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So what was your answer to a dead MFI Injector relay?

Vince

Well-known member
Joined
Jan 31, 2015
Messages
72
Location
Puget Sound, WA
Yeah, it has just happened to me, and of course it is a long out of production part.
Arte the Eclipse relays compatible? Those even cross to a new Standard something ,RY- something at $120+.
I'm not afraid of the price as much as not wanting to spend the cash and not be compatible.
What has worked for you folks?
Technically, it is nothing more than a self latching relay, which I can buy generic and wire in myself, but a plug and play option would be nice.
Any words of wisdom?
Thanks!
 

toybreaker

iconoclast
Joined
Apr 30, 2006
Messages
3,581
Allan,
...you are correct that it's basically two relays in the housing, but there's actually three modes of operation.
There's a leg that's hot 24/7 with starter engaged, and then the normal "run" leg. There's also a "prime" function on the fuel pump side all controlled by the ecu.

This system has a few excellent safeguards built into it

Co-located in the same housing is the engine power side of things, on it;s own dedicated coil

... so it's not quite as simple as tossing an aftermarket relay, if you want to keep all the factory functions and safeguards intact

That's good lookin out on posting the link to an aftermarket unit, but I would try and keep things as factory as possible on a normal build. If you're doing a big power build ( or want the factory system to live forever ), it's not a bad idea to rewire the system at the back of the car and use the factory relay ( and wiring ) to trigger your aftermarket relay.

That's how I've done it since the beginning of time, as the current will be handled by the aftermarket relay.
By taking the high current loading out of the factory mpi relay and delegating it to a dedicated heavy duty relay in the trunk, It keeps things simple, reliable, and easy to troubleshoot down the road.
Hella makes a bad ass 70 amp relay with an anti fly back diode already installed from the get go. I've installed hundreds of these, and have yet to see one fail, ( and many of them are on pretty stout builds with huge pumps )

Vince,
I've written many posts over the years on how to troubleshoot this system (and rewire the pump correctly )
... I don't have time to search, but if you enter relay into the search field, and my user name into the posted by field, you'll find many posts on how the system operates and how to troubleshoot things

I can probably dig up a known good used unit and get it shipped out, but it will be a few days as I'm on the road a lot. The factory units last basically forever if the rest of the system is stock and in working order.
It will also last forever on a correctly rewired system

Good luck, and hope you get this sorted!
 
Last edited:

Vince

Well-known member
Joined
Jan 31, 2015
Messages
72
Location
Puget Sound, WA
Thanks all,

I just found a replacement on rockauto. Might as well do it right.

Peace!
Vince
 

VR6Eater

Well-known member
Joined
Jan 22, 2013
Messages
87
Location
Bristol, WI
Vince

Since you were messing around with this, what was your voltage coming out of the MPI relay going to the fuel pump? Mines rewired to an aftermarket relay and have changed the MPI thinking it was bad. I only get a coulple volts to and figured it should be 12. Now thinking ecu has something wrong with it.
 
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