intermittant fuel to cyls.3&4

[davidhill@48]

motor is 175 merc 2.5Lxri fuel injected sn. odo87897 my problem is very intermittant but there is excellent spark to all cyls all the time.all compression the same and is good.motor runs perfect then i lose power like it has 2 fouled plugs.the dead cyls are 3,4 i will check ohms thru injector harness plug next weekend.my manual says the inner switch box can cause this problem.can i switch the inner and outer switch boxes without causing harm to any components.also anyway to check out ecu card other than replacment?anything else i should check out? i can usually get it to clear out and run perfect if i just cruise around but it wont get the hull on pad until it clears .it just goes away and then runs like nothing was everwrong.