1992 Indy 500 SP EFI fueling issue?
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1992 Indy 500 SP EFI fueling issue?

This is a discussion on 1992 Indy 500 SP EFI fueling issue? within the Polaris forums, part of the Brand Specific Snowmobile Discussion category; Hello , I am new to the forum although I have been gathering great information from here as I work on this sled. I am ...

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Thread: 1992 Indy 500 SP EFI fueling issue?

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    1992 Indy 500 SP EFI fueling issue?

    Hello , I am new to the forum although I have been gathering great information from here as I work on this sled. I am also new to snowmobiling. I have never owned one and haven't even been on one for 25 years.


    This sled sat for at least 6 years without moving. Mice got into the throttle bodies and wreaked havoc. The mouse piss locked the throttle bodies shut and pitted the butterflies and the air horns have mild pitting. After hours of cleaning and lubricating, they finally operate smoothly and snap shut fully again. TB butterflies had to be removed for cleaning. They were green from the mouse piss. Recoil rope snapped first day. The primary is noisy with worn weights and rollers, but will get addressed if I can get it running correctly. It is currently removed. I refuse to spend a dime on anything unrelated to motor function at this point.

    Currently, it starts and idles nice and is very crisp and responsive to about 3000-3500 RPM's Once there, it bogs and the RPM's surge. It took forever just to get it to this point, since I didn't know the fuel line had fallen off in the tank and fuel level is below the output fitting.


    Here's what I know so far:
    120ish PSI on both cylinders.
    New BR8ES plugs.
    Fuel pressure is right on the money, but fluctuates with sled running. Will build quickly to 60 with return/overflow line pinched. However, it bleeds down very quickly after each fuel pump cycle.
    The prestart prime works every time and the fuel pump cycles with each pull of the starter rope.
    Running 91 octane with no ethanol. 4.5 gallons of fresh fuel added to tank after shop vacc'ing the debris in the tank.
    No codes, but codes will get thrown if I unplug sensors. Codes correctly correspond to the sensor that is unplugged.
    New pre-pump fuel filter installed, new post pump metal filter ordered. Pre pump filter shows much debris already.
    Fuel lines replaced inside and out of tank. If there is an in tank filter, it is rolling around in there where I can't see it. I weighed down the replacement line with a brass tee fitting for now while i source a pickup filter.
    TPS ranges from 436 at fully closed to 4.6K at WOT. There are ZERO dead spots in the TPS full range of motion.
    Current spark plug caps Ohm out at 4.68 and one was open when I got the sled. Stole one off the brother in laws Mach 1 for now. New NGK plug caps on order.
    CDI unit is brand new, came with sled, I installed.
    Battery being used for testing is a deep cycle marine battery at 12.6v.


    Plugs are dirty and soaking wet every time I pull them, yet the sled starts with 2 or 3 pulls every time. I am on my 4th set of plugs during this diagnosis hoping it would clear up eventually.


    I am working long hours this week on a plant shutdown, but I will check the thread nightly and follow up on any feedback or advice if I can. I may not be able to work on it again until next weekend.
    Sorry for the novel, but I don't want to give up on this. I have gotten a ton of great info from this site to help me get this far. I am at a loss and need some fresh perspectives. The snow will hit us soon here and I am excited!

    Thanks in advance, as I can tell from posts I have read this is a helpful group!

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    you said that the primary is currently off, so you're running it with no load on the motor? I would put the clutch back on (even if it isn't in the best shape) and run it to see if it acts differently. Also make sure that the battery charging circuit is working correctly. You should be around 14 volts at 2 to 3K RPM. I have the same sled and mine wasn't charging the battery. Found that the brown ground wire was just about snapped off at the regulator/rectifier and was only holding on by a couple of strands of wire. I crimped on a new fitting and it was charging like it was supposed to again. An ECU that's not getting the proper voltage will have you chasing your tail.

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    I really appreciate the input and I will check and try both. I will also reply with the results, but it just might have to wait until the weekend. Thank you.

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    Well, I reinstalled the primary and ran the sled with the same results. I did confirm that the charging circuit is working and saw more than 14v DC with the sled running. I also changed out the metal fuel filter that is after the pump. This thing starts so easily. Two pulls even after sitting all week. One pull restarts after its primed.

    Once it is running, any attempts to throttle up just result in a surge that feels a lot like a rev limiter. It goes between 3k and 3.5k, but never beyond.

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    Update. Since I can't seem to figure out if it is too much or too little fuel, I tried misting fuel in with the throttles wide open. The motor bogged even more. This indicates to me I am getting too much fuel.

    Suspecting a bad/dead ambient temp sensor, I set my meter to ohms and checked the function. Ohms started at 2.78 and rapidly dropped with my brother in law holding a lighter about six inches below the sensor. I had read here or somewhere else that a bad air temp sensor may not throw a code but would default the ECU to thinking it is -40. No idea if that is true or not but a reading like that would seem to create a rich condition.

    I realize I am more or less talking to myself at this point, but I am hoping something I put here will trigger someone else's memory with a similar problem.

    Still open to any and all suggestions.

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    Not sure if you have any kind of service manual to reference but you can download a pretty good one on this site that has helped me with my EFI. At the top of the home page, click on communities, then albums, album gallery, scroll down to documents. Once in documents, get to page 5 and scroll to the bottom and click on "Polaris 1985 through 1995". Starting on page 242 of the pdf is the EFI section. You also may want to look into the Select Moniter for PC by Rensuit. It has been a great help to me and it would tell you what temp your ambient sensor is actually reading. The program is free to download but you have to buy a USB/driver cable through Digi Key for around $30. You also have to download the driver software which is free online. Let me know it you want more info on that. Good Luck!

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    Thanks, Ben. I will do that. I am sure I will need it at some point.

    I haven't been able to get up to the shop today, but I have been doing some more reading. It appears these Fuji motors have crankcase drain plugs. If that is the case, I think I better pull them just to insure that I don't have a crankcase full of fuel and oil. It would definitely explain the extremely rich condition and unwillingness to build RPM's.

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    Well, I did have a decent amount of fuel and oil in the crankcase. I drained it. Started sled and the crankcase was flooded with fuel again within a short time frame.

    The injectors are simply supplying WAY more fuel than the motor can burn. I checked the dropping resistor and it was in spec at 6.4 ohms. The injectors were at 2.3 and 2.4 ohms. I have no clue where to go from here. The entire system seems to be working as designed with the exception of too much fuel.

    Hoping someone here will have and ideas as to why my injectors are flooding the motor with fuel.

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    Is there a regulator in the fuel system? If it fails it will flood your sled out

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    There is one. I am certain it is working, though.

    It is both, returning fuel to the tank, and maintaining the correct fuel pressure in the rail.

    I could be wrong.

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