Can anyone tell me what this is?

A

acerbus80

New member
First off the technical stuff.

1976 Scout II
4x4
automatic transmission
304 v8
Holley 2 barrel carb

don't know diddly about the ignition, fuel, or brake stuff.

Anyway I've been having starting problems lately, and after tracing wires out and doing some basic troubleshooting I've come to the conclusion that I have no idea what this thing is or does. There are no markings on it other than trw, and it seems to be a relay with some vacuum tubes on it, but nothing was connected to them. It's mounted on the firewall on the driver's side.

When ever starting the Scout this little box makes a ticking noise like the relay engaging.

The Scout will actually start and run fine without it.

Outside


Plug


The guts


My friend thinks it's something aftermarket that's not needed, and I'm curious if it serves any distinguishable purpose or if it's something that can be eliminated.
 
It's the dtm(decel throttle modulator) relay box used for smog emission purposes. It uses a signal from the distributor to open/close a vacuum source going through it to a diaphragm on the side of the carb. Upon deceleration this vacuum diaphragm pushes open the throttle until the engine drops down around 1500 rpm and then releases to fully close the throttle. By doing this it helps prevent an overly Rich condition when slowing down.
 
Thanks for the info.

So will it help improve engine performance if I get it all hooked up again, or is it something that can be done without?
 
It doesn't necessarily improve performance but it does improve drive-ability especially with manual transmissions. With the throttle being slowed down by the modulator the vehicle isn't as jerky upon accel/decel. But yes you can do without and most do.
 
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