2009 McXpress 270 Nytro Losing Power.

[SydneyACE]

So I have a 2009 Nytro with the MCX 270 kit.

Starts, idles and runs great. When I go full throttle, it pulls really hard for around 1-2 seconds then kinda cuts-out and stutters. Feels like it's dropping to around 200hp instead of 270hp.

It doesn't do this every time I go full throttle either. Going down the road flat and level it pulls very strong, full power for several seconds... until I have to let-off because I'm going too fast. Seems to act up pretty consistently once I get off the trail into the powder or climbing a hill though.

When it loses power it makes a very rapid stuttering sound like it's missing, almost like a "fluttering" sound. I initially thought it was running out of fuel under boost, but according to a couple people I talked to, they said when they run lean it's VERY dramatic and they sound like they're gonna blow up. Not sure...

I turned-up the fuel pressure regulator a little at a time, making pulls in-between. That seemed to MAYBE help a little... it would still cut-out and loose power, but it seems like that might have delayed the power loss by an extra half second or so. I'm not sure...

My boost gauge broke on me last year, but it doesn't feel like a boost leak.


Things I have checked so far;

I took the fuel pressure regulator apart to see if the diaphragm was torn, spring bad or gunked-up or anything. It looks fine.

Did a compression check.
Got 140 across the board for all 3 cylinders with all plugs out and throttle open (engine cold).

Changed spark plugs for new NGKs, set at factory gap (whatever is on the belt guard, can't remember at the moment). (I've heard that some guys run them at like 18-19, but I just gapped them at factory.)

Smoke checked the intake and exhaust to look for leaks. Couldn't see any boost leaks, there was a little leak at the collector on the exhaust, but I don't think that's related to my problem. I had a pretty good exhaust leak on it a couple years ago and that caused excessive lag, not full power then loss of power.

Ran it with a fuel pressure gauge hooked-up. Set at 46psi at idle it ramps up to around 60psi at full throttle. It's kinda hard to get a good look at it when you're riding full throttle but it doesn't seem to go below 60psi even when it's losing power. When I ramp up the idle pressure to 55psi, it looked like it only got up to around 62-64ish at full throttle... which seemed a little strange. A 1:1 regulator should add about 13psi at full throttle right? The MCX 270 DOES run a 1:1 regulator right?

Checked the strainer in the fuel tank for gunk. It's clean.

Took the in-line filter off an blew through it. It seems fine. (Will try a new one on my next ride.)

Looked at everything else that I can think of, wiring, vacuum lines, etc.

The fact that it's intermittent is driving me nuts. If it was a fuel issue, it seems like it would do it all the time. Seems like it only happens when it's "under load"... but in-theory, doesn't the clutch load it to the max whenever you're at full throttle? Hooked up a boost gauge so I will check boost tomorrow.

Any ideas guys?

 

[SydneyACE]

Forgot to mention...

I dead-headed the fuel pump (crimped-off the return line) to see how much pressure the pump could muster (engine off). Pressure went up to 80psi, then the pump quit. Pump wouldn't run, got a code 45 for the fuel pump relay. Got a new relay, but turns out it was actually just one of the 10amp fuses on the starter relay that was blown. Pump works again with new fuse, will build up to 90psi with return line crimped.

 

[mbarryracing]

So no boost gauge and no AFR gauge?

 

[SydneyACE]

So no boost gauge and no AFR gauge?

I hooked up a boost gauge that I had laying around and am about to ride today so I will post some results. I haven't had one on there for a while though.
I'm also bringing the GoPro so I will get some video of it acting up in case that helps.

If I still don't have any ideas after today, I will probably break down and get an AEM Failsafe so that I can see if it's actually going lean.

 

[T-rav 27]

I hooked up a boost gauge that I had laying around and am about to ride today so I will post some results. I haven't had one on there for a while though.
I'm also bringing the GoPro so I will get some video of it acting up in case that helps.

If I still don't have any ideas after today, I will probably break down and get an AEM Failsafe so that I can see if it's actually going lean.

 

[T-rav 27]

Mine was doin the same issue today withcmy 2008 apex mcx 290 kit i found i had a gas leak and my vent line had a kink in it and had fuel in it also my o ring on fuel pump was bad need to order one and see iff problem is solved please let is know what u find as i may jave same iasue thanx

 

[SydneyACE]

Well, I'm very happy to say that I figured out what the problem was!

Having the boost gauge hooked up was the key. I noticed that when it was acting-up, the boost was dropping to around 10psi and the needle was fluttering. So I knew I had a boost leak. After a while of just sitting there looking at everything that I could think of, I found a little aluminum bracket which was broken. It connects the inter-cooler to the frame on the left side at the top. When boost pressure got high, it would blow the inter-cooler with throttle bodies attached back off the cylinder head enough that the boots would leak. When I let off the throttle, vacuum would pull the boots back tight up against the cylinder head.

Still not sure why it was fine when going down the trail...

Anyway, I put a couple of zip ties around the bolts that attach the bracket, and spent the rest of the day with full power and no hiccups. Most fun I've had riding in a while!
I'll attach some picks of the broken bracket. I forgot to take a pic before I removed it. I'll also attach a GoPro video of when it was acting up. Hopefully it will help someone else so they don't spend as much time wracking their brain as I did.

And this is where that bracket was located:

 

[mbarryracing]