Which wire goes where for the cylinder head temp sensor on to hook up to MegaSquirt?

Tippy · 09:10 PM

Since my other thread may not get the visibility for this question, what wire of the CHTS is what?

This is to hook up the CHTS to MegaSquirt II v3.57.

Does it matter?

cmonref · 03-09-2012, 04:08 AM

If you read the Megamanual as suggested in your other thread, you would find that it the temp sensor is a resistor and does not have polarity -- hook it up either way.

If you read the manual -- really study it -- you will gain answers to questions that have not even occured to you yet. You can't ask enough questions on this board to gain you the same amount of information that studying the manual will give you.

Tippy · 04:29 AM

Quote:

Originally Posted by Brian K. Haggard

If you read the Megamanual as suggested in your other thread, you would find that it the temp sensor is a resistor and does not have polarity -- hook it up either way.

If you read the manual -- really study it -- you will gain answers to questions that have not even occured to you yet. You can't ask enough questions on this board to gain you the same amount of information that studying the manual will give you.

I have never read about using the head temp sensor as the CLT. If I would have, I would have not asked this question. I was originally going down the path of using the GM CLT sensor until recently.

I'd like to add that the CHTS has added what many here have called a ground. Can you see why this can be confusing??? The original CHTS was a one wire. It is now a two wire.

But, you are right though, I just realized the "current" megamanual works for all versions, not just MS III - which is what I thought the "current" megamanual was for.

Not to mention there are so many links to stuff that even after dozens of hours of reading the MS website over about a year, it is very easy to miss things.

Thanks for the answer and yes I will refer to the megamanual.

billjam · billjam's Garage

Cory,
This might help. Not sure which MS diagram applies to your situation or if you have seen these in the MS manual.
I have a two wire CHT sensor and it connects to pins 21 and 1 as per the second MS diagram and the bottom two diags.
Email me if you want a full copy of my MS3X wiring diagram.

Tippy · 03-09-2012, 06:21 AM

Thanks Bill.

Where did you get diagrams 3 and 4?

gsmith660 · 03-09-2012, 07:00 AM

I have a GM coolant sensor and it hooks up to 21 and to ground works like a charm. Is this what you are asking about? Brian please chill brother he got it about reading the manual, may I suggest that if you are going to chastise also please try to educate in other words don't chew on somebody without adding a solution to the problem being asked thank you oh and I was pointing out the VR sensor is polarized not the coolant temp sensor in the other thread because that gave me fits and I just wanted to pay that forward.

Tippy · 03-09-2012, 08:05 AM

Quote:

Originally Posted by gsmith660

I have a GM coolant sensor and it hooks up to 21 and to ground works like a charm. Is this what you are asking about? Brian please chill brother he got it about reading the manual, may I suggest that if you are going to chastise also please try to educate in other words don't chew on somebody without adding a solution to the problem being asked thank you oh and I was pointing out the VR sensor is polarized not the coolant temp sensor in the other thread because that gave me fits and I just wanted to pay that forward.

I originally was going to use the GM CLT (which I did purchase), but realized that I already have the head temp and why try to engineer (mounting the sensor, figuring that oil heats slower than the cylinders, etc.) something that is already present?

Thanks

gsmith660 · 03-09-2012, 11:39 AM

The head temp sensor wont work for the coolant sensor for warm up for 2 reasons first it wont have the right calibration curve I am sure since it registers much higher temps and second because of those higher temps the ECU will exit out of the warm up cycle before the motor is actually warmed up. Go ahead and pop that GM coolant sensor into the chain cover so it gets exposed to oil and you will get a nice smooth warm up cycle just make sure it has metric threads. BTW the GM sensor has the same calibration curve that is programed into megasquirt.

jpnovak · 03-09-2012, 11:50 AM

Cory, The CHT sensor will work.

However, you will have to build your own calibration values (these are listed in the Bentley manual) and you will have to develop your own warm-up table. Neither are difficult.

The only issue you may have is that the CHT sensor will get hotter than a traditional CLT sensor. Simple fact, the head runs that much warmer, especially on an air-cooled (oil) head. There is an extended range .ini file on the board that will allow for air cooled motors to be setup properly. Otherwise, the engine temperature (CHT) gauge will likely run off scale all of the time except during initial warmup.

Tippy · 03-09-2012, 02:36 PM

Thanks Jamie, I figured that. What if you put the highest temp resistance of the CHT at say 180 coolant temps?

I haven't read enough on this but I figured you can simply trick the computer?

Kind of like putting a resistor on a MAF for super/turbocharged apps to make the ECU think it is not at full throttle on blow through applications.

billjam · billjam's Garage

I am also working towards using the CHT sensor with appropriate setup. I remember coming across this setup buried somewhere in the manuals and figured that it was easier than adding yet another device. I also considered using the same signal from the OE temp sensor and that's my fall-back position if I can't get the CHT sensor working correctly.

The parts of wiring diagram above are from my own diagram for my current 3.6/MS3X/88 Carrera project with COPs and ITBs. The whole diagram looks a bit like this. I am still finalising a few details, but it's basically 99% complete. If you want a clear PDF or Visio copy, email me (at username link).

Tippy · 03-10-2012, 05:36 AM

Thanks Bill! Email sent.

sjf911 · sjf911's Garage

I have been using the CHT sensor for years as my coolant sensor and have not been happy with it. Initially, the MS software would not support a larger range of temperature to fit the head temperature max and I had to create a pseudo-curve to fit the MS range but this has been fixed, at least for MS3. The other issue I have is here in a colder climate, there is quite a bit of inconsistency in warmup performance depending on ambient temperature, hot restart time, etc.. Given that you are in south Texas, you may have better luck than I had (I really miss Texas come the winter here but don't miss the humidity). I am actually going relocate my sensor to an oil source during my current build. I may keep my CHT but just to be able to log head temps.

Tippy · 03-10-2012, 09:31 AM

You would think the air temp would sense really cold air even though the CHT sees a warm cylinder and maintain richer conditions. Would assume then that the CHT has more impact than air temp - reason you have cold climate issues.

gsmith660 · 03-10-2012, 11:14 AM

I am trying to get my mind wrapped around the concept. Megasquirt did not design the warm up map to be used with the CHT probably because the curve for that is not linear it is more of a parabolic curve if that is the right term (rises logarithmic then tapers off at the top and changes with engine load) where the coolant temp rises in a fairly linear curve and tops out and stays there plus the temp. rise per time increment lends to a smooth warm up curve. I also realize you can write a custom calibration curve and warm up table to use that sensor but the question I have is why? Just because you have the CHT sensor doesn't mean you should, it makes sense to hook it up so you can log the temps on each cylinder since that would let you know if you have an injector getting clogged and is leaning out a cylinder so you can prevent a costly meltdown but the coolant sensor is 30 bucks and designed to control the warm up enrichment and there is a plug in the right side chain cover that you could remove and put it there or take out the thermo time switch in the left chain cover and put it there. I put mine on the right side because the charge pipe for the turbo interfered with it on the left side. This is just my thoughts on this and it not intended to cause debate or anything else I am just curious as there was a debate on another forum and what ended up happening on that board was the guy wrote his custom curve and inserted it in the code and hosed his firmware and had to go through a real hassle to get it back to where he could flash his firmware back to the way it was and then tried it again and failed that time too. I have no idea what he was doing or trying to do or if it was the right way to go about it but it just seems like there are better things to tweak than this and limit compatibility with updates in the future. I am with Cole for most things and use the K.I.S.S principle on most things which is why I went with Megasquirt as some of the others are complicated by nature and some even require a tuner with special equipment. Richard Clewitt sold me a coolant sensor with the proper metric thread and the GM calib. curve that plugged right in and works very good takes about 10 min. to warm up and exit the enrichment curve without so much as a stumble or surge in the process, ok I am done thanks for listening.

Tippy · 03-10-2012, 11:52 AM

Well, I can go either way. I have the GM CLT and conn/piggy and an AMP Jr. Timer conn/piggy for the CHT.

Ah decisions.....

Tippy · 12:04 PM

***

prebordao · 06-13-2014, 12:08 PM

I'm ressurrecting this thread...

Tippy, where did you end up mounting you CHT sensor ? In place of the TTS ?
And which part was it ?

I'm starting on a similar path, so any help...

Tippy · 06-13-2014, 12:14 PM

I have a 3.2, so it already has one built into head 3.

Folks have used a lot of different areas, from cylinder fins to chain covers. OEM is tapped into the fins.

Ferrino · Ferrino's Garage

What's the current verdict on using the factory CHT sensor as the "coolant sensor" on the Megasquirt, please? Planning my Megasquirt setup and wondering if I can get away with the factory sensor...