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

I have been tracking down fuel related issues on my 300CE for a while. This afternoon, I drove it about 10 minutes, shut it off and tried to start it again in an hour so - car just cranked and cranked. Didn't sound like it was getting fuel...

Let it sit for 4 hours or so and tried to start it again - same thing, although it tried to catch this time. Unplugged the EHA valve and it started right up and drove home just fine.

What's going on here? Any suggestions or ideas?

ryan

need more info...and "fine" is relative.:)

Read CSI-E Tuning if you have the time. Without the EHA you should be delivering more fuel. You can also get more fuel by turning the idle/CO screw CW. If that does not get you starting again, you will need to go through the whole process. What kind of mileage do you get?

Read what? Are you referring to a specific document on CIS-E systems??

I have been getting poor mileage - usually around 14 mpg in city, although on the last tank, 3/4 highway, probably got closer to 18-19. Poor mileage is what got me started on this...numerous posts already on this board...

I have already fooled around with the mixture, etc. and have read most of what I can find on CIS FI. Tested the EHA with the EHA harness, etc (see other post under my username). But, I've never had it not start like this...and then start up like normal with the EHA unplugged. I'm just trying to figure out why/how unplugging the EHA would cause the car to start?

thanks, ryan

CIS fuel systems are basically mechanical in design. Fuel pressure is the key to correct operation.

The system you have is CIS-E that means electrically enhanced basic CIS.

Since the car seems to run "good" w/o the electronic enhancements?
Most likely a bad input from that system.

Testing signals from temp sensor, O2 sensor, & air flow positions sensor would be a starting point.
Also making sure that the O2 sensor has control of the mixture, Lambda reading

http://www.peachparts.com/shopforum/showthread.php?t=289982&highlight=cis-e+tuning

This should be good reading after reading doc's post. Make sure you read all the way to the end.

EHA varies pressure and cuts fuel under no throttle coasting above 1000 or so RPM. Overall you are delivering too much fuel, but you can fix that with adjustment. As doc pointed out, it could be as simple as an O2 sensor, but as he also pointed out the system is mostly mechanical and decades old. The good news is that you can fix it. :)

I have read thru that post before - trouble is, I am, and have been using a different technique to do all of this. I have been measuring EHA current with the EHA harness and testing duty cycles with a meter on pins 2 & 3 on X11. Since I am not enough of an expert in this stuff, making the transition to your approach is difficult (I have no idea what an AFX Air-Fuel monitor does or measures. I did re-read the part about the FD plunger and the air flapper - haven't done much there, nor have I tested the MAS (potentionometer - sp?). I have replaced the O2 sensor very early in this process, although I guess it could be fouled by now, and I did replace the IAT sensor. I also believe that I have a bad throttle microswitch - and I'm not sure, but I think I have a throttle valve switch issue as well...

But, thanks for the link and I have printed it out.

ryan

Well, I'm really confused now. Came home and tried to start the car and started right up with the EHA disconnected, but, plugged the EHA back up and it started up! Ran it for quite a while with the EHA connected w/o problems....so I have no idea what's going on.

I think the EHA thing might not be related, just coincidental. From what I understand the EHA should have no affect on how the engine starts, at all. It's primary job is enrichment control above 2500rpms or so.

I'm thinking CPS. Have you ohm'd out the crank position sensor to rule it out? Its also possible your throttle microswitch on the throttle valve is bad, which would account for your poor mileage.

It's interesting that you mention the CPS - I have pulled a code 17 with my homemade code reader - meaning crankshaft position sensor. How do I "ohm it out"?

And, I'm pretty sure I have a bad microswitch as well...

ryan

Well then that's the cause of your no start symptom.

FWIW. my M103 is so on the hairy edge of running lean that it won't start easily in colder weather (all winter). It can crank for a good 10 seconds and won't start. When warm it has no issue. Now that the weather is warming up here in NY (50 degrees) it starts within one second of cranking. This all happened when I replaced the EHA. When I replaced it (to cure the common seeping EHA) the motor seemed to run richer. I didn't want to mess with the EHA adjustment until the weather warmed up and just cranked the mixture to as lean as I could get it. The rich condition was much better but the starting problem showed up. If you adjusted the mixture before this started you might want to richen the mixture a quarter turn and see what happens with your starting problem. Like I said, FWIW.

Also, I just pulled 4 additional codes - code 7 (TNA - signal rpm at CFI control module illogical), code 9 (current to EHA is illogical), code 10 (throttle position switch - closed throttle position fault (idle)), and code 27 (data exchange between CFI control module and ignition control module).

Any ideas?

ryan

code 7 (TNA - signal rpm at CFI control module illogical),
code 9 (current to EHA is illogical)
code 27 (data exchange between CFI control module and ignition control module

All those point to a bad engine (fuel) ECU.

code 10 (throttle position switch - closed throttle position fault (idle))

There is your microswitch on the throttle valve.

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?

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!

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

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

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.

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

Ryan,

The CPS can be intermittent, as you have found.

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.

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

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

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?

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.

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