2001 mountain cat 800 wont rev past 6500.

[hansenmac]

got a 2001 mountain cat 800. it needed a new fuel pump and regulator so i put in a good used one. sled starts and runs, seems to smoke enough but acts normal at idle but has lack of power and 95% of the time doesnt rev past 6500 or so. the power valves have been cleaned and it has one new piston. the old piston had a crack in the skirt. if you hold the throttle pinned with the belt off of the sled it revs to 6500 or so, you let of and the power valves cycle right after you let off. sometimes it will rev cleanly and it runs perfect but most of the time it just doesnt rev out. i checked the ecu and it wasnt throwing any codes according to the led light on the bottom. it never dies or bogs out, it just doesnt rev out. its not clutching because i have the clutch off and it still doesnt rev up. does any one have any ideas. thanks.

 

[truckyeah]

you could try unplugging the TPS

 

[hansenmac]

tps or tss? the throttle safety switch is unplugged, the kill switch doesnt work i have to use the key.

 

[kiliki]

tps or tss? the throttle safety switch is unplugged, the kill switch doesnt work i have to use the key.

TSS not TPS. the power valves open at 6500 are your cables and servo working at that rpm?

 

[hansenmac]

i opened the power valves by hand at the servo and it still didnt rev up. the servo cycles when i let off of the throttle, and sometimes it will rev out cleanly and the valves open on there own. the valves are freshly cleaned too. thanks for the replys by the way.

 

[boondocker97]

Did the other old piston lose it's skirt now? Different machine, but had an old 580 that wouldn't rev out. Idled and ran fine up to a point. Found out the skirts broke off the pistons due to fatigue. Old single cylinder 2 stroke Polaris ATV engines could do the same.

Have you tested the stator? I've heard ones that don't go totally bad can give weird RPM problems.

 

[hansenmac]

compression is 120 on both cylinders. fuel pressure is 48 psi at the rail. Mag side spark plug looked too clean like maybe overfueling out of that injector? The odd thing is that sometimes when riding it it will rev out and pull like crazy. most of the time it hits 5500 to 6500 and either doesnt rev up or if you hold it long enough it might work its way up and then take off. If it hits 7000 or so the power valves do open. i think im going to pop the injectors out but leave them on the rail and see if they have the same pattern. I havent tested the stator yet but i will have to find a diagram for doing so with specs and get that done too. Thanks for the ideas.

 

[kiliki]

efi or carb? I have seen the choke plunger leak fuel past it due to cracked rubber parts.
or have the cable too tight and it not seat all the way.

 

[hansenmac]

efi, the injectors both shot out nice and they looked the same pattern. i wish it was throwing a code. i think the next step is checking the stator voltages. it just has no snap when you hit the throttle its like the ecu is pulling a bunch of timing out of it.

 

[hansenmac]

stator tested out well on the ohm test as did the water temp sensor and air temp sensor but the ignition pickup tested to 99 ohms and the spec is 152 to 228

 

[Readymedic]

First of all, you never "HOLD THE THROTTLE PINNED" without a belt. You will over rev your engine and BOOM!!!!!!!! How do you plan on stopping the drive clutch??
With your hands??????
Watch your power valve motor. Put the belt on and feather the rpm. If the power valve motor cycles twice, there is a problem. Cables wrong, backwards, loose, wrong OHMs.
Make sure you have the cables on the right direction.. Thats big or they wont open, impossible.
What make you are using a quality meter, not junk to be accurate.
Check your plug wires, going to the caps. Unscrew the caps off of your wires. Cut them back 1/4 inch so you have a good connection with the wire, then screw them back on. You can do the same thing to the coils. Name of the game here, is check for good connection, tight. If you don' t have consistent spark, your wasting your time. Keep it simple, start simple.
Don't do your testing on a stand. Its not realistic. Put the sled on the ground and drive it. On a stand does not simulate driving for the clutches, etc.
The stators were also famous for problems, even though they are manufactured by Suzuki.

 

[hansenmac]

after cleaning clutches testing stator and crank trigger checking and cleaning clutches ohming injectors checking reeds swapping ecu's checking compression swapping coils checking fuel pressure checking to make sure the crank hadnt spun where pressed together i found it had something to do with the tss being UNHOOKED i read in probably over 20 places that having them unhooked is fine and thats what you do if your tss is cousing problems. i ohmed out the tss and the kill switch and both switches opened and closed. but when hooked up the sled would die if the throttle wasnt depressed slightly to press the tss in but if you let off the tss microswitch the sled would die. i ended up snipping the pink or purple wire plugged the harness back in and it runs perfect just the tss and kill switch doesnt work. I dont know what is going on since the tss switch seems to be working when i ohm it, or why it doesnt run right with the harness unplugged. thanks for all the ideas and for warnings.

 

[spoon]

I would be looking at Throttle Position sensor on the throttle bodies. The TSS and TPS sensor work together to kill ignition in case of stuck throttle. The TPS can also cause your lack of RPM if it is giving erratic readings to ECU. The fact it dies with throttle released tells me the TSS is good and doing its job. Testing the TPS is easiest if you have or can borrow the plug in tool that puts power to sensor so you can watch the live reading on an ohm meter while cycling the throttle with engine off.

 

[hansenmac]

i suppose if the tps is reading that its above idle but the tss is not depressed the ecu is assuming the throttle is tuck open and thus killing the engine. im really thinking about buying one of the cat diagnostic tools for 400 bucks on ebay, would have saved a ton of time diagnosing.