Help with fuel pump wiring!!! (non Z, a bit long)

[datsunlover]

I've posted elsewhere, but I thought maybe I could pick some brains here too. I'm building an 86 rx7 an using a 350 tbi/700r4. I'm trying to figure out how to hook up the mazda fuel pump and I'm a little confused.. I know a few of you guys have RX's, and possibly you've run into this.. Heres whats going on;

 

I ripped out the mazda ECU tonite. (left all the wiring harness un-molested for now, till I figure this all out) I grounded the wire that used to go to the AFM, and I found the black w/red stripe wire that gives power to the 'circit opening relay' under the steering wheel. (am I on the right track so far?) Now is where things get silly..

According to grannys speed shop (web site), there are two coils in the relay under dash:

 

The "run" coil gets it's power from the ignition switch in the "run" position (black w/ white stripe wire in Ba-01(F-08)). The ground leg of this coil (brown wire in Ba-01(F-08)) goes out to the airflow meter, where it is grounded when the airflow meter senses actual flow. If the ignition is on, simply grounding this wire will close the relay contacts and power up the fuel pump

 

Thanks for any help guys.

 

I tried that, and nothing happened. (I just have the battery hooked up, nothing else.. do I need the alternator wired up for the mazda wiring to work properly?) Thats when I decided to put direct power to the black w/red stripe wire.. because according to another page on the grannys site;

 

Black w/ red stripe...this wire used to go to the rotary's ECU, which sent out 12v+ thru this wire to energize the circuit opening relay and turn on the fuel pump until the airflow meter switch was closed.

 

I assume they mean from the ecu, when it powered up. So I found a 12V source (plug for the radio, it's out right now) and pushed a jumper wire into it. I assumed that I could jam the other end in the black w/red strip, and the pump would run when I turned the key. Wow was I suprised when the pump turned on right away! The fuel lines are not hooked up to anything yet, but luckily I pulled the wire off before gas sprayed out.

 

Sooo... what's going on? My key was only turned to acc, but the pump came on when I put 12V to the black w/red stripe.. does that mean the 'other coil' (in the circuit opening relay) has constant power all the time?!?! In which case, I have to find a 12V source that ONLY comes on with the key in 'run' or 'start' positions?

 

Assuming thats all I have to do, how do I get it to 'prime' (pump for a few seconds to build presure then shut off till motor turns over) properly? Grannys says something about an oil pressure safety switch, but.. wouldn't that mean I'd have to crank the engine a few times (to create some oil presure) to make the pump come on? That doesn't seam right...

[getZ]

I don't know much about RX-7's, but I'm okay with electronics.

 

First you probably need to invest in a voltmeter or borrow one. Cheap ones can be had at radio shack for 20-30 bucks. When in doubt you can measure the output yourself, when things switch on and with how much voltage.

 

When you use another wiring harness for another engine you have to integrate the wiring harness to the existing harness if you want everything to work. Sometimes you even have to run two seperate computers.

 

If you send a set of shematics for the tbi motor I can have a look at it. I'm guessing the fuel pump should no longer hook up to the stock mazda harness. From what I have seen, electrical fuel pumps are set up to shut down when the engine stops running. so in case of an accident the car is not constantly pumping out gas. Which means the engine computer controls the fuel pump.

[datsunlover]

I have a decent voltmeter, and that tool is the only reason I even figured out what wire needed power! Also which wire to ground out, 'fooling' the car..

The mazda uses a similar setup as Z's where the AFM has a switch that will shut off the fuel pump if no air is moving through it (engine not running) and the engine harnes is compleatly separate fromt the rest of the cars electrical system. With no ECU (ripped out) I hooked up the batery and evrything else still works (lights, fan, horn, wipers, ect) All that is needed is to ground that one wire.

 

From what I've figured out so far, the mazda uses a relay box under the dash, that gets a signal from the ecu (I assume it just pulses this for a few seconds for priming) to turn on the fuel pump. Really, I'd like to figure out a way to keep all the mazda pump wiring intact, as it is engineered and working.. all it needs is that 12v to the right wire, and it goes.. I'll see if I can scan the crapy diagram I have of the tbi ecu and maybe you can make sence of it...

[getZ]

The "run" coil gets it's power from the ignition switch in the "run" position (black w/ white stripe wire in Ba-01(F-0). The ground leg of this coil (brown wire in Ba-01(F-0) goes out to the airflow meter, where it is grounded when the airflow meter senses actual flow. If the ignition is on, simply grounding this wire will close the relay contacts and power up the fuel pump

 

This part doesn't sound right. I maybe wrong but I was thinking an airflow meter gives you a variable resistance like a gas tank sending unit. You could get zero resistance at either fully open or closed but why would you want to be running the pump only then? There is something wrong with the above information. My guess is either a piece of information is missing or it is not the airflow meter but maybe the throttle position switch like on the 280z engine. I can sit here and theorize the whole thing bur without schematics, I'm shooting in the dark.

 

By the way what year is your engine?

[datsunlover]

I probly should have clarified that.. I understand it, and it is correct. It's a weird electrical system the mazda uses to control the fuel pump. The pump relay is controled by that piece, which needs power put to it (from the computer, or in theory, any 12v.. like off a toggle switch) which turns on the pump relay. Kind of a relay controling a relay imo...

 

The AFM does give variable resistance, but at full closed position there is an EXTRA switch in there (separate from the resistor, but mechanicaly attached to the flap mechanism) that doesn't make contact if the flap is not moving. When the engine is running, (flap moving) it will make contact and allow the fuel pump to run. This relies on the computer to 'prime' the fuel system before starting. I think I'm closer now, as I went to my local GM dealer and got some photo copys of a ahop book. It gives me all the pin outs for the ECU, and imagine that; there's one for the fuel pump! (2 sec prime, and pump run) Oh, the engine is from an 89 Caprice, ex police car.

[getZ]

okay, assuming you are going to need a grounding circuit to make the fuel pump work, does the AFR point you are hooking the fuel pump relay go to ground?

 

To test this your meter will have to be able to measure resistance. (I hope this is not to trivial of an explanation since I have no idea what type of electronics backround you have if you need more explaination let me know). Put one lead to chasis ground and the other on the AFR output to the fuel pump relay (keep the ignition off). Resistance measurements don't need power (that might actually screw up the meter readings with power on). Push the AFR flap in and check the meter readings. If it gets pretty close to zero Ohms for a reading, you should be getting a good ground. If not then there's your problem.

 

If you need real time help send me schematics and I will send you my cell number and I'm sure we can work fix it. Just send me a pm. I gotta solve my ignitor problems this weekend.

[datsunlover]

Thanks man, I think I have things figure out now. I do have a pretty good understanding of automotive electrical, and my multimeter has been a big help over the years! Mine has a beep function for continuity testing, which I like as you dont have to look at it.. just listen.

 

The thing that freaked me out was that the chevy harness is a MESS with wires basicaly going in a big loop. ECU - engine bay -fuse panel - some back to the ECU - WTF?!?!? Basicaly the EFI/engine harness is integrated into the chasis harness.. Serious waste of wiring and very hard to work with. I spent tonite sorting through the harness, and basically 'chasing my tail' doing continuity tests (beep.... beep... beep... ARRGGG!!!!! ) and pouring over the ecm pin identification photocopys. There is one 2 wire clip I have no idea what it does or where it goes.. but I'm hoping it'll drop into place when I wire the rest of it up. It's actually going to be easier than I thought, because the chevy appears to use exactly the kind of fuel pump wiring I need for the rx7..

 

Basically, I ground that afm wire, 'fooling' the mazda fuel circuit (2 coils; if they're both on, the pump runs) into thinking the car is running. Then, I take the wire that comes out of the chevy fuel pump relay (turned on by the ECU for a 2 sec. prime, then a constant 12V after startup) and conect it to the other 'side' of the mazda circuit, and it should power the mazda pump. No hacking wires, no messing with the factory relays/fuses. Aside from wiring a few ign. on 12v (ecu power) , park/nutral switch and brake switch for the tranny, evrything else should just plug in as if it was still in the chevy caprice. Just need exhast and driveshaft now...

[getZ]

Oh yeah, I forgot to mention something important when checking continuity on cars.

 

There are a lot of natural shorts built in to the car which make it difficult to check grounding. Every electrical motor is basicly a wire to ground if it is hooked directly up to the battery.

 

When I check for ground connections I disconnect the starter from the battery and the fuel pump. I suppose other cars may have even more than that. Doh!

 

It is much easier to measure voltage on cars than resistance.

[datsunlover]

Yah, I've noticed that... I was trying to figure out if a thick black wire (seems stupid to me to use black for a hot wire, but they're all over the place in this car) was a ground or a 12V by doing continuity between it and one of the battery terminals (battery out of car) It didn't work too well. Got a beep off the +, AND a beep of the - as well! WTF?!? So I threw the battery in, and did a voltage check; it's a ground. I'm going to try to hook it all up to the car today.. problem is, I have no driveshaft, or exhast maifolds/pipes on it yet, so I probly won't be able to try firing it for another week. I'm planing on leaving evrything accesable though, in case I need to check conections (passenger side carpet/seats, and dash board plastics are all removed) but hopefully I've got things right.. Thanks again man.