changing out Main Computer

[dschallmo98expo]

I currently have a 98 expo. I installed a new 99-01 new 5.4L V8 with the goal of supercharging the engine.

Now before I do that I want to make sure the motor is broke in and working correctly. Here is the issue I am having.

I am getting a knock or spark Knock after running the truck after an Hour. (from startup to one hour the truck is awesome and runs great no noise or issues) After 1 hour there is a Knock. It sounds like the computer is programed to do long term fuel trimming and making the engine run lean.

I purchased a SCT Tuner and the software to directly program the computer. I have had some tuning however none of the tuning has addressed this correctly.

My thinking is there must be something different from a 98 computer and a 99-01 computer. If I could get a default tune I could compare, However since I don't, I was wondering if I put in a computer from a 2000 into my 98 with the exisiting program in it would the truck start and run? Would I also need the Keys and ignition tumbler? Would I also need the instrument panel as well?

If any of you would know what to change in the computer program I could change that and solve the problem.

As far as the supercharger, when this problem is resolved then the supercharger goes on. I now have acquired all the parts from a Lightning to install. YEA!!!!

thanks

 

[stamp11127]

Your issue isn't with the pcm. The engine is in closed loop for an hour before the problem arises. If it was the pcm why wouldn't you have the knock once it reached operating temp instead of waiting an hour?

 

[dschallmo98expo]

Temp does not change the performance in this instance. I think it is somewhere in the fuel table where fuel is trimmed based on time. 0,40,60,80,120,240. The values change around 60.

However I do know that the MAS also plays a role in this as well. So without a owning a dyno I'm having to do this by feel ( for lack of better words).

So I guess if I put it in open loop, I could datalog it and see where the issue may be?

 

[stamp11127]

What information are you using that states the LTFT is based on time? Time has nothing to do with air/fuel ratio according to the info I have available once the system is in closed loop. The pcm uses the O2 sensors to calculate the required air/fuel ratio.