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!
