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I just fired up my LS project for the first time yesterday. I am having some issues getting proper power through the circuit opening relay to the fuel pump.
I followed the grannyspeed instructions to flip the pins around at the relay connector, removing the black/white wire and replacing it with the brown wire (previously grounded through the AFM, now connected to the LS c101 D green/white wire, which is fuel pump relay control.)
I've tested voltage at this brown wire and I get the short prime 12v in ignition on and 12v when starting. I've also jumped 12v to the blue wire (power to fuel pump) and I can hear the pump whine. However, for whatever reason, I can directly jump these 2 wires and the pump will not run.
My understanding would be that the PCM cannot supply the amperage to run the pump. But how else could it work? Where is the relay supposed to get this 12v power for the pump? Looking at the diagram for the relay it doesn't make sense to me.
The black/white wire from the connector that the grannyspeed instructions said to remove and replace with brown is a 15amp fused from ignition switch on. I can jump from this wire to fuel pump power blue wire and it will run. Is there anything wrong with wiring it like this? Only difference being that it is not PCM controlled.
Hopefully someone who understands this relay better than me can help out.
Let's take a step back and look at the circuit opening relay wiring diagram on a series 4 non turbo from the service manual. This is page 50-36. There are two coils inside the relay and 5 wires. The light blue wire is the one sending juice to the pump itself, and a black/white wire feeds the power as well as supplying power to one of the relay coils. Each coil needs a ground wire, so there are two of those, and there's another power wire just to switch one of the coils.
The power for the pump (black/white wire) is ignition switched. There is ignition circuit 1 (accessory position and run position), ignition circuit 2 (run position only), start circuit (cranking only), and battery (constant power).
One ground for that one relay coil comes from the airflow meter (on series 5 and later, the ECU itself). This is a safety feature to turn off the fuel pump in an accident. The airflow meter is bypassed by the yellow 2 pin check connector near the strut tower under the hood. This is the fuel pump diagnostic connector.
The other power comes from the same circuit that supplies 12V power to a lot of other items on the engine control system (wiring diagrams are bit murky but it's the same wire color). Then there's a ground that goes to the chassis.
Now, let's see what we have after we follow the instructions. The power itself doesn't change at all. Ignition #1 circuit supplies the power, light blue wire sends it to the pump.
What's changed is the coil. The second coil, the one depicted in the middle of the relay's diagram, is no longer triggered. The coil to the left is now triggered by the LS1's PCM. If you look on the right side of the below pic, I show the factory wire color locations at the top, and below that the reconfigured version. "pump Power" and "to Pump" and the black chassis ground wire haven't changed at all.
So, on the stock system, the airflow meter provided a GROUND to activate a coil in the relay. On your rewired system, the PCM is supplying low amperage 12V to trigger a coil in the relay only, not to run the pump.
I appreciate you taking the time to help me understand the relay and its operation. If I would like the pcm 12v wire to control the fuel pump, would I be better off buying a new 4 prong relay and ditching the circuit opening relay from the mazda? I don't know why I would need the black/red 12v wire (top left of relay) if I use the black/white fuses ignition 12v for the power in, and just the pcm/brown wire in to trigger it.
It would be simpler to use an aftermarket relay, BUT if something isn't working and you're following the instructions, it's possible that you don't have power getting to the circuit opening relay. And that could indicate another wiring problem.
What the instructions did is basically convert the factory 6 pin (5 pin here) relay into a 4 pin relay. Upper left (black/red) wire is deleted and becomes the PCM wire (here, brown). Black/white wire is the same. The original brown wire goes away. the black wire to ground the coil stays.
Actually, per their instructions, the black/red wire remains, the black/ white wire with ignition voltage is the one replaced with the brown wire, now coming from pcm.
Either there's something wrong with their instructions or there is something wrong with the service manual diagram or I'm reading something wrong. I'm assuming that your vehicle was automatic or ABS equipped, and thus it has a black/red wire in the upper left pin shown in the diagram, rather than having two separate black/white wires.
Do they really power the fuel pump from the ECM? That doesn't make any sense. Below is the section from the LS1 wiring diagram. It outputs +12V from the ECM to power the fuel pump relay. Is there continuity between your brown wire and pin 9 C2?
Note that on the Rx-7, the series 4 cars use the ground from the airflow meter, and on the series 5 and 3rd gen cars it uses a ground from the ECU, not +12V from the ECU, to switch the circuit opening relay. So the LS1 is sending +12V and the Rx-7 is sending ground.
Locating & Re-wiring The RX-7's Fuel Pump Control Relay(s)...Mazda calls the main fuel pump relay the "Circuit Opening Relay", a square relay with a 6 terminal connector Ba-01(F-08) (2 rows of 3), which is located under the steering column. For the non-turbo models, this is the only fuel pump control relay. The Turbo II models used an additional relay called the "Fuel Pump Relay & Resistor", located in front of the passenger side strut tower under the stock air cleaner, using a round connector (F-09) with 6 terminals (2 rows of 3). The wiring modifications are as follows... ...ALL Models-...The RX-7 circuit opening relay's Ba-01 connector is a retangular 6 pin connector located below the RX-7's steering column. Perform the following modification steps 1 and 2 to the wires/pins in the connector (step 3 is performed at RX-7 connector X-16/FEM-02/X-11)...
......STEP 1- remove the small black w/ white stripe wire from the connector's center pin (opposite the blank hole). This wire will not be used, but it needs to be insulated from the others (as well as from the other wires) and taped back out of the way.
......STEP 2- remove the brown wire/pin from the connector and re-insert this wire into the upper center hole (spot formerly occupied by the black w/ white stripe wire we removed in step 1)
......STEP 3- connect the brown wire in the RX-7's X-16/FEM-02/X-11 connector to the LS1 C101 connector's terminal "D" dk green w/ white stripe wire.
These modifications allow the LS1's PCM to control the RX-7's Circuit Opening Relay as a fuel pump relay. ...Turbo II Only-...On the turbo models, there is also the "fuel pump relay and resistor". It's function was to provide extra fuel pressure under boost conditions by closing an internal set of contacts to effectively bypass a voltage dropping resistor. When installing a LS1, we bypass this entirely by connecting RX-7 connector Ba-01's blue wire w/ red stripe wire directly to the RX-7 connector X-13's blue wires (both blue wires are connected inside the harness - Mazda used 2 parallel blue wires thru the connector to reduce connection resistance). These blue wires power the RX-7's fuel pump.
I picked up a 4 prong 40 amp relay today, I will double check the wiring tonight and If i can't keep the factory relay I will just use the new one. I was very frustrated last night and gave up, hopefully better luck tonight. Thanks again for the help.
Got it! Here's how I got it to work. I removed the top left red/black 12v completely, and replaced it with the brown/pcm control wire. Otherwise it was left the same, and it functions as it should. So the grannyspeed instructions were incorrect. Thanks again for the help arghx!
06-25-18, 07:03 AM
