Mcx 08 nytro 1/2 to 3/4 throttle stumble.

Tuesday · Mar 11, 2014

Last weekend at 1/2+ to 3/4 range it would start to stumble (randomly) like it was getting way to much fuel. If you could get it past the point it would pull full boost . So low end and top end seemed ok. My AF gauge is still down but I am pretty sure it was very rich. I checked all the basics again and everything appears ok.

I am starting to wonder if my fuel controller is "acting" up.

Sled is firing on all 3 cylinders so I dont think its just a stuck or miss firing injector.

Anyone ever had this problem before? Wish I knew someone that had a mcx box that I could swap in and try to see if it was my control box.

Duke · Mar 11, 2014

Does it run fine at WOT? Sounds like a lean condition, usually rich is lazy in my experience. Have you tried bumping your fuel pressure up 1/4 to 1/2 turn at a time, could have backed off? I wouldn't rule out a coil either, they do weird things!

Tuesday · Mar 12, 2014

It can pull full boost/wot if it gets past this stumble point.

usually rich is lazy in my experience (I am not sure what you mean by this)

Hmmm I just put on newer coils.

Tuesday · Mar 12, 2014

From Erik at mcx:

Hi.
Check so the stock TPS is working fine.
This is possible to see on the stock dash board if you run it in diagnostic mode.
The MCX box can be faulty, but it is much more common that it is something else.
The latest and our best and most reliable MCX-EFIbox is our gen 5 box.
The price is 4400 sek.
It fits in the stock 16 pin Nytro connectors.
Best regards Erik Marklund

Around 800$ ca.

Tuesday · Mar 12, 2014

What about a TPS or TORS problem? I was not getting any codes though.

M5- · Mar 12, 2014

Check your fuel pressure regulator, we've seen a few get corroded inside and stick. Clean it up and mount it pointing down so moisture can't accumulate in there. You may have corrosion on your connectors for the MCX box. If you are running a Gen II box the big one with fins they can go south as well. What happens is the pressure sensor inside the box fails and needs to be replaced, we've done 2 now. The sensor is cheap but its best to get a geek to install it on the board, all in a 60 buck fix.

M5

Tuesday · Mar 12, 2014

Only 2 rides with a new fuel regulator on.

Pins and connections on outside of box look good and currently is swimming in di electric grease as that was my original thought that the connector must be getting wet.

Any info on this pressure sensor install? Any pictures. I have repaired circuit boards before but it depends on how complicated it is. Yes mine is the Gen 2 with the big fins.

Thanks M5

Wonder what the other rides did with their mcx control box that installed the boost it kit.

I dont mind replacing/upgrading my fuel box I would just like to know if thats actually the problem.

M5- said:
Check your fuel pressure regulator, we've seen a few get corroded inside and stick. Clean it up and mount it pointing down so moisture can't accumulate in there. You may have corrosion on your connectors for the MCX box. If you are running a Gen II box the big one with fins they can go south as well. What happens is the pressure sensor inside the box fails and needs to be replaced, we've done 2 now. The sensor is cheap but its best to get a geek to install it on the board, all in a 60 buck fix.

M5

pelon · Mar 12, 2014

My friend has the exact same problem on his 08 mcx and I'm sorry to say, so far there has been no resolution. The box was even sent to Leipheimer with no luck in finding a problem

Good luck,

M5- · Mar 12, 2014

Its been a while since I have done one but what you do is cut around the silicon and pull the guts out. Where the tube that senses baro goes in there is is a small sensor on the board that needs to be replaced. I cant remember the number on it but you can find it on google. This is the part where you need to be good with a soldering iron or take it to a geek. Replace the sensor re-silicon it up and you are done. If you have the box tested and they tell you its screwed this is likely the problem with the box. Is there somewhere you can get it tested? Walts used to do it but they may be done now.

M5

APEXXPRESS · Mar 12, 2014

Tuesday said:
Hmmm I just put on newer coils.

Did this start after you changed coil ?
What coils did you install ?

Northernboy · Mar 13, 2014

I find it strange that it works at WOT, I would think if it is toast it wouldn't work there either. Unless it is not seeing the low boost or TPS readings on the lower end.
The box is pretty easy to test with the proper equipment. If I was closer I could look at it for you.
When I switched to Boost-it I sold the MCX controller to Brandon maybe he has a spare?
Datalogger really helps for troubleshooting these kinds of problems, glad I have mine.

Also if anyone has anyone old MCX controllers that don't work, I would be willing to look at them to see if they can be repaired.
I am also looking for a used Power Commander V to test to drive MCX injectors instead of stock injectors.

Tuesday · Mar 13, 2014

APEXXPRESS said:
Did this start after you changed coil ?
What coils did you install ?

I changed the coils about 300km before this started happening.

Tuesday · Mar 13, 2014

Northernboy said:
I find it strange that it works at WOT, I would think if it is toast it wouldn't work there either. Unless it is not seeing the low boost or TPS readings on the lower end.
The box is pretty easy to test with the proper equipment. If I was closer I could look at it for you.
When I switched to Boost-it I sold the MCX controller to Brandon maybe he has a spare?
Datalogger really helps for troubleshooting these kinds of problems, glad I have mine.

Also if anyone has anyone old MCX controllers that don't work, I would be willing to look at them to see if they can be repaired.
I am also looking for a used Power Commander V to test to drive MCX injectors instead of stock injectors.

We also found it strange it would pull full boost. It was like there was too much fuel and if it had enough chance to burn it, it would take off and pull full wot. Also sometimes when you backed off throttle it would would stumble and sometimes it wouldnt.

I will check my tps this weekend.

Northernboy · Mar 13, 2014

Could be something with the stock system too. I find the weak point in the stock wiring is the splice connectors on the harness. Found some that where corroded, so I would cut them off and solder/insulate them. Someday Ill remove them all from mine to eliminate a possible problems.

pelon · Mar 13, 2014

I will check my tps this weekend.[/QUOTE]

We did that to and nothing.

I think it's the box but we have not found the knowledge base to figure it out yet.

BigFish BC · Mar 13, 2014

is it doing it when it first starts to build boost?watch your boost gauge & see if it stumbles right when the boost starts to come on,if it does its your secondary injectors or the box controlling them thats causing the prob.

Tuesday · Mar 14, 2014

pelon said:
I will check my tps this weekend.

We did that to and nothing.

I think it's the box but we have not found the knowledge base to figure it out yet.[/QUOTE]

Did you try putting on a new EFI box?

Tuesday · Mar 14, 2014

BigFish BC said:
is it doing it when it first starts to build boost?watch your boost gauge & see if it stumbles right when the boost starts to come on,if it does its your secondary injectors or the box controlling them thats causing the prob.

I would say it starts it around 5-10 lb boost area. Either stabbing the throttle wot or slowly rolling up on made no difference it would still randomly act up.

Tuesday · Mar 14, 2014

pelon said:
I will check my tps this weekend.

We did that to and nothing.

I think it's the box but we have not found the knowledge base to figure it out yet.[/QUOTE]

Did you check the tps at the display or at the pins with a volt meter?

Northernboy · Mar 14, 2014

If you check the TPS with a voltmeter on the MCX harness it should start at about 0.7 to 4.0. Should increase smooth as you open the throttle and not jump around or drop.

Mcx 08 nytro 1/2 to 3/4 throttle stumble.

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