Engine 'mutters' off-throttle/runs ragged EFI content

[rodekyll]

A constant for me with my FI bikes is some level of 'muttering' -- a gentle backfiring -- at low speeds and fairly neutral/slightly overrun throttle -- like easing through a school zone on level pavement.  I also find some rpm point, regardless of adjustments, at which the engine feels rough and a bit 'sharp'.  I've spent a lot of years tinkering with things like initial throttle open angles, linkage synch, plug gaps, etc.  I can change the qualities of the muttering and ragged feel, but I've never been able to eliminate them.

Fast forward to my 'test platform' -- the trike.  Since I've reinvented about everything about it, all bets are off in terms of what the factory might have done.  It's a great opportunity to look at technologies in their purer forms.  And having muttered enough about the muttering, I'm trying to do something about it.

I've swapped ecu's from Quotas, Lemans, V11, and cali.  Changed cams.  Tried other plugs and gaps.  Different cables and coils.  Different fuel and additives.  I've changed intake runner length and velocity cones.  Nothing in the naturally aspirated inventory eliminates the soft popping and that narrow rpm band of rough feel.  I can move the rpm and throttle ranges that they happen at, but they are always there.

Fast forward some more.  When I was setting up the EFI I asked here what the magic number for fuel pressure is.  I was told ~42#.  Groovy.  I set it there and there it has been.  It mutters on throttle roll-off.  It has a bit of a ragged feel between 42 - 46mph.  Fuel quality has an immense effect on the effects. 

Yesterday I got out the allen wrenches to adjust the air pressure switches on my suspension system and decided to tweak the fuel pressure, too -- easily done with the adjustable pressure regulator.  Bringing it from 42.5# to 44# changed the personality of the engine completely.  The muttering on overrun has all but stopped, and the power pulses have a more "rounded" than "ragged" feel in the offending rpm range.  A lot of the floorboard vibration is simply gone.  I have not yet tried for performance runs with the tweak and I've only got about 50 miles on the adjustment, but in the absence of any "data", the "feel" is more power and smoother operation.

Before the obvious is argued -- I know that the increase in pressure is increasing the amount of fuel per injector pulse, and this in turn riches up the mix throughout the throttle range.  So this sort of experimenting will only work with an open-loop FI, and without a cat-con.  I also know that a single tweak yields a single data point -- I need to dial it up and down from here to see the effects and maybe find an optimal pressure for my engine.  And I know that the engine feeling 'different' and the engine being 'better' are two different concepts.

I have some work ahead of me, but this starting point has me encouraged.  Opinions?  Has anyone else played with fuel pressure to get around these annoying little problems?

[normzone]

"  Has anyone else played with fuel pressure to get around these annoying little problems? "

No, my attempts have been limited to noticing that when I wash my bike it runs better, but mine has all the muttering and grumbling symptoms that yours does, and you can count me along for this ride...

 

[fotoguzzi]

good info.. the one other thing that comes to mind is the trim setting.. do you have the VDST or other diag tool to reset trim?

[rodekyll]

Yes, I have the vdst on my computer.  It tells me a lot.  One of the things it says is that occasionally an ecu can reset to odd idle values.  Another thing is that there are very different initial timing points for the various ecus.

"  Has anyone else played with fuel pressure to get around these annoying little problems? "

No, my attempts have been limited to noticing that when I wash my bike it runs better, but mine has all the muttering and grumbling symptoms that yours does, and you can count me along for this ride...

 

What is the 'washing' to which your refer? 

[lazlokovacs]

interesting stuff...

waiting for the FI gurus to chip in...

[pete roper]

David? Have you tried just adding fuel to the map at the points you think it needs it rather than upping the pressure? Upping the pressure seems like a very crude way of achieving higher delivery.

Pete

[twhitaker]

A constant for me with my FI bikes is some level of 'muttering' -- a gentle backfiring -- at low speeds and fairly neutral/slightly overrun throttle -- like easing through a school zone on level pavement.

At the risk of stating the obvious 'They all do that.' was what I was told after I got my Cali 20 years ago. I sealed the exhaust, I tried the powdered comanche with some success. Now it's character.

[rodekyll]

David? Have you tried just adding fuel to the map at the points you think it needs it rather than upping the pressure? Upping the pressure seems like a very crude way of achieving higher delivery.

Pete

Not since I retired my Power Commander.  It was an annoying process for me.

[beetle]

Upping the fuel pressure can be beneficial at WOT.


By 'muttering', are you referring to the grumble on the overrun, as opposed to popping?

[normzone]

So (exposing my ignorance here, and a no doubt unjustified faith in tech and designers), upping the fuel pressure does not simply result in the FI moderating the pulse duration to compensate in an attempt to deliver the same amount of fuel?

[beetle]

For most Guzzi's that I would consider 'affected' by this thread, no. I can't speak about the 7SM in the Cali 1400, because I don't enough about it yet. If the 7SM is capable, I doubt Guzzi would bother anyway.

[rodekyll]

So (exposing my ignorance here, and a no doubt unjustified faith in tech and designers), upping the fuel pressure does not simply result in the FI moderating the pulse duration to compensate in an attempt to deliver the same amount of fuel?

A 'closed loop' FI would notice the extra fuel and attempt to compensate for it.  My 15M is an 'open loop' FI -- no O2 sensor or cat -- so it doesn't monitor the mix.

Beetle -- By "muttering" I mean a soft popping, almost intermittent burbling sound, like it's making comments under its breath.  I can't really tell if it's coming from the intake or exhaust side.  It sometimes gives a pop strong enough to feel, but it's more of a noise than an outright stumble.  On a Convert this can be bad, since a good belching backfire is sufficient to strip the hex off the ATF drive shaft.  Since my 'verts have all been converted to FI, the potential for the popping to become a backfire is a real concern for me.

[rodekyll]

 It was mentioned above that altering the mix along the entire throttle range is a ham-handed approach to dialing out discrete drivability complaints that a simple map tweak at a handful of points would also accomplish -- without affecting the properly mapped parts of the table (ok- so I paraphrased Pete.  He wishes he'd put it that way.     ).  And to the extent that he's 100% not asking for any beer to be held as he points out that I am, he's 100% correct.  It's the equivalent of those O2-cheaters folks try to use on closed-loop efi. 

But what if the problem is always just a bit there no matter how tight your exhaust clamps, well adjusted your valves, and finely tweaked your TB synch?  I've gone so far as to disassemble and reseal my throttle shafts, and I know from topics here that others have chased the frustration to the same nit-picky level.  And the final answer has always been:  don't ride it there, don't ride it there much, and when you do ride it there, mutter back, just a little, under your breath.

Do you suppose the factory actually checked the regulated fuel pressure when they built the early generations of EFI bikes, or is it possible that some of these problem cases among (at least) the early, open-loop FI variants are actually due to the pressure being low or out-of-range?  Could the pressure value of the relief valve change over time?  Is the true source of the oft-quoted "lean running from the factory" complaint low pressure along the entire throttle range?  Is it why one OEM bike isn't as "hot" as it's siblings? 

[dramatic music and fade to black]

I just did a full tank of fuel out of the 3VL-TWIN and got 30.014mpg in sloppy Sitka driving (we'll call it 30mpg).  For lack of a dyno (and horrified at the thought of abusing my machinery that way), I'll run 100 miles with the pressure turned to where I 'feel' it should be and report back.  It will take a day or two to tweak it to adjust it to that pressure point, which appears to be +2# or less.  If I can accel and hold the hills better through the areas I've been measuring performance, AND hold or increase fuel economy, AND reduce or eliminate the floorboard buzz, muttering, and that narrow, raspy part of the power band, then I'll feel that for this machine, the fuel pressure was low.

An FYI -- if this shows promise, it should be easily adapted to any external pump FI bike for about $30.  Even easier for the potseed tank conversions to efi. 

[beetle]

Still can't get my head around what you mean by 'mutter'. Unless it's actually popping or backfiring, a burble on the overrun won't hurt anything, and is a sound I enjoy.

Is the true source of the oft-quoted "lean running from the factory" complaint low pressure along the entire throttle range?  Is it why one OEM bike isn't as "hot" as it's siblings? 

Er, I think that's a stretch. You can blame Euro 3/4 and 'trim it until it's lean, bitch' factory approach. The latter is suspect until properly setup and tuned.

[rodekyll]

It's a slight popping or backfire that happens at low speeds and even or slightly downhill terrain as you roll back the throttle and/or a slight amount of engine braking may just be noticeable -- or you could be at that point of 'coasting'.  In other circumstances I'd attribute it to the early throes of running out of gas.  I enjoy a proper burble and the sound of engine braking as the throttle is snapped off hard.  This is not it.

I'm legally deaf, so you have to cut me a little bit of slack on the nuances of this thing you call noise and where it might be coming from.  From my point of view it's a good day when I know noise is out there.  Intake or exhaust, muttering or burbling -- through a helmet, knows?  To me everything sounds like a radio station not-quite-dialed-in, like it's raining hard on what I want to hear or that people are talking in the next room.  Don't get me started on the tinnitus.