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2014 Massimo MSU 400 engine dies when accelrating

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2014 Massimo MSU 400 idles perfect, runs ok up to half speed.  From half speed if you step down on the gas pedal all the way engine dies.  Engine is fuel injected, the map sensor, and the throttle body idle control sensor, and the fuel injector have been replaced.  Also the fuel pump was removed and fuel pressure is ok, and fuel was checked for water.  Air box and air filter have been cleaned, also replaced spark plug.  From a dead stop if you step right down on the gas pedal all the way it dies, if you baby it, and go easy it will run ok until about half throttle, then after that it will  die as you start to push down more on the throttle for top speed.  Any ideas?  I appreciate anyone's help...

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Sounds like it's choking out. Seems I read somewhere that the pump needs removed, cleaned, the tank needs flushed as well as the fuel line, and a filter installed in the fuel line between the pump and the throttle body. 

Just a thought. I read that on the internet while searching for something else. You could also use some throttle body cleaner on the throttle body itself. Get all the areas as clean as possible. 

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The fuel pump was removed, cleaned and pump pressure checked.  Fuel was removed from tank, tank was wiped out with rag since fuel pump was out.  Fuel line is new and there is a fuel filter inline which is new also.  Thank you for your thoughts, I appreciate it...

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Oh well, it was worth a shot. Any issues with the ignition system? Coil and/or wire? Maybe the throttle body is in need of cleaning?

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Have not resolved the problem yet.  There is no sure way to test the ECU and I hate to purchase one if that's not the problem.  I have pretty much covered everything else.  Fuel pump tests ok, no water in the fuel, new plug, new map sensor, new throttle body idle control sensor, new air filter, no vacuum leaks, not sure where to go from here.  The machine was running perfect, and we parked it for about three weeks and when we went to use it again, that is when this all started.   It starts right up, idle's perfect, if you go easy with the gas pedal it will run ok up to about half speed.  If you step right down on the pedal it will die out.  If you baby it up to half speed and step right down on the pedal, it will die then also.  I appreciate everyone's help. 

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Have you checked the coil and any connections? Are the valves adjustable, and if so, have you adjusted them? 

I don't know how the ignition timing works on these things, but maybe the issue is somewhere in there?

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What about the fuel return line? Did you clear that out when you had it apart? Or the crankcase ventilation? Is there a throttle position sensor on that thing? Either way, if its ECU controlled, there should be a way to get trouble codes. After all the things that you've done to it. It really sounds like a sensor problem though. 

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I had a similar problem with a vehicle. Exhibited the same symptoms. Ignition coil was bad. It ran fine just cruising in low rpms, but give it some throttle and it would bog down and begin to misfire. To me it sounds like a fuel delivery or ignition system problem. But I don't have much experience with powersports engines. 

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A coil problem could cause it. I've also heard of one acting in a similar way, that had a clogged fuel return line. Or it could be as simple as a clogged vent gas cap. But I do believe that it's a fuel delivery problem. With everything else being replaced. It could easily be the sensor that controls the air/fuel mix, based on the throttle position. Since it runs good otherwise. 

But these things usually have trouble codes, so it shouldn't take guesswork. The trouble code tests are easy, and don't cost anything. So I'd start there. 

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8 hours ago, T-boss 410 said:

How do you do the trouble code tests? It would be good to know for future reference.

Thanks 

It appears to be that the clock display will blink. You count the blinks. Each sequence means something different. I didn't read the specifics, but YouTube has videos. And the pdf download service manual appears to go into written detail, giving the different values.

For a single, specific problem, you could probably find the stand alone information, without the manual. But I consider a full service manual to be a requirement for any, and all equipment that I own.

Mostly because, after a few short years have passed. This type of information can become frustratingly scarce. It's money well spent. 

The way I see it, a piece of junk will soon find a new home away from me. The service manual can go with it. They're not expensive. Good riddance to both.

But a solid, reliable piece of equipment will be around for years. A full, shop service manual is usually the first casualty on the list of things that are no longer available for a piece of equipment. Offered for only a surprisingly limited time. Some people rely on the downloadable version. I prefer a hard copy.

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Finally found the problem.  The exhaust pipe that has the O2 sensor  was the problem.  The exhaust pipe is a pipe within a pipe, I noticed a lot of exhaust fumes were coming out around where the O2 sensor threads in so i knew there was a exhaust leak.  I removed the pipe and plugged one end and plugged off the O2 sensor hole and applied air pressure to the other end, i sprayed the pipe with soapy  water and noticed it was leaking around the O2 sensor hole .  I then took a die grinder and cut the outer pipe apart removed the piece i had just cut and the inner pipe was all rotted out near the end that bolts to the head.    So the O2 sensor certainly could not do it's job.  I replace the exhaust pipe and life is good once again.  I greatly appreciate every one's help.....

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Glad to hear that you got it worked out! And thanks for the follow up on the ultimate solution. So many times, people will solve the problem on their own, and then just leave us hanging lol.

Even more frustrating, is when you're searching for the identical problem that your machine has. Then find it in a thread that's several years old. And there's no record of the outcome. So congratulations, and thanks again!

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I stand corrected! Turns out it was a sensor issue as you said earlier.  I gotta say, there's way too many sensors in today's engines. I understand that those sensors are necessary for the fuel injection to operate, but I think that can be engineered out of the system. I know that it's dependent on the EPA and their rules and regulations, but a backyard mechanic could go crazy trying to diagnose these problems, unless you have the expense equipment needed to do that diagnosis. I like to fix things myself. It's satisfying for me, not to mention cheaper. 

You mentioned that the error codes are read through the clock? I have a digital instrument cluster. How would I read those codes?

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The sensors aren't really necessary for a fuel injection. Nor does the fuel injection system even have to be electronic. I once owned a car that had a mechanical fuel injection system. It had less than a half dozen moving parts, and worked great! I miss that car. But they do the sensor thing for efficiency. So I guess that I can live with it. I could go either way, as long as there's a way to get fault codes. Otherwise it would be a nightmare to diagnose most stuff. It does make some things easier though. What I really don't like about today's vehicles. Is everything is so tightly packed. 

9 hours ago, T-boss 410 said:

You mentioned that the error codes are read through the clock? I have a digital instrument cluster. How would I read those codes?

According to the information that I read. It sounded like the clock on the instrument cluster would blink all by itself, if it sensed a problem. You had to fix it to make the clock run normally. Actually interpreting the blinks and what they mean, was covered in a different part of the manual. So I have no idea how detailed the fault code chart is. There's not much to these things, so I wouldn't expect much. That could be a good thing though. 

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I saw no mention of a procedure to clear the codes. And I've edited my previous post to reflect that. So presumably the codes will go away after the necessary repairs are made. What I saw of the owners manual gave very little information about the process. If you need an owner's manual, I saw that there's a thread floating around here about that. One of our members has generously offered to share what is likely a digital version. 

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I have an owner's manual downloaded. I am hesitant on spending the $75.00 for the service manual, though. Just seems a bit expensive, IMHO. I suppose I should just bite the bullet and spend the money. I was hoping that I could locate a copy elsewhere for a better price, but so far that hasn't been the case. 

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I can certainly understand that. It would be nice to get a look at it first. If it's a skimpy attempt, like one of those nearly useless auto parts store, car manuals. Then 75 bucks would be way overpriced. But if it's a full comprehensive shop service manual, it would still be a bit overpriced. Mine is for a mule, and it covers literally everything. It only costs 40 bucks at the high priced dealership. But if you keep the machine longer than a couple of years, it would eventually pay for itself. I have no idea which version that our fellow member is sharing. But I think that it'd be worthwhile to ask him.

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