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

rgnprof · #1 04-17-2011, 10:15 PM

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

KJZ78701 · #2 04-17-2011, 10:40 PM

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?

rgnprof · #3 04-17-2011, 10:48 PM

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

mbdoc · #4 04-18-2011, 08:24 AM

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

KJZ78701 · #5 04-18-2011, 09:44 AM

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.

rgnprof · #6 04-18-2011, 11:17 AM

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

rgnprof · #7 04-18-2011, 07:32 PM

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.

JohnM. · #8 04-18-2011, 07:37 PM

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.

rgnprof · #9 04-18-2011, 08:54 PM

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

rgnprof · #10 04-18-2011, 09:09 PM

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

benzworldrefuge · #11 04-18-2011, 08:59 PM

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.

JohnM. · #12 04-18-2011, 08:57 PM

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

Quote:

Engine cold. Ignition off. Multimeter set to Ohms. Unplug the L5 sensor (CPS) at the EZL. Positive probe on inside of pin. Negative probe on outer part of pin. Spec is 680 -1200 Ohms. If no, rplc CPS sensor.

JohnM. · #13 04-18-2011, 09:18 PM

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.

rgnprof · #14 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. · #15 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!