OK I finally found my computer which is an MD21. I just bought a mass air harness and A9L computer. Which computer should I use for the convertion. My MD21 or A9L.

 

If you are converting, you can't use the stock computer, it isn't mass air. What engine and transmission do you have?

 

351 w and ZF 5 speed.... Ive got the harness and computer for a 5 speed but im not sure which size injecters to get or how big of mass air. Is the a 5 O upper intake that will bolt up to the truck intake. I want to use a single throttle boty if possible. Also do I have to add a second o2 sensor and different distributor..

 

The A9L utilizes two O2 sensors, I would recommond using both of them. If this is a stock application (with some bolt-ons) then you should be fine with the 19's and stock air meter.
The runners on a stang intake are different so you'll need to get both the upper and lower.
You don't need to change the dist.

 

well I built a 94 roller motor added a mild cam and windsor jr heads. I have about 600 miles on it. I pulled the plugs and every one of them look as new as the day I gapped them. I lack power from what my old engine had. I was wondering if it was because of the small injectors or if I needed mass air. Im not sure whats all involved with the convertion but I have done alot of reserch. where should I put the second sensor. From what I have read all I need to do is replace computer and harness direct plug in, add an o2 sensor, Built a Y pipe for mass air or change to a mustang intake and throttle body, and thats it. how hard can it be. someone who has done this convertion ,,,,,, PLEASE SHOW ME THE LIGHT.... I would also like to change the pathetic little cam with something that works better with the heads I have. however too much cam in a crewcab can be a bad thing. Ive heard that you can make alot of torque with smaller setups but im not sure what the compare small too.

 

Being that your combo is not "stock", I'd recommend some type of aftermarket tuning for the parts you have....it will help tie everything together and allow it to perform better...especially for speed density.

On a sidenote, I average about 13+ psi of boost, Ford Powerstroke intercooler, 42lb injectors, long tube headers, 3" mandrel bent exhaust, dual fuel pump tank trigger, 255lph inline pump and a few other things, and I'm still utilizing the stock, speed density, PCM. I do have tuning software that allows me to make changes to keep it all together though. I did a mass air conversion on my rig and it still needed tuning to dial everything in....mass air is NOT a plug&play, set it and forget it, system until it has been tuned properly (for applications that are not stock).
However, I did notice slightly better throttle response with the mass air setup/tune I was running, and it was easier to tune one the transfer function was dialed in.