Ok here it goes (a long one but please stay with me!)

I did a roller swap into my 1988 5.0 F250. I bought a complete long block roller setup with gt40P heads. The cam that they installed was a B-Cam (I wanted the E-Cam, Ohh Well). I installed the engine and used all of my accessories. I left the knock sensor disconnected because there wasn't a port drilled in my new engine.

I've been troubleshooting this for about 2 months and It's getting closer but still not quite right. The rig idle's ok but a little rough (like a large cam) the problem is that it feels like it is missing and sputtering until I reach about 3000 RPM's then it runs like a raped ape. It feel's like I have about two cylinders not firing until I hit 3000.

I've checked wires, plugs, gaps, compression, computer codes, vacuum leaks, and connections to no avail. The only thing that I had a problem with was vacuum. I have 11 pounds at idle. This seems low but I was told with the B-cam to expect low vacuum. I've tried both systems (mass air and Speed density) and the mass air system definatley runs better but not right. I've removed the intakes and had then plained to no avail. No change in vacuum. I've even hooked a smoke machine up to it and found no leaks.

I'm thinking that maybe with the low vacuum that something isn't running right (remember with the mass air there is no Map sensor used for vacuum). I'm thinking that maybe I should install a different cam. What do you all think?

 

I would say to get a new chip burned for your combo. Even a mass air system can't work very good with only 11 inches of vacuum.
Roger Lane