Popping and misfiring

[Guest IanJ]

So, I've had this problem for perhaps the last 500 miles. I'll be riding along, usually at cruising speend (4k RPM in 3rd or 4th gear), and the bike will suddenly go "k-PUH!" simultaneous with a tapping feeling near the front of the engine, hesitate for a second, then proceed as if nothing had happened. I have gone through a lot of testing and elimination and determined that it's likely to be the pulse sensor or something related to it.

 

The misfire happens anywhere from idle to above 4k RPM. The bike has been anywhere from just started (began misfiring within a few seconds of engine start) through to pretty warm (20 minutes into the ride). The air has been cool, between 40 and 55 degrees F. Misfires usually happen far apart, with 5 or 10 minutes between events (some rides even go entirely misfire free), although I have noticed a series of events happening in rapid succession, usually when decelerating.

 

The misfire usually happens under very light acceleration -- typically just enough power to maintain 30-40 MPH in traffic. I had noticed a correlation between power application (specifically accelerating with moderate power away from a stop, decelerating slightly to match speed, then resuming speed-maintaining acceleration, at which point it would wait from 5 to 60 seconds, then misfire), but it later proved to be true only some of the time. I have now had the misfire happen twice under moderate acceleration, both times with the engine turning faster than 3500 RPM (exact speed unknown).

 

Due to the highly intermittent nature of the problem, my attention was quickly focused to electrical systems. The bike had been leaned out to try and correct low gas mileage, but the problem remained after re-enrichening the mixture. My dealer pulled out the pulse sensor itself, and discovered that the gap was too large by about 1mm, so it was reshimmed to the correct gap; the problem remained. The condition is so intermittent that it's unlikely to be a mixture or fuel delivery problem, unless the fuel pump is momentarily shutting down. However, the misfire feels like it's just one spark in one cylinder (unknown whether it's only one cylinder suffering from the problem) going missing.

 

The pulse sensor is the sensor that reads teeth on the crankshaft, and which tells the ignition computer the current crankshaft orientation. This information is used to time the spark, and when the pulse sensor signal goes missing, the computer shuts down that spark cycle to prevent damage to the engine.

 

I just called MGNA today to discuss the problem with them (on my dealer's advice) and their answer was "we'll look into it." Who knows what timeline they're working on, though.

 

Why am I telling you all this? Just to share mostly. I'm also very curious to know if anyone else has seen the problem, and particularly whether you were able to fix it. If more people have had the problem, please share your stories, it might help figure out what's going on.

[RichMaund]

My bike had this problem when new. I'd be cruising along at 4k rpm and it would "cough!" and then go back to normal. Just happed once a week or so.

I had balanced the TB's with mercury sticks. My Dealer then set them up with a Twin Max and proved to me that my mercury sticks weren't as accurate! After he balanced them with the Twin Max the problem went away completely and has never returned.

These bikes are very sensitive to throttle Body (TB) balance. It has to be nailed!

I hope your problem is as simple as mine was!

[emry]

My bike did the same as Rich's, but after a dealer service, with the TwinMax, the problem would still occansional happen. Never happened often enough to find. Hasn't done it the past 2000 miles though. The only mod I have made was to increase the fuel pressure to help the "pinging."

[Guest marcialc]

I've got a similar problem with my scura. Sometimes while idling, i've got the idle set to 1100 rpm, the bike will "hiccup" and the idle will drop down to around 600-700 rpm, just for a second and then resume idling at 1100 rpm.

 

I've also experienced "coughing" around 3000 rpm. I've richened the fuel mix via a powercommander by using the buttons [0 low, +1 mid, +1 high] and that temporarily stopped the "coughing". I still get the occassional "hiccup" though while idling.

 

....anyone else experience this "hiccup" at idle?

[dlaing]

I have had it hiccup at idle but, just a few times. I have also had it hiccup at medium light throttle while below 3000RPM. A little enrichment from the powercommander fixed it. The hiccup bites when you are going around a slow speed turn and it hiccups

[Orson]

I've had occassional hiccups...usually at stop lights. I think Guzzis just hate city traffic cuz, out on the open road it's great. I keep hearing Guzzis get stronger with age...maybe it's just going through the process of "loosening up"...nod nod...ya, that must be it (positive thinking)

 

[Guest rotorhead]

I am new to this forum so pls bear with me. I have a 2000 sport with which I have suffer many growing pains, least of which was the malady described here. After much investigation by myself and dealer and after working with MGNA we found that the temp sensor located in the airbox was outta whack causing the ECU to assume that the outside air temp was 125 degrees when in fact was much lower. This caused a fuel adjust by the ECU causing serious "k-PUH" problems for me. My hiccups were much more severe than those described here and in fact rendered the machine unrideable. Hope this helps those in need.

 

I have one question for "emry" please. How do you go about increasing fuel pressure? I too experience pinging under WOT at roughly 4-5k rpm and am interested in trying this fix.

 

Thanks for any help!! I love this site and forum!!

[Guest Brent]

Soon after I experienced a problem with the fuel-pump relay, and had it replaced, I had what seemed to be the same problem. But after swapping out the fuel-pump relay and still having a problem, I suspected that the problem was that most of the relays were loose (I don't mean they were falling out, it's just that I could jiggle them back-and-forth with little effort). I placed a folded rag on top of the relays so that the rag would be compressed by the seat, and the problem(s) went away! I rode to my dealer to have them look at it, and although I can't tell you exactly how they did it (tightened connectors, etc, but didn't replace block), all the relays now are very tight and I've had no problems since (except vapor lock)--not even a hiccup in city traffic. I wonder if many of our phantom problems are simply loose relay connections? It's worth a look.

[Guest Guest]

To increase my fuel pressure I took a old rubber tire valve (schreder valve style) and cut of the bottom portion of it. This was the large round portion that normally goes inside the rim. Then I trimmed some of the rubber covering off to expose the inner metal core. Took a small piece of hose and attched it to the core, the other end of the hose went on to the small air fitting on the bottom of the fuel pressure regulator. (On my Scura it is on the right side of the tank in the rear.) I have a very small air pump that I used to then inflate the valve to 10psi. +10psi is the result. The pump I use is from Suspension Technology and is made to adjust the air-pressure on old style "air" forks that were used un the 80's. If you are going to do this I would not recommend going above 15psi or the diaphram in the regulator may result.

[emry]

I meant to say that damage to the regulator may result.

 

Oops now I forgot to register too.

 

I feel so dirty....

[Guest Guest_vkerrigan]

My 02 LeMans would "stumble" occasionally at low rpm when the ambient was over 85 degrees. After adjusting the valves to .005 (I) & .007 (E), I have had no further problems and it has not affected either power or rpm up top. The only down side would be valve lash clatter which for dinosaurs like me are music to the ears.

[Guest John Sears]

Yeah, I've also had an occaisional "hiccup" - just a momentary stumble at idle. I just blip the throttle and it's gone. I haven't noticed it while underway.

 

John S.

'01 V11S, approx 5000 mi.

[Guest IanJ]

I just talked to Moto International again, and they said that MGNA called them and talked with them about the problem, and they're asking me now to borrow the bike for "a few weeks" to see if they can figure it out. Micha (the mechanic working on this) mentioned that the throttle position sensors might be suspect. I'll mention the airbox temp. sensor as well, though, that could be a candidate. I hadn't thought of intermittent relay connections, but that seems just as likely as anything else (although the bike doesn't pop every time it goes over a bump, and even pops while riding over completely flat ground).

 

I'm glad (in that "good thing I'm not alone" way) that other people have experienced this. Too bad it has to happen at all, though. <_< I'll keep you all up to date on whatever happens with my bike.

[Guest russ]

Ian,

 

Hope they give you a loaner

[Guest IanJ]

That would be nice, but I suspect they won't offer. They know I have a BMW R100 sitting in my garage that I can use. We'll see what happens, but I'm definitely planning on asking what they would do if I didn't have a useful spare bike available.

 

Interestingly, the bike didn't do any of its k'PUH tricks this morning, which has been the coldest time I've ridden the bike, so it's not apparently the external temperature causing the problem...