<font face="Verdana, Arial" size="2">Originally posted by Glenn91L98GTA:
Good information Bruce. I am noticing that the MAT sensor seems to handled very differently from ECM to ECM.

On my SD L98, I noticed that the MAT has a very real effect on the fuel mixture (injector pulse widths) and the operation of the EGR. But, I have never noticed any effect on my Spark Advance. Other than the typical tables (Spark Advance, Coolant, PE and Highway Mode), the only other thing that affects the Spark Advance on the 7730 appears to be that horrible "Octane Retard" routine, which will retard the spark for almost the entire time the engine is running, until your restart the engine and reset it.

However, I WISH that I did have some control of the Spark Advance based on MAT, especially for WOT. I am noticing that with the recent spell of hot weather where I live, that I had to back off my spark advance by a couple of degrees or I would encounter audible ping. I think that adding a "routine" to the source code to adjust the spark advance for WOT based on MAT readings would allow me to further tune my eprom so I could use the same settings all year round. Instead of my current method of having to re-program the eprom for "winter" and "summer" so I could have my spark advance optimized for WOT.</font>

<font face="Verdana, Arial" size="2">Originally posted by Grumpy:


In review, I have a GN with the 148 ecm.
I relocated the ATS (Air temp sensor) to the upper plenum, but it is not thermally isolated from the manifold, so it's temp is reflective of both engine and air temp.. The amazing part, was how much I could change the timing without changing the coolant temp., yet being able to change may MAT temp.
If I am reading this right the basic observation of this test was that by changing the timing a bit the heat that was generated/lost was transferd into the manifold (up to the MAT) & would be substantial enough to change the Engine efficiency, but the T-stat would keep the water temp constant (Radiator efficiency not being overcome)

In the past few days I was able to do some serious highway mode testing. ie logged 1,000 miles of interstate driving, in two long sessions.

The 10d change in temp vs 2d timing at **LOW** load conditions is very real. The trick is channging the timing to get lower MAT temps..
At one point I was making 4d timing changes with no change in TPS, but yet dropping MAT, and Injector Pulse Widths.
does this imply that by changing the timing by a small amount was effectively altering the engine efficiency (I think so) & this was not only evidenced by the lower MAT's, same throttle position & of course, increased mpg? if this is a correct assumption, this is a visual tool for Tuning in timing (for some applications) where you not only can look @ velocity : tps : IOT but also MAT's as another indication of efficiency.


Heat soak from Freeway and General driving are two very different items. Under a given set of circumstances, MAT from around town would get to about 110d, and from a freeway blast be 130d.

I am not following, my MAT is also in the manifold & when I sit in the staging lanes (or sit in traffic) the MAT goes up, but by the time I an 1/2 way down the track (1/8 mile or so), the temps are dropping, Assumably due to nice clean air coming from the front of the car (home made cold air package). This is @ WOT, compared to sitting in the staging lanes, @ idle. If i am following you right, yours is doing the opposite (IC efficiency droping, due to higher load (more air)). OR, is this a heat sinking issue with the manifold designs? OR both

I think just as important is the implication of efficiency of the engine. You are forced induction, but also intercooled, are your IAT's going up due to IC efficiencies & mine going down cause of "clean air", I wonder?

Again, equally interesting, if the ECM is looking @ the MAT to base timing or Fueling decisions on then I could be messing with the calibration (making it worse) by using cold air if it affects the timeing or IOT calibraions in an adverse way.


Changing brands of fuel could generate a 2d timing change for best MPG. Changing timing takes about 10 mins for the MAT to stabilize from the new operating temps..

Yes, While you need to add timing for low load hot conditions, you need to take some timing out for high MAT high load conditions.

Getting the timing just right netted a little over 26 MPG at 75-80 MPH. Was running a PW of 2.8 to 3.2 and more at 2.8 then 3.2. I run highway mode AFR, none feedbeack so that was a given. Also, late MAF that is temp compensated.

In one past calibration, I was taking .75d timing out per 10dF in the WOT area, with the *base* setting starting at 32dF.

Youe mileage will vary, and the above numbers are what were/are working for me.

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<font face="Verdana, Arial" size="2">Originally posted by Glenn91L98GTA:
Good information Bruce. I am noticing that the MAT sensor seems to handled very differently from ECM to ECM.

On my SD L98, I noticed that the MAT has a very real effect on the fuel mixture (injector pulse widths) and the operation of the EGR.

Hmmmmmmmm, this adds another level of complexity to it.


But, I have never noticed any effect on my Spark Advance. Other than the typical tables (Spark Advance, Coolant, PE and Highway Mode), the only other thing that affects the Spark Advance on the 7730 appears to be that horrible "Octane Retard" routine, which will retard the spark for almost the entire time the engine is running, until your restart the engine and reset it.

However, I WISH that I did have some control of the Spark Advance based on MAT, especially for WOT.

Makes you think that if you could change the hard code to look @ MAT (or better yet IAT) instead of coolant, (or in addition to), if this would not strengthen the already strong ability of this setup.


I am noticing that with the recent spell of hot weather where I live, that I had to back off my spark advance by a couple of degrees or I would encounter audible ping.
If I am following Grumpy right, maybe using this observation to re-tune in your timing table, would allow the ability to run less timing when the Amb air is cooler so when it warms up it is not so close to that threshold that it actually pings, w/o altering the efficiency or HP of the engine during the cooler periods.

I think that adding a "routine" to the source code to adjust the spark advance for WOT based on MAT readings would allow me to further tune my eprom so I could use the same settings all year round.
This sounds like the best of both worlds

Instead of my current method of having to re-program the eprom for "winter" and "summer" so I could have my spark advance optimized for WOT.</font>

<font face="Verdana, Arial" size="2">Originally posted by Bobalos:
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<font face="Verdana, Arial" size="2">Originally posted by Grumpy:
Light load vs heavy load, was what I looking at, not just heat soaking the engine. Heat soak from staging is just a matter of fans, and under hood venting.

When you post as you did you make it hard to reply too.

Yes, I was able to change the engine effeciency enough to affect a change in MAT without a coolant change.

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<font face="Verdana, Arial" size="2">Originally posted by Grumpy:
That was why I was specific about which ecm.
What is funny is that in the 148 there is a MAT bias and timing table, that are 0'd out, and in the N/A 148 applications they use it.
thou both use the MAT in the air calcs...

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<font face="Verdana, Arial" size="2">Originally posted by Glenn91L98GTA:
I was more fascinated by the way the 148 operates based on the IAT/MAT compared to the 7730. It REALLY makes me want to "dive into" other hacs/disassemblies and see how they handle certain driving conditions based on certain sensor readings.

For 165 guys, they may want to see if they could combine the way the MAT works on both the 7730 and 148 to provide additional "correction". However the $6E is so damn tight, it would be like trying to have Fi-Fi Boom-Boom Toulouse trying to wear a training bra. I wonder if it possible to take some of the routines out of the ROM such as you are doing with the 148 and use 256s (for the additional 16K) on 165s?</font>