1G MPI Relay Testing

[Breadvans]

So i was trying to test my mpi relay because my injectors aren’t firing. I used this diagram from the no start thread and i don’t have continuity between pins 2 and 4? It just stays at 0l. Is this bad or am i doing something wrong?

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[motomattx]

First go out and check for +12v on one side of each injector harness, to do this turn the key to the on position until the cluster lights up fully but dont start the car, take a test light or a voltmeter and put one side on a good ground, such as the negative battery terminal, and the other side on each of the injector harness terminals, do this with the injectors unplugged, one side should either light the test light or show 12v on the multimeter if you have B+ like you should to your injector harness. Btw do you get a check engine light when you first turn on the key for about 5-10 seconds and then it goes out? As far as how your testing is being done on your relay, you need your meter set at the lowest Ohm setting that you have unless you have a meter that self adjusts for it, I have never seen a MPI relay fail yet if thats any indication of how often they fail, not saying that its not possible as they are getting pretty old now, but they dont fail very often.

 

[Breadvans]

First go out and check for +12v on one side of each injector harness, to do this turn the key to the on position until the cluster lights up fully but dont start the car, take a test light or a voltmeter and put one side on a good ground, such as the negative battery terminal, and the other side on each of the injector harness terminals, do this with the injectors unplugged, one side should either light the test light or show 12v on the multimeter if you have B+ like you should to your injector harness. Btw do you get a check engine light when you first turn on the key for about 5-10 seconds and then it goes out? As far as how your testing is being done on your relay, you need your meter set at the lowest Ohm setting that you have unless you have a meter that self adjusts for it, I have never seen a MPI relay fail yet if thats any indication of how often they fail, not saying that its not possible as they are getting pretty old now, but they dont fail very often.

Yeah i got 12v going to each injector clip, and im not sure whatcha mean by b+? And my cel light turns off for about 5 seconds and turns off. My boost gauge zeros out. I checked me ecu just in case and there’s no scorching marks or odd smells or anything. And yeah i had it set to the 200 option cuz that’s as low as mine goes.

 

[motomattx]

Ok, well next I would actually put a test light across those terminals where the 2 and 4 pins are in the MPI connector and see if it lights up when you turn the key on and crank the car, a volt meter could also be used for this of course, although if your cel is coming on for a few seconds and then turning off, this should rule out the MPI relay, but you can check just of peace of mind. How do you know that your injectors are not pulsing? have you used a noid light on them while cranking? have you checked your fuel pressure or heard the fuel pump turn on?

 

[Bud92gsx]

Sorry im not answering your question. But I always prime the engine first start of the year by pulling the mpi fuse.
Back on topic

 

[Breadvans]

Ok, well next I would actually put a test light across those terminals where the 2 and 4 pins are in the MPI connector and see if it lights up when you turn the key on and crank the car, a volt meter could also be used for this of course, although if your cel is coming on for a few seconds and then turning off, this should rule out the MPI relay, but you can check just of peace of mind. How do you know that your injectors are not pulsing? have you used a noid light on them while cranking? have you checked your fuel pressure or heard the fuel pump turn o

I thought one relay could go bad in the mpi but not the other? So you could have the cel come on but not get any fuel because of it at the same time? And we’ll i used a noid light and got nothing, then i physically took them off and cranked and no fuel came out. I got a walbro so i very clearly hear my pump turn on, and have also confirmed i have fuel to the rail. I have not measured it with a gauge tho

Sorry im not answering your question. But I always prime the engine first start of the year by pulling the mpi fuse.
Back on topic

I primed the fuel rail and used an impact on the oil sprocket. But gotcha for future reference for further priming

 

[motomattx]

If your getting fuel to the rail and 12v+ on one side of the injector harness its not that relay.

 

[Breadvans]

If your getting fuel to the rail and 12v+ on one side of the injector harness its not that relay.

Gotcha. How do i test the ecu trying to ground the injectors? Just back probe the corresponding wires with a multimeter and put the other side of the multimeter on one of the constant 12v?

 

[motomattx]

A mulitmeter wouldn't be the tool of choice to do that with, a test light would be the way to go, have you checked for +5v on the cam/crank sensors? and ground to them?

 

[Breadvans]

I haven’t checked with a multimeter or anything no. I broke a wire and wasn’t getting rpm signal so i put the wire back together and was getting rpm signal so i assumed it was working. I’m getting spark, can a cas cause spark but no fuel? I was under the impression if cas was the culprit it’d cut both

 

[steve]

I just assumed that this was a 1G question but you posted the page for a late 2g MFI relay.

Is this thread a continuation of your no start and the injectors not pulsing threads?

 

[Breadvans]

I just assumed that this was a 1G question but you posted the page for a late 2g MFI relay.

Is this thread a continuation of your no start and the injectors not pulsing threads?

Well now it is, i was originally looking for more advice on the mpi

 

[steve]

Well now it is, i was originally looking for more advice on the mpi

Have you read this? https://www.dsmtuners.com/threads/1g-basic-ecu-mpi-circuit-function.435961/

If so what do you think needs more/better explanation?

 

[Breadvans]

Had you read this? https://www.dsmtuners.com/threads/1g-basic-ecu-mpi-circuit-function.435961/

If so what do you think needs more/better explanation?

Nothing really, should i still test it all? Or is the fuel pump working, cel light working properly, and boost gauge zeroing out enough?

 

[steve]

That your getting power to the fuel pump when commanded and that the ECU is powering up prove that the MPI relay is working as it should.
Assuming none of it is hotwired to do so. (Added in case someone comes in later and tries to apply this logic to their situation).