4 stroke "thought problem"

[RaWarrior]

This doesn't relate to my Vmax, but rather a 4 stroke Polaris snowmobile that won't start(go figure there).

Parallel twin, 750cc, EFI, turbo. It's the stupid kind of motor where both pistons go up and down at the same time, just one on the compression and one on the exhaust(so it always shakes and the exhaust sounds like a fart).

Anyway, it ran OK before, but was permanently stuck in "limp home" mode with the check engine light on, so it wouldn't go over 6000rpm. It got brought to two different dealers who plugged it into the special proprietary polaris software(only way to get or clear codes), it said some sensor was out of whack. The sensor was tested and was good, a new one tried and still the same problem. Apparently these sleds are known for wiring problems, and the dealer essentially said with these "ghost codes" to just replace the entire harness with an updated one. So we did.

Initially after the wiring swap the motor started right up, but was running ******, knocking, and didn't want to idle. After a few re-starts, it started to run better and would idle consistently. We took it for an easy drive and it was knocking badly under load and had absolutely no power. Wasn't hitting a rev limiter like in limp mode, it just had no balls whatsoever. No CEL though. Parked it for the night. Next day, won't start. Initially I got a few farts and pops(and a big backfire in the mix), but now I get absolutely nothing. I tried a spare ECU(from the same model of the same year), with the same results.

-It does have spark on both cylinders
-Both sides have 150psi compression(normal)
-Both injectors are working and firing(popped fuel rail out but left it hooked up to see)
-There is no water in the fuel

So I have fuel, spark, and compression, but not even a pop when cranking. What could be preventing it from starting? Still no CEL.

any ideas on what else to try? The only thing it needs to run are the coils, injectors, and crank sensor which were all checked. It's got loads of other sensors but the manual says none will prevent starting(just may trigger a limp mode).

 

[The Beekeeper]

Make sure the plugs are clean, hit the ******* with some starting fluid and see if it fires, if so it's probally a fuel issue, if not it may be weak spark..........Kinda curious how things went downhill after changing the harness tho..........Tom.

 

[twistedmax]

This may be out there but..........................it happened on a car I had took a loooong time to figure it out.........................The crank sensor had magnets to pick up the signal to fire the right cyl(i belive the magnets may have been behind the timing cover on this car) and one of the magnets had come off somehow and it prevented the car from starting even though it had spark and fuel. could be somthing simaliar?

 

[bazwell]

My first thought when reading your story was the timing of the spark is out.
You said it's got compression, and the injectors are putting fuel into the manifold.
So if it gets a spark, it should go bang, unless the spark is way off.

twistedmax may be onto something there.

With the ignition on can you wind the crank manually until 1 plug fires? Then you just have to check if that cylinder is on compression.

 

[gamorg02]

could a resistor or something in the new harness be throwing off the timing as these gents suggested.

 

[Bill Seward]

These engines have DOHC? Timing belt? Maybe it jumped time, and if it's not an interference motor it still runs, but badly...

If that fails, plug the laptop power cord into the USB hub..........:bang head:

 

[RaWarrior]

This one is a chain drive SOHC 8 valve motor. I had considered the timing jumped, but that seems really unlikely, and due to fantastic polaris design, the motor has to be lifted to get the valve cover off. In fact, the motor has to be lifted to get at just about anything.

This motor also earns top honors for the most complicated oil change procedure of all time, coming in at 34 steps in the service manual. It literally tells you to disconnect one of the oil lines, point it in a jug, install a special jumper into the harness(which requires 20 min of work just to access, and is not available to the public) so you can crank the motor w/o starting it, then just holding the key down until the motor pumps all the oil out of itself. Apparently they don't believe in drain plugs.

 

[bazwell]

This one is a chain drive SOHC 8 valve motor. I had considered the timing jumped, but that seems really unlikely, and due to fantastic polaris design, the motor has to be lifted to get the valve cover off. In fact, the motor has to be lifted to get at just about anything.

This motor also earns top honors for the most complicated oil change procedure of all time, coming in at 34 steps in the service manual. It literally tells you to disconnect one of the oil lines, point it in a jug, install a special jumper into the harness(which requires 20 min of work just to access, and is not available to the public) so you can crank the motor w/o starting it, then just holding the key down until the motor pumps all the oil out of itself. Apparently they don't believe in drain plugs.

Oh my goodness! There's a design award, right there! :rofl_200:
And I complained about having to pull Jesus bar from above the passenger door on my old BMW, just to get the dash out.
34 steps!! Wow.

 

[PDWeyand]

I have never had the joy of a snow sander, I am sure it would be fun to ride on one. I have watched many a video on ytube and some of the crazy things people will do on them. I have no clue on why it is not running but 34 steps to just change out oil sounds like true pain. Good luck in getting back up and running.

 

[a113ycat]

I had an issue like this before. You have only checked 3 of the four parts of the engine processes. In a four stroke engine you have
SUCK
SQUEEZE
BANG
BLOW
On the one I had very similar issues with there was an obstruction in the exhaust system. You may try checking the headers and exhaust ports maybe a critter took up residence in the baffle???
Just trying to help.

 

[RaWarrior]

Things like 34 step oil changes are just the beginning of the joys of Polaris ownership. My buddy has a 2010 Rush 600, and it just cooked the motor at 1800 miles. Not holding it to the bar across a lake or anything, just putzing through the woods and waaaaaahhhhhhohhhhhhhdead and locked up. While my 2005 Cat with 5200 miles ran like a champ all day long. That pissed him off all over the place since he's a huge polaris fanboy and thinks cat's suck.


Exhaust is clear and the turbo spins up while cranking. It's always stored indoors, in the student shops, no mice or critters to wreak havoc with it.

The spark timing being off is my only thought, though I don't know why or how. Even still since it's not firing all the fuel being squirted in there can't be all blown out the exhaust, and the spark would light it at some point....at least a whiff or backfire, but I have nothing. Not even a pop. Like it doesn't have any fuel(but plugs are wet after cranking)

 

[The Beekeeper]

I know you said you have good compression but try squirting a bit of oil in the cyls to help seal the rings............................Tom.