Why is my MPI relay not working right?

[white_dsm]

The one circled in red:

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Ist that the fuel pump or the mpi relay? ^

That coils' connection doesn't close when the car is attempting to start, just the right one. So I foldeda piece of paper and stuck it in the left one to make it close and the car starts up just fine.

Why is my relay doing this? I plan on buying a new one if it's just defective but if it's something else lmk.

It's on a 1990 eagle talon awd.

 

[steve]

I believe that is the MPI side based on it having the diode in the coil circuit but you should just check to see which pins it's connected to.

If you leave it along does the CEL turn on for 5 seconds and the boost gauge go to zero when you turn the ignition on?

 

[white_dsm]

I believe that is the MPI side based on it having the diode in the coil circuit but you should just check to see which pins it's connected to.

If you leave it along does the CEL turn on for 5 seconds and the boost gauge go to zero when you turn the ignition on?

K, well did your tests.

First I did it with the piece of paper out of the relay, turned the key on and just regular dash lights come on. coolant, brake and of course it wouldn't start. Boost gauge didn't work.

With the paper in the relay the boost gauge went to zero and normal lights came on. Then it started..

No CEL's at all.


So what does that mean Steve?

 

[steve]

K, well did your tests.

First I did it with the piece of paper out of the relay, turned the key on and just regular dash lights come on. coolant, brake and of course it wouldn't start. Boost gauge didn't work.

With the paper in the relay the boost gauge went to zero and normal lights came on. Then it started..

No CEL's at all.


So what does that mean Steve?

What I was trying to say was that as part of the bulb tests, that go on when you first turn the ignition on, the CEL bulb lights and goes off after 5 seconds. I wasn't looking for a CEL otherwise. If it doesn't like you say it didn't then the ECU isn't powering up.

From what you describe, you have power to both sides of the relay. (because the car runs when you force the relay to activate)

The fuel pump side works correctly.

If you really did run the tests than you would have verified that the MPI side works correctly when you apply power across pins 10 and 8 and that would have told up that the problem is pin 8 isn't being grounded to turn on the MPI relay.

That in turn points at the circuit that activates the relay when you turn the ignition on.
you should see battery voltage at ECU pin 110 when the ignition switch is in the RUN or START positions. If the ECU doen't pull pins 63 and 66 low it needs repair. (which is very common due to capacitor leakage)

 

[white_dsm]

What I was trying to say was that as part of the bulb tests, that go on when you first turn the ignition on, the CEL bulb lights and goes off after 5 seconds. I wasn't looking for a CEL otherwise. If it doesn't like you say it didn't then the ECU isn't powering up.

From what you describe, you have power to both sides of the relay. (because the car runs when you force the relay to activate)

The fuel pump side works correctly.

If you really did run the tests than you would have verified that the MPI side works correctly when you apply power across pins 10 and 8 and that would have told up that the problem is pin 8 isn't being grounded to turn on the MPI relay.

That in turn points at the circuit that activates the relay when you turn the ignition on.
you should see battery voltage at ECU pin 110 when the ignition switch is in the RUN or START positions. If the ECU doen't pull pins 63 and 66 low it needs repair. (which is very common due to capacitor leakage)

Well I didn't do THOSE tests but just the one you asked first.

Before I ask about how to properly run 12 volts across pin 8 and 10 I did a quick test with the voltmeter.

I grounded off the - voltmeter pin and applied the + voltmeter pin to pin#10 and it read 11.9 volts, then did the same with pin#8 and it got 0.3 volts. So it's getting power, just not enough. (Pin #8 is a black wire with blue stripe and red dashes fyi...)
How would I get + power to both pin 8 and 10 simatanously? Paper clip? spare speaker wire? Or is it some special trick? When I do apply power I'm looking for the relays connections to close right?


After that I'll check the ecu out, and I should check for voltage at pin 110? I got the diagram from a search on here... But then the ecu pulling pins 63 & 66, what do you mean? Whats + and -? Are all pins + except pin#106 on the ecu?


Thanks for your patience man,I appreiciate it.

 

[steve]

I grounded off the - voltmeter pin and applied the + voltmeter pin to pin#10 and it read 11.9 volts, then did the same with pin#8 and it got 0.3 volts. So it's getting power, just not enough. (Pin #8 is a black wire with blue stripe and red dashes fyi...)

Yes, pin 8 is the black with blue stripe.
Was the relay attached when you did this? What position was the ignition switch in? Pin 10 (larger back with red stripe) should have battery power all the time so you can do this test with the key out.

If the key was out or off and the relay was connected then it sounds like the coil might be bad. Since the coil is just a long piece of wire you should see battery voltage at both ends until the ECU grounds it's end.

How would I get + power to both pin 8 and 10 simatanously? Paper clip? spare speaker wire? Or is it some special trick? When I do apply power I'm looking for the relays connections to close right?

You don't, pin 10 gets +12v and pin 8 gets the ground. That should cause the relay to click.
This testing is usually done out of the car with jumper wires to a battery. In the car, since you know pin 10 has +12v on it you could connect a wire to pin 8 and plug in the relay and then carefully ground pin 8 with the wire. That should turn on the MPI relay and the MPI circuit. (Turning on a SAFC if you have one)

After that I'll check the ecu out, and I should check for voltage at pin 110? Got a diagram for that too?Then the ecu pulling pins 63 & 66, what do you mean? Whats + and -?

Getting at the ECU pins with the ECU connected is a challenge. If you reach this point in your debugging it's highly likely you will find out that your ECU is bad. Sometimes the ignition switch goes bad but it about 100x more likely that the caps leaked.

When measuring voltages in the car the black probe of the volt meter goes to ground and the red probe is your to check the voltage. Like I said a little earlier up until the ECU tries to ground pin 8 of the MPI relay there should be battery voltage at the pins. The ECU grounds it when it gets 12v on pin 110. ECU pins 63 and 66 are connected to the MPI relay pin 8 if that wasn't already clear.

You can download the circuit diagrams from the Factory Service Manual from the gifts section of the Backup manual CD site. www.manualcd.com

 

[white_dsm]

Ok, well I did what you said and put a wire in the pin 8 female connection, then put the relay on. Ran the wire to to a ground and what do you know, the MPI relay clicked and stayed shut.

So it's a bad ground? Does this mean I go to the step and check pin 63 and 66 on the ECU? LMK what's up and I'll do it. I love progress

 

[steve]

So it's a bad ground? Does this mean I go to the step and check pin 63 and 66 on the ECU? LMK what's up and I'll do it. I love progress

It means that there is a 99% chance that the ECU is the cause. You can check the wiring between the MPI Relay and ECU by just grounding pin 63 at the ECU connector. You should still make sure that pin 110 sees 12v from the ignition switch before faulting the ECU.

This is one of the typical symptoms from cap leakage. It one that finally gets people to fix the problem because the car no longer works. I'd say almost half of the bad ECUs I get sent are because the MPI control circuit finally getting eaten up from the leakage. Sometime you don't see any other indication that they leaked until you pull the caps off.

 

[white_dsm]

K,
With they key on I inserted + pin from voltmeter into the female connector of the ECU onto pin 110, then 63, and then 66 and grounded off the - voltmeter pin onto a good ground. All are getting good voltage. Triple checked... So just a bad relay or something?

Or something still internally wrong with the ecu?

 

[steve]

So with the key on (RUN or START position but not ACC) your seeing battery voltage at pin 110. That's good but you shouldn't be seeing battery voltage at pins 63 or 66. That fact that you are says that the MPI relay coil is good but you should be seeing close to 0v on them if the ECU was working correctly.

 

[white_dsm]

Hmm..

I read your thread:
http://www.dsmtuners.com/forums/articles-tuning-ecu/246467-how-identify-ecu-pin-numbers.html


Maybe I got it backwards?? Anywho if I didn't and 63 and 66 are getting voltage, what can I do to correct the problem?

 

[steve]

Anywho if I didn't and 63 and 66 are getting voltage, what can I do to correct the problem?

Get a new ECU or send yours out to be fixed.

 

[white_dsm]

I can't fix it myself? It seems like something small..

 

[steve]

I can't fix it myself? It seems like something small..

I don't know, are you a EE?

 

[white_dsm]

Electronic engineer? No..


But I did do some searching again, I read:

"ECU needs power to work. That comes from two places, the room fuse than also maintains the radio's setting and the MPI fuse on the battery positive terminal."

I forgot to mention that my room fuse under the dash did cause a draw in my charging system, so I took that fuse out until I find out why. Would that prevent the ecu from powering my mpi relay?

 

[steve]

The room fuse should cause a power draw. That's how it maintains the radio and ECU settings. Try putting it back in and see if fixes the problem with the ECU.

 

[white_dsm]

Going right now.

 

[white_dsm]

Dam IDK, put it back in but still the same thing. Even tried the to ground off pin 8 to the car and the relay on it wouldn't click.

No start unless MPI is forced to make contact.. waah wah waah..

Well I'll go again in the morning. Thanks for all your replies, if it comes down to it I'll send the ECU off to you.

 

[white_dsm]

Updates:

ROOM FUSE OUT/ KEY OUT/ MPI RELAY IN

VOLTAGE AT:

Pin 66 - MPI control relay (11.3v)
Pin 63 - MPI control relay (11.3v)


ROOM FUSE OUT/ KEY ON/ MPI RELAY IN

VOLTAGE AT:

Pin 110 - Ignition Switch (11.3v)
Pin 63 - MPI control relay (11.3v)
Pin 64 - Check engine light (11.3v)
Pin 66 - MPI control relay (11.3v)
Pin 56 - MPI control relay (11.3v)
Pin 18 - Vehicle speed sensor (1.6v)
Pin 3 - Turbo Gauge (11.4v)


ROOM FUSE IN/ KEY OUT/ MPI RELAY IN

VOLTAGE AT:

Pin 103 - Battery backup power supply (11.4v)
Pin 63 - MPI control relay (11.4v)
Pin 66 - MPI control relay (11.4v)
Pin 18 - Vehicle speed sensor (5v)


ROOM FUSE IN/ KEY ON/ MPI RELAY IN

VOLTAGE AT:

Pin 103 - Battery backup power supply (11.4v)
Pin 110 - Ignition Switch 1g (11.4v)
Pin 63 - MPI control relay (11.4v)
Pin 64 - Check engine light (11.4v)
Pin 66 - MPI control relay (11.4v)
Pin 56 - MPI control relay (11.4v)
Pin 3 - Turbo Gauge (11. 4v)
Pin 18 - Vehicle Speed Sensor (4.86v)


ROOM FUSE IN/ KEY OUT/ MPI RELAY OUT

VOLTAGE AT:

Pin 103 - Battery backup power supply (11.4v)
Pin 18 - Vehicle speed sensor (5v)


ROOM FUSE IN/ KEY ON/ MPI RELAY OUT
Pin 103 - Battery backup power supply (11.4v)
Pin 110 - Ignition switch 1g (11.4v)
Pin 64 - Check engine light (11.4v)
Pin 3 - Turbo gauge (11v)
Pin 18 - Vehicle speed sensor ( 4.7v)


ROOM FUSE OUT/ KEY OUT/ MPI RELAY OUT

VOLTAGE AT:

None


ROOM FUSE OUT/ KEY ON/ MPI RELAY OUT

VOLTAGE AT:

Pin 103 - Battery backup supply (11.4v)
Pin 110 - Ignition switch 1g (11.4v)
Pin 64 - Check engine light (11.4v)
Pin 3 - Turbo gauge (11.4v)
Pin 18 - Vehicle speed sensor (1.7v)




Hopefully these tests can help narrow it down.

 

[steve]

Hopefully these tests can help narrow it down.

As I've described, your ECU isn't turning the MPI relay on. I'm assuming you checked all the pins listed but didn't write down those that were grounded in each test.

Dam IDK, put it back in but still the same thing. Even tried the to ground off pin 8 to the car and the relay on it wouldn't click.

No start unless MPI is forced to make contact.. waah wah waah..

Interesting It was working before. Maybe it's damaged now or it was just late and you had a case of operator error.

Ok, well I did what you said and put a wire in the pin 8 female connection, then put the relay on. Ran the wire to to a ground and what do you know, the MPI relay clicked and stayed shut.

 

[white_dsm]

As I've described, your ECU isn't turning the MPI relay on. I'm assuming you checked all the pins listed but didn't write down those that were grounded in each test.



Interesting It was working before. Maybe it's damaged now or it was just late and you had a case of operator error.

What do you mean?

btw, I did notice that in every test except the test with the mpi relay out the mpi relay was getting voltage. And you said it's not supposed to. Does that mean it's not grounding?

I tried to open the ECU but the screws are in their tough, I'll try again and post a pic of the board. Maybe you can see something I can't.

 

[white_dsm]

Here are the pics of the ecu, I noticed that their were some burn marks, maybe why my MPI relay isn't working right. Sorry about the quality, light sucks and so does the camera.



BACK SIDE

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OVERVIEW OF BOARD

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BURN MARKS

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CLOSE UP

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If you need the numbers where the burn marks are by lmk.

 

[white_dsm]

Oh I see what's missing, I looked at vfaq and noticed the capacitor replacement tech. Saw a pic then compared, his pics are more clearer so I can use his for example:

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That's what's missing, I'm guessing they are micro fuses? (circled in red) Don't know how they blew but looks like that could be the problem. Can't a local computer shop fix this?

 

[steve]

The parts circled in red are SMD capacitors. Your ECU has a bad case of capacitor leakage.
Since it's a EPROM version, I think it would be worth having it fixed.

 

[white_dsm]

K, so hopefully that was the problem. It wasn't that bad, cleaned up a little bit with a q-tip.

Can I take this to a computer shop to have it repaired? I see you can buy these SMD capacitors pretty cheap and are local.