Dear Ralph: I’ve been riding a ’97 Arctic Cat ZR 580 EFI for a while now since frying pistons in another sled, and it...

Dear Ralph:
I’ve been riding a ’97 Arctic Cat ZR 580 EFI for a while now since frying pistons in another sled, and it has a few problems. I’m not sure if this is a mechanical or electrical problem or what, but two dealers have had it on the scope and found no problems.

On a cold start after sitting out overnight (even at –17 F) she starts fine. On a semi-cold start, like 1-2 hours after being shut off, she starts fine. On a warm start after five minutes…well, not so fine. The sled fires once, then dies instantly and won’t re-fire for quite some time.

Something that may be related; once in a while on the trail or lake, if I hammer down on the throttle it acts like I have a fouled plug. If I let off gas completely and coast for a couple of seconds and try it again, it’s back to full power. Could this be part of the same problem? Ideas or suggestions? Please don’t tell me what the last Cat dealer said, “Next time it happens drive it to the dealer right away.” I would have if it’d started!
Scott Garrison

Yes, these two problems could be related. It sounds like your sled is getting too much gas when you’re trying to warm start it. The bit about the way it acts like a plug is fouled every now and then when you punch it would lead me to suggest an intermittent throttle position sensor that goes out of spec when it gets heat-soaked (sitting there with a hot engine after you shut it off) and flukes out once in a while running otherwise normally. This could be a tough one to diagnose, but your dealer should be able to monitor this after getting the sled good and hot and seeing what the TPS output does. Fixing it is yet another issue. This is pretty much a factory-only replacement item (the TPS is factory-calibrated to the throttle body) but I believe Cat offers a rebuild program where your throttle bodies can be sent in and they’ll install a new sensor and calibrate it.

Too much fuel when warm could also be caused by a faulty water temp sensor, or even an air temp sensor. Again, they may be out of spec when they get heat-soaked, or one of them could be offset, meaning they consistently read colder than they should. One of the two dealers who’ve looked at this should have checked both of these sensors if they had their analyzer hooked up looking for fault codes. If the sled sits somewhere for several hours, then both sensors should read the same temp, within a few degrees. If the water temp sensor is off a ways, it would trick the ECU into calling for more fuel than required, especially during a warm start. This would also hold true for an air temp sensor that reads too cold. Either one could go wacko only when heat soaked, but the water temp sensor would be more likely due to its location. The air temp sensor should be fairly isolated from a heat soak when you shut the engine off.

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