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

rgnprof · #1 04-18-2011, 11:30 PM

Could codes 7, 9 and 27 all come from unplugging the EHA and driving that way for a while??? I assume you mean the box behind the battery - with the knob on it, right?

JohnM. · #2 04-19-2011, 12:03 AM

Ah, I forgot you were driving with no EHA. Reset and see if those codes come back, but don't unplug the EHA this time around. Your ECU is probably fine then.

So CPS!

rgnprof · #3 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 · #4 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 · #5 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 · #6 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. · #7 04-19-2011, 03:02 PM

Ryan,

The CPS can be intermittent, as you have found.

KJZ78701 · #8 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 · #9 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