Reference Resistor (R16/1) for EZL Ignition, 1986 2.3-16V No resistor = no retard
 

Sorry to be so long winded here, but...

In the hunt for the old "PEP" my 86 2.3-16 used to have I attempted to check the ignition timing, but have been stymied by lack of visibility of the timing mark no matter what I do. Also my timing light seems to cause cylinder #1 to stop firing when I connect it up.

SO--looking at the Intro to Service Manual for the 16V I notice that the original cars had an adjustable timing for the europeans that would allow them to compensate for poor octane gas. There was an adjustable plug with 7 positions, each one being 2 degrees of additional retardation from the basic timing.

My US 16Valve only has a single "Reference Resistor" (R16/1) whose value is 750 ohms. This corresponds to the 6 degree retard position of the Euro plug. I believe that the base (no retard) position of the Euro plug was an open circuit (infinite ohms). Therefore it seems that if I add resistance I should get some additional ADVANCE. In fact, if I remove the resistor entirely, I should get about 6 degrees of additional advance.

Given this logic, I made an empirical test, changing the 750 ohm stock resistor to 2.2 K ohms (didn't want to be greedy). Took the car out for a test drive (sometimes called an Italian tune-up) to see what happened. Perhaps a little more performance but not significant. Then I removed the resistor entirely--and now I got a SIGNIFICANT difference. Car now pulls strongly to redline in gears 1-4. I chickened out in 5th.

Can anyone verify/comment on the above analysis? Any downside to what I have done? Anyone else play with this? I am aware of the concern about too much advance and what it might do--and I really need to figure out how to do the timing measurement anyway.

Thanks for any commentary.

Tom Elerding

reference resistor
 

any results or feedback on your experiment?

i talked to a buddy of mine at a local mbz dealership, and he says that you should not take the resistor out. for what reason, i forgot.

let me know what you find out.

andy

Ignition Reference Resistor
 

Andy:

I am running with the resistor out at the moment. Definitely better performance on acceleration. I can't hear well, so I had my wife ride with me and ran the car through enough load conditions to let her listen for any pinging. She never heard a thing. So at least that empirical timing test was satisfied.

I still need to do a real timing check. Seeing the index mark and degree wheel is a real bear on this car due to placement of front-of-engine pulleys, belt and accessories. I am going to get with a mechanic friend next week and see if he can find a way.

Glen Tokuhara (Glen on this list) sent me a picture of his engine with the intake air box removed. Looked like you could see the wheel on his car, but I have not been able to duplicate that view on my car.

If you think about it, please ask your mechanic friend why he said the resistor should not be removed!!

Regards

Tom Elerding

same for my car. . .
 

Tom,

always wondered what's magic about 2.4K for the "Reference Resistor" (R16/2). Here's what it says about a 119.xxx engine.

Fuel ------- Resistance Trim ---- Resistance ----- Ign angle correction
Prem 95---- 015 545 67 28 -------- 2.4K ------------- 0
Reg 91----- 015 545 71 28 -------- 220 ------------- -3

Theres also a 015 545 68 28 that's 1.3K ohms for -3 deg and 015 545 70 28 that's 470 ohms for -4 deg correction.

Also 015 545 69 28 that's 750 ohms for -6 deg correction.

All of the above was according the MB engine manual but the values vs Ign correction don't seem to make sense.

Also says: "If NO resistance trimming is used, the ign timing is retared at FULL LOAD by 3 deg".

But these numbers check with what you said. I'm going to remove my 2.4K and see what happens.

Reference Resistor values
 

JimF:

Your manual values don't seem to be consistent; that is they don't have a monotonic relationship of resistance to retard value!!

From the 1986 190E 2.3-16V Introduction to Service Manual:

No resistor = no retard
2.4Kohm resistor = 2 degree retard
1.3Kohm resistor = 4 degree retard
750 ohm resistor = 6 degree retard (standard in my US car)
470 ohm resistor = 8 degree retard
220 ohm resistor = 10 degree retard
0 ohm resistor = 12 degree retard

European cars had a 7 position switch with these resistor values installed to allow compensation for poor octane gas.

I would listen for "pinging" under load after you remove the resistor. Hopefully your car is easier to check the timing with a timing light.

Good luck.

Tom

EZL
 

hey guys

i have a pinging problem with my 1989 300E (3.0L). whenever you full throttle (full load) the vehicle in hot weather, the car starts pinging. it does not do this in cold weather. (i assume due to richness).

anyways, i replaced everything on the vehicle (air flow sensor, fuel distributor, ignition coil, ezl ignition box, rr crank sensor, throttle body and sensor, air filter, spark plugs, spark plug wires, and fuel filter), and i only use super unleaded gas. i even used sea foam carbon cleaner in my intake, gas tank, and engine crankcase. all this treatment seemed to help dramatically, but it still seems to ping a little in hot weather and full load.

this did not cure it 100%. i already bought an ezl resistor from a mbz dealer. i opened it up and saw no resistor but an actual diode. what's this all about?i went from a resistor type to a diode type.

should i change it to a resistor type and change the value? would this solve my pinging problem under full load? if so, should i use the values you describe for my retard?

let me know.

andy

. . . are you sure
 

that it is a diode?

It's probably a very high stability resistor mounted in glass envelope to give a hermetic seal to ensure long term stability in the car's stressful environment; heat, humidity, cold, etc.

An ohmmeter will tell for sure. A diode will typically measure about 20 ohms in the forward direction and open in the reverse.

yup, a diode. already did the ohmmeter test.

any feedback on the problem that i am having?

andy

Resistor or diode
 

Andy:

It would be interesting to know how the diode fits in the circuit; that is does it have positive or negative voltage across the diode when operating.

If the diode is back-biased (negative voltage) it will look like an open circuit (high resistance). If it has a positive voltage across it, it will have low resistance.

Based on my car, if you want to retard timing a little bit, you go to a LOWER resistance value. I would find out what resistance you had in the original Resistor you removed. I would also ask the dealer why the original resistor was replaced with a diode. Try the original resistor back in the car. If it pings, go to a smaller resistor--you can buy them at Radio Shack or other electronics store. You probably need a thin-film 1% resistor for permanent replacement, but can use any type just to try it out.

Let us know what happens!

Regards

Tom Elerding

thanks for the info.

the only problem is that i threw away the original resistor. i guess i will check my service manual.

should i use the values that you first mentioned?

andy

What to do next...
 

Andy:

I would try to get some information out of the dealer. Barring that, I guess I would start with a 750 ohm resistor, which should be about 6 degrees of retard. I start here, because that value (750 ohms) had the same retard value for my car and for JimFs. Should be the same for yours, but no guarantee.

If no pinging, and you are happy with the performance, that's it. If it pings, go to a 470 ohm resistor. Keep reducing resistance until pinging goes away.

Remember that under load on a hot day is the worst environment for pinging to happen. If it only pings in those conditions, and never under normal driving, you shouldn't have to make much of a change in the direction of retard to cure it.

Of course, you should really check the timing with a light and verify that it is within specifications.

Good luck

Tom

Wow, a diode!!!
 

That's hard to swallow! Are you sure that MB gave you the right part number because a diode would not work!!

As Tom points out, diodes are usually under bias, etc. and that uses for the R16/x are definitely not biased.

The circuit "maps" the resistor value into the internal values of the analog IC to arrive at the correct angle. A diode would not do that.

Re what Tom said: Make you own R16/x: go get some values of resistance per the table and try them as Tom suggests. When happy, glue it down! Make sure you get some thin film 1% tolerance resistors to do this test.

To test a resistor, all you need do is 'straddle' the resistor across the center and ground connections, with a stabile secure connection.

yup, definetely a diode. i already asked mercedes parts, and they said that is the correct part.

if you guys want to double check for me, go to any mbz parts dealership and ask for that resistor for an 1989 300E. you'll probably give you the same thing.

anyways, i looked in my service manuals, and it does call for a 750 ohms resistor for my vehicle.

i will play around with it and see what happens.

thanks,
andy

Expert Opinions Out There??
 

How about you expert Mercedes mechanics out there??

Any explanation of the use of a diode in place of the reference resistor in the electronic ignition??

Someone out there surely knows more about this than we do!!

HELP!!

Tom

you'd be surprise on the so-called factory trained mercedes tech's here in california. they don't know either.

ai

Diode seems reasonable
 

Hi I was searching for timing tips for my 1983 230E when I came across your thread.

In analog circuits zener diodes are often used to provide a fixed reference voltage (zener diodes are available in many set voltages). This essentially accomplishes the same thing as a resistor (increasing your resistance lowers your reference voltage.) A zener diode is superior as the output will remain steady even with slight input variation thus providing a more stable reference voltage. You could adjust your timing by substituting a different voltage zener.

Hope this helps.

...Nicholas

Not an expert, but we use diodes to cut battery voltages in R/C aircraft applications.
About 1/2 volt drop in a series circuit. So there may be a simularity ....

Use of Diodes
 

Nicholas:

I have been thinking about how I might trick the circuit to get additional advance. At the moment, I don't know how the resistor is used. Right now it is out, so no current is flowing obviously.

I am not sure a zener diode would do anything in the circuit. It would depend on what voltage is driving the circuit, I guess.

But you have suggested to me that I make a couple of tests:

Measure current with stock resistor; measure voltage across terminals with and without resistor. These measurements might shed some light on how the circuit works.

It might be possible to place a small battery in the circuit to cause the electronic ignition to actually advance beyond the normal open-circuit baseline value. Have to be careful here because those EZL ignition controllers are expensive to replace!

I'm looking for some Bosch Manual information on the EZL but have not found any so far. MB manuals don't cover details of operation. I know there is a Bosch ignition manual out there but got out-bid on ebay! Maybe a forum member has a copy??

Thanks for your interest. More to come after some tests.

For your information, a forum member (Jim Villiers) made some acceleration tests in his '87 2.3-16 with/without resistor. Made a difference of 1.5 seconds in acceleration in 3rd gear, 2000-6000 rpm. That's fairly significant. Calculated HP differences were of the order of 20 HP out of about 160 HP! That supports the seat of the pants evaluations the group of us 16-valvers have had.

I have put together a spreadsheet which allows calculation of HP curves from acceleration and deceleration tests made on a vehicle. Process comes from a book published by Chris Jacobs of Jacobs Electronics ignition fame. Interesting book with lots of ideas. Anyone interested can email me.

Best regards,

Tom Elerding

. . . zener diodes
 

they must be biased (typically 5 to 10ma depending on wattage) in order to act as a 'zener'.

In my DI module there is NO bias so it would not be possible to use one even if you wanted to! Also the zener impedance is low and does not equate to a resistor's impedance.

Zeners are only biased up to their threshold voltage
 

Tom and Jim:

How are you testing your diodes? To my knowledge zeners are biased until the potential difference across the terminals exceeds the zener voltage, at this point they breakdown and loose their bias. Zener voltages typically range from 2 to 200V so unless you were testing at a low voltage, say 1v (more than the 0.6V internal resistance) it would appear unbiased as JimF stated.

What is the voltage that you get between terminals without a diode in place? Is it steady or intermittent?

Your ignitions are more recent than mine (I have the euro-adjuster plug) so I have a couple of other questions toward an alternate solution.

Does your ignition measure crank position with a hall effect (sensor) at the crank(or flywheel, or balancer) or, does it sense it in the distributor (usually below the rotor)?

Does your distributor still incorporate vacuum advance/retard?

There is a Bosch parts distributor near my house I know he sells fuel injection data/testing/troubleshooting books I will inquire about EZL ignition books.

Purely out of curiosity what plug gap are you using?

...Nicholas

Buy the European resistance control module
 

I simply got a hold of a parts yard in the UK and had them pull the adjustable resistance knob from a 190E and ship it to me. I installed it in place of the R16 resistor module and now I can change the retard or advance on the timing when ever and to what ever I want. it works just fine and and I paid about $20 for the part and the shipping. I can change the timing in my 2.3-16v according to my driving style and the fuel octane I am using.

Resistor or wire?
 

Tom,
How were your results running without resistor?
Did you have it completely removed or did you installed a wire in place of it?
Thank you
Tony.

Hello All,
I have a 1988 260E M103 2.6. I have had this car for almost three years and love it. Except for one problem. It is extremely slow on take off.

It is so slow that I will often turn right out of my subdivision and drive 3 additional miles to avoid having to turn left across traffic and into traffic (USA) because I might not be able to get out of the way in time.

I had read on this site and others that the R16 mod is nonsense. But after reading this thread and seeing the values of the resistors and what they do I decided to give it a try and remove it.

There is in my case anyway, a very noticeable improvement. While not a rocket ship by any means, it will get up to speed quicker.

I think the spark being advanced allows just enough torque to get the RPM's up faster and into the power band. I don't think I found any additional HP but I feel I moved it into the lower RPM's a bit where it is beneficial.

Thanks for all the information.