Fuel Pump Operation

Gojuu said:

Thanks @City Garage

I’m kinda already headed the way you suggest - ecu to relay. The output from the ECU is definitely consistent - it consistently tests ok - but Im thinking a high resistance joint or similar where the relay seats to that connection.

As you say - there’s no issue most of the time and it performs really well - I’d expect a fuel pump to cause more issues than this.

I’ll unseat the spade lug in the connector and see how it looks next. I have open barrel crimps and a fair array of connectors, if one matches I’ll likely reterminate it.

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Gojuu said:

@TonyA you've got to remember I'm still a bit new on this bike! This has been a bit of a process I guess. What had happened was, I'd ridden the bike to work - after not long owning it. Then, it just decided not to start. Cranked good......then not as great.....thought the dreaded "I'll flatten the battery soon"......you know the routine. Luckily at that time it started. Happened a few times since, but I tended to notice it at first start when cold, rather then I was somewhere.

It did it a few more times randomly, but I was still learning about the bike and simply wasn't listening for the fuel pump. Lucky each time it started. In some cases, was near traffic or in an area I wouldn't hear it anyway. Some of these times were prior to me doing the throttle body and then ECU change as well - and back then I was also dealing with a bike that stalled at traffic lights when hot, and intermittently idled like a complete donkey. When I did the throttle body change, as well as smooth out the idle, the delete of the IAC had an interesting affect. Ever since then the bike cranks much faster and starts a lot easier. I put this down to the fact that the throttle body lets very little air in for idle, where the heavier load cranking was due to the IAC being opened at crank. I see this as proved by the fact that the bike turns over significantly slower if I crack the throttle.

When it's happened, I thought - well it cranks strong and I know it now idles really well etc. I pulled a plug and there was heaps of spark. Then I just happened to notice one time that I didn't hear the fuel pump start. At that point I didn't actually know if the fuel pump started every time or not (hence all my questions)- but started paying attention.

With regards to the "why doesn't it stop when riding", I believe that is down to the behavior of a relay itself - and a big part of the reason I don't think there is anything wrong with the pump. Relays have two ratings, A Must Operate Voltage and a Must Release Voltage. The MOV is the voltage to switch, and the MRV is the voltage needed to keep it switched. They are sometimes called the Pickup Voltage and Drop out voltage. Almost any relay takes more power to close than it does to stay closed - but have a look at some spec sheets for relays and you will see the values are very different. If I'm dealing with a high resistance joint, as I expect, this explains that behavior.

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Voodooo said:

So maybe I missed something here, you’re saying sometimes it’ll start and sometimes I’ll leave you stranded but it always cranks over strong?

If you unplug the fuel pump and put a voltage gauge on the fuel pump harness with the key on or with a jumper wire or switchable relay, do you get 12 volts at the fuel pump plug? Are you getting a good ground? Are you getting good continuity to the plug and ECU plug? No wire breaks?
If you pass all of this and you already jumped the fuel pump and the pump test good, I’d check or swap the crank sensor.

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Gojuu said:

Thanks @Voodooo - the only time it doesn't start is when I don't hear the fuel pump at key on. Crank signal is no problem (have checked that in SXTune).

I measured the resistance from the ground under the seat to the harness, then from the relay connector harness to the fuel pump (by removing the relay and putting the probe in the connector) and its zero, so I'm saying yes.

I can go and turn the key, say, 10 times, and 9 times I hear the fuel pump start. The other time it's silent. That's the time it doesn't start. apart from that, starts every time and no issue when running.

At the moment, the simple solution is, if I don't hear the pump start I just don't try cranking, key off and key on again.

@City Garage completely agree about the charged battery.

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Voodooo said:

Those 9 out of 10 starts, the 10th one, the pump may be on a dead spot on the fuel pump commutator or brushes might be in a dead spot. Try tapping on the fuel pump base next time you notice it not coming on when you turn the key on. If you then hear it buzz, that’s the problem.

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Gojuu said:

@Voodooo given that my fix is "off and on again", wouldn't the commutator be in the same spot when I tried again?

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Voodooo said:

When you turn the key or bike off, there is a 10% chance that the bike won’t start again because the fuel pump isn’t coming on correct?

It’s possible the pump can have a flat spot. When that happens next time, lightly knock on the fuel pump on the bottom side of the fuel tank taking care not to hit the fuel line fitting.

Do this with the key on, while knocking on the pump and if it starts pumping (whining) that will tell you.

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Gojuu said:

@TonyA you've got to remember I'm still a bit new on this bike! This has been a bit of a process I guess. What had happened was, I'd ridden the bike to work - after not long owning it. Then, it just decided not to start. Cranked good......then not as great.....thought the dreaded "I'll flatten the battery soon"......you know the routine. Luckily at that time it started. Happened a few times since, but I tended to notice it at first start when cold, rather then I was somewhere.

It did it a few more times randomly, but I was still learning about the bike and simply wasn't listening for the fuel pump. Lucky each time it started. In some cases, was near traffic or in an area I wouldn't hear it anyway. Some of these times were prior to me doing the throttle body and then ECU change as well - and back then I was also dealing with a bike that stalled at traffic lights when hot, and intermittently idled like a complete donkey. When I did the throttle body change, as well as smooth out the idle, the delete of the IAC had an interesting affect. Ever since then the bike cranks much faster and starts a lot easier. I put this down to the fact that the throttle body lets very little air in for idle, where the heavier load cranking was due to the IAC being opened at crank. I see this as proved by the fact that the bike turns over significantly slower if I crack the throttle.

When it's happened, I thought - well it cranks strong and I know it now idles really well etc. I pulled a plug and there was heaps of spark. Then I just happened to notice one time that I didn't hear the fuel pump start. At that point I didn't actually know if the fuel pump started every time or not (hence all my questions)- but started paying attention.

With regards to the "why doesn't it stop when riding", I believe that is down to the behavior of a relay itself - and a big part of the reason I don't think there is anything wrong with the pump. Relays have two ratings, A Must Operate Voltage and a Must Release Voltage. The MOV is the voltage to switch, and the MRV is the voltage needed to keep it switched. They are sometimes called the Pickup Voltage and Drop out voltage. Almost any relay takes more power to close than it does to stay closed - but have a look at some spec sheets for relays and you will see the values are very different. If I'm dealing with a high resistance joint, as I expect, this explains that behavior.

Click to expand...