jbtvt

I was poking around on my 90 while putting my dash back together and under the driver side dash, about level and to the right of the steering column I found a "fuel pump relay" (at least so it says right on it) PN 28380-44030. By my understanding, and according to all the diagrams, like at http://www.ncttora.com/fsm/1990-1995...e/fuelpump.pdf for example, power runs from the battery, through the EFI relay under the hood, and through +B to FP, whether that's in the diag box jumper or the COR, straight to the pump. Anyone know what this thing actually does??

MudHippy

It controls the speed of the fuel pump. Which is why it's also refered to as a Fuel Pump Control Relay. Allowing for high speed fuel pump operation(when the engine is cranking, at high rpm, or under heavy load), and low speed fuel pump operation(during all other engine operating conditions).

See page 5 of this pdf for more details http://autoshop101.com/forms/h22.pdf

That's my best guess anyway...though it makes no sense to me either, at the moment.

MudHippy

Well, this is interesting. It's also the same part number used for a

"AUTOMATIC DISCONNECTING DIFFERENTIAL RELAY"
http://www.toyotapartszone.com/Page_...reName=NE5535F

Does it make any more sense to you now?

jbtvt

Ah great! That must be it, I do have the ADD on this one. So nothing to do with my fuel system and I can eliminate it from my trouble shooting. Thanks.

LumpyKleier

It controls the 4-wheel drive. I found out when my '91 4Runner stopped going into 4x4. When I pushed the shift lever to engage 4High or Low, I heard a loud "CLICK" when the shift lever hit the switch on the transmission.

After removing the lower driver side dash, I engaged the shift lever repeatedly while I friend listened for the click. We quickly found the Fuel Pump Relay and could feel the click. We unplugged the relay and the truck started and ran fine. The local parts guy said Toyota used this relay for many functions unrelated to the fuel pump. Replacement is $119.54 in California.