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2011 RZR 800 fuel problems?

4K views 12 replies 5 participants last post by  Dillancoe1116 
#1 · (Edited)
So this RZR hasnt run right from the time I bought it about a year ago. It seemed like a good deal when I bought it. It ran, but not good. All in all, it idles, but very sluggishly. When I first start it up, it will rev up and is really responsive(when it's primed I'm guessing), but if you let it sit there running for few seconds and then try to rev it up, it starts to spit and sputter. It acts the same when it's in gear. When you first start it up it will run like a champ, but if you wait 10 seconds before you try to go, it will be going about 2 mph while it backfires. It seems that whenever I restrict airflow, it responds a little bit better.
The guy who I bought it from had gotten the cylinders bored out, but I don't think he did anything else to compensate for the larger cylinders, and pistons, and increased airflow. He also put an aftermarket snorkel system on it.

What I know:
The cylinders have been bored out, with oversized pistons.
It's getting the correct pressure (39 psi) at the fuel rail.
Fuel tank, hoses, rail are all clean.
Fuel pump, pressure regulator, fuel screen,and injectors are all new.
Has an aftermarket snorkel system.

What I don't know:
What sized they bored it to.
A lot

I'm not sure how these things are worked on. It has to be fuel related. I just dont know if the ECU needs to be reprogrammed for more fuel, or if I can get a higher-rated fuel pump, pressure regulator or injectors.

I am completely open to any suggestions.

Thank you for any help you can provide

Edit: I had taken it to a mechanic, and he was the one who did the pressure test. He just told me it had the correct fuel pressure
 
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#2 ·
So this RZR hasnt run right from the time I bought it about a year ago. It seemed like a good deal when I bought it. It ran, but not good. All in all, it idles, but very sluggishly. When I first start it up, it will rev up and is really responsive(when it's primed I'm guessing), but if you let it sit there running for few seconds and then try to rev it up, it starts to spit and sputter. It acts the same when it's in gear. When you first start it up it will run like a champ, but if you wait 10 seconds before you try to go, it will be going about 2 mph while it backfires. It seems that whenever I restrict airflow, it responds a little bit better.
The guy who I bought it from had gotten the cylinders bored out, but I don't think he did anything else to compensate for the larger cylinders, and pistons. He also put an aftermarket snorkel system on it.

What I know:
The cylinders have been bored out, with oversized pistons.
It's getting the correct pressure (39 psi) at the fuel rail. Is this while it is running poorly?
Fuel tank, hoses, rail are all clean. Does this include the vent lines? Tank vent?
Fuel pump, pressure regulator, fuel screen,and injectors are all new.
Has an aftermarket snorkel system.

What I don't know:
What sized they bored it to.
A lot

I'm not sure how these things are worked on. It has to be fuel related. I just dont know if the ECU needs to be reprogrammed for more fuel, or if I can get a higher-rated fuel pump, pressure regulator or injectors.

I am completely open to any suggestions.

Thank you for any help you can provide
 
#3 ·
Backfire indicates a lean air/fuel mixture. Attach fuel pressure gauge to rail and drive around with it to see what the fuel pressure is under load.


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#4 ·
So this RZR hasnt run right from the time I bought it about a year ago. It seemed like a good deal when I bought it. It ran, but not good. All in all, it idles, but very sluggishly. When I first start it up, it will rev up and is really responsive(when it's primed I'm guessing), but if you let it sit there running for few seconds and then try to rev it up, it starts to spit and sputter. It acts the same when it's in gear. When you first start it up it will run like a champ, but if you wait 10 seconds before you try to go, it will be going about 2 mph while it backfires. It seems that whenever I restrict airflow, it responds a little bit better.
The guy who I bought it from had gotten the cylinders bored out, but I don't think he did anything else to compensate for the larger cylinders, and pistons. He also put an aftermarket snorkel system on it.

What I know:
The cylinders have been bored out, with oversized pistons.
It's getting the correct pressure (39 psi) at the fuel rail. Is this while it is running poorly?
Fuel tank, hoses, rail are all clean. Does this include the vent lines? Tank vent?
Fuel pump, pressure regulator, fuel screen,and injectors are all new.
Has an aftermarket snorkel system.

What I don't know:
What sized they bored it to.
A lot

I'm not sure how these things are worked on. It has to be fuel related. I just dont know if the ECU needs to be reprogrammed for more fuel, or if I can get a higher-rated fuel pump, pressure regulator or injectors.

I am completely open to any suggestions.

Thank you for any help you can provide
Yes, it is putting out 39 psi while running poorly, and the venting components are also clean.
 
#5 ·
So you are thinking it is fuel related but everything on the fuel side is checking out.

Maybe confirm that it is fuel related or not by using starting fluid. While it is running poorly, hit it with some starting fluid. If it is fuel related, it should clear up. If it does not, time to look elsewhere.

Maybe electrical.

As the motor was recently apart, is it timed correctly?
 
#6 ·
How many hours on machine?
How long ago did they redo the cylinders? If it's fairly recent, you might be able to put a scope in the spark plug hole and read numbers off pistons and google what they are.

Does it smell rich or get warm smelling like it's lean?

What's your idle speed?
 
#7 · (Edited)
What other mod's have been done? Does it have an aftermarket pipe, air filter, or head/valve work?

In my experience adding a big bore you will need to increase your fuel. If your fuel pressure is right then you need to add a fuel programmer like the power commander or a dobeck. Dobeck's are cheaper and they are re-branded by other companies like Wiseco, Alba, Dragonfire etc. etc. (all the same programmer with a different shell). The Dobeck's are limited in the range of what they can do so if you can afford it I would recommend PCV.

The fuel programmers plug in between the ECU and the fuel injectors. They intercept the signal being sent and increase the amount. Don't let this intimidate you - they are fairly simple to use.

If you run a programmer I would also recommend installing an O2 sensor so you know exactly what your AFR is. Otherwise, you'll just be guessing how much fuel actually needs to be added and at what rev's.

And the backfire is either a lean condition or you have an exhaust leak somewhere.
 
#8 ·
#10 ·
See the attached from BMP website. This is for their 800cc Big Bore Kit.

On a bone stock machine no EFI controller is required, but you will run safer and pick up power with one.

This kit takes the stock 760cc motor to a true 800cc. The OP only has an over bore and not a big bore kit.

It is very possible that the OP has other performance parts and I think the EFI controller is a good idea but I do not think it will fix his current issue.

I would stay focused on a mechanical or electrical problem to fix the machine. Add the performance goodies once it is running to improve performance.
 

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#11 ·
For the Rzr 800 there isn't an over bore. If you bore the cylinder you'd also have to Nikasil plate it so this is NOT common. Stock is 80mm but anything else is considered a big bore kit: IIRC Holtz BBK is 81.5mm, lots of versions of 82mm, 83mm, Muzzy 84mm, and a couple 85mm BBK's out there.

The difference between some of the 82mm are compression ratio varies with 10.2:1 on the Cylinder Works to 12:1 Wiseco which would require race fuel.

When you go from 760cc to a true 800cc engine (82mm) that is 40cc's more air going through the engine. The stock fuel map is typically on the rich side so it may or may not be able to handle the extra. This is why an air/fuel ratio sensor & gauge would be important and show exactly what is happening.

Depending on where the OP lives/rides elevation will be a factor too. At higher altitude where the air isn't as dense will mean he will need less fuel to maintain the right AFR. But at ocean level he would need to richen it up. The EFI tries to compensate but the map is somewhat limited and the fuel controller gets it beyond that.

Also with the Rzr 800 a fuel controller isn't much of a performance goodie designed to add HP but mostly just compensates for the lack of fuel. Adding a controller won't give you more performance by itself. Once the engine starts getting modified you will need to change the fuel maps and either increase or decrease fuel amounts in the various RPM's.

I agree it still could be mechanical with a leak in the air intake or head or exhaust sucking in more air than it should. It could be a dirty MAP sensor. Or, he simply needs a fuel controller - especially if he has a pipe that flows more air.
 
#12 ·
Hate to go here... but I am... Maybe the dude you got it from was full of poop? Prob not a big bore kit.

With some mods we have to our motor, it runs with stock fuel and a little better with the fuel box.

What intake do you have on it? Look down the air boot and check for any signs of dust. Our motor would do similar things like yours before it crapped the bed from dust injestion, but didn't suggest this as it was claimed to be recently rebuilt. Even if it was recently rebuilt. Possibly previously dusted and did a minimal rebuild to sell it. Dusted motors need new everything for the tune of about 3200 USD.

Check the intake boot on the motor side of the throttle body, dude might have cleaned it up real good before selling it. Unless you knew the guy personally, you may have gotten hoodwinked.
 
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