Intake Temp -40F
 

I was sooo pissed off. Jerry and I were working on some ground and ignition issues, and I thought I was finally going to get a chance to really test the car out since making some modifications. Not so lucky, MegaTune reports Intake temp is stuck at -40F. :td:

I assumed that the most likely issue would be a failure in the connections between the temp sensor wiring and the AFM harness. So I opened that up (which was a PITA due to the 50lbs of electrical tape I used to mumify the connection). But alas, the connection was sound. The other connections seemed solid, but I didn't have time to conduct further investigation; I've got family in town.

The intake temp sensor is a GM open element. I assume it's just a thermistor. Does anyone have a reference chart (V vs temp) to check the sensor for proper operation?

This never happens when it's 70F outside. Nope, it waits until it's 100 so I have to sweat my ass off. :vash:

what about the wiring to the IAT sensor?

seems ok, didn't have a lot of time. I had continuity between the two wires, and did not have continuity between either wire and chassis ground. did not check for resistance or voltage.

My vote is on sensor are you running stock air intake sensor or the GM if the GM i think you either have a wiring issue or a bad flash on the easytherm for stock AIT sensor maybe :dunno: well given your last quote it seems like a shitty ground to me

i could buy failed sensor, but doubt MS software/firmware issue. That's why I was hoping someone had temp vs voltage data for the thermistor. Becuase then I could put it in a pot of hot water and compare voltage output to a thermometer.

I should have clarified, with the 2 wires from the sensor not hooked to anything else, I had no continuity to ground. Meaning I didn't have a short to ground.

do you have a multimeter? That would help quite a bit. As for the resistance you are looking for, why not open up easytherm and look at the GM default values. Also, I cant verify that it is correct, but it probably is, I found this after a quick google search. Looks like just what ya need: http://www.innovatemotorsports.com/f...php/t-988.html

cool, thanks ryan. that was what i need. so in ambient 90-something I should get around 2.3-2.4V.

ya just turn your car on and test that shit right now

I lol'd at work. Would be a bad thing if anyone with a DIY based (or just plain DIY) ECU did not have a multimeter.

The ultimate, and basically only, tool needed when it comes to diagnosing electrical issues.

Pulled sensor and probed. 0V :td:

for sure, i actually thought about editing that out. I am pretty sure that Ben is competent when it comes to cars and whatnot, but Ive been surprised by people in the past.

well theres your problem right there, I bet there are available sensors for like 10 bucks at the dealership. Wait, make sure that you are getting the 5v reference voltage from megasquirt first, but its kinda hard to screw up a temperature sensor wiring.

I should have 5V between the 1st and 6th pins on the AFM harness, right? (those are the ones that the temp sensor hooks to)
I have 0V there.
The thermisistor does change resistance with ambient temp. I had 4000k ohms outside and 3600 ohms inside

Wait... why are we talking voltage and temp sensor? They are resistance/ohm based...

<-- confused.

:inout:

Right, but it's a circuit so it needs power. Should be 5V goes in, the thermistor adds resistance based on temp, so less than 5V comes out. Resistance decreases as temp goes up.

My sensor does change resistance based on temp, it seems. R should decrease as temp goes up. However I'm getting some mixed readings, but probably due to the fact I have to hold it in my hand.

MY MS shows -40F which is the bottom of the scale. Which would mean 0V/infinite resistance.

I have 0V at the AFM harness. There is a connection somewhere. I do not know which pin at the ecu suppies 5V to the AFM, but suspect (hope) that's where the problem is.

NO based on the inputs you have post earlier you not getting a resistance...

IF 5V is been supplied power... based on the scale you posted... MS is reading 4.9XXXXX. Should then you voltmeter been reading say 5v across since that is what -40 means? It sounds to me like you where probing the wrong pins. 0V should read 300F not -40.

Maybe I am getting everything flipped in my head, I am still fucking dead, but that was logical pops first.

the scale below is wrong. web info isn't always right, as that's not how a thermistor works. its resistance approaches 0 as temp increases, and resistance apporaches infinity as temperature decreases. The MS is supposed to supply the thermistor 5V, the thermistor will drop the voltage, and the MS calculates delta V to determine temperature.

I think the thermistor works, but it's not receiving power.

I dont remember how I wired it for sure, but I think I hooked one wire up to the megasquirt and the other wire to either a ground or a 5v source on the ecu harness.

Jerry, If/When you read this, could you please post which wires at the ECU harness go to the pins at the AFM connector that we plug the AIT sensor to? I'd like to probe out the +5V source for functionality, and then just directly wire from the MS to the AIT sensor without going through the AFM wiring. Assuming there's no type of filtering circuit in the AFM harness--which I doubt is the case.

Megasquirt diagrams all show one to ecu and other to ground. The ecu wants a 5v reference, and the setup works by using the IAT sensor as another bias resistor.

This is for the GM and other sensors just wired up.

AIT on a stock harness is 2P, red with a green stripe.....6th over on the big harness on the bottom.

here:

http://i10.tinypic.com/5xqh93r.gif


the 5vref is 2K



this will help as well:

https://www.miataturbo.net/~web1_bra.../ecupinout.jpg

Thanks I thought it was the R/G @ 2P, but my diagram wasn't anywhere near as clear as yours.

So, one lead from the AIT sensor to 2P, and the other to the sensor ground (on the head, pass side, by fuel rail) should be the ticket. Or does 1 lead go to 2P, and the other to 2K? I dunnooo....
:dunno:

According to MS site... one is ground other is to ecu.

But mine isn't exactly reading right yet. :p

Hi Ben,

You should see 5 volts on pin 2P with the IAT sensor disconnected. The MSPNP sends a 5 volt signal on that line; there's a 2.49K resistor inside the MSPNP, and the IAT sensor forms the second half of a voltage divider.

So with the IAT sensor in place, you will see a somewhat lower voltage. You'll only see voltage on the red and green wire; the other wire is a ground.

Let me know what you find there; we'll get this one fixed one way or another.

Thanks Matt.

Today I have 4.77V at the AFM harness.
I am going to try to re-crimp those tiny little spades onto the IAT sensor wires and reconnect to the harness. Wish me luck.

AIT sensor works again.
All wiring believed to be good.
Problem suspected to be loose ribbon cable connector inside of MSPNP unit. It was not pushed firmly into the daughterboard. (my unit has been opened up 2 or 3 times for modifications)

I was not able to get a good crimp on one of the spades. The connection is more or less taped on now. I'll deal with it in the next few days.

hmmm

Hurm... i measure 2.41v for my temp sensor... I also compared the sensor ohm wise to another new sensor.. .and its fine.

I wonder wth is wrong with mine.

Got to drive the car appx 50 miles today, temp sensor seems fine.

<-- jealous

haha, then I won't tell you about my WOT pull through the gears until 6100 rpm in 5th. I was going for 7k, but I let off because w/o the undertray the front felt floaty and there was oncoming traffic.

and I also won't tell you that my ignition misfires seem to have gone away since we did some ground alterations.

all-in-all, it was a good day for the miata.

Then be a saint... and help me remedy my IAT issue :p

The GM sensor may or may not be a good choice, the thermistors used in the LS1's react quite slowly, you're better off buying a thermistor for $10 in the right range....
I can supply a source and part # if you need, just chop the "cage" off the GM sensor and solder in the new, then glue cage back on, done.

the one on the GTO was quite poor and the IAT->timing tune very conservative, so at a light the IAT would go up, and the thermistor wouldn't read a cooler temp until into 4th gear, making for the suck.

Now someone thinks about that... I want to at least get it running off the gm sensor first. I can muck with a nicer sensor later.

I'm running one side to 2C ground (blk/lt.grn) and 2P (iat sensor).

Going outside now (at neo's prodding) to try the ground directly to chassis/motor. I'll be back in a min.

:confused: why not just test it with an ohm meter?

I am, it reads fine as far as i can tell. I get solid ohm readings and voltage when on.

So it must be a MS config issue... bah!

black/green is a sensor-->motor ground. look over on the pass side, between the fuel rail and firewall. there's like 8 black/green wires between 2 bolts.

my car had some major grounding issues. we ended up running 2 extra main grounds from the MS to the motor. we also ran all the acccessories that were formerly grounded with the MS (gauges, wb controller) to the same ground point on the motor, but through their own wires.

yesterday was the first test ride, and I believe everything to now be good.

Philip, I'd be interested in that replacement thermistor. Though I don't see that type lack of response with my sensor. I was watching it with a close eye yesterday.

www omega.com

part #44005

cool thanks. might be a fun experiment

http://www.omega.com/ppt/pptsc.asp?r...ERMIS_ELEMENTS

Back from the salt...

FYI to all, anytime you see -40 on your temp sensors (IAT or CLT) it's not connected... that's the default temp MegaTune will show for an unconnected sensor. So it's either wiring, or 'could' be a bad sensor though that's pretty rare. Usually wiring...

Glad it's sorted Ben!

Found, I'm having issues with only IAT at this point... i've tried another sensor and get similar readings. My wiring is literally to the ecu and to a ground.

Could i be so severely butchering my easytherm stuff.. that it is the issue?

probably bias resistance and/or easytherm values.

well, i have a 2.2ohm resistor in there, which i put into easytherm. I then use the GM default values and the rx7 clt values... CLT works... but IAT reads super super super low.

So you're using GM CLT and IAT sensors? And 2.2ohm resistors for bias on both R4 and R7?

Did you put the .inc files in the proper folder in MegaTune after Easytherm generated them?

airdenfactor.inc
matfactor.inc
thermfactor.inc

All three need to go in:

C:\Program Files\MegaSquirt\car1\mtCfg

or the mtcfg subdir under whatever project folder you're using... I used car1 in this example as it's the default.

250mph ?

I have the 2.490 in for CLT and mazda sensor. r4
I have a 2.2 in for IAT and the GM sensor. r7 (i had pulled/damaged r7 per misreading advice, and could only find a 2.2 locally)

I get 2.4v (at least on last check) with the GM sensor and a generic replacement i tested the other day. Both were reading about -14c on a nice 24c (clt reading) day.

I've also moved the .inc files to the proper location after creation.

Bloody hell... i think i might know the issue now.

I kept dropping the .inc files into the Megasquirt/mgCfg folder... not the car specific one.

BLARGH!

I'll report back tonight.

grrr.... 211mph with 2 cylinders acting up-- valvetrain issues. We dropped an exhaust valve on that 211mph run yesterday and holed a piston.

But as they say, That's racin' -- we'll try again ;)

The Buick set 2 records in slower classes in the 135-142mph range. They were going back for a 3rd today.

Freiburger's car (Hotrod Special) had set 2 and was going back for a 3rd as well.

So a MS'ed miata went 200+mph :eek: :D

Sorry-- I should have clarified... that was a twin-turbo 515ci Studebaker-- MS'd though ;)

It's the one on our website.

I'm toying with the idea of building a landspeed car-- I've got to scour the rulebooks and recordbook to see what makes sense. If a Miata makes sense that would be cool. I'd love it actually. I know there was one that ran a while back and did 152mph but I'm not sure if he ever came back for more.

Awesome Jerry, yeah i think leadfoot on .net did a bonnevile miata.

Put the INC files in the proper folder. The main Megasquirt mtCfg folder is NOT the right spot :p.

Put the files into Car1 and all good :)

Oh... and I timed the car... was at like 24 degrees instead of 10 :p