2006 SUZUKI DF140 4 STROKE stall

[bdb333]

Well today, from a cold start, it will turn over but will not run. I went ahead and measured the volts with the key on, the exhaust temp sensor is showing 3.78 volts however the coolant temp sensor is only showing 2 volts. I am getting fuel to the fuel rail, I have spark and I have suction from the intake. Heavy fuel smell out of the exhaust. One thing to also note is today has been our warmest day for the year, around 90F, humidity 70%. Heat seems to play a factor, last year when the problem first arose, I remember it being unable to start from a cold start on our hotter days that summer but not every day.

[redlowrey]

If you have around 90F the exhaust temp sensor should be closer to the engine temp sensor voltage, lift the warm up lever and open the throttle and crank, both sensors have the same resistance value so they should be close to each other.

I would expect to see 3.78 volts in winter. I am doing some tests on a DF140 today in temperature of around 15 degrees Celsius l will post back the results in a few hours.

[redlowrey]

What country are you in

[bdb333]

I'm in the US, Texas. I tried lifting the warm up lever opening the throttle, same results. I switched the two sensors, since they are the same. After the switch the exhaust temp sensor was measuring 2 volts and the coolant temp sensor is measuring 3.78. So, I definitely have a weak/faulty sensor. Since I now had the good sensor in the coolant temp location, I tried to start it. It busted right off and has been running great since. I let it warm up and have killed/restarted it 30 times. I suppose the cooling temp reading is more important than the exhaust temp reading and with the good sensor now in the coolant temp location it is allowing everything to happen correctly. I plan on going ahead and replacing the low testing sensor that is now in the exhaust temp location, what do you think?

[redlowrey]

I tested both sensors at a temp around 15 degrees celcius and both sensors were at 2.8 volts dropping below 1 volt at operating temp.

The engine temp is the main input but they need each other and the iat sensor is a trimmer monitoring the air temp.
All you have to remember, the higher the signal voltage the more fuel the injectors will inject.
It probably wouldn’t hurt to change both the engine is fifteen years old, and there not expensive.

That problem didn’t take long to solve.

I think the ecu has been confused seeing two different signal voltages this is why it plays up at different temperatures one minute not injecting enough and then injecting too much fuel.

To try and diagnose problems over the internet is hard but when you get the right clues it makes the job easier

[bdb333]

I went back and checked the volts on both sensors after the engine was at operating temp, the good sensor (the one testing at 3.78 before warm up) was still reading 3.5 at operating temp and the weak sensor was testing just under 1. So with what you have taught me, that means the "good" sensor is actually faulty at operating temp and is over fueling which is most likely why I have fouled looking plugs and have a heavy fuel smell from the exhaust. I will go ahead and replace both and check those readings and let you know those results as well. I really appreciate your time and knowledge. No one, our local mechanics or our Suzuki dealer mechanics has even been able to suggest a solution or perform a system check like you have been able to help me with. Thank you again and I will post the volt test of the new sensors when they come in.

[ECU1984]

I went back and checked the volts on both sensors after the engine was at operating temp, the good sensor (the one testing at 3.78 before warm up) was still reading 3.5 at operating temp and the weak sensor was testing just under 1. So with what you have taught me, that means the "good" sensor is actually faulty at operating temp and is over fueling which is most likely why I have fouled looking plugs and have a heavy fuel smell from the exhaust. I will go ahead and replace both and check those readings and let you know those results as well. I really appreciate your time and knowledge. No one, our local mechanics or our Suzuki dealer mechanics has even been able to suggest a solution or perform a system check like you have been able to help me with. Thank you again and I will post the volt test of the new sensors when they come in.

I have been perusing old DF140 threads tonight just trying to learn more trouble shooting and "testing" procedures, as I have a DF140 and enjoy doing my own work.
That's how I ran across this thread
Redlowrey's Suzuki expertise is beyond impressive, he has helped me several times and takes the time to explain how and why certain parts or systems work and interact with each other.
Whoever he works for has one helluva Suzuki service technician