Are there EMP like weapons that can shut down weapons large and small that rely on power

The Lathe Worlds, a Dark Heresy supplement introduce "Haywire" weapons, which can completely shut down electronic spirits by rolling on the table. It's the closest thing to EMP that currently exists in the game. Presumably their absence can be explained by the lack of atomic weapons (we have lances now), technology being simplified with built in consecrated safeguards, or Tech-spirits actually being real and unaffected by EMP.

Haywire weapons also exist in Black Crusade, and there is an item called an "EMP grenade" in the Deathwatch core book (whose effect is 'Haywire (3)').

Personally, I don't believe that the whole "Haywire" concept is the same as actual EMPs, since the Haywire effect is much more similar to something like DnD's antimagic field, rather than shutting down powered machines and causing them to restart. Personally, in my mind I've always explained away the lack of EMP weapons by imagining that most races are so well protected from such things that there's no real point in using them - tyranid biotech, Ork diesel engines, Eldar wraithbone psy-tech, insanely robust STC designs, and so on.

So yeah, Haywire is what's there.

I would say that most technology used is either too simple or too advanced to be affected by simple Electro-Magnetic Fields.

After all, we are talking about extremely advanced spaceships and vehicles that pass through things literally made out of chaos, not to mention cosmic radiation and solar flares, let alone the myriad of effects on the battlefield, whether it's lightning-guns or straight-out atomics.

The interpretation as to exactly what "Haywire" is, is up to you. I prefer to think of it as a combined EMP-like scrapcode-inducive signal device that burns out and fries on use, confusing advanced systems by overloading them with information, just straight-up hacking them and filling them with scrapcode, or otherwise cause electrical failures and strangenesses around them.

So.. No to "simple" EMPs, but Yes to Haywire Grenades, Rockets and weapons.

The Arch Heretek can gain a Talent called Luminen Desecration where they generate a 'violent techsorcism pulse' which can disable technology that it hits.

This is the closest I've seen to an EMP that I've seen aside from the already mentioned haywire grenades.

Haywire comes across as a more broadband form of EMP. It shuts down any powered technology. That does not effect anything that does not use power, such as SP, most flame, and most grenade weapons. The only exception I have ruled is Necron tech (resistant, reduce effect by one category). The Techxorcist Gun/Cannon from the Lost Dataslate or Haywire grenades are your best bets for this. My RT has a small group of trained soldiers who rely on non-powered equipment and biotech using such weapons. They are remarkably effective on most high tech foes. The Guns do pretty good damage (1d10+4 E Pen 4) and can fire 3 round bursts. Just remeber that if you are too close you are effected as well. Of course, dropping a haywire grenade at your own feet makes power weapons far less effective against you, as well as crippling heavily augmented melee attackers.

I dunno about that. The rules in BC state that "all actions utilizing technology" fail, so technically you won't be able to see through your glasses, buckle your belt, walk while wearing shoes, and the list goes on.

Taking things a little more seriously, though, the rules further specify that "any ranged weapon without the Primitive quality" is affected, so SP weapons and Flamers should not work, barring house rules.

I only checked BC, though, so newer rules may differ.

Disruption Macrobatteries are "EMP" shooting guns.
You could use the rules for it if you want to build a bomb.

I run a Rogue Trader game with heavy Ad Mech presence, so I tend to pull from Dark Heresy and Rogue Trader. I am at work, so don't have my books but I don't remember the "any ranged weapon without the Primative quality". I tend to think of Haywire as energy disruption/absorbtion weapons. I don't see them as directly effecting purely chemical reactions, so allow weapons that only use them. Note, this does not include chain weapons as the motors use some form of electrical ignition. I will have to check it when I get home tomorrow morning.

Reviewed my books this afternoon when I got up. RT has haywire grenades that effect electrical/powered technology. The other systems use the 'not primative weapons' ruling. Note that at higher levels of effect chain and powered weapons become unpowered as well. As I run a RT game, and I used those ruels as my first example, I am going to keep it according to the RT rules way in my game. It makes more sense based on how haywire seems to work. I find the idea that a black powder gun works but a well build revolver doesn't a little too strange.