Engine cuts out at moderate throttle opening

[datsaxman@hotmail.com]

Was running the MERA 5nDime rally.  Ten days, 10,000+ miles, going to bonus locations to get photos, etc.  9490 miles and nine days into it, the Concours started running rough and I could not get it fixed in time to stay on schedule, so I ended up with the dreaded DNF.  Bad gas?  flushed and refilled, then added chemicals.  It got better.  Then it got worse again.  I kept trying to understand the problem, while still staying on the bike and heading toward the Finish. 

Power Commander fail?  Ground trouble?  Trying that next.  There are some clues: Runs great with a full tank, progressively worse as the tank empties.  Is this a familiar problem? 

Thanks in advance if it is.  The problem solving is further complicated by the fact that it runs well for an hour or two, then starts running crappy again.

saxman 

[maxtog]

Well, we just had a thread about clogged fuel filters... might be something you want to check.

[datsaxman@hotmail.com]

Thanks, Max...I just read that a couple of days ago (limping home from the rally), and again now.

I just replaced the fuel filter, so that is not it.  Fuel lines clean, straight, etc.  Electrical connections from tank are perfect. 

re: that other thread...I doubt that it is the fuel pump, despite what the dealer says.  I am a factory trained tech too, some years ago.  They are guessing, since it is hard to make the problem appear when you want it to. 

Mine:  Shutting off the ignition reboots the system, and the problem goes away at least temporarily.  Worse in hot ambient temp.  Much worse with low fuel level.  (Yeah...makes it sound like the fuel pump, doesn't it??)  I rode the thing home 1600 miles like this, so there is some data.

I am going to run a direct ground to the PC and see if that helps.  The problem is really made more complicated by the fact that it is intermittent. 

saxman

[MAN OF BLUES]

So looking at your first post, and reading twixt the lines, you are running big throttle bodies now... they ned to be fed well. Couple this with running almost 10k miles, or maybe even more, since you replaced that boogered filter, i'd place my money on the filter is once again goobered. Think about it, you ran in excess of 40 tank fulls of questionable gas from who knows where/ or what was in the stations underground cesspools..... pull the filter again. We have seen bikes with 5k on them with filters that looked like coalmine airfilters...do the simple stuff first... that is an easy job....compared to chasing unknowns.

[gPink]

While you've got your tank out of the way you might as well check the air filter.

[maxtog]

I can't think of anything that could possibly explain the behavior as changing depending on the level of fuel, other than fuel filter or fuel pump. 

You say it is worse with high ambient temp.  And the fuel is likely to be much hotter when there is less of it in the tank.   Your description doesn't really sound like pre-ingnition or ping.... but are you using the correct octane fuel?  Could be a hot spot on one or more of the spark plugs?

[B.D.F.]

The Power Commander is the next place I would look to, starting with the ground wire to the P.C. and then eliminating the P.C. entirely to see if the problem goes away.

Unfortunately, the fact that it gets worse as fuel level drops does NOT point toward anything electrical or involved with the ignition but back to the fuel delivery system. It is possible that something other than the screen is wrong with the fuel pump ass'y, such as the pump itself, the pressure regulator or even something simple like a fracture in the plumbing inside and around the fuel pump. Any / all of those things would cause the symptoms you describe. While a bit more difficult to diagnose, it is straightforward to test the entire fuel delivery system by putting a pressure gauge in the fuel system and watching the pressure in 'real time' as you ride the bike. If it drops or changes more than 1 or 2 PSI then there is a fuel delivery problem.

Brian

Thanks, Max...I just read that a couple of days ago (limping home from the rally), and again now.

I just replaced the fuel filter, so that is not it.  Fuel lines clean, straight, etc.  Electrical connections from tank are perfect. 

re: that other thread...I doubt that it is the fuel pump, despite what the dealer says.  I am a factory trained tech too, some years ago.  They are guessing, since it is hard to make the problem appear when you want it to. 

Mine:  Shutting off the ignition reboots the system, and the problem goes away at least temporarily.  Worse in hot ambient temp.  Much worse with low fuel level.  (Yeah...makes it sound like the fuel pump, doesn't it??)  I rode the thing home 1600 miles like this, so there is some data.

I am going to run a direct ground to the PC and see if that helps.  The problem is really made more complicated by the fact that it is intermittent. 

saxman

[Rembrant]

The problem solving is further complicated by the fact that it runs well for an hour or two, then starts running crappy again.

saxman

If it isn't the Power Commander, it's likely fuel related.

Did you change the fuel filter after this problem started and it did not go away? Or did you install a new fuel filter before the trip?

A friend of mine just went through this exact same problem. Installed new fuel filter shortly before leaving on a trip, and ended up having to drain the tank and clean the new fuel filter in a hotel parking lot. It was dirty, and once cleaned, the problem disappeared.

The fact that it doesn't happen when the tank is full points to two different things imho. The pump's NPSH...or net positive suction head...if there is a suction issue, the more fuel in the tank will help relieve the problem by increasing the suction head. (I work with pumps for a living...lol, I'm used to these issues;)

http://en.wikipedia.org/wiki/NPSH

Also, could be fuel tank venting. If the tank is not venting properly, you will pull a vacuum in the tank when the fuel level drops. I know it's more of an issue for gravity fed carbureted motorcycles, but it's still a possibility. You can test this by popping the fuel filler cap open when the fuel level is low, and see if you still have the same problem.

I've been around a lot of Power Commanders, and I've personally never seen one fail. Ever. I have however seen some of them cause problems due to chafed wires and/or poor grounding, which are installation issues. If I work on a bike with "issues", I always disconnect the PC first, just to rule it out.

JMTCW,
Rem

[datsaxman@hotmail.com]

Thanks for all the replies.

Brian and Rich: Yes, it was a fresh fuel filter with just a few miles on it at the start of the rally.  Probably I was replacing the stocker at 70,000 miles.  Tank is full right now, but once it is empty I will certainly check that.  And will check fuel pressure in real time if simpler things don't work first.

PC is properly grounded with a dedicated wire to the frame.  No measurable resistance to the battery negative post.  I disconnected the PC terminal blocks, and the ground, and cleaned the connections to see if that will help, but have not tried that yet.

Max, it is not an octane or detonation or pre-ignition problem or spark plugs, but thanks for the suggestions.

Rembrant, are you saying you think their is cavitation?  I never had the fuel level low enough to see the LOW FUEL warning, which means appx. 1.0 gallons remaining, at least on mine.  The cutting out is really throttle position dependent, FWIW.  Agreed that venting, thus low ambient tank pressure, might be a problem. 
 

saxman

edited to fix the spelling of people's screen names.  sheesh. 

[datsaxman@hotmail.com]

Oh, and re: fluid and suction head...

Aux. tank raises the gravitational head more than the whole tank height.  Opening the (gravity fed) tank valve should give it a fat boost there.  Yet it actually filled the aux. tank from the main tank at one point.  That makes it sound like there is + pressure in the tank.  How else to push the fuel uphill into the aux tank?  The tank is supposed to have a slight + pressure, right?  Thus all of the hardware around the filler cap.

Venting problem??  Checking today...


saxman

[B.D.F.]

Possible but not likely a venting problem IMO. Cory (Rembrant) is right in that a clogged or failed vent will raise havoc with a carburated motorcycle but for better or worse, the main result of a failed vent on a F.I. bike is a crushed tank. It is all about the pressures (and vacuum but I hate that word in this application becuase it conjeurs up the idea that there can be negative pressure.... which is IMPOSSIBLE). As F.I. engine fuel pumps normally generate 70 + PSI, a mere 14.7 PSI atmospheric pressure is no match and when push comes to shove, the tank will simple collapse, literally, with the engine running perfectly all the while. No warning either until the space between your legs gets narrower :-( 

Again, I propose a fuel pressure test (in real- time, as the bike is ridden) as a definitive measurement and valid test of your bike based on the symptoms you describe.

Best of luck with this.

Brian

Oh, and re: fluid and suction head...

Aux. tank raises the gravitational head more than the whole tank height.  Opening the (gravity fed) tank valve should give it a fat boost there.  Yet it actually filled the aux. tank from the main tank at one point.  That makes it sound like there is + pressure in the tank.  How else to push the fuel uphill into the aux tank?  The tank is supposed to have a slight + pressure, right?  Thus all of the hardware around the filler cap.

Venting problem??  Checking today...


saxman

[Rembrant]

Rembrant, are you saying you think their is cavitation?  I never had the fuel level low enough to see the LOW FUEL warning, which means appx. 1.0 gallons remaining, at least on mine.  The cutting out is really throttle position dependent, FWIW.

Well, you can forget the word cavitation...it doesn't really matter. If a pump does not have access to all of the fluid it requires on the suction side, it may cavitate. For all intents and purposes, I was just trying to say that the pump couldn't get enough fuel, and was theorizing as to why it worked better with a full tank.

Brian, have you seen these pumps fail mechanically? I mean, forget about the electric motor, and forget about the pressure relief valve. I'm referring to the impeller and casing?
Or are pump failures basically limited to weakened pressure relief valves?

What I'm wondering is, what happens if you operate an EFI motorcycle for an extended period of time with a clogged fuel filter? Does it just perform poorly until the filter is changed, or does it actually damage the pump the longer you go?

Just curious of course. Rem

[VirginiaJim]

Based on anectdotal evidence from this forum, I can't say that I remember (going back to the summer of 2007) anyone reporting a 'bad' pump per se.  As the filter is integral with the pump, many have probably been replaced because of clogging.  As far as an actual pump going bad.....?

[B.D.F.]

I have seen these types of fuel pumps fail (got a bad one in a Ford Expedition right now) but none in a C-14 specifically. No matter, there are only something like three (3) pumps that are used on more than 95% of the world's production vehicles.

Low fuel pressure and low fuel volume are the typical modes of failure (both together, not one or the other) and I do not know exactly what fails. The pumps are true turbine pumps with no mechanical displacement and no physical contact so it is curious to me how they fail. I know running them dry will allow the hydrodynamic bearings to 'clank' around inside the housing and destroy the bearings, even when full fuel flow is restored. Perhaps the OP's pump was starved of fuel long enough to cause a bit of damage to the bearings and now the pump cannot achieve full pressure? Pure speculation but the symptoms and results makes sense at least.

But in the end, low fuel levels bringing on poor running really indicate a fuel delivery problem IMO and IME. And because the fuel pump ass'y is, well, and assembly, not much point in wondering what specific part it is 'cause the new one will cure it :-)  About $90 from Ebay if you catch one at a decent price, otherwise a bit more.

Brian

Well, you can forget the word cavitation...it doesn't really matter. If a pump does not have access to all of the fluid it requires on the suction side, it may cavitate. For all intents and purposes, I was just trying to say that the pump couldn't get enough fuel, and was theorizing as to why it worked better with a full tank.

Brian, have you seen these pumps fail mechanically? I mean, forget about the electric motor, and forget about the pressure relief valve. I'm referring to the impeller and casing?
Or are pump failures basically limited to weakened pressure relief valves?

What I'm wondering is, what happens if you operate an EFI motorcycle for an extended period of time with a clogged fuel filter? Does it just perform poorly until the filter is changed, or does it actually damage the pump the longer you go?

Just curious of course. Rem

[datsaxman@hotmail.com]

Thanks again for all of the discussion and info and stuff.

I can get a brand new //pump// for $35, delivered...or a used //assembly// for $90. 

Used. 

As in ... "questionable provenance at best."  As in "what I already have."  Underwhelming.

So it seems that the putative failing/failed part really does matter.  Oh, and the pump comes with a shiny new teabag filter, too.  Which may be the culprit all by itself anyway.

History: // I // have never run the fuel level down to the point where the pump was looking at less than about 3 litres of fuel.  20 miles into the DANGER, WILL ROBINSON...LOW FUEL zone.  I wonder how low it has to get before the pump begins its rattly dry self-destruct sequence.  But who knows about the original owner?  P.S. Chet, I have TWO C14s these days...this is the other one.


More:  Rode 300 miles yesterday, no issues whatsoever.  Including a couple of short, full-throttle blasts at (fairly) ludicrous speed...smooth and good when there is lots of fuel.  Will be extracting the pump tonight or tomorrow to investigate further now that the fuel level is low enough to do so.


saxman

[datsaxman@hotmail.com]

One
More
Thing

Brian, what would you use to measure fuel pressure, specifically?  Do you have/use such a thing?
Make, model, etc.  The concept is simplicity itself, just trying to save a little investigative time and effort.

Thanks,
saxman

[B.D.F.]

Again, pretty to test the fuel pump- an empty container and full pump flow for XX time and as long as it meets minimum volume it passes test #1. The other test is a fuel pressure test; ideally under real usage and in real- time but also useful to test a pump static- just make sure it rapidly rises (easy boys!) to spec'd pressure and stays there (this also tests the pressure regulator).

As far as how low is too low... as long as the pump can 'sump' or draw enough fuel to make full pressure, there is sufficient fuel. Put another way, about two seconds before the first symptoms of running out of fuel is fine; it is only the point where the pump is not drawing pure gasoline and instead starts to such air that is a problem. So it is really a enough / not enough line rather than a range of acceptable fuel left in the tank.

Brian

Thanks again for all of the discussion and info and stuff.

I can get a brand new //pump// for $35, delivered...or a used //assembly// for $90. 

Used. 

As in ... "questionable provenance at best."  As in "what I already have."  Underwhelming.

So it seems that the putative failing/failed part really does matter.  Oh, and the pump comes with a shiny new teabag filter, too.  Which may be the culprit all by itself anyway.

History: // I // have never run the fuel level down to the point where the pump was looking at less than about 3 litres of fuel.  20 miles into the DANGER, WILL ROBINSON...LOW FUEL zone.  I wonder how low it has to get before the pump begins its rattly dry self-destruct sequence.  But who knows about the original owner?  P.S. Chet, I have TWO C14s these days...this is the other one.


More:  Rode 300 miles yesterday, no issues whatsoever.  Including a couple of short, full-throttle blasts at (fairly) ludicrous speed...smooth and good when there is lots of fuel.  Will be extracting the pump tonight or tomorrow to investigate further now that the fuel level is low enough to do so.


saxman

[Son of Pappy]

So, 2 C14s?  Do tell, and FWIW, Silverdammit is the way to roll!!!!!

[SpazOnaConcours]

FWIW, I had this same problem in NM coming back from the TN rally..... it was a venting/vapor lock issue. The combination of a long haul in the high heat, poor cap venting (I had to use some grease to lube the cap lock a few states prior), and the fact that all my emissions hardware has been capped and removed led to the perfect storm near the end of a tank of gas.

 Hope you get yours figured out OP.

[Jeff]

  Oh, and the pump comes with a shiny new teabag filter, too.  Which may be the culprit all by itself anyway.

There's your problem right there! Replacement part is 49019-0013

I've had to replace mine a couple of times, while the weight of the full tank helps get the fuel through as soon as you get low you've got a problem. Last time it happened to me I was coming back from Kalgoorlie and had to keep topping it up what a PITA.

Hope this helps.