Ford Repair: diagnostic test, contamination testing, flex fuel vehicles

Question
i have a 99 ford ranger v6 flex fuel its been at a ford garage for almost 8 weeks my question is they ran a test and received a flex fuel modual code. the garage ran the test again after about 5 weeks. I was charged 129.95 and 1.6 hrs of labor @$78 per hr both times. they said the first time they ran the test the received the flex code but the spark plugs needed to be replaced first cause they were bad. so thats reason for the second test. doese this make sense.spark plugs failing the test?(now mind you the truck was fine it was a case of bad gas) thanks john

Answer
Hello and thanks for the question...I'll try to help.
 First off, I am sooooooo lost, it's not funny. 8 weeks? What for? Are they waiting to recreate a condition? Or Christmas? I can see spark plugs causing a misfire, running rich/lean condition, but I can't see how it would affect a fuel module. I know Ford has a Fuel contamination testing kit, at least for gas. I'm not sure IF that works on the flex fuel vehicles.
Hope this helps,
Erik