2014 Bennche Bighorn 700 Won't stay running

[Hutch]

Okay everyone, need some help here. I got my 2014 Bennche Bighorn 700 from my father inlaw. He has had it since new and as far as I know never had any problems with it until recently. It began with it being hard to start and having to give it some throttle for it to start up. Then it wouldn't stay running once it did start. If you go to start it, it will fire right off and only run for a split second and then die. If you give it some throttle it will start and stay running as long as your foot is on the pedal. While it's running its pretty rough and backfires. Here is a list of everything I've done so far. Initially I checked compression and it was low. I changed the cylinder, piston and rings. Took the head apart cleaned and laped the valves. Checked timing a few times. Adjusted the valves. New spark plug. Checked the air filter, it was fine. New battery. Changed the fuel pump because of a broken fitting. Changed the fuel filter, lines and fuel injector. Dumped the old fuel and put new in. Changed the air idle control, TPS, MAP sensor, Voltage Regulator, ECU and harness. I was getting codes 31, 107, 113 and 122 on the display. Once I changed the ECU no more codes have been displayed but still have the same issues. All fuses look good and as far as I can tell Grounds are good unless there are some I can't find. I'm at a loss here. Not really sure where to go. Compression was better after everything I did but I don't remember the numbers. I'll have to check it again if someone thinks that could be the issue. Any help would be greatly appreciated!

[Savage3]

Compression is an important factor as you know. I'd check it again, make sure no mistakes were made in top end.

Have you looked closely at the spark? For instance, when it dies, is it because it is losing spark?

Is something grounding the circuit or is it losing ground?

 

How about fuel? Is it losing fuel after start? For instance, if you sprayed fuel source directly to intake after start will it keep running?

Is there a safety switch shorting to ground immediately after starting?

Verify these things and get back to us. Maybe someone else has some ideas as well.

Hope this gives you some ideas Boss

[Andy Dickerson]

If your model is fuel injected then look at the AIC valve/servo motor that is located under the throttle body. My 2021 Hisun i.e. Axis 700 periodically does the same thing and the cause is the AIC sticking. The AIC has a small mushroom shaped piston that is internal threaded that opens and closes based on the input to the ECU. The symptom's you described are exactly what I have when it sticks. It did it again to me this last week. The fix for me is to remove it very carefully as it has some small part that can get lost rather easily and clean the carbon off the piston. This time I think I'm going to add a little grease to see if it stops sticking. I might even polish it up gently with buffing compound using a Dremel. I actually loosen the throttle body and turn it to get access to the thing.

[Hutch]

I was messing around last night and put a new o2 sensor in didn't seem to help but I haven't done an evu reset since I installed it. I did spray some carb cleaner in the intake and it stayed running. Finally had more codes pop up. 122 and 650. So TPS and MIL Circut Malfunction. I think there is something going on with the TPS which I've already replaced but would make sense if it's not reading correctly that it wouldn't be getting the correct amount of fuel. I'm going to check it with a meter tonight and see if something is messed up there.

I've already replaced the AIC and I'm not getting any codes for it anymore. Not really sure what's going on with the MIL Circuit Malfunction but not too worried about it right now. 

I'll do my best to keep yall updated. Haven't had much time to do any work with the holidays lately.

[Hutch]

I was messing around last night and testing the TPS. It seems like I had a dead spot in the new one so I put the old one back on and it tests fine. Did an ECU reset and still no luck. I'm getting codes 122 and 123 which are both for TPS. Seems like I'm narrowing it down but still stuck. I put the new harness back on and it wouldn't start at all so I'm guessing the new harness is garbage.

[Alex]

Added UTV info into topic title 😀

[that guy from Canada]

Did you ever adjust the idle setting on the throttle body? As it only runs with throttle applied some people adjust this as a try to fix but it will only throw the tps out of whack with ecu.

Also if tps isnt fixed mount try adjusting its position, but only a little bit at a time.

Lastly bad temp sensor can cause similar issue as well. 

If atv idles too low for another reason the computer can throw tps code, it thinks tps is out for current idle rpm. I have seen this caused by plugged muffler or blown out baffles. Also bad or old fuel.

Why i prefer carburetors... lol

[Hutch]

I need to try the temp sensor. Thats the only sensor I havent changed yet.

I was looking at it Saturday, I unplugged the TPS and it started up and ran at 3k. Plugged the old TPS in and turned it with my finger and the idle raised. Went to adjust the throttle cable and when it went under 2k it would start to fall off again. When I mounted the TPS back in to the throttle body it idled lower but wouldnt stay running. 

I agree with you on the carbs lol this thing would have been running by now.

[Andy Dickerson]

Something else you might want to consider is the hudhacker software tool for our ECU. More than likely it would have been cheaper and easier to diagnose with the software and the adaptors. This is the link for the software which I have and have used. HUD ECU Hacker (netcult.ch) It will probably tell you want sensor is actually bad as it's scans the ECU and ECU faults. There's a write up how to here on the coleman UTV forum. 

[Andy Dickerson]

2 minutes ago, Andy Dickerson said:

Something else you might want to consider is the hudhacker software tool for our ECU. More than likely it would have been cheaper and easier to diagnose with the software and the adaptors. This is the link for the software which I have and have used. HUD ECU Hacker (netcult.ch) It will probably tell you want sensor is actually bad as it's scans the ECU and ECU faults. There's a write up how to here on the coleman UTV forum. 

 

[Hutch]

4 hours ago, Andy Dickerson said:

 

Thanks! I will look into all this tomorrow.

[Hutch]

Got the cables ordered and ECU Hacker downloaded. Tried starting it and like usual it would stay running. I unplugged the TPS and it started but the RPM's raised to about 4300 RPM. Here is a screenshot of What it was doing. Not too sure where the parameters need to be on these. It seems to be pointing to the TPS since anytime I unplug it, it stays running. With a new harness and TPS I'm not sure why. Is there any calibration I need to do for the TPS and/or the AIC? There is also a screenshot with the fault codes.

[Andy Dickerson]

You can use the software to clear all the old error codes and start from a clean slate. If the TPS continues to fault out it could be a connection issue i.e. a pin in a connector pushed in creating an open. If you leave the TPS in will it still throw the TPS error code?

The TPS is nothing more that a potentiometer and you should be able to check it with a volt ohm meter. It should have three wires going to it 12V from the battery, center tap that goes to the ECU and ground. The ECU uses the center tap to determine the position of the throttle and adjusts everything accordingly. I would check the TPS with the key turned on and use volts on the meter. Place one lead on ground the other on the center tap then press the throttle and the voltage should change incrementally as the throttle is pressed and then return back to the idle setting. You can find a schematic on this page at the bottom https://motorcycledoctor.com/parts/utv-700-bucket-seat/

[Andy Dickerson]

The other thing to consider is that the IAC is sticking up inside the throttle body due to build carbon buildup. Even if you replaced it and there was build up the new one would stick as well. If the IAC sticks shut it won't idle and will only stay running if you give it throttle. Mine stuck again a month ago but is ok now. I'm going to polish the end and clean up side the throttle body with the spray carbon remover. I might even put a little dry lube PTFE on the end after I polish it.

[Hutch]

6 hours ago, Andy Dickerson said:

The other thing to consider is that the IAC is sticking up inside the throttle body due to build carbon buildup. Even if you replaced it and there was build up the new one would stick as well. If the IAC sticks shut it won't idle and will only stay running if you give it throttle. Mine stuck again a month ago but is ok now. I'm going to polish the end and clean up side the throttle body with the spray carbon remover. I might even put a little dry lube PTFE on the end after I polish it.

I did clear the codes and they came right back. I'm not sure why so many codes are popping up especially since I've replaced everything. I did check the TPS and the voltage and resistance were good. I did replace the IAC and also cleaned the throttle body. When it shuts down I can hear the IAC reset so I don't think it's sticking. Also when I unplug the IAC it won't run at all. I'm not sure if there is a need or a way to calibrate the sensors, other than resetting the ECU.

[Andy Dickerson]

This is really pointing to something common like a wire, either ground or power. It's pretty much calling out codes for all of the sensors that provide information to the ECU. If you look at the schematic I gave you a link to, look for a common wire connection or possibly a loose or corroded ground wire. For all the codes to come back there has to be a common source. A no signal and low voltage warning indicate no voltage present or a missing ground i.e. a lack of reference to ground.