got out and everyone with a CIS-E (KE3) equipped engine thought it would increase their performance.

In my U.S. spec, 1987 190E-16V, removing the R16 made a difference only above 3000 RPM and only that the engine revved faster to redline from 3000 RPM on up. Yes, this is by my butt dyno and not verified with actual measurement. I have since acquired a Euro-spec rotary resistor 'switch' and hope to run some tests with a G-Tech accelerometer to verify any improvement if any with the different resistance values.

But anyway, thanks for posting your results!
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  #4  
Old 06-18-2003, 03:11 AM
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Glen,

I would like to see results others obtain using a timing light, accelerometer or better still a dyno. Yours will be interesting being a 16V. I think the more results that are obtained for a range of different models and years and for different markets (US, Euro, Oz, etc.) the better picture can be obtained.

Greg
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  #5  
Old 06-18-2003, 05:18 AM
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Greg,

some additional information on this.

If you have the tables from Mercedes (Mercedes Benz Tabellenbuch Personenwagen) concerning the ignition for different engine versions (non-cat / cat or RUeF/KAT) you will see, that there is only a few or no difference in ignition at idle and at 3000/min if you change the value of R16.

Others (Paul Wurm, well known developer of catalytic converter systems for older vehicles in Germany) did the same you did and tried to find out, how R16 influences ignition... and got the same result, no ignition advance by different values of R16.

I really would like to do some dyno testing with modified R16.

On the other hand, these engines M102 and M103 where developed to run with leaded fuel ROZ 98 and R16 set to "1" or removed and R=infinit. The german manuals clearly say that moving the adjustable R16 from "1" to "2" to "3" (or from 3 to 4 to 5 for unleaded fuel) will adjust the ignition to poor fuel quality by moving the ignition 2 per step backwards (retarded) resulting in less engine power and less fuel efficiency.

Logic says that this process will work in both direktion, moving R16 to "1" ... you know the idea.

In the workshop documentation for the W201 2.3-16 Mercedes states that best engine power and fuel efficiency is reached when setting R16 to "1" and using premium fuel ROZ 98.

Furthermore the (early) KE-ECU had two programs, that where switched by different plugs R17. One program for leaded fuel ROZ 98 and a car without cat and another program for unleaded fuel ROZ 95 and cat. R16 set to "1" or infinit was only used in conjunction with R17 for leaded fuel ROZ 98!

During the 1980s catalytic converters became standard in Germany and leaded fuel vanished from the market. In the 1st Modellpflege (update) in october 1989 mercedes made some changes in the ECUs, at least the ignition program for leaded fuel (and maybe the KE program as well) was not built in any more. This is written in the workshop information of the changes of october 1989 I have in my archive.
I still have no information on changes in the KE-ECU...

What could this mean for the "famous" R16-mod?
If you have an ignition-ECU from late 1989 or later (e.g. W124 with chrome strips on the bumpers and large plates on the doors) - there is no max. advanced ignition line anymore. Setting R16 to "1" or infinit by removing the plug does not set ignition to the old and most advanced value (in case it ever did).

All this technical details are valid for the standard vehicles in Germany, national versions (AUS, J, USA etc.) may vary. I have little 1st hand information on this and most resulsts are from backward-engineering

Personal experiences on R16:
I own an early 1989 300TE and setting R16 to "1" changes things a lot - according to my pants-meter.
I know from a buddy in a german forum, that newer ignition-ECUs don't like to have R16 removed and will behave like R16 is set to 4 or 5 in that case (some kind of error-mode I think). You will recognize the effect...

Still an interesting topic!

bis denn,
Christian

1989 300TE
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  #6  
Old 06-18-2003, 11:53 AM
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On my 1992 W201 2.6l, removing the R16 netted a noticeable "seat of the pants" performance improvement.

I have dyno'd many cars before/after mods and my "seat of the pants" meter is pretty accurate.

As per your post Chris, I believe this dis-proves your theory about post 89 models "not setting ignition to the old and most advanced value".

My service CD does state that the R16 affects iginition timing on the post 89 W201's (up to 1993).
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  #7  
Old 06-18-2003, 11:56 AM
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Thanks for the thorough testing and analysis.

I'm interested in retarding the timing on my '88 190E 2.6 in order to achieve a better passing margin on my California emission test, which is done on a dyno at 15 and 25 MPH in second gear (manual trans).

I was hoping that removing the resistor and shorting the plug would retard the intial timing from its 9* setting, but you indicate this is not true. Can you verifiy?

I believe my relatively high emissions are due to too low EGT as IR gun measurements indicate only about 500* at the exhaust manifold and lower entering the main converter on a fully warmed up engine after several minutes of idling. My hunch is that the idling causes the converter to cool down to the point where is it not as efficient and this causes relatively high emissions on the first test (15 MPH), but since the 15 MPH test is done under relatively high load, the converter heats up and the 25 MPH test has much lower emissions relative to the 15 MPH test.

Retarding the timing at idle or any operating speed will increase the EGT, but even if shorting the plug doesn't change idle timing, it should reduce the timing during the test, which should heat up the converter faster.

My duty cycle is in the correct range and all indications are that there is nothing amiss with the engine or control system. Anecdotal evidence indicates that a lot of other 103 owners are seeing high emissions. My hunch is that it's an EGT issue, which could probably be changed by retarding the timing, especially at idle.

The idea of shorting an electrical is a scary thought, so I want to confirm that shorting the plug did not cause any harm and that it did not change the initial timing. Thanks!

Duke
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  #8  
Old 06-18-2003, 12:31 PM
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Rick,

>On my 1992 W201 2.6l, removing the R16 netted a noticeable "seat of the pants" performance improvement.

It is not the first time, we are discussing this, right? I "feel" the same effect as you do, there are (few but) some additional horses.

>As per your post Chris, I believe this dis-proves your theory about post 89 models "not setting ignition to the old and most advanced value".

Sorry, precisely this was stated for the M102 only. The M103 was not mentioned. It is from the manufacturer's documentation, if you like a copy, send me an email.

>My service CD does state that the R16 affects iginition timing on the post 89 W201's (up to 1993).

You are right, R16 was used up to 1993 (end of the KE-engines) and still does affect the ignition - but only up to 2400 Ohms. Maybe the other ignition lines have been erased.

bis denn,
Christian

1989 300TE
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  #9  
Old 06-18-2003, 04:09 PM
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Got it Chris, sorry about that, missed the M102 part.

I agree, its not a magic mod that nets a high hp gain
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  #10  
Old 06-18-2003, 05:10 PM
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interesting. with all the talk about the r16 i did a little test today. i have recently installed an A/F meter and have used it to tune the mixture a little. these 4 runs were made with the car up to operating temperature, on the same road in the same directions. what i did was made a run down and back on a local road with the r16 in, then one with it out, then in again, then out again. my A/F meter indicated more rich at WOT with the r16 out. now connecting and removing the r16 isn't likely to do anything to the engine's fuel delivery. likely, it does affect the conditions in the combustion chamber, leading to a more or less complete burn. so, what does it mean that with the r16 plugged in i'm getting a more lean exhaust, indicating a more complete burn with the same amount of fuel? anyone? i have an idea but someone out there has got to know more than i do about the subject.

thanks,
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  #11  
Old 06-19-2003, 08:42 PM
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Thanks for the replies

I'm pleased this has generated some healthy discussion. Chris Martens has raised an interesting point regarding a possible change to later ignition modules having fewer programs. My testing seems to indicate that for my both my 1990 M102 and M103 EZL-KAT AUS versions, there are only a limited number of R16 values that give a valid result, and open circuit R16 is not one of them.

Duke2.6,
My results showed that the shorted R16 condition (like the open R16 condition) resulted in the most retarded ignition. I must repeat that the greatest effect of R16 is at higher engine speeds and minimum vacuum (high load or WOT).

jasondew,
I would interpret your air/fuel ratio result of a more complete burn as possibly being due to more advanced timing allowing longer time for combustion prior to the exhaust valves opening. Others might have greater expertise in the combustion process.

Obviously experimenting with R16 is inexpensive and worthwhile. If my original post inspires those who have tried the modification to, at the very least, check their car with a timing light, then I am happy to have posted this thread. Thanks for reading and contributing.

Greg
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107.026: 500SLC, 4-speed auto, thistle green, green velour.
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  #12  
Old 06-20-2003, 03:47 AM
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Greg,

>Obviously experimenting with R16 is inexpensive and worthwhile. If my original post inspires those who have tried the modification to, at the very least, check their car with a timing light, then I am happy to have posted this thread.

This is the table of ignition timing Paul Wurm collected some months (years?) ago. Maybe that is of some use for you all.

The columns are titeled as follows:
Datum = date
Fzg = model
Bj = model year
Fgnr = VIN (german coding)
Schlnr = german code number
Motornr = engine number
ZZP Soll LL = ignition timing at idle (factory value)
ZZP Soll 3200/91Okt = ignition timing at 3200/min with fuel ROZ 91 Normal Benzin (german standard fuel) (factory value)
ZZP Soll 3200/95Okt = see above with fuel ROZ 95 (german premium fuel) Super Benzin (factory value)
Codierstecker = part number and description of R16 plug
Stellung Cod.st. = position of the adjustable R16 plug
ZZP LL = ignition point at idle (actual value)
ZZP 3200U/min = ignition point at 3200/min (actual value)
2.Durchgang = 2nd run
3.DG = 3rd run
4.DG = 4th run

mU = with vacuum at the EZL-computer
oU = without vauum at the EZL-computer

kindest regards,
bis denn,
Christian

1989 300TE
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Old 06-22-2003, 09:48 PM
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Very interesting, thanks Chris

Chris,

Thanks for the link to Paul's table, it provides some interesting results. The first is that R16 has no effect on timing with vacuum connected or at idle (which supports my findings). Only without vacuum (high load) and at higher engine speed is any difference seen. Secondly, it is interesting that progressively higher advance figures are not achieved at R16 settings approaching 1 (higher resistance) as some have suggested. The M102 engine listed only gave maximum advance in position S (1300 ohms in this case) with all other positions providing less advance. For all the engines listed position S (750 ohms on these M103s) gave what could be considered optimum, although for the M103 engines listed, position 1 (open circuit) did also achieve maximum advance, supporting the findings those who have achieved good results with R16 removed.

Again, I would suggest anyone contemplating the modification to either check results with a timing light or only use a value for R16 that corresponds to position S for their engine. As best as I can tell, for the EZL-KAT (catalyst equipped) M102 N = 470 ohms and S = 1300 ohms and for the EZL-KAT M103 N = 220 ohms and S = 750 ohms.

Thanks again Chris for providing the information.
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  #14  
Old 06-25-2003, 10:38 AM
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this all seems a little complex can some one explain it a little clearer maybe.
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  #15  
Old 06-25-2003, 08:08 PM
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Quote:
Originally posted by Mike300ce
this all seems a little complex can some one explain it a little clearer maybe.
Mike,

It may help if I direct you to this thread on another forum. Have a look at the page from the owner's manual that jff2k attached in his first post on the thread at:
http://forums.mbworld.org/forums/showthread.php?threadid=42714
It shows the multi-position selector that Euro deliveries got, but Aus and North American deliveries missed out on. The owner's manuals (printed in English) for my 300TE and 190E also show the selector, even though we missed out on it. The multi-position selector allows the ignition to be easily adapted to fuel of varying octane ratings throughout Europe. You will note that the selector has seven positions. Each position corresponds to a different resistor value. Of the seven positions, one is marked S for super or high octane fuel and one is marked N for normal or low octane fuel. The owner's manual suggests the use of position S unless only low octane fuel is available when position N should be (temporarily) used. Both my 300TE and 190E had the single R16 resistor fitted corresponding to the value for position N for that motor. In each instance I have replaced it with a value corresponding to position S and make use of high octane fuel. The seven positions available on the R16 selector in Europe are 1 = open circuit, 2 = 2400 ohms, 3 = 1300 ohms, 4 = 750 ohms, 5 = 470 ohms, 6 = 220 ohms, 7 = 0 ohms (short circuit). All information I have found suggests that for a catalyst equipped M103, N is position 6 and S is position 4. For a catalyst equipped M102, it appears that N is position 5 and S is position 3. For my 300TE (M103) I am using 750 ohms and on my 190E 2.3 (M102) I am using 1300 ohms. Some have found that resistors (or lack of) corresponding to positions other than N or S are valid, however my findings (and Paul's table that Chris refers to) do not support this for all engines.

I hope this has made it clearer. If you want to discuss it further, come and talk to me at a club meeting or event.

Greg
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107.026: 500SLC, 4-speed auto, thistle green, green velour.
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201.028: 190E 2.3 Sportline, 5-speed manual, arctic white, blue leather.
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