Fuel pump not priming with a twist

[donniekak]

This all started with me looking for a coolant leak. I had the tank tilted up with the bike running to see if there was a leak from the thermostat area.

 

Out of nowhere I turned the key on and the pump didn’t prime. I checked all the relays that control the pump and the tilt over switch, all ok.

 

 

Here’s where it gets weird. It’ll start for a few seconds, but dies 2-3 seconds after I release the starter button. If I hold the starter button from returning fully, the bike will run fine as long as the starter switch doesn’t return fully, as soon as it does it stops running.

 

The engine kill switch doesn’t seem to have an effect on the fi light either.

 

 

I’m an engine builder and car builder by trade and have lots of experience reading diagrams and diagnosing issues, I’m stumped here guys.

[BillyZ]

Sounds like a problem with the starter switch.

Sent from my SM-J327T1 using Tapatalk

[Grum]

The Start Switch has additional contacts to turn OFF your headlights as you press the Starter switch. When you fully release the switch the contacts make again to energise the Headlight Relays. A faulty Starter Switch would mean either No Headlights OR No cranking

 

So are the Headlights On and bright when Ignition is to On? Do they turn OFF the moment you press the Starter Switch?

Does the bike crank ok? (Battery in good condition?)

You do have an unusual situation, haven't heard of that one. I would firstly pursue the Fuel Pump NOT priming at switch On as a starting point. Bear in mind that if the Kill Switch is faulty the bike will NOT crank over.

There are frame Ground points at the rear of the Fuel Tank, could you have disturbed them? Are they tight to frame? Also in raising the tank have you checked the Fuel Pump connector is properly connected?

Is all the wiring stock standard? Are all Fuses O.K.?

 

Attached is a good drawing to help you pursue the Fuel Prime function. At switch On there should be 12v at one side of the Fuel Cut Relay, the ECM provides the switching ground to energise it and fire up the fuel pump for a couple of seconds, as soon as you start cranking the Fuel Pump should be running anytime cam or crank pulses are received by the ECM.

Good Luck, keep us posted.

 

[donniekak]

Well, figured out the problem.

 

The battery in the bike was low and died. For a while it was working fine with a jump box, but out of nowhere stopped working correctly. In addition to not priming the pump the lcd display would read incorrectly at times.

 

i believe I have a failing diode in the rectifier of my power supply. I don’t know a lot about Honda electronics, but a lot of other engine management systems react poorly to transients and 60hz ac leaking into the power.

 

When some parts arrived the other day I installed the battery and out of habit turned the bike on to make sure the battery was good. The fuel pump primed right up.

[Grum]

Glad you got it sorted, yep failing batteries can cause some weird effects. Interesting, not too sure what excessive ac ripple injected into a battery might cause, sounds like it may have damaged yours.

Might pay to confirm your charging system on the bike. Should see around 14.5volts with engine running.

Thanks for the follow up.

Cheers.