Possible dying fuel pump? - Sportbikes.net
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post #1 of 4 (permalink) Old 04-17-2007, 01:57 PM Thread Starter
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Possible dying fuel pump?

This might be long. Apologies in advance!

First, the background. I had a bit of a highside at the end of last season. Long story short, cold ground + cold tire = little traction. Part of the damage required a new right-side clipon. Since the throttle cables were already disconnected at one end and I was going to change plugs anyway, I decided to change the throttle cables as well as the clutch cable. Everything went smoothly and the bike showed no signs of trouble after buttoning everything up and starting it. Due to the glorious misery that is New England weather, there have been few riding days since the beginning of "spring". The bike sat in the garage for a two to three week period. During that time, I purchased an HTEV eliminator from Hass Motorsports (a side note: they are great folks to work with. The part is well constructed and was a cinch to get installed. Nice work by those guys) and installed it. It also came with a new PC3 map, which I dropped in. During my season maiden voyage, I noticed things I hadn't before. For starters, it seemed that the fuel pump was running a little louder than normal. While I noted it, I didn't pay all that much attention because I was being overly critical of noises since I'd had the bike apart over the winter. While riding it and within the powerband, I heard VERY different noises coming from under the tank (I believe). It sounded like some sort of pressure build and release when I would get on or off the throttle, respectively. Having had some strange sounds coming from automobile exhausts in the past, I added that to the list of possible causes. I've since emailed Hass, and they don't think and have never heard of this sound being generated from the removal of the HTEV.

So, here's what I've got. Something, I'm guessing the fuel pump, is making sounds when I'm in the powerband. It's loud enough that you can hear it over normal engine noise (the engine will drown it out when you get to higher revs) on accel- and deceleration. On decel, if I close the throttle completely it's quite a distinctive sound. It almost sounds like a blow-off valve or something. It's more difficult to hear on acceleration, but it's there nonetheless. At idle if I put my ear close to the tank, I can hear the pump running, which I don't believe I've heard in the past. I've taken the bike for a few rides and the sound has been consistent. I don't notice any performance loss or jerkiness which I would expect if the fuel rail wasn't adequately pressurized at all times. Quick on-off-on produces what I'd expect, a wheelie - no bogging or anything like that.

Here's what I've done. Swapped the PC3 map back to what it was before the installation (just a Jardine slipon and K&N), assuming that the new map just plain needed more fuel in certain rev ranges. No noticable difference in the sound, but noticable on performance. (I guess those things really do work! ) I've raised the tank and looked for pinched fuel and/or vent lines. Didn't see any. As I mentioned above, I confirmed from Hass that it isn't an odd-sounding exhaust noise. I haven't put the HTEV valve back on there because I'm pretty convinced that it's not the part causing the issue.

I'm not what the next step is going to be. Check with you guys first, then bring it to the dealer which is conveniently right down the street. I don't want to send it to them for repair, but have one of the guys ride it and hear what I'm hearing and offer some suggestions. I'm leaning towards a failing fuel pump - perhaps it got "damaged" (though there was no tank damage) in the highside? As of the end of last season the pump was fine however I'm not sure if they "start to fail" as opposed to "work one day, dead the next".

Whaddya think, and thanks in advance.

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post #2 of 4 (permalink) Old 04-17-2007, 04:38 PM
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Warning: the following is based entirely on my speculation. I have no practical experience in this.

Ok, my first thought about the fuel pump is that I don't see why it should be "strained" when you're in the powerband. Certainly more power demands more fuel, but since there is a pressure regulator (right? I'm assuming your bike is like most cars) and return lines, it seems to me that the demand on the pump should be fairly constant - ie: it's always pumping at the same rate and to more or less the same pressure, with the key difference being whether the fuel flows through the injectors or back through the return lines. All of this is assuming your pump is flowing enough fuel, which, considering you're not complaining of stumble at WOT, it is.

My second thought is, "Why would the pump be noisy on decel?" Even if my first thought is wrong, on decel the injectors are flowing very little fuel, if any at all. So this shouldn't be affecting the fuel pump much differently than if the bike was just sitting at idle, for example. As long as the pump is electrical (it is, right?) there should be no direct correlation between it and engine RPM.

The only possible thing my amateur mind can think of regarding fuel that could be causing your noises, is a connection to the fuel pressure regulator. Now I have no idea where these parts are located on your bike - or even if they exist - but EFI systems on cars have a vaccuum line connected from the intake manifold to the pressure regulator. What it does is alter slightly the amount of fuel pressure based on the amount of vaccuum in the manifold (so that the injectors allow in consistent amounts of fuel regardless of the amount of engine vaccuum). I can imagine if that connection isn't tight, you could be getting some hissing and sucking noises, especially on decel at higher RPM, when engine vacuum is high.

My best guess: leaking vaccuum line, leaking exhaust or kinked fuel return line (although I know you say you already checked for pinched lines).

Good luck and let us know what it is. You have my curiousity.
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post #3 of 4 (permalink) Old 04-17-2007, 04:47 PM
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Yes, a lot of (if not all) bike with fuel injection have fuel pressure regulators.

A similar noise has been described by triumph owners who have forgotten to connect the hose to the pressure regulator when they remove their tank for whatever reason.

Check BOTH ends of this hose, not just the one on the tank..

Hopefully that may help.

Oh- and in my experience, fuel pumps work. Or they don't. There's not much in-between. usually you can get a fuel FILTER that does not work all the way...

But this does not sound like a fuel pump problem.

Also- check the vents on your tank, as well as the crankcase breather lines.

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post #4 of 4 (permalink) Old 04-17-2007, 05:27 PM Thread Starter
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Thanks for the ideas, fellas. Work brings me to LA this week, so I won't be able to test this stuff till next weekend. I don't recall ever reconnecting a line to the regulator, but then again I don't recall disconnecting one either. I'll certainly keep you updated.

Thanks again.
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