1971 LS5 misfire
 

Hello,I am working on a 1971 LS5 and I have a lean misfire on cylinder #8. I
have found that the wiper actuator relay is leaking vacuum through the
vent. Vacuum source is from the intake manifold fitting in the #8
runner causing cylinder 8 to have a lean misfire. I realize the vent is to release the vacuum, but should it
cause a constant vacuum leak? The top holds vacuum and the wipers/head
light doors work perfectly. TIA John

Plug the vacuum source and see if the miss goes away. That will tell you.

The miss is gone with the vacuum leak blocked. I need to know if a new relay will not leak vacuum through the vent all the time.

There should be no vacuum leak. Only time vacuum is used is to move wiper door, headlights and dash vents. Once they reach their desired position no vacuum should be used anymore.

we can't see from here where the vacuum leak is. start at the intake and move down stream checking every hose and conection you can get to. goes in to interior and back out to engine compartment. try capping everything where it comes out for headlights and wiper dor. if you still have the miss, go inside and cycle all the vacuum switches and see if miss goes away.