I have heard stories about PR7’s fuel pump failure but I guess same as everyone else, I thought – “meh, it won’t happen to me!”… well it did, and I believe it did more damage than I ever expected. More about it on the next post.

Problem with my old fuel pump was that it didn’t stop working completely, but for whatever reason it was too weak to deliver plenty of pressure for everything else to run the way it should, and from there – things just got worse…

Just to be clear, I haven’t checked what pressure output my old fuel pump had to provide, or used to provide when it was working fine, but I know for sure that when it was running fine, fuel lines where fairly hard to squeeze with fingers and when AJP’s ignition was switched on, pump gave enough pressure to open the pressure relief valve inside of the tank.

When it failed on me, while still on the side of the road, I pulled the pump out of the tank, and I noticed that when priming, the fuel pump was still buzzing, however fuel lines were soft and the pressure relief valve was not opening  – yeah, I know – a very scientific way to tell… but anyway, I didn’t think much about it at the time, as I thought the battery itself might be weak by that time as I had tried to start it quite a few times before checking it. 

Now, not sure why AJP decided to plug the pump to the ECU and give it only 10-11volts instead of all 13-14volts, and if that has something to do to its failure, but sure that doesn’t sound right and for that reason there is another mod to eliminate this problem by connecting a relay to the fuel pump…

Since the fuel pump was not up to the task anymore – it was time to replace it, and obviously I didn’t go the easy way as I could not see the point of taking something that didn’t last, and replace it with something that might also won’t last, so started looking for a better replacement…

Started looking for a better replacement, and I found this: Standard fuel pump I believe is: DELPHI T12 (T11 is more common, but delivers only 230KPa, and AJP has Pressure valve rated at 300KPa) and Replacement Model: HFP-389, fuel pump made by Quantum Fuel Systems. They call it a Quiet pump for some reason (but it’s not by the way, however it is quieter than standard), and it comes with Lifetime Warranty – can’t be any better than that!

AJP PR7 Fuel Pump Replacement

Replacement itself was not too difficult, but it did involve quite a few things. 

• Taking the fuel pump out of the fuel tank was a bit frustrating, as it had to be moved and turned around in order for it to come out.
• Quantum fuel pump was not a direct replacement to the standard pump.
• Old pump had to come out with all its plastic housing, as the new one will not fit in it (good in a way, as it eliminates the problem with split O-ring in there – some had that issue).

• To secure the new pump there was a need to get a replacement 10-12 mm Nut & Bolt Mini Fuel Hose Clip (jubilee clip – those with worm gear – not suggested to use here)
• There was a need to replace one of the Female Spade connectors on the original wiring, as the original fuel pump uses two 3mm, and Quantum – one 3mm and one 6mm connectors. Had to be soldered too.

• Out of many fuel filters that came with the new pump, I used one that was closer to the size of the original, secured with a very tight clip that nearly broke my finger trying to push it on! Seriously, it was super tight!
• After testing the fuel pump, it pressurised fuel lines so much that the fuel line of the top of the housing popped off, exposing very very useless fitting – good sign I suppose, as if original pump couldn’t do it, and new one exposed this weak point meant that it gave more pressure than original ever could! Well, or perhaps that Fuel Pressure Relief Valve couldn’t keep up? Anyway…

• Had to make some cuts with the drammel on that useless fuel line fitting on top of the housing to give more grip for the fuel line.
• Secured the fuel line on top of the fuel pump housing with another 10-12 mm Nut & Bolt Mini Fuel Hose Clip.
• After another test, the fuel pump pressurised the fuel lines so much again that the braided line that I used to fit the replacement fuel filter just expanded and started leaking everywhere, so I had to replace that with a more decent one, used a chance to reroute them too.

• Fitting the fuel pump back inside of the tank was another nightmare, as again, it had to be twisted and turned to make it drop back in its original position.

Quantum Fuel Systems – more details about the fuel pump itself here. (Not sponsored by the way!)

And that’s about it, and it is only small part of the cure for the never ending saga of problems! 

Once I managed to start the engine again, it started pretty much straight away, and still does no matter what,  so in my opinion, part of the poor start problem that PR7 had, was a weak pump perhaps. In any case I am planning to do the fuel pump relay mod too as i’m not very happy to keep 12v fuel pump running on ~10v…

Explore more!

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• Important things to know about your AJP PR7 – Torque Vales / Bearing / Seal Sizes / Manuals and Stuff.
• How I stored All my Trail Tools and Spares on my AJP PR7.
• AJP PR7 Tool Sizes.
• Cheap ways to make your motorcycles clutch lighter! (Part 2/3).
• How to make a Hydraulic clutch lighter on your motorcycle! (Part 3/3).
• Is it possible to fit the New Athena ECU on the old AJP PR7?

All AJP PR7 MODS:

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AJP PR7 Faults, Fails and Fixes

• AJP PR7 Wheel Spacers.
• AJP PR7 Wiring Problem and how to fix it (random stalling problem).
• Not AJP’s Fault – Radiator cap that nearly gave me a heart attack!