RC 390..top end power loss,overheating,running lean? ,low oil pressure.

GOJO

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Was just wondering if it only happened at elevation if it could be a barometic pressure fault or map sensor , air pressure would be just over 10% difference (thinner) at a 1000mtr from sea level so would have the effect of running rich over fuelling . Altough im not sure how much of a effect it would have Just a thought.
 

shreeshar7

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Was just wondering if it only happened at elevation if it could be a barometic pressure fault or map sensor , air pressure would be just over 10% difference (thinner) at a 1000mtr from sea level so would have the effect of running rich over fuelling . Altough im not sure how much of a effect it would have Just a thought.
Nope..all those sensors replace.. Plus ive ridden at even higher altitides with no issues.
 
D

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Any updates on this problem? I'm experiencing similar issues.
 

ReidMcT

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I would check the brakes, to be sure they are not dragging when the bike is hot. Also, as mentioned above but maybe not yet addressed: have the battery load tested.
 
my two cents :
reading again this thread, I'm thinking it could be also a clogged vent hose from fuel tank : everything OK at the beginning, then the fuel pump does not succeed to provide enough pressure difference with tank, so fuel pressure drop slowly.
If the workshop check the pressure, it will be good, because it's only after a distance that it would drop...
 

Akshay

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I'm also thinking on the similar lines, infact replaced my battery as it was weak. Thought that could be one of the reasons why the fuel pump could not pump sufficient fuel for those speeds. You make a valid point about the fuel hose I better get the fuel hose checked.
Only thing I assumed left out was to the fuel pump all together. But it's again strange because the fuel pump works perfectly normal at lower RPMs.
my two cents :
reading again this thread, I'm thinking it could be also a clogged vent hose from fuel tank : everything OK at the beginning, then the fuel pump does not succeed to provide enough pressure difference with tank, so fuel pressure drop slowly.
If the workshop check the pressure, it will be good, because it's only after a distance that it would drop...
 

Excellrec

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Hopefully there was a solution to this? I too am having the same problems. I was plagued by an intermittent low oil pressure warning. Replaced oil and filter and pressure sensor twice, all to oem spec. Pulled apart the oil pump, checked passages with no clogs, all looked great and to spec. Oil pressure wasnt coming on testing around town so I went to the track and by the third lap it showed low oil pressure at all RPMs and couldnt get above 50 mph. Pulled in and it showed max temp, low oil pressure, etc. Assumed an internal engine failure and pulled the entire motor apart. Unfortunately, the motor looks brand new inside No signs of oil starvation, busted seals, scraped bearings or anything. I will be reassembling and measuring everything to make sure, but it literally looks like a 100 miles on the motor so I'm suspecting something outside the motor. I've an extra motor that I'm going to try but maybe I should check something else as I do that? Would fueling issues trigger low oil pressure even though the engine is spinning well above 4k?
 

1JZSupra

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Hopefully there was a solution to this? I too am having the same problems. I was plagued by an intermittent low oil pressure warning. Replaced oil and filter and pressure sensor twice, all to oem spec. Pulled apart the oil pump, checked passages with no clogs, all looked great and to spec. Oil pressure wasnt coming on testing around town so I went to the track and by the third lap it showed low oil pressure at all RPMs and couldnt get above 50 mph. Pulled in and it showed max temp, low oil pressure, etc. Assumed an internal engine failure and pulled the entire motor apart. Unfortunately, the motor looks brand new inside No signs of oil starvation, busted seals, scraped bearings or anything. I will be reassembling and measuring everything to make sure, but it literally looks like a 100 miles on the motor so I'm suspecting something outside the motor. I've an extra motor that I'm going to try but maybe I should check something else as I do that? Would fueling issues trigger low oil pressure even though the engine is spinning well above 4k?

The only way I could see fueling affecting oil pressure is if the injector was stuck open and fuel washing the cylinders so badly that it got past the rings and into the oil enough to thin the oil out. I would imagine it would hydrolock the engine before that could even happen. Did you try cleaning out your oil jets? Additionally, what kind of oil do you use and could you describe the process that you use when checking your oil level, please.
 

Excellrec

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Hello. I've inspected the oil jets and all but one in the cam were perfectly clear as well as all the passages. The one in the cam may have been partially blocked. Though, a blockage in this jet would not prevent oil to go by the passage it is attached and onward to the oil pressure sensor, and therefore shouldnt cause a true low oil pressure warning.

The oil changes were all done by the book. Usually I measure in around 1.8L, or whatever the books says, then check and correct the level in the sight glass after the motor has been brought up to temp. Bike flat on a lift, standing straight up and down. Oil has always been motorex 15/50 with oem filters. I should mention I've ridden 390 engines hard at the track for a couple years, and many oil changes, and never saw a low oil pressure warning before. This bike is a new to me race bike previously built and ridden for one season. It has bazzaz zfi and several other minor modifications to the harness (e.g. kickstand delete, ignition removed, etc). My only guess at this point is that (assuming it's a problem in the motor) somehow, though they look near new, a rod or crank bearing is seeping too much oil by, or maybe the cam tower wasnt sealing flat to the head. I'm busy stuffing a different motor in the bike right now but I will be going through this motor with a fine toothed comb to find the issue if the other motor runs fine in the bike. Crossing my fingers for the other motor or I'm going to be beyond frustrated.
 

1JZSupra

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Hello. I've inspected the oil jets and all but one in the cam were perfectly clear as well as all the passages. The one in the cam may have been partially blocked. Though, a blockage in this jet would not prevent oil to go by the passage it is attached and onward to the oil pressure sensor, and therefore shouldnt cause a true low oil pressure warning.

The oil changes were all done by the book. Usually I measure in around 1.8L, or whatever the books says, then check and correct the level in the sight glass after the motor has been brought up to temp. Bike flat on a lift, standing straight up and down. Oil has always been motorex 15/50 with oem filters. I should mention I've ridden 390 engines hard at the track for a couple years, and many oil changes, and never saw a low oil pressure warning before. This bike is a new to me race bike previously built and ridden for one season. It has bazzaz zfi and several other minor modifications to the harness (e.g. kickstand delete, ignition removed, etc). My only guess at this point is that (assuming it's a problem in the motor) somehow, though they look near new, a rod or crank bearing is seeping too much oil by, or maybe the cam tower wasnt sealing flat to the head. I'm busy stuffing a different motor in the bike right now but I will be going through this motor with a fine toothed comb to find the issue if the other motor runs fine in the bike. Crossing my fingers for the other motor or I'm going to be beyond frustrated.
Evening Excellrec,
When you say that the bike is flat on a lift, standing straight up and down are you saying you have it on a paddock stand? Or are tires flat on a motorcycle lift and then balanced vertically before observing the oil level?

I wonder if there is a way that an oil pressure gauge could be installed to monitor oil pressure.
 

Excellrec

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Yes to the latter. On a lift with both tires flat on the lift. I had the same thought about mounting an additional sensor and made an adapter plate to mount a mechanical gauge at the oil filter cover, as the manual describes to check the oil pressure with a similar adapter plate ktm sells. I did it there so I could also have the factory sensor mounted at the cam and see what the mechanical gauge read when I got the low oil pressure warning. But, despite getting on it as hard as I dared a loud non street legal track bike in the neighborhood over several outings, I could not get the low pressure warning and pressures looked reasonable on the mechanical gauge. I didnt run the mechanical gauge at the track because it was a little sketchy zip tied to the dash with oil lines running where they could be ripped open if I went down. I thought about rigging up something more permanent, but once it lost power and overheated with the low pressure warning I figured there was no way around opening the motor at that point.
 

1JZSupra

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Yes to the latter. On a lift with both tires flat on the lift. I had the same thought about mounting an additional sensor and made an adapter plate to mount a mechanical gauge at the oil filter cover, as the manual describes to check the oil pressure with a similar adapter plate ktm sells. I did it there so I could also have the factory sensor mounted at the cam and see what the mechanical gauge read when I got the low oil pressure warning. But, despite getting on it as hard as I dared a loud non street legal track bike in the neighborhood over several outings, I could not get the low pressure warning and pressures looked reasonable on the mechanical gauge. I didnt run the mechanical gauge at the track because it was a little sketchy zip tied to the dash with oil lines running where they could be ripped open if I went down. I thought about rigging up something more permanent, but once it lost power and overheated with the low pressure warning I figured there was no way around opening the motor at that point.

Do you have a photo of that setup by chance? What oil pressures were you seeing at idle and under load? I suspect an electric oil pressure sending unit would be the safest bet, but then again this doesn't address why your bike continues to think it has low oil pressure. How did your cam journals look?
 

ReidMcT

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Having now had this Low Oil Pressure problem (not overheating) with two engines, and having done a lot of fruitless testing/replacing/pondering, I'm presently thinking maybe it's caused by an overfill of oil that gets frothed by the transmission gears.

That could explain why the low pressure only happens when underway, never while sitting in neutral.

As for the warning light staying lit until shutdown and restart, I'm suspecting that is just the ECU latching the light on once it is triggered, so that the rider will know there was at least a momentary problem.

I am pretty well convinced that the pressure sensor is not at fault. There is a real low pressure event happening, and damage is accruing quickly. The camshaft bearings are the canaries. And I fear replacement cylinder heads may be hard to come by these days.
 
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