Engine bay temperature data

[sjf911]

Since going to a full bay intercooler I have been plagued with hot restart heat soak issues (lean running with misfire after restart for a number of minutes). There has been debate on the MS forums about whether this issue is related to sensor heat soak or fuel injector dynamic changes. So, this winter, using an add on IOx box, I wired in additional temperature sensors (thermistors) placed in front of the fan, in the IC core, on a fuel injector, and on the right hand fuel rail. This is in addition to a 3.2 CHT sensor, a Bosch CLT sensor in the engine breather cover, 2 GM open air element IAT sensors pre and post IC (the main IAT sensor), a Ford MAF sensor with an integrated IAT sensor (post IC), and a double ambient external temperature sensor (one for full time logging, the other switched with the main IAT sensor). I wired a relay to switch between one of the ambient sensors and the GM sensor post IC based on after start time and engine coolant temperature to cope temporarily.




The top photo shows the primary IAT sensor (MAT) in a weld on bung on the piping to the throttle body. The lower pulls back and shows the MAF (Ford blade style) in the outflow from the IC and the IC core sensor wire laying over the IC.




The top photo is the homemade double sensor shown installed in the lower photo behind the bumper.




The "ambient" engine bay temperature sensor and pre-IC IAT sensor (bung on the "up pipe").



There are 2 sensors here, one on the rail and the other on the injector shown before wrapping.

[sjf911]

I was finally able to get a first log yesterday after having to wait about 30 minutes after shut down picking up my son from baseball practice. It was a relatively short drive home at no more than 40mph.



Compressed view of the entire drive.



This shows the Ford MAF IAT reading on the left and the difference between the Ford IAT and external ambient on the right.



This is the Ford IAT again on the left with the true IAT signal on right. You can see where the relay switches between external and internal sensors at 5 minutes.



The left graph shows the difference between the primary signal and external ambient while the right shows the difference between the MAF IAT sensor and external. Again, the sudden change at 5 minutes is the relay switching between external and internal sensors.



This is the IC core temperature on the left with the MAF IAT on the right.



Engine bay (pre-fan) on the left with the difference between engine bay and external ambient on the right.


So, it looks like the IC core and MAF IAT cool down relatively quickly and are at about ambient between 4 and 5 minutes. The MAT sensor, on the other hand, is still substantially warmer than ambient when we finally see the real signal at 5 minutes and it has not reached thermal equilibrium by the time the log ends at about 12 minutes.

The MAT sensor is a GM open element sensor set in a bung on the throttle body adapter so there is a lot of metal without much airflow. The Ford MAF, on the other hand, has a much smaller sensor that sits more centrally in the tubing with much less metal directly around it. Also, the tubing that the Ford sensor sits in is one piece with the outflow side of the IC so is cooled, in effect, by the IC.