103 ignition timing
 

Is it possible to change the base ignition timing on a 103 engine ('88 190E 2.6), or is the timing map completely controlled by the electronics?

Duke

With that design you would have to modify the flywheel or the crank sensor location!

Tbanks, Doc. That confirms my suspicion. The TDC sensor on the torsional balancer does not appear to be adjustable, and I could find no other way to change the initial timing.

Being as how my HC is high in the first test (15 MPH) on the CA ASM emission test, I was hoping to retard the timing a few degrees to increase the EGT. The exhaust manfolds only read about 470F with an IR gun near the head interface after several minutes of idling. I was surprised they were so cool with only 9 degrees ignition advance at idle. I suspect the converter is cooling off after several minutes of idling, which gets me near the limit on HC until the converter heats up. The HC on the second test - 25 MPH - is much lower relative to the limit, but still above average for my year group.

My most recent test a couple of months ago yielded 113 PPM HC at 15 MPH, and it did not help that they lowered the limit to 116 from 141 two years before. In that prior test I intentionally went in on a rainy day and asked them to run the "tire dry procedure" where they operate the engine at about 25 MPH on the rollers with no load for about a minute, then go right into the 15 MPH test. The HC was 87 PPM, and the O2 content was zero. In this last test with 113 PPM HC there was 0.1 percent O2, so a hotter converter will promote the use of that last bit of O2 to oxide the HC and CO. The O2 content for the 25 MPH test was zero in both the most recent test and two years ago. For my next test in a couple of years, I'll go on a rainy day again!

My '88 190E 2.6 has been identified as a "high emitter profile", and this may apply to other models with the 103 engine. There was a lady ahead of me in a '91 300SE and she made the 15 MPH HC bogey by only 1 PPM!

Duke

Yes you can
 

Check this and associated posts out:

http://www.peachparts.com/shopforum/mercedes-benz-performance-paddock/32224-read-free-hp-w201-w124-owners-pictures.html?highlight=w124+ignition+timing

I removed the resistor to increase advance, but you should be able to find or rig one up to retard.

Good luck.

there is a "timing trimming socket" located near the ignition system ECU in the engine compartment. It is a socket with a number of fixed value resistors in it. The socket can be rotated to different positions to alter ignition timing. It is usally preset at the factory for the octane rating available in area where the car was originally sold. The socket I believe has 7 differnt positions.

Re: Yes you can
 

Thanks for the link! I found the resistor on my '88. It's inboard of the battery - taped up as you say - and tie wrapped to a slot on the inboard plastic panel. The battery has to come out to get to it - no big deal.

The link says that a zero ohm resistor will provide 12 degrees of retard, which is six degrees more than OEM for US models, and no resistor is full timing. My question is: Does changing the resistance value affect base (idle) timing, or does it only effect timing at higher engine speeds?

JDUB - Yours is a different method. Are we talking apples and oranges? My EZL unit has two harnesses connected at the bottom of the assembly with round rubber connector housings about an inch high. Are these what you are referring to? The brake lines to the ABS modulator run right above them, so they might be tough to remove without unbolting the EZL unit and moving it to get some clearance.

Duke

The only reference I have found to the EZL is in the Haynes manual, and I don't believe that it is installed on US cars - the resistor is used instead.

If you do a search and explore some of the other threads, I think you will find out more about how the resistor works.