Which is the Coolant Temp Sensor?
 

On the M103 engine in my 88 300E there are two coolant sensors near the rear of the cylinder head on the drivers side. I know that one of them is crucial input to the fuel injection system and can cause an ill idling or no idling engine. Which is the sensor for the FI, the rear one or the next to the rear one?

Does anyone have the resistance table for this sensor. I am not at home and won't be able to look in my CD until this weekend.

Thanks for any help that anyone might offer.

Larry
Here is a link to anlther post about the same topic that has the answer you are looking for.
http://www.peachparts.com/shopforum/tech-help/113165-wheres-coolant-temp-sensor-how-do-i-test-86-300e.html

This might help clarifying which is which.

See Benzmacs comments.

http://www.peachparts.com/shopforum/tech-help/19247-w124-coolant-sensor-location.html?highlight=coolant+temp+sensor

Well according to a chart found on one of the referenced threads, mine is only reading about 50 Ohms too high at 85 C. It is reading a good bit higher at about 40 C.

My trouble is that it won't idle after starting when the engine is hot. It starts and idles fine when engine is cold, or at least as cold as it will get this time of year in Texas.

I have already cleaned the Idle Control Valve and the hoses seem fine.

Thanks for all the help.

Larry, is it only at idle that your having a running problem? and is there any change in mpg? I wouldn't think those readings would cause it to stall. Did you check the duty cycle reading since this started?

Also see this post: http://www.peachparts.com/shopforum/747535-post3.html
From this thread: http://www.peachparts.com/shopforum/tech-help/108133-icv-whats-can-high-idle-hurt-trans.html?highlight=microswitch

The problem ONLY effects hot idle immediately after restarting engine. After engine has been running, you can pull up to a stop, kick in the clutch and it will idle like a pussycat.

There is no fuel mileage issue that I know of and in every other way besides the hot startup idle problem it runs fine.

I'm not one to start throwing parts at a problem, but I am very close to replacing the idle valve hoses even though what I can see of them looks okay. I have not exhaustively searched for vacuum leaks since it idles so nicely when hot after running down the road for awhile.

I have not checked the duty cycle, but I will the next time I'm at home. I also will put it on the lift and see what the idle hoses look like from underneath.

Thanks for the response.

The Accumulator located near fuel pump helps to maintain fuel line pressure after shutting off vehicle.

When it grows tired, the line pressure is not held and hot starts become an issue.

Based on when it's symptomatic, that seems like a good part to pursue.

http://www.peachparts.com/shopforum/tech-help/15549-hot-starting-problem-r129.html?highlight=fuel+accumulator

Larry 50 Ohms off on the reading is ok. They are not perfect and the table is intended only for a guide, the only time the CIS-E cares about temp is 80C and below 40C. At 100C it supposedly cares as well to lean the mixture or raise idle to compensate for the higher temp. Certain years raised idle and certain ones leaned the mixture. Depends on if it is a KE-II or KE-III Jetronic! There were two diferent EHA's used. One that could sweep negative to accomodate leaning and one that could not and had its center point higher. So if it could not lean enough at 0V then it would increase idle to lean. I would check the O2 first as this could be bad and thus causing the EHA to not respond properly. The EHA does all the work for the CIS-E system using values from the Water Temp Sensor, RPM, and O2. The IACV and EHA do the rest to control Mixture. The EHA does it all when not idleing.

Based on some of these responses, I will hook up and check fuel pressure next time I get home, but I can't imagine this being the problem because the problem is ONLY idle. By revving it up at startup when this problems occur, the car is a rocket ship. Unless there is something about the KE that I don't understand, and there are PLENTY of things about it that I don't understand, I don't see how it could run so good above idle with low fuel pressure.

Thanks again and please keep the info coming.

Larry - I'm not sure that a fuel pressure test is going to comfirm a faulty accumulator. See what Benzmac had to say in the following thread:

http://www.peachparts.com/shopforum/tech-help/25013-fuel-accumulator-failure.html?highlight=accumulator

In my case, there's a small 5.5mm hose that goes from the accumulator to an elbow on the primary fuel line. My fuel pump is a single pump unit; yours may be a dual arrangement, but you may still have this 5.5mm hose. Part number in my case was 126 470 40 75. Was only able to find it at the dealership. I experimented with all sorts of FI pressure-rated fuel line in this approx. size and felt uncomfortable with the fit. I have a special tool(Lisle) that I use for removing hoses w/o damaging them. Beware of this bugger. You won't find it at MacParts at 10pm.

Based on your response in the other thread, you have a bad Water Temp Sensor. Look at my post in there for explanation. And yes I spent a lot of time figuring out the CIS-E KE-II and KE-III Jetronic systems and all that junk. Took me a year of playing around to get my engine back to where it should be running and smooth idle. I bought a very neglected 190E. I did not know how neglected when I bought it, but have and fun and a great learning experience getting it perfect.