'91 300CE (M104) won't start - disconnect EHA & it starts! Why?? - Page 2 - PeachParts Mercedes-Benz Forum

rgnprof · #16 04-19-2011, 12:09 AM

Which plug on the EZL is the rear crankshaft sensor - you referred to it earlier as the L5...?

rgnprof · #17 04-19-2011, 12:36 AM

I think I found it - it's the only one with one plug in it. Ohms checked out at 900 ohms...so I'm not sure now.....

ryan

Ferdman · #18 04-19-2011, 06:06 AM

Ryan, the ECU (or EZL) is mounted on the left (driver's side) inner fender. A new one costs around $2,500 so be sure to maintain your ignition system (spark plugs, distributor cap, distributor rotor & ignition wires) to prevent failure of the ECU. I went through that experience with our daughter's 1991 300CE.

rgnprof · #19 04-19-2011, 09:46 AM

Yea, I know about the EZL issues. I have just recently replaced the cap, wires, plugs, rotor, and coil...

JohnM. · #20 04-19-2011, 03:02 PM

Ryan,

The CPS can be intermittent, as you have found.

KJZ78701 · #21 04-20-2011, 12:48 AM

Ryan,

A wideband O2 sensor will tell you the air/fuel (AF) ratio. An older O2 sensor (like the one on the car) varies voltage from 0 to 1. 0.5 is the calibrated setting for "perfect" AF ratio. The computer gets that signal and sends a signal (current) to the EHA to vary pressure to maintain that "perfect" AF ratio under "closed loop" conditions (no or little engine load). The AFX is an NGK brand of wideband O2 sensor that outputs a voltage from roughly 0 to 5 volts (perhaps 1 to 5) and has a chip inside the display to convert that input voltage to a number we can understand. 14.7 being the "perfect" ratio for no or little load running and 13.x being the "perfect" ratio for making power. As an aside, forced induction motors may be tuned in the 11s at max boost to keep "things" cool.

I too started the "other" way and after chasing the "problems" spelled out in the literature, I came up with my last post in the "CSI-E Tuning" topic.

I had issues with the wiring AT the connectors. The copper is probably brittle and green. In some cases, I cut about an inch off the wires at the connector and re-soldered. This is why I suggested that you check the sensors AT the ECU connector. Find a helper and have them wiggle the wires and see if the signal changes. I bet you find that at the CPS.

I have not had that issue so I do not know if the CPS will cause your poor mileage, but I suspect not.

It is VERY easy to check your idle microswitch. Remove the air filter and you will see it on the throttle linkage near the firewall. If you have the car running at idle, pull the throttle cable just enough to move the linkage away from the switch. Any change in idle? Yes, MS okay. No, turn car off and check for continuity at the switch. Nothing? replace switch. Working there? Check at the ECU. Not working there? Check your wires. Working at ECU, MS fine, time to check the Idle Air Control Valve. With car running pull plug at IAC valve. Car should die. If not, check continuity at ECU. See a pattern here.

Lots to do, sorry. Once you are sure the wiring is good, we can get your AF properly managed by the ECU.....after you check and match your injector flow rates. There really is no shortcut, but at $4 per gallon the time you take now will pay off nicely in the year to come.

rgnprof · #22 04-20-2011, 08:58 AM

KJ,

Thanks for the reply - and I went back and re-read your post. On further reflection, I did look into - briefly - a monitor like the one you used, but a duty cycle meter was much cheaper ($30 compared to $260), so I went that route.

Can I ask a few questions? Can you describe the "flapper" and "plunger" a little better? I'm not sure exactly what you are referencing here, nor do I understand how you adjusted it. And, which ECU are you talking about? I am assuming the MAS control unit behind the battery?? The CPS connects directly to the EZL on the left fender wall...is that the ECU you are talking about?

Also, my car is the M104 - does everything you talk about apply to my motor as well?

Thanks, Ryan

rgnprof · #23 04-22-2011, 09:42 AM

Quick update: Car has run great the past few days - no starting problems, etc. Cleared all of the codes and they have not returned - except for Code 17 (Crankshaft Position Sensor). I can get this code to clear, but when I turn the car off and back on (KOEO), the code returns...I don't even have to start the car.

ryan

KJZ78701 · #24 04-23-2011, 09:36 AM

Ryan,

I do not know the M104, just the CSI-E fuel system which I believe you also have. If so, the "flapper" can be seen when you remove the air filter box. It's brass and round maybe four inches in diameter. When you open the throttle, the butterfly at the start of the intake (below the flapper) opens. The extra air the motor now pulls will suck that flapper down. That flapper has a lever that pivots near the O2/idle screw and pushes UP on the plunger in the middle of the FD = fuel distributor (the round silver "thing" with all the fuel lines attached to it) to deliver more fuel.

You need to remove all of the fuel lines and the three Torx bolts in the middle to pull the FD. Once there, you will see the plunger. If you loosen the outer nut you will be able to rotate the inner section around the plunger which will move the plunger with it. Turn it into the FD body for less fuel and turn it out for more fuel.

HTH!

EDIT: I call the main brain the ECU. In my M103 / W124 3.0 it sits behind the battery on the passenger side between the MAS control unit which is really just a relay box (solid state I presume) and the OVP relay. The ECU on my US car has three rows on the connector. The non-US cars seem to have wiring harnesses with two row ECU connectors.

There is another "brain box" behind the ECU, which I presume is the ABS control unit. Anyone know for sure?

porkface · #25 04-23-2011, 09:28 PM

regarding code 17-koer is the way to check the speed sensor. koeo mean there's no signal for the ecu to read and it assumes the speed sensor is dead. good luck, chuck.

duxthe1 · #26 04-24-2011, 12:40 PM

To elaborate on the previous poster, the car shouldn't throw the cps code if scanned with the engine running.