B4 750 low rpm stalling, intermittent rough running - MVAgusta.net
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post #1 of 13 (permalink) Old 08-17-2019, 12:10 AM Thread Starter
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Question B4 750 low rpm stalling, intermittent rough running

Bike stalls/comes close to stalling at low rpms, more severe when under load (riding through a parking structure vs testing it in park). Sometimes when I start it, it runs really rough and stays that way, like it's in a "Limp Mode." Sorry for the long post, wanting to get out all the information I've gathered:

Bike:
2004 Brutale S. Microtec w/ a map sensor and lambda controller that I've been autotuning with and refining the fuel map with Chris. Current fuel map was working pretty great for months, and since this problem is inconsistent, I don't suspect the map.

Shorai LFX19A4-BS12 battery

Stalling:
Seems to be more likely when the engine is hot, and most sensitive when the fan is running. I can avoid stalling by using much more throttle and feathering the clutch vs how I'd normally ride, but this gets problematic when lane filtering or trying to be respectful going through parking structures or rolling into/out of my apartment driveway. It's fine at idle, this only happens with slight throttle. Above 2,500rpms or so and everything is groovy, except when...

Limp Mode:
This ONLY happens from a start, my bike never "switches" to this problem while running. VIDEO HERE. This is monitoring the microtec readout. It's running normally at first, and I'm trying to just crack the throttle to get it to stall (which it does.) Then when I start it immediately after, we're in Limp Mode. Notice how low the rpms are even when I twist the throttle far open, and how lean it's running.

Don't read into the battery voltage reading on that screen. That's always been 1 to 2V lower than what I read on a multimeter connected to the battery at the same time.

Does it seem like it's only running on 2 cylinders? I've never experienced that before so I don't know what it would be like. And if so... why would it be so intermittent?

Last thing done on the bike:
My 40A fuse blew at the starter relay. I checked everything over for a short, didn't find one. Disconnected and sanded all cables and contact points to the charging and starting system. Also cleaned up and tightened the 4 spade connectors that plug into the starter relay.

Other Data:
If I start the bike from a controlled shut-down, it is less likely to run poorly. If I start the bike after stalling it, it's a much higher likelihood of being in limp mode

I get 0.1 Ohms of resistance through every cable in the charging system, which is the inherent resistance between the leads of my multimeter to begin with. With bike running normally, I get about a 0.5V voltage drop between the alternator B post and battery positive at 5,000rpm, and less than 0.2V testing the ground side.

The battery isn't the issue. It was on the shorai charger to recharge and then rebalance after the 40A fuse blew and triggered the low voltage warning light, and then sat disconnected for a month without dropping below 13.31V. Bike cranks and starts right up, whether it's going to run properly or not. Open voltage on my battery is typically 13.4V+, drops to about 12.3V while engine cranks to start. When running normally, I get 15V at the battery at 5,000rpm. Somewhere around 14.5V at 2,000rpm. This is normal for my bike

If there's a higher electrical load on the bike, Limp Mode is more likely: If I hot start the bike above fan-running temp, it'll almost always be limping. If I kill the engine, let the fan run and cool down until it stops, and then start the bike, it's often times fine. BUT--this also happens in other circumstances, too. Happened yesterday trying to start while the engine temp was 184*F (my fan is set to come on at 212). Happened the other day when I rolled it out of the garage first thing in the morning. In both instances, I shut it off, and started it again almost immediately--didn't move the bike, was still sitting on it--and it ran fine except I could feel it's desire to stall at low RPMs

Attempted Fixes:
Went back through all the charging wiring, cleaned, reconnected. Checked resistances and continuity to grounds all over again. Made sure the fuel lines weren't pinched or kinked against the crossbar of the frame when I put the tank back on. Tried older versions of my fuel map. No improvement anywhere

chris chandler
2004 Brutale S

Last edited by chandler325i; 08-23-2019 at 07:03 PM. Reason: relabeled Shit Mode to Limp Mode because that is a more correct term for it. Thanks Chuck
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post #2 of 13 (permalink) Old 08-17-2019, 01:59 AM
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Quote:
Originally Posted by chandler325i View Post
Bike stalls/comes close to stalling at low rpms, more severe when under load (riding through a parking structure vs testing it in park). Sometimes when I start it, it runs really rough and stays that way. I refer to it as "Shit Mode." Sorry for the long post, wanting to get out all the information I've gathered
Does the microtec have tune history/restore points? Whenever i have something like this i load an old tune of which i am sure it is good and i switch the plugs. Did you switch plugs? I flooded and killed the plugs a few times. Gave the same type of issues. Now whenever i have a problem i switch the plugs and load a restore point. Solves the issue 9/10 times. Honestly 9/10 issues i had were caused by myself because of an incorrect setting in the tune. How did you verify the running on 2 cyl? I also had the stalling issue on hot days on a hot engine when the ignition coil dwell was set too low. How is the map sensor set up? For Baro correction or for manifold vacuum?

Also don't use iridium or other fancy plugs at all when playing with ecu settings. Iridium plugs are very good on a well tuned engine but they are also very sensitive and will fail easily when over richening. Just get the basic cheap plugs recommend for your engine when playing with the tune. They are also cheaper to replace and when the tune is fine you can still switch to iridium plugs.

2003 MV Agusta Brutale 750S

Last edited by Robbedoes; 08-17-2019 at 05:17 AM.
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post #3 of 13 (permalink) Old 08-17-2019, 03:26 AM
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Quote:
Originally Posted by Robbedoes View Post
Does the microtec have tune history/restore points? Whenever i have something like this i load an old tune of which i am sure it is good and i switch the plugs. Did you switch plugs? I flooded and killed the plugs a few times. Gave the same type of issues. Now whenever i have a problem i switch the plugs and load a restore point. Solves the issue 9/10 times. Honestly 9/10 issues i had were caused by myself because of an incorrect setting in the tune. How did you verify the running on 2 cyl? I also had the stalling issue on hot days on a hot engine when the ignition coil dwell was set too low. How is the map sensor set up? For Baro correction or for manifold vacuum?
Long story short,try fitting Iridium spark plugs.Fixed my bike on low RPM stalling.
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post #4 of 13 (permalink) Old 08-17-2019, 03:58 AM
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Like Mitchy says, although I've not fitted iridium plugs. New plugs make a huge difference. I've found mine to drop both plugs and coils randomly. Also I have a Microtec from Chris. Long story but I tried auto tune and wasn't a fan. Much better to find a good map and play with it from there. Also a throttle body balance is good.

Cheers

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post #5 of 13 (permalink) Old 08-17-2019, 05:27 AM
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Quote:
Originally Posted by Deano View Post
Like Mitchy says, although I've not fitted iridium plugs. New plugs make a huge difference. I've found mine to drop both plugs and coils randomly. Also I have a Microtec from Chris. Long story but I tried auto tune and wasn't a fan. Much better to find a good map and play with it from there. Also a throttle body balance is good.

Cheers

Deano
The thing with Autotune by Air fuel ratio and dynotune by maximum torque (hp) is that you can optimize the tune for a specific AFR or max power very close but is does not necessarily mean you will get the best response, smoothness, driveability etc. You can't Autotune that. For that you need somebody with experience, who knows the ecu and engine (like Chris or Adam).

2003 MV Agusta Brutale 750S
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post #6 of 13 (permalink) Old 08-17-2019, 07:37 AM
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You need to see what voltage is when the fan is on while trying to crank.

As you say it goes into shit mode then.

Sounds like a voltage issue to me. If the ECU has a voltage cut out, like the stock ECU, then it could trigger limp mode when voltage is low.

Now, why did the 40 amp fuse blow? If you haven't found the cause, it is still lurking....you get high amperage with low voltage...

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post #7 of 13 (permalink) Old 08-17-2019, 08:42 AM
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I think you have some poor electrical connections...not necessarily on your charge system. I would have a good hard look at the connectors for the coils and injectors.

And fresh plugs (what do the plugs you take out look like?)....

And don't forget fuel delivery.....hows that filter and hoses?...and air leaks, how are those little hoses to the frame sides and their caps?

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post #8 of 13 (permalink) Old 08-17-2019, 09:05 AM
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Shouldn't your idle rpm be 1200+, from seeing your video it's high 900? It doesn't seem like much but it really makes a difference.
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post #9 of 13 (permalink) Old 08-17-2019, 12:31 PM
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this sounds as if it needs a tune up your idle should be 1100-1200 rpm i have just had very similar problems with
my 910s brutale it was 35c and ran like a pig cut out when hot ran shit at about 2000-2500 rpm got home
and reset everything TPS, Throttle sync, and reset idle screw and reset co , the only difference with your setup is you have a microtec ecu
my bike runs when hot with fan on no cutout picks up clean right through the rev range hope this helps.
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post #10 of 13 (permalink) Old 08-17-2019, 01:33 PM
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Mine idles at 1450 - 1500 rpm... But like said before, the most important thing is the CO value!

If its too high, it will be a pig when hot, and stall. Crank it leaner untill it runs properly?

F4 750 with Brutale 910S motor
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