Carry over from my build thread. I am having issues with my MX-6. I'm not getting a 12v source to the light green (LG) wire to the Air flow meter. I've been tracing the wire to a relay as shown on page 50-29 of this link: Repair manual
The car still runs, but badly. I want to test the relay labeled D-5. I'm pretty sure it's not my problem, but I want to be 100% sure.
On to my question. How to test this relay?
I'm a wiring noob. This is the multimeter I'm using:
Generally speaking on a 5 pin, two of the pins run the coil, of the other three one is in, the other two are out, energizing the coil flips which out pin the in pin connects to. Usually there's a little block diagram on the side showing what pin is what and which way its normally (no power)closed.
You also need to check if you have power and ground in the socket for energizing the relay and feeding the input pin, all when its supposed to be, and whether or not you have good continuity in the wires going form the socket to whatever part you suspect is having a problem.
Looking at the wiring diagram, it appears to be a two coil relay and I don't remember how those work. If you can find numbers on the pins, 30 will be your common, 85 and 86 should be one of the coils, 87a should be the "output", but I don't remember how the second coil gets hooked up.
How do I check for continuity? The relay has nothing on it. No diagrams, no labels, nothing.
If you go to the next page in the manual, it shows the pinout for that relay in the upper left corner.
Well, if you shut the car off and pull the battery cable, you should be able to test continuity to ground from each of the pins. One of those will be the ground for (at least) one of the coils. That's pin 85 or 86. Then I'd hook up the battery, leave the key off, and see where you get +12V on the relay. That will be your common. Next, I would put the key to "run" and see where else you get +12V and that would be 86 or 85. But I don't know what to tell you about that second coil...
That's a fuel pump relay. Does the car run at all? Then it's working. Move on.
This wiring looks awfully familiar. The same dudes did the 1.6 Miata.
The dual coil means the relay can be triggered from two different sources. In this case, it's triggered either off the LG wire by the ECU (when the key is turned on, to prime the pump) or the AFM (there's airflow, so the car is running - this means the pump will stop if the engine stalls). The other side is triggered by the starting circuit so there's fuel to actually start the car.
Sequence of events: turn on key, ECU runs the pump for a few seconds to prime the system, then shuts it off. Turn the key to start. Starter circuit turns on the pump. Car starts. AFM sees airflow, keeps the pump turned on.
You can also hardwire it by jumping two pins in your diagnostic connector. That'll run the fuel pump any time the ignition is on. It's a workaround or a test of the pump itself. But like I said, if the car starts and runs at all, this relay is not your problem.
To test. I'm going to refer to the wire colors, not the pin locations. This is a little funky to test because one of the terminals is shared between the trigger and the switched circuits.
Set your multimeter to check continuity and check across the B/W and W/Y pins. There should be none. Now apply 12v to the B/R pin and ground to B. The relay should click and you'll have continuity. That's one coil.
Now set your multimeter to check voltage. Put 12v on that B/W terminal and ground the LG one. Click. You should now have 12v on the W/Y terminal.
How to check continuity: set your multimeter to either one of the RX settings. Touch the probes together. Don't worry, there's not going to be a spark. The needle should have swung right to the maximum reading. That shows you have continuity between the two probes.
To test continuity, put one probe (doesn't matter which) at each of the two things you're testing such as two ends of a wire or two terminals of a fuel pump relay. If the needle pegs, you've got continuity. If it doesn't move, you don't.
Yes the car runs so I'm guessing it's good. Still learned a lot from this thread. I just don't know why I'm not getting 12v from the LG wire to the AFM.
Stupid question, but it looks like LG should be switching inside the AFM to B/LG which appears to go to ground. You're checking for negative on LG not positive, right?
That's what you should be doing. The AFM, the ECU and the diagnostic connector all provide ground to trigger the relay.
If you attach one side of your multimeter to 12v and the other to that LG wire, you'll see voltage when the car is running - or, if you want to screw with it, when the ignition is on and you open up the flapper in the AFM.
Relays like this don't fail a little bit and only provide some fuel. They either work - fuel pump runs - or they don't work - fuel pump doesn't run and car stops. There's not really an in-between state.
ScreaminE wrote: How do I check for continuity? The relay has nothing on it. No diagrams, no labels, nothing.
Set meter to lowest ohm scale, measure between points, make sure you have a good connection, readout in the double digits is bad, more than 20 its definitely got something wrong with it, no movement at all means its open.
Its an analog meter so it first has to zeroed by crossing the probes with it on the low resistance setting(Rx10 for you), and fiddle with the dial on the side so it reads 0.
that's how us anal electronic tech would do it … but to just see if there's actual continuity between pins … any res. setting will do, and without zeroing it …. if the needle moves then you have continuity
wae wrote: Stupid question, but it looks like LG should be switching inside the AFM to B/LG which appears to go to ground. You're checking for negative on LG not positive, right?
Hmm. I have been testing for positive 12v on the LG wire. That may be my issue. I may not have an issue. I was going off this figure that says nothing about checking for ground at the LG wire.
I'm testing at the AFM. All of the other wires are within spec when testing for positive. I know that I have a poor connection at the plug that causes pin Vc to lose 10v whenever the plug is just left loose. Whenever I push hard on the plug, I get a 10v power back. I have a new plug set to arrive tomorrow.
I will test LG for ground tonight and see what happens I suppose. Thanks for everyone's input.
Installed Brand new AFM plug tonight with solder/heat shrink. Now the car runs like poop. Instant CEL for the AFM.
Good news is now I'm getting all the right voltages, and yes you were right on the LG wire being ground. Bad news is the fact that when the car starts sputtering and missing, I see the voltages drop to nothing.
At this point I'm just going to buy another AFM and see if that fixes it. I just don't know what else to do at this point.
Do you need to reset the ECU? Maybe it learned the settings from the bad AFM, and need to be cleared out? On my volvo. its as simple as disconnecting the battery, tapping the brakes a few times, and then re-connecting the battery. Or on some cars you can touch the battery cables together.
In reply to mrwillie:
That's true. I will try that. I know the procedure is on mx6.com somewheres.
mrwillie wrote: Do you need to reset the ECU? Maybe it learned the settings from the bad AFM, and need to be cleared out? On my volvo. its as simple as disconnecting the battery, tapping the brakes a few times, and then re-connecting the battery. Or on some cars you can touch the battery cables together.
This worked....until I hit the gas. The car ran smooth after resetting the ECU. Whenever I hit the throttle, the CEL came back on and the car starting running like poo. Tested the AFM per the repair manual and the ohms are off. Opened the top of it and it's a corroded mess on the inside. I'm guessing the AFM works during idle but when it sees a load it looses its mind. Replacement on the way via eBay.
That makes sense to me. It didnt have to do many adjustments at idle. When it actually had to work and do some calculations, it fell on its face.
Good catch. I'm glad you were able to figure it out. I hope u get to enjoy your car soon.
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