Foton 254 : RPM Gauge and oil pressure sensor problems

[D0TC0M]

My RPM gauge doesn't work. I traced out checked the wiring and everything looks alright. I removed the sensor and it looks alright. Anyway to test the sensor? I was thinking of using a drill and spin a piece of metal in front of it. Is there a way to check the gauge itself? How to you adjust the sensor? I'm afraid to screw it in too far and shear the end off.


The internal resistor in the oil pressure sensor seems to be burnt open because even with the engine off my gauge is pinned to the max. I'm reading open circuit to ground and when I short the terminal to ground the gauge reads zero so the wiring is good. The other terminal of the oil pressure sensor that illuminates the light works but not the gauge. What is the resistance range. I see many sending units on ebay but need to know what the range is to make sure it will work with my gauge.

 

[doxford jim]

To set up the speed sensor, with the tractor NOT running, screw the sensor in until it just touches the flywheel, then screw it back out again one half turn. That should give the approximate clearance needed. If you took the sensor out completely did you notice if it was dirty ? Being magnetic it will attract metal chips, shavings etc., which in turn will cause a false reading. The sensor must be clean for it to work properly.
Don't know what your oil pressure gauge is like, but the sensor for those are often adjustable. You would also need another mechanical gauge to use for comparison purposes. If the electric gauge is shot, I would advise installing a mechanical which will be much easier to maintain
Let us know how you make out. If either sensors are bad, you will be better off buying new of course.
HTH

 

[D0TC0M]

Thanks again Jim for replying to all my posts.

yes there was a a couple metal chips stuck to the end, I removed them and re-installed to the depth it was before. I'll set it the way you described.

The oil pressure sender is open circuit. It should have some resistance value so my gauge is clipped to the max. Fortunately the oil sender terminal that operates the low oil pressure light still works. I'm sure it's the sender that bad. Do you know what the resistance range is supposed to be of the sender so I can cross reference it? I'm assuming its probably standard. There are many senders on ebay that look like they might fit.

This is what it looks like OIL Pressure Sensor Gauge Sender Sending Unit Part 0 150PSI W TWO Terminals Plug | eBay
Input: 0-150 psi(150psi=1Mpa)
Resistance:10-180 ohms

 

[doxford jim]

Without seeing it I have no idea (oil sender unit). Try checking with Tommy at Affordable Tractors (Texas) or Ken and Joan at Asian Tractor Parts (Ontario), I am sure they will be able to help you out.
Regarding the tacho pickup - it needs to be 1/2 turn back out and then locked in place with the lock nut.

 

[RonMar]

Also when you set the RPM sensor, lesten to it with a nechanics stethescope or put your hand on it while someone else cranks it over with the compression release on for the first time. The front face of the flywheel does not always run true, so 1/2 turn backed out still may allow the flywheel to contact the sensor head. Once installed without contact, unplug it and connect a digital voltmeter to the sensor leads. With the engine running, the sensor should generate nearly 0.5 VAC from the ring gear teeth and gaps passing thru the sensor heads magnetic field. Much less than half a volt AC signal level and the tach unit cannot sense the teeth passage rate and drive the needle. I have to finish a clutch slave cylinder on my 4runner but after that I will back the tractor out and check the oil sender resistance for you(tractor needs run anyway since it has sat for a few weeks).

 

[D0TC0M]

Thanks ron. I also noticed my hour meter isn't working. Does it have to sense RPM for it to count time? I'll take out my fluke multimeter and check the ac signal as you said. As far as the oil sender if you could measure resistance with the engine off and when you start it please note the oil pressure so I can roughly calculate the full range resistance.

Thanks for your input.

 

[RonMar]

OK, the sensor is a dual function unit, one terminal to ground provides a path to drive the low oil pressure idiot light, so it is a short circuit measured to ground with engine off/low oil pressure(light on), and an open with engine running and normal oil pressure(light off)

The other terminal drives the oil pressure gauge. This terminal to ground is about 10 ohms with engine off/low oil pressure and 80 ohms to ground with engine idling. Once I put the leads back on the terminals and restarted the engine, cold engine oil pressure indicated while idling was around 0.35MPA or more simply put, just a hair to the right of straight up

Good Luck.

 

[D0TC0M]

Thanks RonMar that was exactly what I was looking for. We have a major snow storm hitting us right now so I have about 3 feet of snow in my driveway. I just got the tractor started after working at it for several days. I coach minor hockey so I haven't had much time to work on it, fortunately the storm cancelled our 2 games today so I was able to get at it most of the day. She's ready to blow except I have a both the RPM and the oil sender to fix. I also am not getting much temperature on the temp gauge and its not blowing much heat inside the cab so I'm assuming maybe the thermostat is stuck open.

 

[quicksandfarmer]

It has to sense RPM to count time.

 

[RonMar]

Quicksand is correct, it has to sense RPM to operate the hour meter.

Diesel with a radiator and fan large enough to keep itself cool at sustained full load on a hot summers day won't get warm in near zero temperatures... Hmmm I wonder what the problem could be

Ever notice the 18 wheelers who operate in the winter with the zippered cover over the grill? They have the same issue. Too much radiator for the load with supercooled intake air. All thermostats bypass a little water so the hot water can reach and open the thermostat in a timely fashion. But when you have the supercooled air keeping the radiator so cool, this little trickle of very cold coolant flow and your cab heater is enough to remove all the BTU the engines is generating unless you are really loading the engine. Snowplowing in my experience isn't much of a load. I a pretty sure your thermostat isn't even opening

I take a page from the truckers playbook when it gets really cold here and hang an old towel over the front of the radiator only leaving an inch or two along the edges for air to pass thru the cooling fins. Keep an eye on the temp gauge untill you get the hang of how much is needed, What you want is to cover enough that the temp gauge reaches op temp and stays there without cycling(gulping cold fluid). The goal is a steady temp so the metal parts maintain a stabil size and some heat makes it into the engine oil. If it starts to creep up above the normal run point, you have too much covered, adjust accordingly. This happens to me in the summer when running the brushhog when the radiator screen gets clogged and restricts airflow. Then I have to stop and clean the radiator to get it back to a normal stable op temp. Properly covered in the winter, the tractor should warm up and behave the same as it does in the summer without the cover...