Where should I stick my probe?

[David124T]

"From WIS, the air temp and coolant sensors should have the following resistance
(coolant sensor is a 4-pin dual unit with the resistors wired to the diagonal pins, test BOTH - they need to be the same).

Air temp sensor in the intake plastic, coolant horizontally on the thermostat housing (I think for your car!).

0C 5900ohms, 10c 3700, 20c 2500, 80c 325, 90c 245. Spec all +-5%."

The above was a reply (thanks 124coupe)to a problem I am experiencing with my 1990 300TE 24v failing the MOT on the CO emissions (not CO2 as I stupidly stated in the title).
The subject has gone from fuel to electrical, hence the new post.
I own a multimeter but don't have much idea what it does apart from indicating current when the needle swings. I know that ohms are something to do with resistance but I am at a loss at how to measure it. I have attached a photo of the coolant sensor showng the socket where the four pins engage. Do I test the sockets or the pins? Should the engine be running or do I just have the ignition switched on? If someone could "walk" me thru the proceedure, I would appreciate it very much.
I have also attached another (blurred) photo showing a sensor that doesn't seem to belong anywhere. (it emerges from the wiring just above the injectors). From the part number, it is an air temp sensor but I can't see where it connects to. Does anyone have any idea?
Thanks in advance
David

 

[David124T]

Here (hopefully) are the pics.

 

[Myros]

David

you have to test the sensor, that's the sockets bit, as it is the bit stuck to the engine. The pins bit are just the power feed and output. If the sensor checks out ok, then test the feed an output cable. As for which is which, I've no idea, but I'm sure Malcolm or someone else will help.

 

[Hibbo]

To use your avo (alalogue multimeter) to measure resistance, set it to the ohms setting, either by way of the rotary switch or where the leads are plugged into it. Touch the ends of the probes together and the meter should swing all the way over to the right, indicating zero ohms.

You don't need the ignition on as you are testing the sensor itself, not the ECU or wiring.

The two thermistors in the sensor are on diagonal pins, so connect the probes (doesn't matter which way round) to the top left and bottom right pins, take your reading then do the top right and bottom left.

Do it engine cold, reconnect it and run the engine up to temp and then check again.

 

[eric242340]

where should i stick my probe

"From WIS, the air temp and coolant sensors should have the following resistance
(coolant sensor is a 4-pin dual unit with the resistors wired to the diagonal pins, test BOTH - they need to be the same).

Air temp sensor in the intake plastic, coolant horizontally on the thermostat housing (I think for your car!).

0C 5900ohms, 10c 3700, 20c 2500, 80c 325, 90c 245. Spec all +-5%."

The above was a reply (thanks 124coupe)to a problem I am experiencing with my 1990 300TE 24v failing the MOT on the CO emissions (not CO2 as I stupidly stated in the title).
The subject has gone from fuel to electrical, hence the new post.
I own a multimeter but don't have much idea what it does apart from indicating current when the needle swings. I know that ohms are something to do with resistance but I am at a loss at how to measure it. I have attached a photo of the coolant sensor showng the socket where the four pins engage. Do I test the sockets or the pins? Should the engine be running or do I just have the ignition switched on? If someone could "walk" me thru the proceedure, I would appreciate it very much.
I have also attached another (blurred) photo showing a sensor that doesn't seem to belong anywhere. (it emerges from the wiring just above the injectors). From the part number, it is an air temp sensor but I can't see where it connects to. Does anyone have any idea?
Thanks in advance
David

Where should i stick my probe, is this a leading question or what?

 

[Myros]

I should wear my specs more

sorry David, and thanks Hibbo. I could have sworn the thing in David's fingers in the picture looked like sockets to me.

 

[television]

I do not know anything about this type of thing,but I will try and explain.

The meter you have is analogue, so you must calibrate it by putting onto the Ω range that you are measuring ; ie if the article has a Ω figure of 2.5kΩ then the meter must be set to the next range higher than this figure.
Next you must touch the 2 test leads together,and adjust the zero Ω knob so the the meter indicates 0Ω. do take note the resistance Ω readings are backwards to the volt readings and read out on the Ω scale.

The things that you are measuring are the sensors them selves and not the plugs attached to wires, sensors always have a socket. You then measure the resistance accorss the pins reffered to and note the reading, also the ambiant temperture at the time of measuring.


Malcolm
This is worse than writting technical manuals

 

[eric242340]

I do not know anything about this type of thing,but I will try and explain.

The meter you have is analogue, so you must calibrate it by putting onto the Ω range that you are measuring ; ie if the article has a Ω figure of 2.5kΩ then the meter must be set to the next range higher than this figure.
Next you must touch the 2 test leads together,and adjust the zero Ω knob so the the meter indicates 0Ω. do take note the resistance Ω readings are backwards to the volt readings and read out on the Ω scale.

The things that you are measuring are the sensors them selves and not the plugs attached to wires, sensors always have a socket. You then measure the resistance accorss the pins reffered to and note the reading, also the ambiant temperture at the time of measuring.


Malcolm
This is worse than writting technical manuals

Tell me about it, ive never, in my life heard this sort of question

 

[television]

Tell me about it, ive never, in my life heard this sort of question

Its OK eric, it will not be here when I wake up

Malcolm

 

[David124T]

Thanks to everyone for taking the time to reply. I really do appreciate it. What a brilliant site this is. Not only do you get technical questions answered but lessons on how to use your tools (that is not meant to be a leading comment).:!:
It's about 4 degrees here and the reading is 5100 so I guess that this sensor is OK (can't start the engine at the moment, need to re-connect quite a few bits). I will test the rest of the sensors later.
Did anyone recognise the other sensor? I really can't see where or if it should be connected.
Also, thanks to a thread from earlier this week, I now know that I don't have a belt tensioner on this engine:roll: All good fun or what?

David

 

[124coupe]

Just looked at your second pic - I can confirm its a special sensor called an "out-of focus blob". I have several on my car!

Both the air intake sensor and the coolant sensor can be taken out and tested in water - the key is that the air one registers correctly up to 20c (to control cold air intake enrichment) and the water one registers correctly 40-100c (to reduce and then stop cold engine enrichment at the right time).

If the two diagonal readings on the coolant one are the same then its a fair bet its working (as the two sensors are unlikely to fail in exactly the same way).

If my reading of WIS is correct, your car posts faults in 2 ways:

a limited number of "blink" codes via the 16-pin connector (needs a blink tester to read)

a "duty cycle" code from the engine management unit (needs a meter capable of reading duty cycle to read).

Local Bosch dealer should be able to read both for a few quid and may avoid a lot of work to find the fault.

We can help if you have the fault codes.....

 

[David124T]

Point taken. If you guys are willing to offer help and advice then the least I can do is produce a decent image. Hopefully this one is better.
Regards the fault codes, I had decided that the next best course would be to take it to a Bosch centre to plug it in. I just need to remove as much crud from the engine bay as possible before I take it. You may be able to get an idea of the state of the engine from the pics. This weather doesn't help either
David

 

[David124T]

As requested, I am posting back the results of the Bosch test. (Apologies to Malcolm that this thread has reappeard)
Not sure if this makes any sense.
First, I don't have any printout. The tester said he connected the car to the test equipment and first erased the memory?
He then ran the dignostic test and no faults came up.
The excess CO was corrected by adjusting the mixture via the hole in the air box. The CO value is now 1.58% which is within the spec 124coupe stated earlier.
I have to say that whilst I'm relieved that this problem seems to be solved, I'm disappointed that I won't learn anything about fault codes. Where can I find out more on this subject?

Thanks to all for the advice.

David

 

[television]

As requested, I am posting back the results of the Bosch test. (Apologies to Malcolm that this thread has reappeard)
Not sure if this makes any sense.
First, I don't have any printout. The tester said he connected the car to the test equipment and first erased the memory?
He then ran the dignostic test and no faults came up.
The excess CO was corrected by adjusting the mixture via the hole in the air box. The CO value is now 1.58% which is within the spec 124coupe stated earlier.
I have to say that whilst I'm relieved that this problem seems to be solved, I'm disappointed that I won't learn anything about fault codes. Where can I find out more on this subject?

Thanks to all for the advice.

David

Do a google search' MB fault codes' see what you get.

Malcolm