Rotting Fuel Filler Neck on '02 SE

[NHmaxima]

I went to the local Nissan dealer today to have a knock sensor code problem diagnosed (local mechanic said ECM was bad because voltage from ECM to sensor dropped off as engine warmed up, so I took it to the dealer). Nissan tech at dealership found evap leak due to rotten/rusted fuel filler neck & said replacing the neck should the clear knock sensor code. Huh? These seem like two very different problems -- if the voltage from the ECM drops off as the engine warms, that's going to happen whether I have a new fuel filler neck or not, right?
Modified by NHmaxima at 5:27 PM 7/21/2008

[NHmaxima]

Follow-up to earlier post: The Nissan tech @ the dealer says voltage drop from ECM to knock sensor is connected to fuel filler neck problem. He says ECM is dropping voltage to sensor because evap leak is fooling the system. Sound legit? Or bogus?

[johnnyd6404]

Sounds possible I threw an evap code, I dont rember which one but it was from a bad gas cap so I guess it may be related.

[allensteiner]

i doubt it. you can have multiple codes at once but it shouldn't interfere with the rest of the sensors. the voltage drop might be caused by something els or...it might be normal. before the engine is up to operating temp there is more knocking/pinging to be heard as the oil has not lubricated everything thorougly yet - oil has it's own optimal temp for lubing. after the eng is up to temp the voltage may drop slightly because the ks should've heard any signs of detonation or what not.

someone else chip in because i'm just guessing here.

btw got a pic of the rotten filler neck? might be an easy fix but need to see first.