Steve 90 Posted January 19, 2011 Share Posted January 19, 2011 To make a long story short I've just fitted a slightly tweaked 4.6 to my challenge truck. I was kindly supplied an MSQ from Nige which should be a good starting point. But, The truck ran lean. After some logging Nige pointed out that I need to open my eyes as the IAT/MAT sensor was obviously wrong. It permanently shows 99-101 deg Fahrenheit. (we don't expect that temp in Wales until March ) So Ive checked the sensor, resistance seems reasonable and near as damn it identical to 2 other new AT1010's I have. Sensor earth wiring is good, .002v drop, no resistance. All ECU earths seem good. Pin 20 from ECU to MAt also has no resistance and the resistance across the sensor is the same as measured from battery neg to ECU pin 20. I finally load checked the wiring (disconnected it, Used it to power a bulb and checked for volt drop) all still seems good. So I'm confident wiring and sensor is good. If I disconnect the sensor the Megatune drops very very slowly to 77 deg F but will not go any lower. Ive re loaded the old MSQ for the 3.9 (which used to be fine) and it shows the same so I'm confident its not a software issue. So could it be an ECU issue? What would the effect of a fault in the load resistor problem for this circuit be? Any idea's appreciated as I really need to have it running before the end of the week if were going to make the phoenix. Cheers guys. Steve. Quote Link to comment Share on other sites More sharing options...
Steve 90 Posted January 19, 2011 Author Share Posted January 19, 2011 Just a couple more points, I think last time the truck was used it possibly did start to feel a little lean and crackled a bit. So its likely this fault started then but Ive only really noticed it now while trying to set up the new motor. Also, I'm pretty sure the RPM is slightly low (around 200rpm if thats possible), I cant recheck at the moment as the rad pipes are off it but should be able to run it before the end of the week to clarify. Cheers. Steve. Quote Link to comment Share on other sites More sharing options...
Bull Bar Cowboy Posted January 19, 2011 Share Posted January 19, 2011 I have replied to your pm on innovate …………… Quote Link to comment Share on other sites More sharing options...
FridgeFreezer Posted January 19, 2011 Share Posted January 19, 2011 The sensor value will likely not drop much below 77 (or some similar value) with no sensor connected as it is internally pulled up to 5v, the sensor pulls it down. What happens if you short the sensor wire to ground? Also - where is your sensor in the air intake, and is it being affected by heat soak? Bear in mind it will not be measuring outside air temperature unless you mount it on the roof, it is measuring the temperature of the intake air and so is affected by the temperature of whatever it's screwed into. Quote Link to comment Share on other sites More sharing options...
Dave W Posted January 19, 2011 Share Posted January 19, 2011 Have you calibrated your firmware to match the sensor ? Have you got the correct thermfactor.ini files loaded in Megatune ? If you are using standard MS1 or MS1-Extra firmware the only way to calibrate the ECU so it knows what resistance is equal to what temperature is to recompile the firmware with a suitable table to match your senders. With MS2 you can change the settings in the front end and adjust the table on the fly but I assume you'll be running MS1 if Nige has sent you an MSQ. Having incorrect thermfactor.ini files loaded in Megatune won't effect the operation of the ECU but will mess up the displayed/logged data.. "Out of the box" MS1 and Megatune are both set up to match GM sensors although even those of us running a GM engine still end up having to fine tune the tables. Quote Link to comment Share on other sites More sharing options...
FridgeFreezer Posted January 19, 2011 Share Posted January 19, 2011 Dave - the AT1010 is a GM-compatible sensor (albeit actually from a Renault), it works with the standard MS firmware and does not require calibration. Quote Link to comment Share on other sites More sharing options...
Steve 90 Posted January 19, 2011 Author Share Posted January 19, 2011 What happens if you short the sensor wire to ground? Mmm, just tried it now. Grounded it and it showed a steady 170 deg F. Tok the ground wire off and it started to fall again, Re grounded it and it showed maximum value (over 200). Also - where is your sensor in the air intake, and is it being affected by heat soak? Bear in mind it will not be measuring outside air temperature unless you mount it on the roof, it is measuring the temperature of the intake air and so is affected by the temperature of whatever it's screwed into. The sensor is in the intake pipe inside the cab (where it runs between the seats) Its never suffered from heat soak and I'd be supprised if it did. Its a good few feet away from the motor and about 10" lower than the plenum. Ive also pulled the sensor out of the pipe and its still 100deg Cheers. Steve. Quote Link to comment Share on other sites More sharing options...
Steve 90 Posted January 19, 2011 Author Share Posted January 19, 2011 Have you calibrated your firmware to match the sensor ? Have you got the correct thermfactor.ini files loaded in Megatune ? If you are using standard MS1 or MS1-Extra firmware the only way to calibrate the ECU so it knows what resistance is equal to what temperature is to recompile the firmware with a suitable table to match your senders. With MS2 you can change the settings in the front end and adjust the table on the fly but I assume you'll be running MS1 if Nige has sent you an MSQ. Having incorrect thermfactor.ini files loaded in Megatune won't effect the operation of the ECU but will mess up the displayed/logged data.. "Out of the box" MS1 and Megatune are both set up to match GM sensors although even those of us running a GM engine still end up having to fine tune the tables. Errrr what Fridge said! To be honest I don't know, Ive just used it as set up by Fridge and Nige. Its started and run without the slightest hiccup or issue until now so Ive never paid too much attention to it. I'll have to rely on the knowledge of others to make a call on weather the sender im using is compatable "as is" or if it needs to mave some correction. Cheers. Steve. Quote Link to comment Share on other sites More sharing options...
Hybrid_From_Hell Posted January 19, 2011 Share Posted January 19, 2011 AT1010 is correct Hence me call re if you had been 'a fiddlin' with easytherm and FUBARed a setting or 4 AT1010 doesn't need tweaking, and as you have fitted a spanky new one thats that ruled out Nige Quote Link to comment Share on other sites More sharing options...
Bull Bar Cowboy Posted January 19, 2011 Share Posted January 19, 2011 Reload the modified S19 firmware file using the downloader to be absolutely sure ………….. I don’t have one handy but Nige does…………………. Quote Link to comment Share on other sites More sharing options...
FridgeFreezer Posted January 19, 2011 Share Posted January 19, 2011 This explains how it works, might help you to understand what you're seeing: http://www.megamanual.com/v22manual/mwire.htm#clt This shows the response of the standard sensor: GM Temperature Sensor Resistance Deg F Degrees C Ohms -40º -40 100,700 0º -18 25,000 20º -7 13,500 40º 4 7,500 70º 21 3,400 100º 38 1,800 160º 71 450 210º 99 185 So an open-circuit (tending toward inifnity ohms) will register as very cold, and a short circuit to ground (tending to zero) will register as very hot. The Megasquirt has deafult values programmed in for zero & infinity that should read 210degF, however those rely on a "perfect" short or open circuit, so a slightly dodgy connection may give a false low temp, and a partial short (eg water in loom, chafed wiring, etc.) may give a false high reading. Likewise, if there is a stray voltage on the sensor wire. Quote Link to comment Share on other sites More sharing options...
Steve 90 Posted January 19, 2011 Author Share Posted January 19, 2011 Nope, Scrap that post, The sensors are around the 6K ohm so they are OK Steve. Quote Link to comment Share on other sites More sharing options...
elbekko Posted January 19, 2011 Share Posted January 19, 2011 Perhaps you shouldn't be holding the sensor while measuring resistance? 100°F is rather close to body temp Quote Link to comment Share on other sites More sharing options...
Steve 90 Posted January 19, 2011 Author Share Posted January 19, 2011 Perhaps you shouldn't be holding the sensor while measuring resistance? 100°F is rather close to body temp Yea, Thanks for that! Quote Link to comment Share on other sites More sharing options...
Steve 90 Posted January 21, 2011 Author Share Posted January 21, 2011 FIXED!!! I was sure all the external bits (wiring/sensor) were OK. So, I ordered a new ECU (I wanted a spare ECU before we go to the Croatia trophy) . Nige got it to me in double quick time, Plugged it in and the MAT is correct. Just got a TIG-a-thon tonight to get the last of the rear rad pipes welded up and I can get it running again. Hopefully everything will be well, but I have a sneaky suspicion there'll be some more logging and Tuning needed yet. Nothing ever runs smoothly! Cheers guys. Steve. P.S. Old ECU will be going for repair and kept as spare, I'll post up what was wrong when its done. Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.