Hey all. I'd been having intermittent fuel delivery issues, which has caused me to check everything I could possibly think of. I'm pretty sure the fuel pump is no longer(suddenly) receiving power, as I've verified it works with a bench test, but it doesn't seem to work when connected to the car. I would now like to conduct a bench test of the fuel pump relay, and I'm having some trouble understanding where I should connect the power input. I've pulled out the relay, and it doesn't have any kind of diagram on it, so I'm checking the wire diagrams from the FSM. Unfortunately, it's a little beyond my expertise, so I was hoping someone could help me out.

(I'm not sure why this picture came out so large, I shrank it on my post)

The only differentiation between the prongs seems to be the numbers 1, 2, 3, and 5
Which corresponds to the below portion of the wiring diagram, indicating the wire colors


Now, looking at the diagram below (and making some educated guesses), I traced the line from the battery to the relay, and it looks like the pins that should be connected to the multimeter are 1 and 2(with the positive connector on 2, and the negative on 1), and the power supply should be connected to pins 3 and 5(with the positive on 5, and the negative on 3). I just want to make sure that I have this right so that I don't accidentally fry a potentially functional relay


I should note that I've searched the RX7club forums and youtube without anything helpful for this particular relay.

 

Jump the pins BW and LW on the fuel pump relay connector B-06.

 

The fuel pump relay is an NC relay. Meaning, the engine control computer has to actively power the relay coil to shut the fuel pump off.

Why are you bench testing the relay? Everything you need to know is in the car, not the relay.

 

Ahh, it seems I had a fundamental misunderstanding of how the relay works. I guess I'll try to bypass the relay
This answers what would have been my next question. Thank you so very much

 

Update: Put together a bridge wire with a short 12ga auto wire with 1/4" male quick disconnects on both ends, and it didn't work(Thingy I made). Yes, I stripped the rubber coating off both ends before putting on the contact points. I'm assuming I did something incorrectly, because I don't know what else would be preventing the fuel pump from running. I know it works from a bench test, and I've verified that the positive and negative wires on the fuel pump are connected correctly.
I thought it would be impossible to find a proper replacement, even an expensive one. Fortunately, I found a cheap replacement on ebay and decided to just buy it, since it's only ~$15 with free shipping.

 

An aside, since I do do this for a living and forget that sometimes what I see as obvious isn't always obvious

In a diagram with a relay, the relay internals are always shown in the unpowered state. This is very helpful when seeing a diagram with a multi pin relay that has both NC and NO outputs (or inputs, depending on how it is wired) So in that diagram, when you look at the relay, you can see that the contacts are closed. This means that when you power the coil, it opens the contacts.

The connector for the fuel pump is under the driver's side storage bin. If you have the typical wheel well rust and water leak, the connector can get corroded. Both power and ground go through the connector.

 

Double check that you have 12V on the BW (Black White) wire in that connector. The other thing you can do is put 12V and ground directly to the connector in the bin area.

 

Got some readings
The green light indicates continuity





So I guess this begs the question. Is my Engine control module cooked? Everything else in the car seems to run fine

 

Continuity is the wrong way to test a circuit. What are you measuring exactly?

 

I wasn't specifically looking for continuity. I got a smart multimeter that shows whatever it detects. It seemed odd that the connection to the fuel pump in the bin area was switching between continuity and OL. Being inexperienced, I don't know what exactly can cause this. I know that if there's a fault in the wire leading to that point, it can cause it, but I don't know if there are other reasons it would read OL. I didn't really expect to read voltage in the bin area connector, as the relay wiring harness isn't receiving voltage, but the flip-flopping behavior seemed like useful info. I currently suspect that the ECU has a fault, but I don't know if I should also be looking for some fault from the wiring path to the bin area connector.

I'm not having a great time right now. Out of all the problems I've dealt with, electrical problems have been the hardest to learn about and fix.

 

A Power Probe would be great here. You could unplug the relay and check the BW wire at the relay for power. (Key ok of course) That would tell you if the relay is even getting powered by the 20A fuse in the fuse box.

Then, you would check the LW wire for continuity to ground. That would give you the integrity of the connection of that wire, through the fuel pump, to ground.

Then, you could use it to apply power to that wire. It SHOULD power up the fuel pump.

You don't have a Power Probe, but you can make do. Check for power at the BW wires, with the ignition on and negative lead on a good ground like the pedal box or something. If you have power there, run the voltmeter between the BW and LW wires at the relay. You should have battery voltage. If you don't, then keep going.

Run a jumper wire between the BW and LW and make the fuel pump work. If it doesn't, or the previous step didn't show battery voltage, now you can go back to the connector under the driver side bin and check for voltage there. Check between the two terminals, should have battery voltage with the relay pins jumpers.

Note that you cannot easily test for voltage at the fuel pump with everything intact, because the engine computer will turn off the fuel pump if it doesnt see the engine spinning. This requires that you be cranking the engine and the trailing ignition to be functional. (You DO have working trailing ignition, right? )

99% of the time, a failed trailing ignition is why the fuel pump stops working.

 

Okay, wow. So I found a fuse that broke since I checked it two days ago. Replaced it and am reading voltage all the way through to the bin area connector with the jumper wire. The fuel pump still isn't running though. I can't imagine the problem is the trailing ignition though. All new spark plugs and wires, new ignition coils, new ignition distributor rotor and cap. I also got the leading and trailing timing correct while the vehicle was still running.
Does this mean I'm looking for a fault between the bin area connector and the fuel pump? Is it possible I used the wrong type of spliced wire butt connectors? I used some butt connectors I had left over from working on the sound system of another vehicle. I thought the only difference would be in the gauge of the connectors.

 

Are you checking for voltage against ground or voltage against the ground in the connector?

 

Nevermind. I'm just a dumbass. I had the positive and negative wires on the fuel pump connected incorrectly. I didn't take a picture when I disconnected the fuel pump, so I googled how to identify which is pos/neg, and wikihow told me the solid black wire was positive. I actually can't believe I just went through all of that and had the damn wires mixed up. Everyone please bully me

 

Mazda has caught out a lot of people by liking to use solid black for positive!

One thing they do do, that is nice, and I don't know if this is a JIS standard of any type or just a Mazda internal standard, is that generally white stripe is power in to a switch and yellow stripe is that circuit's switched wire..

 

Glad you figured it out. Doing this troubling is a great way to learn. These types of experiences will not be forgotten.

 

Over the years I have learned "more" from the things I've done wrong, than I ever did getting something "right" the first time.