1989 300E starting problem
 

My 1989 300E has a starting problem. When I turn the key to start the car it cranks for a while and then starts but sometimes it will not stay started. When the car finally starts for the first 5 min the car has a very rough idle and I noticed that the rpm are very low and sometimes I need to have my foot on the gas to keep it from cutting out. After driving for a bit the shaking and rough idle goes away.

Please help!

Also a very stupid question. What size wrench would I use to remove the oil pan plug?

Thanks,

Fab

Water Temp Sensor!

Where is it located?

look up your part here on the "buy parts", it will show you a picture,it will be somewhere by the valve cover.You should find it from there.

It's the rearmost (standing in front of the engine) sensor on top of the valve cover (2 pin or 4 pin)

You want to test it with an ohm meter for the correct resistance values... (a bad OVP would cause the same symptoms by removing the cold start circut from the system)...:

Ohm's range from the temp chart in the /Engine Manual-Combustion Manual-07.3 Mechanical/electronic gasoline injection system (KE injection)-121 Testing electrical components of KE injection system. page 60

Temperature °C........Resistance kΩ
-20........................15.7
-10.........................9.2
0............................5.9
10...........................3.7
20...........................2.5
30...........................1.7
40...........................1.18
50...........................0.84
60...........................0.60
70...........................0.435
80...........................0.325
90...........................0.247
Same resistance values apply to KE intake air temp sensor.
I think this chart applies to these 2 sensors for all KE systems but don't know for sure.

I agree with the water temperature sensor diagnosis. My 260E had the exact same symptoms. Replaced rear water temperature sensor and it fixed it. By the way, there is a second water temperature sensor in front of the one you need to replace. That one controls the auxilliary fan. If you find the auxilliary fan keeps running, its the other water temperature sensor.

as for the oil pan plug, use the socket that fits. I found mine had an oversize bolt cos the PO had stripped the threads

I called the dealership up to see if they had a water temp sensor in stock and they do $37.00 CND plus taxes (not bad). When I looked at the engin to see where it was located it is not the very last sensor. The very last sensor has 2 push wires coming out of it. What sensor is that? Any ways I am going to purchase this sensor today and see what happens.

Also I need the exact size for the oil plug so I can buy that size wrench. So soes anyone have the size of the oil drain plug.

Thanks

Fab

oil plug wrench
 

it's been years since i've changed the oil by removing the plug...

...but i do remember the correct size wrench is in the factory tool kit.....

Fab:

You have the M103 motor in your car - same as mine.

13mm wrench or socket gets the oil drain plug out. There may be a large plastic encapsulation panel underneath the car that will also have to come out first in order to expose the pan area. The 126 models with the M103 motor use 4 metal type screws with an 8mm head to secure this panel. I seem to recall looking at the photos of the underside of a 124 car(your model) and there were maybe 6 or 8 screws holding the panel on.

As I said, there are apparently 2 water temperature sensors. You want the one in the back. My independent mechanic referred to it as a "fuel sensor" however, my understanding is that it is a water temperature sensor. However, if you want to, change the other one and then when it doesn't work you'll know you got the wrong one.

It is named strangely. It is called the Water Temp Sensor, but in all honesty it is for the Fuel System. This is what tells the CIS-E controller the temp of the engine to determine if the cold start enrichment is needed or not and to keep the air/fuel mixture enriched until the engine reaches 60 degrees. Then enrichment is cut and normal operation is started. It also will have the ECU lean the mixture when the engine temp is over 100 degrees. They came in two flavors. One two prong plug, with two individual posts that are water tight connectors. And a four pin version that had a round top and water tght connector.

I was under the impression the cutoff point was 80 degrees.

Some places I have read that and some I have seen it state it is higher. I think that may have been the diference between KE-II and KE-III Jetronic CIS-E systems. Mine is KE-II and stops at 80.

i think logic would suggest there isn't actually a cutoff point and the mixture continues lean out as the engine gets warmer. The incremental change in resistance drops as the temperature rises until it hits optimum at operating temp, which also explains why it would lean the mixture still further when engine temp rises past normal.

i had an interesting few weeks with my 300E in this area when I overhauled the cooling system after the visco fan clutch failed. Replacing the radiator brought operating temp down from 87 deg to below 80 deg, which meant the car was always running rich thinking it was in still in warm up cycle. Really noticeable going up the mountains, the car just wasn't happy pulling up a hill.

Turned out the PO had compensated for poor radiator performance by replacing the thermostat with one that opened at a lower temperature. Replacing it with the OEM spec unit sorted everything out