Worked on 300E, now it stalls with idle valve connected! - Page 2 - PeachParts Mercedes-Benz Forum

babymog · #1 12-12-2008, 02:30 PM

The short version is that the CIS-E is basically the mechanical CIS (Constant Injection System), with electronics added to control emissions via a frequency-valve (can't remember what it is called here) on the side of the fuel distributor. With a fault in the system, such as un-plugging the O2 sensor, it will revert to the mechanical system where the air-flow sensor plate moves a metering pin and directly changes the injection flow rate (all six cylinders, all of the time, at the same rate).

You are indicating through your experimentation that the basic CIS including mechanical parts such as the fuel pressure regulator, and the fuel pump, the injectors and injection distributor, seem to be operating correctly, and likely (not certainly) within spec. When the electronic brain is put back into the loop (plugging in all components), it fails, which indicates that somewhere in a sensor, the computer, the wiring and grounds, there is something out-of-spec. There are restistance vs temperature values for the temperature sensors, and I believe values for the O2 sensor available and the sensors can be measured with a good DMM/VOM. They can also be bypassed using a resistance-substitution box and a few BOSCH connectors cut from junkyard cars to see if the proper resistance will create the proper running condition.

It is my further opinion, that the ignition system is in adequate condition based on your experimentation and previous postings.

Check the sensors, a couple of sensors out of spec can really make a car run poorly. I'm betting someone here knows the correct resistance for that intak-air sensor for example, you'll need the temperature at which you measured it BTW.

pawoSD · #2 12-12-2008, 03:02 PM

The only other maintenance I am doing is fluids/thermostat (runs too cool).....with the electronics taken out of the loop it runs fine, and you can't even get it to stall if you try. (even when cold, bumping the throttle, putting a big load on it (electrical, A/C, ect...) it still won't stall)

I'll keep checking sensors....I'm guessing the air intake one is bad...its not in very good shape physically....however the engine temp sensor is brand new. What other sensors should I check? Or, what others are there that could cause that problem? The air intake sensor is cheap, I'll pick one up sometime in the future and try that....perhaps the computer itself has issues....I'll figure it out eventually....

Oracle12345 · #3 12-12-2008, 03:21 PM

" I need your email for those docs btw"

"Did you read Lyle's docs, they explain much of each components functions?"

Never got his email addy so I figured he didnt want them anymore.

But your stalling problem is the reaction of the pcm taking the inputs of all the sensors and devices and taking that information and making adjustments to the A/F mixture. its apparent that one of your sensors or part of your fuel injection is malfunctioning.

"thermostat (runs too cool)" is heading in heading in the right direction because if the thermostat is not working properly it will the pcm to run rich and stay in an open loop when the system should be in a closed loop.

Did you pull your plugs and see the color of them?

pawoSD · #4 12-12-2008, 05:04 PM

Quote:

Originally Posted by Oracle12345

" I need your email for those docs btw"

"Did you read Lyle's docs, they explain much of each components functions?"

Never got his email addy so I figured he didnt want them anymore.

But your stalling problem is the reaction of the pcm taking the inputs of all the sensors and devices and taking that information and making adjustments to the A/F mixture. its apparent that one of your sensors or part of your fuel injection is malfunctioning.

"thermostat (runs too cool)" is heading in heading in the right direction because if the thermostat is not working properly it will the pcm to run rich and stay in an open loop when the system should be in a closed loop.

Did you pull your plugs and see the color of them?

I figured its a sensor issue, but I am not sure what all sensors it is looking at (how many are there that play a role?).....one is brand new, and the other is known bad...I'll replace it sometime in the near future. It runs sliiightly rich, but not real bad. Exhaust looks clean but has a slight rich smell to it....much better than it used to be though. Spark plugs have been replaced with the correct non-resistor Bosch. Old plugs were junky champion resistor style, they were a bit oily and dirty (as was expected)....but the engine does not burn/lose any oil. I've driven it nearly 1000 miles since its oil change (M1 0w40) and it has not lost any.

The thermostat could explain the slightly rich running, but not the cold start issue.....as its cold anyways. At running temp right now it hits about 67-69C or so.....tomorrow I'll fix that.

tinypanzer · #5 12-12-2008, 07:18 PM

As temp sensors go bad, the resistance tends to drift upwards, which is indicative of a "colder" temperature.

If this is what's happening (likely), the computer thinks that the car is getting more air intake than it is, since cold air is denser than warm air.

If the computer thinks that it's getting nice thick cold air, it will increase the amount of fuel delivered to keep the mixture correct. But, if it's just a faulty reading then you wind up with a rich condition.

-tp

pawoSD · #6 12-12-2008, 10:53 PM

Quote:

Originally Posted by tinypanzer

As temp sensors go bad, the resistance tends to drift upwards, which is indicative of a "colder" temperature.

If this is what's happening (likely), the computer thinks that the car is getting more air intake than it is, since cold air is denser than warm air.

If the computer thinks that it's getting nice thick cold air, it will increase the amount of fuel delivered to keep the mixture correct. But, if it's just a faulty reading then you wind up with a rich condition.

-tp

Still doesn't explain why it would have problems cold starting with everything plugged in. It starts warm fine and runs fine when warm.

Doesn't matter, it runs fine mechanically.

I'm not going to worry about it for now.....any car that can pull 107mph in 3rd gear at 6000rpm counts as running GOOD in my book.

babymog · #7 12-12-2008, 05:04 PM

If you suspect the intake air temp sensor, and don't feel like continuing to order/pay/wait for each test, look up the resistance value for that sensor at (for example) 0C/32F, buy a reisistor at Radio Shack of that resistance value, plug it into the wire harness and see how it runs. I'm not a big supporter of buying parts until it runs correctly, that's what Betten does for me at ~$100/hour.

pawoSD · #8 12-27-2008, 11:58 PM

Swapped in a new intake temp sensor and idle control valve (both from the junkyard), problem solved! It fires right up now and idles smooooth! Not bad for $10!

I did throw about $250 of parts at it prior to this though.