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Ski Doctor
Ski Doctor, powersports repair specialist
Category: Motorcycle
Satisfied Customers: 818
Experience:  over a decade of double time experience, excellent electrical and mechanical diagnosis capabilties
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I have a 1999 Polaris Ranger 6x6, 500. It will start fine but

Customer Question

I have a 1999 Polaris Ranger 6x6, 500. It will start fine but will not accelerate without backfiring and then dyes. When this first happened there was oil in the air box, i have since changed the oil and filter, cleaned the air box, changered the spark plug, checked compression, cam and rockers are not worn. Still won't accelerate. What next? Thanks Brad
Submitted: 6 years ago.
Category: Motorcycle
Expert:  Ski Doctor replied 6 years ago.

what happens if you use the choke when trying to accelerate?

when you push throttle, then pull choke in for a 1.5 seconds, then push choke back in, all while holding the throttle open.

does this make the ranger accelerate,. or no difference?

try it with air box open too.

Customer: replied 6 years ago.
I just tried both ways and it did not make a difference.
Expert:  Ski Doctor replied 6 years ago.

try to answer these:

1.what color is the spark plug electrode? black, white, tan?

2. does the engine only rev up to a specific rpm, and not higher? or the engine revs up, but then quickly dies and backfires?

3. what was your engine compression?

4. have you recently installed an exhaust, intake, or cdi box? or any other mods?

5: when was the belt last checked?

6. was the engine oil overfilled? do you know how the oil got into airbox? maybe the unit rolled over, or was on a very high angle.

7. has the ranger been sitting a while because this issue? or sitting at all for over 2 months? sounds like your woodriff key may be sheared. have you checked it?

Customer: replied 6 years ago.
The plug is tan, revs up, but quickly dies and backfires, 100psi compression. No recent installs. Just put a new belt on since the problem has started. The machine has not been upsidedown and the oil has not beeen overfilled, the oil in the air box I would assume came from the crankcase vent or the oil resivoir vent that both run directly into the airbox, not blowby from the cylinder. The ranger gets used regularly but not since this issue, about two weeks now. If the woodruff key is fine and the timing is also on the mark. Glad to answer or try anything you can think of, i am stumped.
Expert:  Ski Doctor replied 6 years ago.

1: was that was your engine compression with throttle wide open? and was it hold or cold?


2: make sure the battery is installed tight.

3: fuel filter? check it


4: check for an air leak or broken vacuum hose. you can use brake cleaner to spray around the engine running ( IN NEUTRAL, do this when you 1st start so engine still slightly cold).

the spraying SHOULD NOT affect the idle speed. if you hear the engine revving up when you spray the brake cleaner?

5: remove the air box cover and filter. when you drive the vehicle, spray a shot of brake cleaner into the airbox and then step on the gas..

does it run any different giving the engine more fuel?

6: you have tried running it with the airbox lid open?

7: try to run it holding choke open full, and hold open trying to drive. repeat this with choke fully out, try to drive

Customer: replied 6 years ago.
The compression was 100psi and cold engine, the throttle did not make any difference open or closed and it held compression for ever. Battery OK? New fuel filter. There isn't any vacum hoses, but I did spray for leaks and found none. Spraying in the air box doesn't effect the running at all, just like the choke, the engine still backfires and dies. Tried running with air box lid off, filter off, no change. Choke just puts to much fuel in, does not help the problem at all. What next?
Expert:  Ski Doctor replied 6 years ago.

okay, so here is what we know now:

manually giving the engine more and less air made no difference.

that leads me to believe the issue is not related to the carb or fuel.

it sounds like the unit is loosing spark once the engine rpm speeds up.

you ave visually checked the woodriff key that keeps the flywheel lined up with crankshaft?

next you should check the pickup sensors, also known as the pulse coils. do you know where they are on your unit? (behind flywheel cover)

you will need to unplug it from the wire harness, then use a multimeter on volts AC, and put the leads from the meter on each wire.(the pulse sensor is 2 wires for each one, usually blue and black). so one meter lead on one pulse wire, and the other meter lead on other. it does not matter which lead hooked up to which wire.

with meter hooked up, use engine starter button to make engine try to stat (it will not start with this sensor unplugged-you are only testing signaling output of sensor).

with engine spinning over, the pickup coils should put out AT LEAST 1.2 volt AC.

do tis test. if you need better instruction, let me know.

Customer: replied 6 years ago.
I will do this tonight and get back to you. Thanks
Expert:  Ski Doctor replied 6 years ago.

no problem...

please remember it may take a little longer to diagnose the problem because I cannot see or hear the unit.

hang in there, please know I am trying to get the problem figured out.

If you feel like I am not helping, please let me know and i can refer another expert.

Customer: replied 6 years ago.

No problem, this isn't my first time troubleshooting or repairing, I am just stumped and looking for some help with ideas that I may have missed. I assumed right off the bat it was cam and rockers because of the problems Polaris has had with these in the 500. Not the case. I have an electronic spark sensor that show the spark ramping up as the machine tries to accelerate, then the backfire and dye's. What seems odd is the oil in the air box, this can olny get there from pressure in the crankcase or the resivoir. Right? What could cause this build up? I have not replaced the filter in the line from the cylinder, I can blow through it both directions, but so can I on the new one I purchased. I am going to put the new filter in tonight and try that also.


Thanks Brad

Expert:  Ski Doctor replied 6 years ago.

when the unit backfires and dies, is there still spark, or does the sparking stop, and THEN the engine dies?

can you see which stops first?

the oil in crankcase can be normal, if the engine gets very hot, the oil turns into vapor and then in airbox turns back to oil.

Customer: replied 6 years ago.
There is still spark, but it bakfires and dies out, sputters out, but still showing spark. Weird?
Expert:  Ski Doctor replied 6 years ago.

you should check the pickup coil, which is located next to the stator.

locate the wires coming out of the atlernator / flywheel cover.

Customer: replied 6 years ago.
Got back to it last night. I replaced the filter in the vent line and thought I would try it befre loking at the stator. Started fine and accelerated fine, took it for a ride and it ran perfect. I do't know that this filter was he issue r something else that maybe working now because f all the messing around with parts. So who knows how long this wil last if it is a problem in the staor or pickup? At is point all I can do is run it. What do you think?