Allen, this should get you going. The first page is the testing proc and the second is the resistance-temperature scale to compare your results to for specification at several temps.

With the 4 pin style temp sensor, I believe that the resistance is measured across opposite pins [e.g. 12 o'clock and 6 o'clock]


My M103 has a two connectors, matching the Bosch unit in the online catalog described as
[interesting how vBulletin added the smily in the quote - maybe it's trying to tell me something]


Does this sensor just have one circuit [measure from pin to pin] or two circuits [measure from each pin to ground]?

Time to go to the store an get a better meter anyway [next steps are to look at the 'duty cycle' readings and the output voltage from the O2 sensor - can't do either with my cheapie meter]

If you're talking about your '89 300E, the sensor is actually two identical sensors in the same component. One sensor supplies signal to the KE controller for fuel management, and the other supplies signal to the EZL for ignition management. The 4 pins are indeed measured on the diagonal, pins 1 and 3, then pins 2 and 4. Pins 3 and 4 are ground. The measured resistance for each pair of tests should be identical at the same temperature point shown in the chart above.

My 89 300E has a two pin connector [two circular posts, with o-rings on each one]

Image from the catalog [if this works] http://12.153.160.115/images/catalog...0280130044.jpg

Measuring from each post to ground shows about 2 ohms [cheapie analog meter] at current ambient temp [80F] - that should be closer to 1.7k ohms. If I'm reading things correctly it's time to order a new sensor.

2K Ohms is just about dead on for 80F. The important thing is that both thermistors give similar values at every temp point. I'd take 1 or 2 more readings at higher engine temps, before decididng that the sensor is kaput. So far it looks OK to me.

I'm going to check it again cold, then warm up the engine and test it again.

If I'm reading my meter correctly [log scale] it is showing 2 ohms - not 2k ohms. [time to get a better meter]

I took apart the intake manifold and i checked the intake flap and there is no binding or scoring against the sides,it moves freely i dont understand what you ment by putting a magnet over the bolt cuz theres already a magnet over it? Could you explain further, also i dont know which sensor is the right one for the temp sensor is it one unit or 4 little ones. PLease help, pictures would be great thanks

Allen, the temp sensor involved in these tests is located at the very back of the engine, on the driver side of the valve cover. It's either connected to a big black electrical connector as shown in the photo below, or it's connected to two wires and looks like the photo dlevitt posted in post #34 above. There was a production change in '88 or '89. The big black one is referred to as the 4-pin sensor, the green one is a 2-pin sensor; it's one or the other, but they operate in exactly the same manner. The procedure for testing the 4-pin sensor is what I gave you in my last post above. The test for the 2-pin is slightly different, as shown in the image below.

I don't really know why your '89 has the old style green sensor. Those were upgraded with the black 4-pin component, which my '88 has. Oh well.... Yeah, 2 Ohms isn't right. Is it possible you just weren't doing the test right? Try the test I posted above for the 2-pin, before condemning your multimeter.

It's a crappy meter - one log scale from < 100 ohms to a megohm.

I bought a new dvm [compleat with duty cycle] at Sears this morning. I'll see what readings I can coax out of it this evening.

Had the ABS and check engine light and related issues and ordered a new OVP! Took a 250 mile trip today and had no issues! Guess the OVP was the culprit!

Alright i checked out the temperature sensor, my 89 has a 2 pin, its green like the picture above now i didnt know the exact temperature of the engine i used the temperature gauge in the car and i found that the numbers didnt match up like at 80 celcius i got dead on 0.6 kohm which on the page says should be for 60celcius. Also i want to know does the temperature sensor make the car start hard, rough idle, run like garbage?

Yes, it will affect driveability/idle condition. Using your numbers, the fuel and ignition control units would be interpreting the sensor signal at 80C as if the engine were not yet warmed up (60C), and would adjust lean/rich mixture accordingly. Also important that both sensor pins measure close to the same resistance values, so that the CIS controller and the EZL controller are getting the same information.

Alright so it sounds like a possibility, the way i tested the sensor was i took my volt meter put it on kohm and that was the result. I put both prongs into each end of the sensor, how do i measure each sensor pin separately. I also suspect that my ignition coil could be the culprit because it give me different readings from day to day which means it could be shorting out inside. Im going to swap my 91 300E coil into the 89 or with a 90 190E (2.6L) , are they the same one? both M103 engines only difference is that the 89 is set up front to back while the 91 is set up side to side. Ive been reading about coil problems and thats about the only thing left that hasnt been replaced since ive had it and the problems consist of intermittent starting, rough idling, low torque...which im experiencing all three. Thing that puzzles me is the coil is within spec so we'll see from the swap.

I still didnt have time to change out the ignition coil, i was wondering where and how do you test the crank positioning sensor, any input. Also i know that if the sensor is broken the car wont start which is what happened to me, but i changed it with a used one, can it cause idle, drivability,hard starting problems?