I'm getting close to trying to do some tuning on my '91 L03, and I'm trying to get an understanding on the various bin tables.

One thing I'm confused about is how the manifold air temp (MAT) is used by the ECM. Because the density and thus O2 content of air varies widely with its temperature I was expecting to see some fuel tables that were MAT related.

However for the regular fueling it looks like my $62 mask/16136965 ECM only has the simple table below, which is far as I can tell only comes into play when the intake air temperature is really hot.

Base Pulse Constant Multiplier
Deg.C Multiplier
110 1.17
80 1.17
63 1.06
48 1.00

Is the fuel rate adjustment for MAT just done "behind the scenes" by the ECM?

How well does it work in WOT mode, will it keep the AFR the same on a hot summer day as on a cold winter night or is it best to have a "summer chip" and a "winter chip"?

Thanks,

Paul T.

 

I've never actualy had to mess with those tables. Hot or cold days, once the car is warmed up, my intake temps don't vary THAT much. I run the same tune year round without issues. You have a diffrent ECM than I have though. I would have to look through the code for that mask, to see what it is actualy doing with that table.

--john

 

IIRC, the MAT is really only used in the knock routine. With the stock TBI setups, the manifold and air is pre-heated so the incoming air is fairly constant.

 

My stock air intake on my '91 L03/305 pulls cold air from a snorkel at the front of the engine compartment just under the hood leading edge. There is an exhaust manifold air heater assembly but I'm pretty sure that's only for cold startup, I believe it closes off when the engine is at operating temperature.

So even with the engine fully warmed up it would seem the engine would see a pretty different big difference in MAT/IAT between a 95 degree summer day and a 30 degree winter night.

While in closed loop I can see how the BLM's would adjust for this, but it would seem that in WOT the ECM would have to adjust the fueling for this difference in IAT, is it true that this adjustment is not being done at WOT?

Paul T.