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1G MPI relay

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KaLo_o

10+ Year Contributor
231
0
Mar 9, 2009
Quebec, QC_Canada
quick question about the MPI relay.....what does MPI stand for and will it prevent the ECU from booting if it goes bad? thank you!
 
Multi port injection.
And Yes I beleive that the ecu can not power if that is cooked.
It is actually like 4 relays in 1.
coil/injectors
fuel pump
And I belive it does an In out with the ECU
I would have to check the diagram again.
 
Yes, it will keep your ecu from kicking on. Its the first thing activated by your inigtion and then turns everything on. If i'm not mistaken anyways.
 
ok cause seriously ive ben trying EVERYTHING and my ECU wont boot.... do you guys know if a MPI relay from a 5 speed FWD N/A would work on a 5 Speed TSI AWD ???? im moving in like 2 days and my ECU just refuses to boot...im completly frustrated with this crap
 
yeah its most likely the ECU.....when i went to buy an ECU of a guy it was from a jdm VR4 and its was a dual board ECU wich is not compatible with a 1g. so now i gotta find an ECU to actually see if mine was fried
 
You could always find a pinout for your ecu to see which is the power wire for the actual ecu. Give it a direct power source just to see if it'll kick on. if it does then you have an issue in your harness. If it doesn't your still boned. no offense. I've been there before so I know it can drive ya nuts LOL
 
Did you check the fuse? I don't remember which fuse it was but it was one of the big ones on the battery terminal and had the black wire connected to it. I think it has a yellow stripe.
 
yeah i did....i have another thread on here about this, i tried everything imaginable
 
Actually, the MPI relay is controlled by the ECU, not the other way around.

The way it works is the key turns on and sends a 12v source to the ecu and the MPI relay, at this point you should have a check engine light illuminated. If its not your ECU is bad most likely. Once everything checks out the ECU will send a signal to the MPI relay to switch on.

This is as per the wiring diagram from the 92 talon dealership manual.
 
Actually, the MPI relay is controlled by the ECU, not the other way around.

The way it works is the key turns on and sends a 12v source to the ecu and the MPI relay, at this point you should have a check engine light illuminated. If its not your ECU is bad most likely. Once everything checks out the ECU will send a signal to the MPI relay to switch on.

This is as per the wiring diagram from the 92 talon dealership manual.

according to steve this isn't true read on i believe it's posting no. 4 http://www.dsmtuners.com/forums/tun...75636-ecu-problems-two-wont-start-my-car.html
 
What im saying is basically hidden within what he posted-

Make sure you have 12v at the MPI fuse on the positive battery terminal?
Then check to make sure you get 12v at pin 103 on the ECU. It comes from the room fuse #19 next to drivers left foot.

The ECU expects to get 12v at pin 110 from the ignition switch when you turn it to run. In response it will pull ECU pin 63 and 66 low to turn on the MPI relay. The MPI relay then applies 12v to ECU pins 102 and 107 and the ECU if it's working correctly will boot up, turn the CEL on while the rest of the dash lights go through bulb check and then turn the CEL off.

If you don't have 12v at pin 10 of the MPI relay the ECU will not power up. If you don't have 12v on pin 103 for backup power the settings for long term variables like fuel trims will reset each time you turn the car off.
So in a sense the ECU turns on the MPI relay which in turn sends a singal back to the ECU thus completely "waking up" the ECU. But the thing to remember is that the ECU is first in line and does turn on the MPI relay.

This is the current problem with my car, the MPI relay tested out fine, the wiring is fine but one side of the MPI relay will not lite up because of damage to the ECU. The ECU is just not switching on the relay.
 
ok so my ECU is good! i found a wire not conected to anything neer the MPI relay and when i touched the wire to the chassis...guess what....check engine light came on and now i have spark!! still no start tho....hmmm
 
i get spark, i get check engine light....boost gauge comes on, i rotated the CAS by hand and i get hear the injectors clicking, i have fuel pressure, i tried the CAS in difrent positions and still no Start....timing belt is new and aligned and head is rebuilt so i know for sure compression is good... Still no start

would not enough grounds prevent it from starting? i have 2 brand new grounds both are huge....2 gauge. batt to chassis and tranny to chassis. thats all the grounds i have. I relocated the batt to the back so i made those grounds for that.

should i add a ground at the intake manifold? engine to chassis maybe? i am also wondering if the Starter needs a ground
 
Did you check to make sure that the engine is at tdc when you installed the cas? make sure that when you do that, the cas pointer is set up so that the tang with the groove is lined up with the dot on the back of the cas and then drop it straight into the cam with out rotating it ,then bolt it down . that should get you within a few degrees of where it needs to be. if you have spark and fuel you should be able to start it up.
 
ok i just went and tried that and nope..... engine was at TDC lined up the cas with the dot, only thing i didnt do was bolt up the cas LOL seems really tight on there when i installed it tho

i just hooked up to voltmeter to the CAS and im getting 11.6V at the cas so i dunno im clueless what wire should i check on the MAS plug??
 
are you using a logger of any type? something you could run diagnostic trouble codes with. also is your coolant temp sensor plugged in ? if its bad that little guy will cause some problems. just a thought
 
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