1989 L98 MAT sensor Function
Thread Starter
3rd Gear
Joined: Sep 2024
Posts: 3
Likes: 0
1989 L98 MAT sensor Function
Receiving Code 23. After reading several threads, it appears in the early years( before '89) the MAT only controlled the EGR valve. Also I read, there were a lot of changes to the '89 models, one of which used the MAT to help control fuel mixtures. The production date on my '89 is 10/88. Question is, would it follow the '88 models or '89 models? Thinking about relocating the MAT sensor to the air filter housing. Thoughts Please.
Melting Slicks
Joined: Jul 2005
Posts: 2,200
Likes: 302
Looking at the 6E code in Tunerpro, it seems that only the EGR is controlled by the MAT sensor. So relocating it won't really buy you anything.
Which kinda makes sense... if you have a MAF sensor that actually (as it's name indicates) measures the mass of the air coming in, that measurement already takes into account the air temperature since temperature affects air density, which affects the mass of the air coming in.
On a MAP car (90-91), where the airflow is only calculated by the ECM (and not measured), it needs the air temperature to make that calculation such that it can adjust for changes in air density over temperature. So the MAT sensor relocation can make a difference, but only if you recalibrate the tune for it. The tune takes into account the heat soaking that occurs by having a metal sensor in the plenum. If it gets relocated you need to tell the ECM that.
Which kinda makes sense... if you have a MAF sensor that actually (as it's name indicates) measures the mass of the air coming in, that measurement already takes into account the air temperature since temperature affects air density, which affects the mass of the air coming in.
On a MAP car (90-91), where the airflow is only calculated by the ECM (and not measured), it needs the air temperature to make that calculation such that it can adjust for changes in air density over temperature. So the MAT sensor relocation can make a difference, but only if you recalibrate the tune for it. The tune takes into account the heat soaking that occurs by having a metal sensor in the plenum. If it gets relocated you need to tell the ECM that.
Melting Slicks
Joined: Aug 2003
Posts: 3,389
Likes: 391
From: Lakeville MI
Are you sure its plugged in? Look for the short jumper harness behind the distributor that leads to the MAT under the plenum. Check the wiring integrity and/or resistance if you can get to the two pin weather pack connector on the jumper.
In 89 cars the MAT may also have minor influence on the startup enrichment at high temperature and the idle speed time out keep alive IAC steps. Only applies to a hot-restart situation and only a minor influence at that. These features can be optionally configured to use either the MAT or the Coolant temperature as inputs.
I don't know if I have any $6E data showing the IAC behavior at IGN off and during the keep alive period but I will see what I have.
There is no point in relocating the sensor unless you know what you're doing and can modify the code to make better use of the MAT/IAT for some other purposes.
In 89 cars the MAT may also have minor influence on the startup enrichment at high temperature and the idle speed time out keep alive IAC steps. Only applies to a hot-restart situation and only a minor influence at that. These features can be optionally configured to use either the MAT or the Coolant temperature as inputs.
I don't know if I have any $6E data showing the IAC behavior at IGN off and during the keep alive period but I will see what I have.
There is no point in relocating the sensor unless you know what you're doing and can modify the code to make better use of the MAT/IAT for some other purposes.
Last edited by tequilaboy; Sep 27, 2024 at 04:37 PM.
