This is a CIS KE jet car correct? There should be a procedure somewhere to measure the duty cycle / voltage at the . . thingy on the fuel distributor that alters fuel mixture.

This will give you some sense if the computer is trying to lean out fuel mixture but is at the limit or the computer is forcing things rich.

Has the manual mixture screw been turned at some point in the past? You can get some sense if the mix is too lean by pushing down on the adjuster extension until it engages the real adjuster then pushing a bit farther and seeing if the motor smoothes out. While the adjuster extension is engaged let the adjuster come back up to center, rotate it just enough to grab the real adjuster then pickup, if the motor smoothes out the mix it too rich.

These are very good numbers for a M103 other than HC, and the fact that O2 is 0.0 means the O2 sensor and catalyst are working well.

That leaves excess misfires as the source of the high HC.

What make/model of spark plugs are in the car?

The ignition system is designed for non-resistor plugs (lots of archive discussion on this issue), but they are getting hard to find. Resistor plugs alter the voltage wave form and reduce spark energy at the plug, which can lead to exess misfires - often not enough to notice, but it can show up in the emission test.

RFI resistors are built into the spark plug boots and the distributor cap. The wires should measure about 2K ohms. Pull and twist on them slightly them while testing. It's possible that the plug wires on a lot of M103s have been damaged by pulling the wires off the plugs by hand. I have a special tool that I bought way back when that grabs the metal RFI shield, so no stress is placed on the wire iteself.

There is also a 1 or 2K ohm resistor in the distributor cap towers. My OE cap had a "flaky" tower that would show the proper resistance when holding the cap loosely, but then go to infinity if I put some thumb pressure on the side of the tower, so I replaced the cap.

The combination of resistor plugs and the flaky cap almost caused my car to bust the 100 ppm HC idle limit in the 1995 two-speed no load test. A new cap and going back to proper Bosch non-resistor plugs dropped the idle HC from 100 ppm in '95 to 22 in the '97 two-speed no load test.

Concentrate your effort on testing secondary ignition system components and make sure you have OE equivalent non-resistor plugs installed.

BTW, use periods instead of spaces to line up the data under the proper headings. The software ignores extra spaces but will recognize periods to keep the columns reasonably aligned for easier reading. These are the ASM test results for my '88 190E 2.6 five-speed, done about two weeks ago.

...............CO2....O2............HC...................CO..................NOx
test..rpm..meas..meas..max..ave..meas..max..ave..meas..max..ave..meas

15...1587..15.0...0.0....116...27.....55...0.74..0.09..0.28...791..255...32

25...2638..15.1...0.0.....91...18.....17....0.62..0.07..0.13...730..223...42

Duke

No Im not 100% sure about after market cat. Just been giving a few opinions from people who have tried and didnt work. Geuss Im just gonna take it to a test and repair and run the diognostic and see what the computer says. Thank you everyone for your input.

Ok thank you very much for the spark plug info. I did just have the plugs changed when the head gasket was donr and they might not be the right ones. Im gonna pull them and buy one of the recommended make and models in my owners manuel. Thank you