overpressurizing tanks

I have a strange problem we can't find the answer to and was wondering if anyone on here could help. I have a 2005 Star with a MBE4000. The problem (aside from the fact I bought this thing in the first place) is that it is overpressurizing the tanks so fuel pours out whatever side the cap is tightest on. Yes the vents are open. There is a second problem as well. When you first start the truck it will run fine for about 4 seconds and then stall. You need to ether it to get it going again. we discover that if you floor it when you start it up it will run well for about 4 seconds and then sputter for about 5 and then run great after that.

Here is what it isn't:
fuel pump- we changed it and no difference (we thought pump because our other truck had a fuel issue where it would run great for 10 minutes and then stall and need 9million cans of ether to get it going even with that stupid aftermarket primer we have)

air leaks in the fuel system- we have pressurized the tank and zippo for leaks

check valve- it works fine and the fact it fires right up and keeps running if you floor it tells me it isn't the problem.

crank and or cam position sensor- we took both out and cleaned them and no difference. Also the fact it runs great once it gets a big enough gulp of fuel tells me they aren't the problem.

fuel filter(s)- historically a incorrectly installed or aftermarket filter has caused a million problems but we have changed them and zippo.

Is there any chance that a bad injector could be allowing feedback to the tank and overpressurizing it? We are running out of ideas and diagnostic theories. One other note is that it is returning a tremendous amount of air. Way more than my other truck. How the heck can it return that amount of air?

If anyone has ideas please let me know.

 

Yeah, what you guys are saying makes sense. We are fairly sure that cyl 2 is the culprit. We'll pull it off and see if it's black. I assume the "copper sleeve" the the one that the injector sits in?

 

I don't but my guy is quite capable. Turn out you were bang on. Injector on #5 is blacker than a black boot put into a black blender and mixed with black paint. I found a complete kit from Waterous so I guess that is what we'll do. Thanks a lot guys. We were really banging our heads against the wall on this one.