2G MPI relay problem?

[wickedz]

What is the purpose of a MPi relay? What does it actually control? These are questions that im sure have been answered throughout the years. I hear it's the butt relay of the electrical system. However, I have had no luck with them it seems. There are 2 relays inside a MPi relay. What is what on the inside. When you turn the ignition key on, one automatically closes, not sure if it's suppose to do that. The other one controls the fuel pump. This is where I'm running into problem. It's not activating the fuel pump unless you manually reach over and push the connector down to make contact. Is this a sign of a bad relay (again), or is this ecu or wiring related?

I just had to replace a faulty alt, due to pushing its max amprage and blowing out I believe the MPi relay (my last relay), and also blowing out the D104 resistor on the ECU. According to ECMtuning, that resistor only blows due to a bad malfunctioning alt. We have since then, replaced the bad resistor, over looked the board, installed a good known working MPi relay, and a brand new reman alt. Now my cars fuel pump isn't kicking on at all, again unless I physically push the connection down or straight wire from the fuel pump connection near the battary to the battary. I have a walbro 255 that is not a rewire install.

Any help would be great guys. Thanks alot

 

[NHerron]

It only gets activated once the ECU detects that the CAS is outputting a signal. (Engine cranking)
Yes one of the two relays will close when the key is switched on -thats normal, it supplies power wire for all the engines' sensors.

http://www.dsmtuners.com/forums/newbie-forum/263224-mfi-mpi-relay-2.html#post152847761
http://www.dsmtuners.com/forums/newbie-forum/263224-mfi-mpi-relay.html

 

[wickedz]

The relay that YOU posted a picture of on a 97 GSX is completely different then mine. You have 2 separate relays on one bracket, and the plug is also separated. Mine is one solid connector and MPi relay is different.

 

[steve]

Click on the second link, grasshopper.

 

[NHerron]

Steve snagged my line

What do you mean physically push the connection down? Like a bad connector needing new pins?

 

[luv2rallye]

What is the purpose of a MPi relay? What does it actually control?

What "Engine" fuse and MFI (called MPI on 1g) relay provide power to on a 2g turbo:

Here is the complete list of what the 20 amp “Engine” fuse (in the engine compartment) powers on a 2g turbo:

Battery positive goes to this “Engine” fuse which then goes via a red/black (red with black stripe) wire exclusively to the MFI relay (which is controlled by ECU). From the MFI relay it goes via a red wire to the following (not in this order):

ECU (pins 12 & 25), injector resistors (and from these to injectors), front O2, rear O2, CPS (crankshaft position sensor), CAS (camshaft angle sensor), volume air flow sensor (aka MAF), idle air control motor (aka IAC), turbo waste gate solenoid valve, fuel pressure solenoid valve (this is not the FPR), evap emission purge solenoid valve, egr solenoid valve, and on the 98 & 99: evap emission vent solenoid.