AJP PR7 Fuel Pump Relay Mod

/ AJP PR7 / Electricals, Fuel, PR7_Mods / 6 minutes of reading

So here it is, a very simple, neat and tidy fuel pump relay mod! Almost like it came out of the factory like this too! 

Why add a relay on the AJP PR7’s Fuel Pump?

Here is a thing, PR7’s fuel pump powered up by ECU, and ecu for whatever reason is not providing full voltage to it, now when pump is designed to work at 12-14volts, and only gets 10-11volts – it is not giving a full power, and even thought fuel pump gives enough pressure to open the fuel relief valve (at least when priming) and keeps required fuel pressure, yet problems like poor starting especially when temperatures drop (or AJP stood unused for some time) persist. 

Now I’m not sure if ECU regulates that voltage to the fuel pump in a way that voltage goes up and down with revs or whatever, but ever since I noticed that ECU provides only 11volts when sorting out wiring problem that I had, I was brewing some ideas how to go around that. Way before I could come up with a clear plan of action, someone posted online this simple idea of the relay stashed under the seat. Some boys have already tried and tested this mod with great success. And since last winter I had troubles starting my PR7 in cold weather, I thought there isn’t much I can lose by trying this mod too.

How to make fuel pump relay mod for AJP PR7

I have tried to mark schematics in a way that even those who have no idea what they are doing could understand what’s going on there, so please feel free to have a good look at it, and things will be much clearer. Also, I made it so that there will be no need to cut any of the original wiring, as well as things could be reverted back to original state at any point. 

If things still are not clear, here is the list of parts and tools that are needed for this mod.

Tools: 

  1. Crimp tool, but can be done with normal pliers – crimp tool is much easier, tidier and more secure.
  2. Wire cutters, or wifes best scissors.
  3. Solder and soldering iron (personal preference – crimping stuff works well too). 

Parts: 

  1. 1x 12v 30A Automotive relay with socket. Personally I used a sealed waterproof relay with a mounting tab / bracket. Used the one with separate wiring too, not pre-made as normally those wires are not long enough… 
  2. 1 set of Super Seal 2 pin Connectors and 2 boots. Boots are unnecessary, but they do look good and protect wires too.
  3. 1 set of Sumimoto MT090 2 pin connectors – these are the same connectors that AJP used to connect ECU to the Fuel pump. 
  4. 10A (minimum)  Inline fuse holder and 10a Fuse. 
  5. 2x M6 Ring Terminals and 2 shrink tubes.
  6. 2-3 different colours wiring rated no less than 10A – different colours don’t matter really, can be used 1 color for this simple project – it’s just easier to trace them back later if needed. 

How to wire up fuel relay mod on AJP PR7

Let’s break down schematics into 3 smaller bites that we can chew, and plug, and crimp and solder all connections on the way. Like mentioned before, pressed or crimped terminals are good enough, but soldered connections – even better. Oh, and every time working with bikes electronics – battery should be disconnected, and to start White plug that goes from the fuel pump to ECU should be disconnected and both connectors should be routed to a safe but reachable location (stashed them under fuel filler spout).

Step 1.

(Red and green wires – Original wiring; Pink is the one we will be making in this step)

First, we need to locate a good place to mount the relay, and once we are done, connect 2 wires to the Relay’s terminals 86 and 85, (every relay will have marking next to the terminals).

Route both wires towards the ECU Male connector, find a good spot to hide plugs and trim both wires, crimp and solder both wires to the new Female side of the Sumimoto MT090 plug and plug them together.

At this point there is no difference if the positive wire from ECU goes to pin 86 or 85 on the relay itself, as it’s more like switching a light switch in the room with left hand or right hand – works both ways, and this part of the wiring does just that – allows ECU to switch relay switch on and off (instead of the fuel pump itself)  – just like a remote control, but with wires if you like…

Step 2. 

(Yellow line – Positive wire, Blue – Negative)

Fit one M6 ring terminal on one end of the Fuse holder wires and place it within reach of the batteries (+) positive terminal (slide shrink tube over the wire, push wire inside of the ring connector, crimp it, solder it, and slide shrink tube over the soldered part of the terminal, leaving only ring part exposed and heat it up for tube to shrink),

and one M6 ring terminal on another  wire and place the terminal as close to the ( – ) negative side of the battery as possible.

Route both wires to a good location, or as far as wires that came with a fuse holder will allow, trim negative wire to length (or both), and fit any of the Super Seal plugs on them. If boot is used, it should go on the wires before the plug itself. 

This part of the wiring will provide power to the fuel pump, but only Positive will go via relay switch.  

Step 3. 

(Red and Green – Original wiring on the fuel pump (Colours do not match to actual wiring thought), Yellow line – Positive wire, Blue – Negative)

Now at this point, fit 2 long enough wires to the second part of the black Super Seal plug and connect it to the plug that we made in Step 2. The wire that goes all the way from the battery’s Positive terminal (via Fuse holder) should be routed all the way to the Relay Switch and connected to Relay’s Pin 30 (or 87). 

And then another wire to Pin 87 on the relay switch (or 30 if 87 was used before – doesn’t matter) and route it all the way to the fuel pump’s female plug.

Now this wire that came back from the relay is “Switched Positive” and this wire should be connected to the (+) Positive side of the fuel pump using Male Sumimoto MT090 plug – There are markings on the fuel pump housing which side is positive, which is negative, so if not sure trace it back.

The remaining wire that is still dangling from the black Super Seal plug (Blue Line), is negative and should be connected to the fuel pump’s negative wire terminal on the remaining Sumimoto MT090 plug.

Job done! Almost…

Picture: Almost there!

And that’s as easy as that! Now push the new 10a Fuse into the new fuse holder, and all that’s left is to put the battery back in, not forgetting to connect new ring terminals to the battery! With ignition on, there should be an audible click from the new relay, as well as whizzing sound from the fuel pump. If none is there, switch ignition off and check the wiring again and again till fault is corrected! And if something fails while riding (bad connections, broken wires, failed terminals, failed relay), simply take the fuse out, unplug original white Sumimoto plugs from the new wiring loom and plug Fuel Pump Back to ECU like it used to be and keep riding!

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