I decided to put a longer cable on the manifold air temp sensor and move it around to see if it changes how my 86 with a 383 runs.
how important is it?
i figure that if it is heat soaked
in the manifold, it would add extra fuel to assist in keeping the engine cool.
On the other hand, when the engibe is cold, does it influence the ecm’s fuel ratio into richer to compensate for a cold engine and cold air?
when in closed loop, the cts tells the ecm the engine is hot, does the mat sensor become insignificant? Or, does it fine tune the mixture as a supplemental sensor?
any body with an opinion?

 

The Manifold Air Temp sensor is fairly important and the ECM refers to it quite often. It would be great to move it someplace where it doesn't get heated soaked by the engine's heat. I frequently tell people that the Engine in Open Loop simply uses charts of data but in fact it is referring to the MAT sensor frequently even in Open Loop. It uses both the CTS for engine temperature and the MAT for Incoming Combustion Air temperature and in extreme environments they are frequently different. The Coolant Temperature Sensor is the primary but the MAT is still important in most fueling decisions.

For years they have told us that moving the MAT to someplace not made of metal could help make more power. If it accurately sensed the temperatures and cooler numbers were fed into the ECM the engine could make more power. I have thought about putting the MAT on the tube that connects the MAF to the Air Filter where it would be installed in a non-metallic surface and read the AIR temperature more accurately helping the engine make the most power it can.

The Manifold Air Temperature sensor is important to the ECM of your Corvette.

Relocate it to make more power if you wish but I would not remove it from the system. I have a MAT on my Holley EFI system and it is mounted in the Factory L88 hood itself in the incoming airflow and it shows much cooler air using the L88's Cold Air Intake. The way I mounted it there is little chance of heat soaking the components. It sees the incoming Air temperature and can adjust for it more accurately than just referring to the coolant temperature which simply tells you how HOT the coolant is. The incoming air temperature is very important to the ECM as when your Corvette is warmed up let's say in Upstate NY to have it know the incoming air temperature so it can adjust the fuel ratio compensating for the extra cold incoming air. The warmer the air the less fuel it needs. I would go so far as saying the Manifold Air Temperature sensor is an "Important Component" in your Corvettes EFI system. It in fact does "Fine Tune" the fuel mixture based on the "ambient" temperature not the engine's cooling system temperature.
I hope that this helps clear it up a little for you!

Merry Christmas to you and your families!

 

It was out next to the radiator on a bracket, then i had it up by the small water tube at the back of the engine near the heater hose.
Now it is in the free air just forward of the coolant tank.
it seems to like the ambient free air location next to the radiator the best.
just my 2cents.
but up by the heater hose, the gas mileage was up 1.2 mpg.

 

In 86 and 87-88 L98 maf cars, the MAT sensor is only used functionally as an EGR enabling condition (86: MAT > 30 is needed to enable EGR. This was increased to MAT > 46 for 87-88). The MAT signal is also used for diagnostic purposes in order to set Code 23 (MAT low < 4) and Code 25 (MAT high > 243) which also impacts EGR. If a MAT failure is detected, the default value of 29 will be used, which is just below the EGR enable threshold. The MAT sensor has no influence on the fueling of 1986 and 1987-1988 L98 maf cars. 1989 is a bit different in this regard, but I won't get into all of the details here.

Installing the MAT sensor where it is subject to ambient air temperature will effectively disable the EGR at lower temperatures and accomplish nothing else.

Note: the MAT a/d value is inverted prior to being stored and the scaling is not linear, so a lookup table is required to scale the raw inverse a/d value to an actual temperature. If I'm reading the lookup table properly, a raw value of 30 is about equal to 45 °C or about 113 °F.

Update: On second thought, I think the table that I have shown includes a 40 °C offset, even though it is not explicitly commented that way. With the 40 °C offset subtracted from the output value, a raw value of 30 would be about equal to 5 °C or about 41 °F. For 87-88 cars, a raw value of 46 would be about 15 °C or about 59 °F

Would be nice to see some raw MAT a/d data along with respective data scaled in °C to compare against coolant temperature in °C on a cold, not running engine as a sanity check for the MAT temperature conversion.

2nd Note: I'm not using the factory MAT in my own car, so I cannot easily test and confirm the MAT inverse a/d value vs actual temperature to confirm the accuracy of the lookup table. Instead of the factory MAT, I use the IAT sensor that is integrated with my analog slot-style MAF sensor. Since the IAT has different resistance compared to the MAT, it requires its own unique look up table to make sense of the inverse a/d values along with modified programming/tuning. The IAT responds to temperature changes much faster than the MAT.

Later speed density L98s (90-91) do make some use of the MAT sensor, since a MAP sensor alone is not sufficient to determine air density.

MAT table:



Result looks like this:



Think this is more like it:


After reviewing some old cold start data that I happened to have available, the inadmat-40 table shows good correlation with respect to the coolant temperature from a cold start.

https://datazap.me/u/tequilaboy/cold...&mark=19-37-49

Note: the mat signal scaling in this log (°F) was also a bit off when it was initially recorded and exported to csv, but after correction the resulting raw signal is bouncing between 60 and 61 counts. With the correct conversion to °F with the -40 ° offset applied, 60 counts is 72.5 °F and 61 counts is 73.4 °F, both very close to the 72.05 °F coolant temperature. Close enough for me.

Here is my mat scaling expressed as a 17 row table: