Thermistor Replacement
- Thread starter jnporcello
- Start date
SandyTX
Bronze Member
Dan , thanks again. My 4300 is suffering from the thermistor issue again. Replaced it but it still has issues (bad thermistor?). It does not help that rats found the wires in the dash and ate some. Been repairing the harness over the last few days.
One question on the switch install.
Do you take the thermistor out of the equation all together once you add the push button switch to the process?
Thanks again.
Hi Sandy,
Yes, you can get rid of the thermister entirely once the switch has been wired in. The switch is a total replacement for the thermister.
Sorry about the rodent problems. I have heard that mice love to build a nest right under the instrument panel. There's a very nice little place there where they can live and there's also a lot of wires there for them to chew up. I'll have to open mine up and put a bunch of bait blocks in there if they ever happen to pay a visit.
Merry Christmas!!!
Yes, you can get rid of the thermister entirely once the switch has been wired in. The switch is a total replacement for the thermister.
Sorry about the rodent problems. I have heard that mice love to build a nest right under the instrument panel. There's a very nice little place there where they can live and there's also a lot of wires there for them to chew up. I'll have to open mine up and put a bunch of bait blocks in there if they ever happen to pay a visit.
Merry Christmas!!!
SandyTX
Bronze Member
Looks like its the fuel solenoid. New thermistor and also tried replacing with the push button switch. Still cranks but wont start. The fuel solenoid seems fairly difficult to remove; any tips with someone with small hands.Appear to be 2 bolts holding it on with 1 wire harness connector. Hopefully I can get the fuel solenoid off and clean it out like others have done to get this issue resolved. Going on 2 months now. Fun times ! 
SandyTX
Bronze Member
Anyone have any pointers for removing the fuel solenoid? I will finally have a chance next week to work on this again and am determined to get it fixed. A few weeks ago when I tried it darned near seemed impossible to get to the rear bolt on the fuel solenoid bracket with larger hands.
Egon
Epic Contributor
Take the plate off that is on the drivers side of the solenoid. (4200)
Replaced my thermister last week. Soldered longer wires on sealed with heat shrink. If it goes again I won't have to remove the fuse box to replace it. If I do have to replace the thermister again I plan installing a 2 wire terminal strip to make replacement a little easier. By the way thanks for all the good info on here my 4300 is back up and running.
SandyTX
Bronze Member
Finally had the time this weekend to get on this repair. Purchased a curved set of wrenches from Harbor Freight and removed the fuel solenoid. Once removed the engine fired right up. Shot a little cleaner in it and dried it out. Also replaced the o-ring that someone before me had incorrectly put in place allowing it to be bent over and oil getting past. So all in all wired up the momentary push switch in place of the thermistor; removed and reinstalled solenoid correctly, added a new seat. Back in business again. Thanks again everyone.
after having many thermistor issues, i too, replaced mine w/ a push button.
found out a few interesting things when i tested it:
1) if you turn the key to run, and push the button, then start - there is no voltage.
2) if you are cranking the engine and push the button - no voltage. you have to push the button before you turn the key.
2) once running, if you release the button and push it again - no voltage. but the voltage will be maintained while running for as long as the button remains pushed.
also, w/ the thermistor, i could always here the 'click' when turning the key. usually a sign that my thermistor was acting up, and a little 'manipulation' would bring it back. w/ the push button, i don't hear a click, but then again, i think it starts up much faster which may drown it out. in other words, w/ the thermistor, it seems like the engine would crank for 1 second before starting. now it turns over and is immediately running.
i am not 100% sure this has fixed my problem, but over the last month, i have had several starting issues. so far w/ the button, i have had none (once i figured out when to push it). i have even started it more than i normally would just to test it.
the only downfall is if the button should become stuck closed for some reason, i don't think you'd know.
found out a few interesting things when i tested it:
1) if you turn the key to run, and push the button, then start - there is no voltage.
2) if you are cranking the engine and push the button - no voltage. you have to push the button before you turn the key.
2) once running, if you release the button and push it again - no voltage. but the voltage will be maintained while running for as long as the button remains pushed.
also, w/ the thermistor, i could always here the 'click' when turning the key. usually a sign that my thermistor was acting up, and a little 'manipulation' would bring it back. w/ the push button, i don't hear a click, but then again, i think it starts up much faster which may drown it out. in other words, w/ the thermistor, it seems like the engine would crank for 1 second before starting. now it turns over and is immediately running.
i am not 100% sure this has fixed my problem, but over the last month, i have had several starting issues. so far w/ the button, i have had none (once i figured out when to push it). i have even started it more than i normally would just to test it.
the only downfall is if the button should become stuck closed for some reason, i don't think you'd know.
Got a similar problem with my 4600 (~1200 hrs) - no start but cranks fine. Suspected the thermistor based on the comments here. It was a real PITA to access - used the suggestions in this and other threads. Removed the fuse box and was barely able to get access (very tight wire harness) - found the thermistor
View attachment thermistor_4600.pdf
Clipped the black/white leads and soldered new wires onto the new new thermistor (btw... new thermistor measured 0.6ohms resistance uninstalled with meter
View attachment solder.pdf
on back of fuse box - placed quick disconnect terminals (male/female) on existing wires to allow longer wires in the event I need to replace again
View attachment connectors.pdf
finally - put all back together with new thermistor if FRONT of fuse box in the event I decide to replace or put a puch button switch in its place
View attachment final_placement.pdf
This solved the problem - ceanks and starts up quickly.
Overall - this was not a difficult job but definitely trying - the wiring harness is tight and difficult to maneuver. Interestingly, I DID NOT notice any difference in the "CLICK" when the key was activated post installation.
Many thanks to all for posting their efforts - it made doing this much easier!
View attachment thermistor_4600.pdf
Clipped the black/white leads and soldered new wires onto the new new thermistor (btw... new thermistor measured 0.6ohms resistance uninstalled with meter
View attachment solder.pdf
on back of fuse box - placed quick disconnect terminals (male/female) on existing wires to allow longer wires in the event I need to replace again
View attachment connectors.pdf
finally - put all back together with new thermistor if FRONT of fuse box in the event I decide to replace or put a puch button switch in its place
View attachment final_placement.pdf
This solved the problem - ceanks and starts up quickly.
Overall - this was not a difficult job but definitely trying - the wiring harness is tight and difficult to maneuver. Interestingly, I DID NOT notice any difference in the "CLICK" when the key was activated post installation.
Many thanks to all for posting their efforts - it made doing this much easier!