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coolant sensor, where is it?
Topic Started: Tue Jun 19, 2012 10:34 am (2,359 Views)
colmcork
Newbie
[ * ]
Hi there guys I am looking for a little help. As per the title, I am looking for the location of the coolant sensor that controls the cold start valve.

My car, a 1993 1.8 manual, is a very rough starter and I am trying to get to the bottom of it. Instead of the engine building revs at start-up and dropping off as it gets warmer, my car seems to have a constant rpm weather the engine is cold or warm. I do not have an rpm clock but I am guessing that it sits around the 700/800 rpm range??

Now so far I have taken out the idle control valve and cleaned it. It seems to be working fine as when i apply 12v across the pins out on the bench I can see it operating.

I have also taken off the cold start valve and again, it seems to be operating fine as when I put 12v across it on the bench I can hear it opening/ closing. Now I had the valve re-connected to the fuel distributer but not connected back into the manifold, and with someone else cranking the engine I observed the csv but it didn't allow any fuel through, so from reading as many posts as possible on this topic, it would seem that the next logical step would be to test the coolant temperature sensor. Now apparently it is on the engine block somewhere on this engine model, but me not being a mechanic I just cannot seem to find it.

Another thing that I have noticed and I am not sure if it is of any relevance, is that while driving the temperature guage usually sits way down below the 80 degree mark. When standing at idle the guage will climb up to the 80 degree mark at which point the electric fan kicks in. All the heaters seem to be blowing fine so am I right in thinking that this is nothing to be overly concerned with?

Any help on this would be greatly appreciated guys. I must say that I am thoroughly enjoying working on this old girl, just basic simple nuts and bolts engineering.

Thanks in advance guys,
Colm.
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jimbojones
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Hi Colm,

Glad to see your getting to grips with it!
There a a few temperature sensors on the car,
There is an air temperature sensor that sticks into the front of the air box on the very front of your car.
Then to the left of that, mounted in the top of the cyclinder head you will see a number of sensors, some have wires and others have vacuum tubes coming out of these.
The one that the back that has 4 pins is the sensor for the K-jet fule distribution, and the EZL ignition timing.
Towards the front there will be sensors for your temperature gauge on the dash, the fan and the cold start valve, they may even be incorporated into the one switch as models seem to vary.

i know someone put a picture of them all with labels but use the search bar to look back through the old posts and youll find the one your looking for
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colmcork
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Hi there Jim, thanks for the reply. I see that you have the very same car as myself, even down to the colour :lol: !

I have been trawling through loads of old posts on here regarding the cold start valve control but to no avail......... yet!! I have found the sensor with the round black connector on top and the 4 pins and was lead to believe that this was the control for the cold start valve, but are you thinking that this may not be the case :no: ? Are you suggesting that there may be a seperate sensor again controling the cold start valve?

Al help greatly appreciated,

Regards,
Colm.
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jimbojones
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Most likely it is that 4 pronged pin because that sends the temperature to the Bosch ECU which also deals with cold start,
but there are quite a few temperature sensors that will "fit" the car, i think even cars with air-con have an extra one, which is
why i'm not 100% that that's the one because i have heard others on the forum mention all sorts of sensors with 3 and 2 prongs

There is a good guide here to finding the sensors and testing them under the "Continuous Fuel Injection System" link for the 201:

http://web.archive.org/web/20060602101116/http://mb.braingears.com/201_Chassis.htm

should give you an idea if its working!


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colmcork
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Thank you very much Jim for digging out that link for me, wherever you managed to find it feckknows ?

Anyways i went out earlier and tested my coolant temp. sensor when the engine was stone cold ( car had not been started for 24 hours and kept in a garage ). Instead of getting an expected reading of approx 4000 to 5000 ohm's, I got a reading of about 1800 ohm's, which suggest's that the coolant in my car was between 20 and 30 degrees. Surely this is an indication that my coolant sensor is reading a bit off to say the least?

Now as the engine temperature rose the resistance began to drop off consistantly, until at which point the dash guage read 80 degrees and the electric fan kicked in. By this time the coolant sensor had dropped to approx 140 ohm's, suggesting that the coolant was somewhere between 100 and 110 degrees.

I am hoping that this explains why my car is such a poor starter but when engine temps. get up to scratch everything works fine ( idle's fine, heaters blow hot, does not overheat, electric fan kicks in ). I will try and replace my coolant sensor as it is relatively simple/ straightforward and will see how it goes from there.

I will keep you guys posted as to how I get on. Thanks again Jim for all your help so far.

Regards
Colm.
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jimbojones
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Yeah, the ohm reading for the 100 degrees seems to be correct as that is when the fan kicks in, so if your dial on the dash is only showing 80 it could mean that the wire connecting it to the actual needle is loose, i know mine is and it jumps around alot.
It is possilbe as well that cold start valve could actually read the air temperature rather than the coolant temperature, and the sensor for the air temp is mounted in the frount of the air box, but I'm not sure hopefully someone else here can shed some light on that!
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colmcork
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Well all that I am sure of at this stage is that the cold start valve is not letting out a fuel spray/ mist/ vapour of any kind, and from what I have read on here and benzworld so far, it seems that it is most likely controlled by the coolant sensor.

I will remove the cold start valve and give it a direct 12v supply with someone cranking the car and see if it allows fuel through. If this is sucessful I will re-fit it and give it the 12v supply and see if it helps the cold starting. Fingers crossed I dont blow the damn thing up in the process !!

Thanks again Jim for your help mate :)
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