on the monorail i have to defuse the bomb but once ive defused it, the monorail still blows up

You've got to learn to stop worrying, and love it.

I played this part yestarday, and had look on google for the solution.

I assume you know already who the spy is now, so basically all you have to do is NOT tell him you have found out any clues, then wait for just after 1:00am at the abandoned radio tower, then sneak in, listen & you will hear the guy on the radio talking about the bomb. if you go into the tower & hear nothing, you have done it wrong.

:rofl:

did you just come across the bomb, or did you get there via the questline?

I came about this quest all kinds of wacky ways. First, I ran into the spy just exploring the terminal building and took his quest to place the bomb with no intention of really doing it. I figured I could just turn him in. I didn't want to piss off the Legion until after I talked to Caesar though so I held off on it. After I went to the Fort and got into the bunker, killed Benny and told Caesar I'm not working for him I proceeded to kill every Legion at Cottonwood Cove and hence they hate me now. I went back to McCarren and the bomb wasn't in the trash. The quest marker was there but I couldn't get it and the NCR wouldn't trust me enough to do the mission (I decided to kill the mercs at Jacobstown because I wanted their gear) so I did a couple NCR missions to get in their good graces and then got the mission to find the spy. I went to the tower, heard the spy talk, though he seemed to just mention NCR positions and such and not the bomb but maybe I just engaged him too fast. Long story longer, I reported him, was told to run to the monorail but had no chance of defusing the bomb. The monorail was scripted to take off and blow up as soon as I opened the door. Still got my quest reward and gained NRC fame, so it seems clear you can't defuse the bomb. It's a scripted event.

You have to go straight to the monorail to be able to disarm the bomb.

Exactly. You can't waste time killing the spy or telling Colonel Hsu. As soon as you hear about the bomb, you have to run to the monorail and disarm it.

Ah, that would explain why I couldn't do it.

Oh, well, I'm not a huge fan of the NRC anyway

as soon as you hear the guy mention the bomb on the radio, run to the monorail. Run straight onto the train, don't hesitate or it will leave and blow up. Once you're on it the train won't leave, so you have plenty of time to find and defuse the bomb.

Quicksave or something before you enter the area with the monorail so if u go to far and it leaves u can reload. Once on the train on the side farthest away from where you entered there is an air vent. Walk up it and activiate it to defuse the bomb. I cant remember exactly if you need explosive skill or not. Doubt it.

I eavesdropped at the right place, stairwell by the door. As soon as the objective updated U ran and informed Hsu. After dialogue options with Hsu I immediately ran to monorail and defused bomb. Bomb diffused.

If you go right from listening to the spy (and killing him) in the tower to the monorail, you can defuse the bomb and save the train. If you go to Hsu first, and let him tell you to save the train, you CAN defuse the bomb, but it blows up anyway (glitch in the game I think). Anyway, go right from the tower to the monorail and you should be able to save the train.

ahh thanks i see the problem via this thread and vault wiki i confronted him instead of listening to his radio convo and killed him, which means even if i defuse the bomb it still goes off