PART 1

As helpful as the net has been I would like to give back a bit. My car is a 1992 300E (w124, 103.983) with 200k miles with only about 35k on a new tranny. There is lots of research between some of the steps below, so it took me much longer than it will seem.
In addition to standard tools I also used the AFX Wideband Air-Fuel Ratio Monitor (<$300), an old Fluke multimeter, a propane torch, a fuel pressure gauge and a digital scale. I also have an ASNU injector bench tester, but you really don’t need one. There is an injector cleaning / testing procedure on this site that only requires some carb cleaner and compressed air.

If you have already read up on the CIS-E system you will know that fuel pressures are critical items. For me those came first. The car had been sitting for a couple years before I bought it, so I cleaned the tank and found that it needed a new tank filter and new pumps (note on pumps below). I also blew the old gas out the filter, in the reverse direction (low pressure), and through the entire system from the pump input out the return line at the tank. With it all hooked up and the injectors cleaned (I used the ultrasonic tank on the ASNU), flowed (three injectors flowed about 20% less than the other three) and put back in their original locations, I flow tested the installed injectors.

To do this I pulled the fuel distributor (no wires connected) off the base (three Torx bolts-watch out for the o-ring around the plunger when you pull the distributor off the base) and put plastic water bottles over each injector. I weighed the bottles empty since I did not have seven (cold start injector-CSI) that matched and wrote the empty weights on the bottles. I then ran wires directly from a battery near the rear wheel to both pumps. I ran the pumps for about a minute as I pushed the plunger all the way up into the distributor (WOT). Wide Open Throttle

After removing the bottles and getting the fuel weights, the first run gave the following results.
60 – 65 – 68 – 62 – 64 – 72 with nothing from the CSI - 0

I then removed the cap screw on the bottom of the fuel distributor corresponding to injector 6 and turned the exposed set screw IN one turn and then recapped. Performing nearly the same flow test as above, but this time varying the amount that the plunger was pushed in (simulating varying throttle position), I got the following results.
70 – 75 – 79 – 72 – 73 – 66 (0 CSI) That told me that varied or fully depressed, the flows stayed about the same (relative).
Three runs later and a ¼ turn here and an 1/8 turn there (NEVER touching #4) I ended up with the following results after a longer run (plunger fully depressed since WOT was a bigger issue for me to match than idle).
123 – 122 – 123 – 121 – 123 – 121

Happy, I now replaced all the bad rubber vacuum lines and put it all back together (after lots of cleaning including the old bad gas under the throttle butterfly), and fired it up with the AFX display in the car and the sensor in the tailpipe. Started right up running just over 9 to 1 A/F (way rich). Once it warmed up the idle started to hunt a bit and the A/F moved back and forth from about 11 to 9. Assuming an air leak, I replaced the rubber tubes to the Idle Control Unit (mounted to #2 intake rail). They were hard. Restart, same problem. Pulled the battery and the CIS-E control unit behind it and checked the ohms between pins 5 and 14 (Intake Air Temp Sensor – IAT). Open circuit, so I pulled the IAT sensor (just in front of the air filter. It disconnects without any wires, though it appears it wants to come out with wires attached) and sure enough the wires were good but the sensor was not, so I replaced the small sensor. I also used a propane torch to check the O2 sensor (connector right under the carpet just in front of the passenger seat, 7/8” or 22 mm wrench for sensor). Tip in flame voltage about 1, tip out of flame voltage should drop to near 0 in a few seconds. Mine was bad, so I got a new one.

I also used the X11 (on driver’s fender) 2, 3 and 6 pins to attempt to troubleshoot, but I never really found the information useful. I did get a funny “no TD signal” fault signal at one point, so I removed the MAS relay/control unit (also behind the battery) and checked more of the harness. On attempted restart, nothing. After chasing my tail and lots of time on the phone with Dallas Dave “I fix ‘em” Poole (thank you!) trying to figure out what I could have done to the MAS relay (which replaced the fuel, AC, and air pump relay along with being the go between on other items the CIS-E controls / watches, I discovered I had no gas in the tank. Since it was just running and “all of a sudden” there was no fuel pressure I assumed the MAS relay had gone bad. I removed the MAS relay and jumpered from 2 to 10 to 20 to run the fuel pumps and the O2 heater and saw that there was still no fuel pressure. Four gallons later I was running again.

Once again, rich idle, but it drove. I ohmed the two pins to the EHA, and got 20. Good. (The EHA mounts to the back of the fuel distributor and controls fuel flow within the distributor.) NOTE: You can put the car in constant open loop (runs, but rich) by pulling the EHA and O2 sensor plugs. (Thanks PS2CHO!) This helped me when I could not start the car warm. So, no warm start, pull the EHA and O2 sensors out of the equation and it started right up. This is where the tuning really started for me.

There is a 2 mm Allen adjusting screw behind a cap screw on the EHA which becomes clear after you remove the EHA. I purged the gas pressure each time before I removed the EGA to make sure I didn’t blow the little o-rings out. FP gauge purge button (or crack the inlet line) and push the flapper down all the way. Since I was rich at idle I turned the EHA Allen ½ a turn CCW and turned the CO/Idle adjusting screw (3 mm in the “tower” between the fuel distributor and the air inlet / flapper) ½ turn CW. Oddly, the idle stayed rich 9-1 and high RPM went lean, then it died at idle. Still experimenting, I went ¾ turn CW on the EHA (so ¼ turn CW net) and 1 turn CCW on the CO/Idle screw..no start even with gas pedal on the floor. HMMMM….still 72 psi on the lower port and 78 psi on the upper port of the fuel distributor (upper port faces the valve cover, lower port faces the driver’s headlight). Continuing to turn the CO screw CCW I finally got it to start 1 ½ turns CCW later with a mild hunt (idle going up and down). Going half a turn CW eliminated the hunt, but then it wouldn’t start again.

Then I discovered something very interesting. If I put a small piece of vacuum line between the idle microswitch (right behind the fuel distributor on the throttle linkage) and its actuation arm so that it would not close at idle EVERYTHING changed. AF at idle now went up to 11+-. I then drove observing no throttle AF (coasting in gear) and checked AF under throttle. After many runs and adjustments I found that the EHA setting will determine whether or not the car will start and really establishes overall AF even though the upper and lower fuel pressures really did not move around much. Something internal of which I am still ignorant. Also note that my idle was around 2000 in P and N with the microswitch overridden and the EHA and CO adjustments not where they should have been; Makes sense since the microswitch tells the CIS-E to control the idle via the Idle Control Valve. What I found odd was that in gear the idle came right down to 1000. I also found that once I got the EHA and CO settings where the car was running at 14.5-7 to 1, the idle in P or N dropped to about 1700.