Im having a problem with 2 500 efis i just dropped in. The motors seem to run good but when i pull the plugs both number 3 cylinders have not fired. I replaced caps rotors plugs etc. plugs are fireing but plug has no raw gas smell so its not getting fuel. The plugs are on the injectors so Im thinking the problem is in the ecus. I want to get a good scanner but not sure which one would be the best for my problem. Any advice would be appreciated

Those are batch fire so a single cylinder will not fail because of the ECU. When you say they haven't fired, are they wet or are they showing no sign of combustion in the cylinder?

There was a merc scanner on eBay for 275 early this week

After running for a minute or so 7 plugs show discoloration like the should and the number 3 is as white and dry as when i put it in. The plug is fireing but seems there is no fuel to the cylinder. Compression tested the cylinder at 155 lbs. bad injector?

Have ya checked the resistance thru the inj with an ohm meter? Not sure what it should be, but should be real close to what the others read.

just swap injector with the one next to is see if it moves .

go to a you pull it bone yard,,look for a older 3100 v6 or 3800 v6 ands cut a few of the injector plugs off,,wire it to a 9v battery and test the injector,,put your hand on it to see if you can feel it clicking..you may just have a blocked screan on top of the injector..if thats the case then pull all 16 and spend the few hundred dollars to have them cleaned and tested..a few hundred spent now will give you years of service..

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Investing in a fuel injector quick probe may makes things a little easier.
How To Check Fuel Injectors - YouTube

It does sound like a bad injector, maybe just clogged. If you do get a way to put power to them just pulse it, never hold power on for more than a few seconds. If it is clogged as said before, you should send them all out for cleaning and make sure you change both fuel filters.

Strange problem you have that is affecting both motors at the same time/same spot ???? I can see one injector being bad, but the injector in the same spot on both motors??? With that kind of luck you need to buy lottery tickets !!!! Try swapping parts side to side and see if the problems move around.