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need help ? o6 mcx 280 hp apex popping banging under boost?

9

925rotax

Pro
Joined
Sep 15, 2007
Messages
161
Location
kelowna b.c
I am trying to help a riding partner. He has a 2006 apex w the 280 hp mcx kit. Here is the problem. Sled runs great , just not under boost. When he starts building boost , sometimes {usually] the sled pops and bangs, sputters. This is right at the start of building and continues throughout. Tonight I charged the intake to 18 pds and pinched off the wastegate acuater pressure line. No leaks. Start of the year the sled was running great for him. Any ideas?
 

Almost sounds like detonation, what kind of fuel is he using and how much boost?
 
He isnt running a a/f. Running 14 on 94 chevron octane. It starts as soon as he starts building. It only has the stock fuel pump.N external w his kit. Ill check fuel pressure after the fuel regulater. Maybe the fuel reg. Would you know what the regulated f pressure is.Thanks
 
Sounds as it's definitely not getting fuel thru MCX injectors.
Could be because boost hose to the MCX ECU is cracked, or cable between MCX injecors in IC and ECU isn't connected, or faulty MCX ECU.
Try to add air preassure to the hose that connects to the MCX ECU while sled is running, if sled starting to run rough it's because MCX ECU is working and there is a crack on the boost line, if it's not it's the line between injectors or the ECU isn't working as it should.
 
I missed the "sometimes" part,,, this makes me believe it's the fuelpump,,, don't hesitate, upgrade to the external fuelpump with the OEM pump delete kit!
I know from experience that OEM fuelpump loose it's efficency over time.
 
We already added 12 v to the mcx injectors ,they sprayed. Will add air to the pressure line of the mcx ecm today. I run the secoundary pump on my sled. I didnt know there was a delete for the factory pumps on the 280 kit. So the external pump will supply fuel to both injectors? I have a spare mds pump I could use on it.
 
Could be electrically misfiring, likely blowing the spark out due to added turbulance in the CC..
What spark plugs and what gap are you running?
Stock plugs set at 0.018" gap will solve that problem, but not sure that the fuel pump isn't the problem either.
GET AN AFR GAUGE!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! NEVER RUN A BOOSTED SLED WITHOUT ONE!!!!!!!!!!
 
I believe its a fuel issue. Start there anyway. I charged the injectors w air and they turn on, as well w 12 volts. The intank fuel pump is putting out 49 psi , seems high , maybe the return check valve is stuck open? I am going to check fuel pressure after the regulater. What should the fuel psi be for the mcx injectors? Maybe faulty fuel regulater? If we install my spare external pump. Will the mcx ecu have to be reflashed?
 
I talked to Erik Marklund at MCXpress today about the exact same problem on my Nytro.

He told me it was 90% sure it was the ecu that had failed.
There was some kind of sensor inside the ecu that could fail, causing this kind of problem.

Thumbs up for MCXpress sending out a new unit to me the same hour. No downtime allowed this time of the year ;)!
 
He already sent the ecu to prince george yamaha / mcx dealer here. Returned no issues? Will install the external pump. Installing the external ? Will he need to send the ecu back in ?
 
mbarryracing said:
Could be electrically misfiring, likely blowing the spark out due to added turbulance in the CC..
What spark plugs and what gap are you running?
Stock plugs set at 0.018" gap will solve that problem...
Click to expand...
Did you answer this?
 
I will check his sled for spark plug and gap. The thing is it did run good w same plugs prior to this problem. The plugs were never changed. But will definately look at them.thanks
 
Yeah but that doesn't mean you didn't wax a plug that is now misfiring under boost... A new set of plugs might solve the issue, atleast it's something easy to try if it solves it.
 
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