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  #1  
Old 09-23-2001, 09:45 PM
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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

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  #2  
Old 10-12-2001, 07:02 PM
aiino
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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
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  #3  
Old 10-12-2001, 08:32 PM
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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
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  #4  
Old 10-13-2001, 12:05 AM
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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.
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  #5  
Old 10-13-2001, 06:15 PM
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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
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  #6  
Old 10-15-2001, 12:39 PM
aiino
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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
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  #7  
Old 10-15-2001, 12:58 PM
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. . . 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.
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Last edited by JimF; 10-15-2001 at 01:11 PM.
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  #8  
Old 10-15-2001, 01:23 PM
aiino
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yup, a diode. already did the ohmmeter test.

any feedback on the problem that i am having?

andy
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  #9  
Old 10-15-2001, 02:16 PM
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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
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  #10  
Old 10-15-2001, 02:53 PM
aiino
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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
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  #11  
Old 10-16-2001, 12:40 AM
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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
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  #12  
Old 10-16-2001, 01:08 AM
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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.
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  #13  
Old 10-16-2001, 12:33 PM
aiino
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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
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  #14  
Old 10-16-2001, 01:57 PM
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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
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  #15  
Old 10-16-2001, 03:09 PM
aiino
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you'd be surprise on the so-called factory trained mercedes tech's here in california. they don't know either.

ai

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