Coolant temp sensor 5-6 degrees out

[james]

Hi all I have a bmw m20 turbo having cold start issues and I believe it's temp sensor related as both coolant and air temp are 6 degrees higher than what the temp actually  is, I have looked at wiki but couldn't make sense of how to recalibrate them, can anyone help?

[fphil]

There is tool in VT to calibrate the sensor. This is the first thing to do. I did mine from the specs curve deg/Ohm of the sensor maker, by putting a set of resistances in place of the sensor and tuning the VT curve accordingly.

[james]

I have a Bosch sensor blue plug but am I correct in thinking the spec curve for this sensor is the one on wiki? Or are there many different ones?

[VEMS]

Hello James,


There are a lof of different CLT / MAT sensor curves, there are two choices in putting them in:

• It can be done in VT settings, go to inputs-> coolant (or mat sensor) sensor curve dialog, select coolant sensor-> 17 point curve. on the bottom of the dialog select default Bosch standard CLT, dont forget to BURN changes. If your sensor still deviates after this you will have to re-calibrate each point on the curve or choose the second method.
• It can also be done at firmware upload, you can select an AIR and CLT patch file in which the RRef is the sensor resistance @ 25 deg C; Example if you measure your CLT sensor @ 25 deg C with a DVM (in resistance mode) and your sensor reads 2400 ohm, choose coolant patch files rref 2400 and reupload your firmware, if there is still a difference after this (perhaps your measurement was slightly off) select on item up or down from RRef list and reupload to see if its a closer match. Iterate until both sensor match real temperature

This said, i do not think your cold start issues are caused by the slight deviation in sensor value from real temp, more likely you will have todo some re-tuning on your Cranking, Afterstart, Warmup Enrichment or IAC Reference curve.

Best regards,


Dave

[james]

Thanks for you responses it's a bit clearer now on what I need to do to sort the the temp readings I will see what I can do, the only reason I thought my cold start issue was related to this is because  I primed the fuel rail and opened each injector to eliminate air in rail and it fired up straight away with the extra fuel that came out the injectors, the temperature was around 10 c but the car read 18 c

[DevInAz]

Hi all I have a bmw m20 turbo having cold start issues and I believe it's temp sensor related as both coolant and air temp are 6 degrees higher than what the temp actually  is, I have looked at wiki but couldn't make sense of how to recalibrate them, can anyone help?

Hey James,

can you upload your config? or a log? or email it to [email protected]

I have tuned a few m20 turbo builds, i'll take a look and see if I can spot anything.  Take a log of your car before you start it and keep the log running for 30 seconds or so after it starts and lets take a look.

Load the log or config in "help" - "vems sharing center" then post up the link here if you could.

Devin

[james]

Hi Devin thanks for your offer you will have to  bare with me as working a lot so should hopefully get to the car mid next week, thanks

[james]

http://vems.hu/vemstune/sharingcenter/reports.php?cmd=view&key=ym6o3I
none start log link I think!

[james]

also i tried to set the correct air and coolant temperature patch, can this be done by knowing the temperature of the engine cold then upload the patch that matches  the sensor reading to the cold engine , or do i have to be measure the ohms at 25 degrees and set the corresponding patch? thanks

[DevInAz]

also i tried to set the correct air and coolant temperature patch, can this be done by knowing the temperature of the engine cold then upload the patch that matches  the sensor reading to the cold engine , or do i have to be measure the ohms at 25 degrees and set the corresponding patch? thanks

Hey James,

I looked at your log and you have a ton of fuel (9.7ms cranking pulse width) then once your car starts it drops down to 2.8ms... 

How I adjust this cranking enrichment table is lower it to the point where your car won't start. It should crank and not start then start increasing it by about 1ms each time you start the car while taking startup logs each time.  Since the cranking enrichment is in a percentage valve in the graph that you will be adjusting look in your logs to see what the cranking pulse width is or watch the PW gauge when cranking(I always take logs). When your car starts up faster it means you are moving in the correct direction. Some times this process can take a month or so to get dialed in. Since I live in the desert its 20F in the winter and 120F in the summer... we have a wide range so I can only guess at the temperatures in certain parts of the table until its the correct session.

Edit:  I was just looking through your config more and I see a bunch of stuff I would change. Email me and i'll try to help you sort some stuff out. [email protected]

are these 42lbs injectors?

Devin