Fuel Injection question

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Fuel Injection question

Post by peregrine67 on Sun Sep 26, 2010 6:30 pm

I'm curious to know a little bit more about how my fuel injection system works.

I believe that my double relay has gone bad and I have a plan to replace it. I'd like to know what the relay does. Does it just turn the fuel pump on and off with engine? I noticed that the other side of the relay goes to the electronic controller for the FI. Does the controller flip the relay on and off while the engine is running? perhaps to help regulate fuel pressure? or is it always on when the key is turned? Also, what else does that relay control? Just the fuel pump?

The reason I ask is suppose it blew another relay and I was too far away to just call my wife to bring the truck and tow me home. Would it be safe for me to hot wire the fuel pump past the relay and drive it home? Or does that bypass something else important? I'm not considering this as a permanent solution. Just trying to have a parachute if it happens in the future. Very Happy
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peregrine67
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Re: Fuel Injection question

Post by vwtattooed on Sun Sep 26, 2010 7:41 pm

DO NOT bypass a relay!!! relays are voltage converters,when you bypass one you are overloading the item it controls,or vice-versa not getting enough voltage to the item. relays are small enough you can keep a couple extra in the glove box.
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Re: Fuel Injection question

Post by peregrine67 on Sun Sep 26, 2010 8:21 pm

vwtattooed wrote:DO NOT bypass a relay!!! relays are voltage converters,when you bypass one you are overloading the item it controls,or vice-versa not getting enough voltage to the item.

True, I understand the general rule. I'm not considering by-passing just any relay that goes bad. But in this case the fuel pump relay goes straight to 12v when closed. So by bypassing it I wouldn't overload the fuel pump and it would get the proper voltage to work. I was more concerned about the fuel pump not shutting off if the FI controller regulated that. I wouldn't want the pressure in the rail to get too high. I believe that this is controlled exclusively by the pressure regulator but I just wanted to make sure the relay didn't also play a part.

vwtattooed wrote: relays are small enough you can keep a couple extra in the glove box.

Yes they are small but in this case they are $80 a piece. Just a little pricey to have an extra just in case, especially if 10 feet of wire would also get me home to a more permanent solution.
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