MS-II - CHT Bias Resistor Value

[cygnusx1]

I am studying the MS-II manauls prior to my installation. I found the values for the Stock Nissan CHT recalibration here but where do I find the value for "Bias Resistor Value" to enter into megatune Table Generator for the stock CHT?

 

This value is 2490 Ohms for the GM sensor. What is the value for the Nissan sensor? Do I measure it from the sensor? Im am a little confused on this one thing.

 

It isn't addressed in Mobythevans post.

 

Thanks.

-Dave

[Matt Cramer]

The bias resistor is inside the Megasquirt. Unless you've deliberately swapped bias resistors, use 2490 ohms.

[cygnusx1]

Ahh, ok I didn't see that addressed in the manual and obviously I bought the unit assembled so I didnt know it was in there. Thanks again.

[z-ya]

You can use the Datsun CLT sensor of you use the easytherm program to generate a new lookup table. Personally, I replace all the sensors with new ones when doing a conversion. Cheap insurance against gremlins. You need a GM IAT sensor, might as well use a GM CLT sensor. You just need to re-tap your thermostat housing for 3/8" NPT thread.

[NZeder]

while on the topic of IAT and CLT sensors - if I was to go to the GM sensors I see there are two type of IAT open and closed element. Am I correct in that I can use the close CLT/IAT unit for a NA engine? And the open element IAT is recommended for boosted applications?

[twoeightythreez]

If you search you will find...but I cut and pasted my link for you (when I installed MS-II on my 280z which I have since turboed but still using Nissan CHT sensor. (same values as CLT sensor in N/A motors prior to 1981) This is the one with the bosch type plug, not the one-wire gauge sender.

http://forums.hybridz.org/showthread.php?t=113860

[twoeightythreez]

Here's the stock values if you don't want to read the entire post: It is my understanding that the Nissan CLT sensor is very close to the GM one anyway

Stock 280z coolant temp sensor (not the gauge sensor) values

 

-40F 30-33000 ohms

80F 2000-2500ohms

160F 360 ohms

[cygnusx1]

z-ya, I've been studying the MS-II manuals and MS-II doesnt need Easytherm. It has a separate entry table for sensor values. I will be bench testing my MS-II pretty soon. I think I have it pretty much figured out. I just need to get a grasp on versions, firmware, and all the various file formats that MS-II uses. I am waiting for the Stimulator, which I should have ordered up front with the rest of the stuff.

[twoeightythreez]

"You can use the Datsun CLT sensor of you use the easytherm program "

Z-ya, with MS-II you don't need to use easytherm...you just click under "tools" and then "calibrate sensors" and just put the values for -40F, 80F and 160F and burn to ECU and you're done!

Ya...what he said....He posted as I was writing this!

[twoeightythreez]

I also like using the Nissan one with the P90 head because you can then measure temps from the back of the head, where the coolant (in theory) is the hottest. IMHO I would not want to try to re-tap the HEAD for a GM sensor if I didn't have to. (I've read about people being unlucky and cracking thermostat housings when re-tapping to 3/8NPT definitely would not want to be unlucky with the entire cyl. head)

[z-ya]

Thanks for the clarification, I didn't realize that MS-II had this feature built in. Cool. I've only helped tune one MS-II install. For MS-I users, you still need the standalone Easytherm application. Yes, get the stimulator, it is a great debugging tool.

 

Is there a hole in the rear of the P90 head that enters the water jacket (besides the same one that is in all L6 heads)? The P90 has a head temp sensor, but that is not coolant temperature as it does not contact the water jacket. The sensor must be immersed in coolant.

 

The thermostat housing is the correct location. If you drill it with the correct size drill bit for a 3/8" NPT tap, you will not crack the housing. You need the drill and tap for the IAT sensor anyway, might as well use it for you new GM CLT sensor.

[cygnusx1]

I was under the impression that using CHT in the P90 was as good as using coolant temp. After all, CHT effects combustion more than coolant temp? No?

 

If I have to, I will do the drill n tap but somebody on here runs MS with CHT. I understand that the heating/cooling rates of the aluminum and the coolant are pretty different and the fuel correction curves would be off but is it that dramatic of a difference?

 

It's easy enough to go either way, so this is just a technical "what-if" question.

 

BTW, yes I will be tapping the I/C tube for the GM Open air intake temp sensor. I still haven't figured out exactly how and where I am going to mount it but I know I am.

[z-ya]

Unless you use some sort of heat sink compound to assure good thermal contact with the head, immersing it in the coolant is the best bet. That is where Nissan put it (for good reason). I have mounted the CLT sensor in the thermostat housing for all installs I have done, and have not had any problems. You can buy a 3/8" NPT bung and weld it into your IC pipe rather than trying to tap it. You can also put your IAT sensor in the intake (don't want to open that can of worms again!)

[cygnusx1]

Oh yeah, I've already read the AIT sensor location threads! I am doing my homework for this....it's half the fun isn't it.

 

Rightly so, tapping into 1/16" stainless tubing is not a good idea, lol. I will find a local welder to weld a bung on the tube just before the throttle body. I think I am going to leave the stock CHT sensor in the P90 head and put it's Temp/Ohm values in Megatune in place of the CLT. If I experience strange things, during warmup, I will switch to a GM Coolant Temp Sensor. I'll leave a loop in the harness to be able to make the switch without rewiring. I guess I like being a little bit of a guinea pig.

 

[twoeightythreez]

I'm using the CHT in my '83 head (I think it's an 81 block) because the thermostat housing has no provision for the CLT sensor! (it's blocked off!)

As far as I could tell if you take the CHT sensor out coolant comes out, I think it's in a water passage.

I did use the old CLT sensor in the CHT spot as it's the same one.

I don't have any driveablity probs and I drove cross-country, so I guess preference is the deciding factor.

I do notice that my temp gauge can be around "140" on the gauge and around "210" on the gauge with the MS coolant temp moving between 180 and 197 but I think that's more a function of the inaccurate gauge.

When I overheated it (idling and my 1st electric fan stopped working) the dash gauge and the MS both reported 240 deg. before I shut it off, so I guess it works well in either location.

[cygnusx1]

I suppose no matter where it is, just determine what the reading is fully warm, and remove any correction factors for the maps at that reading or above.

[z-ya]

When you mount it in the thermostat housing, it is right below the thermostat. So the reading in MS should not only match your dash gauge, but it should also correlate to the thermostat opening temperature.

[cygnusx1]

When you mount it in the thermostat housing, it is right below the thermostat. So the reading in MS should not only match your dash gauge, but it should also correlate to the thermostat opening temperature.

 

Yes, that would have advantages. Especially when trouble shooting or watching gauges at the track.

[twoeightythreez]

I'm not disputing the reason to put it in the thermostat housing. I'm just saying there isn't that much of a difference to make it worth my while to either drill a hole and tap in my current housing or find another one,(the spot where teh CLT went in the '78 is "blank" on the P90 head I have.) as the indicated temp (on MS) is within a degree of the thermostat opening temperature.

(Once it opens it does not take long for the coolant to circulate)

I actually prefer where mine is because the coolant tends to be hottest at the back of the block.

I have no problems with overheating, since I'm using the FIDLE output thru a relay to turn on a fan at 210 deg and off at 190. I'm running a 180 deg thermostat and the fan only runs when I'm idling or city driving. The temp at the back of the engine is about 10 deg higher than at the thermostat housing. (When I ahd the 190deg stat in the engine would routinely show 200deg at the back where CHT is)

The stock temp gauge I'm not really worried about, it shows overheating and over cooling and that's about it. (I can be drivng down the road, with the MS indicating 190deg (through CHT) and that gauge, depending on how it feels, will be just about anywhere in between the two calibrations on it (120 and 250) so the gauge isn't accurate at all, but I didn't overheat idling for FOURTEEN hours so I think I'm alright

I also didn't overheat when driving 85-90 mph for hours through west texas on my way home.

[twoeightythreez]

Originally Posted by z-ya

When you mount it in the thermostat housing, it is right below the thermostat. So the reading in MS should not only match your dash gauge, but it should also correlate to the thermostat opening temperature.

It actually does correlate to thermostat opening temperature and MS. (if you subtract 10 degrees..as I measured a 10 deg difference between front and back of the engine)

The stock dash gauge is accurate the way most are, you're either cold, normal, or hot, Z's just have numbers on them to appear sportier.....

All I'm saying is I don't think it makes that much of a difference, except maybe for 'heat soak'.

I mean it's probably better in the housing but I'm not gonna move mine now after I've lengthened my coolant temp sender wires to reach to the CHT location (I am using the CLT that came from the T-housing though)