Symptoms of a bad/failing engine coolant temperature sensor? (4 Viewers)

[BlueCruiser84]

According to thefactory Service manual the engine coolat temperature sensor is something that, when bad, can cause a rough idle, misfire, and general porr running of the engine.

Does the ECT sensor send information to the ECM only? or does it also send information to the guage?

Can the ECT work sporadically? or is it an all or nothing kind of deal?

School me on this sensor!!! I am still trying to diagnose a misfire (https://forum.ih8mud.com/80-series-tech/488045-misfire-shuddering-shaking-lopey-idle.html) and I am wondering if this could be the root of my rich running, misfiring, spark plug fouling 80...

 

[Eicca]

It's definitely possible. The ECT sensor tell the computer when the engine has warmed up. This is mostly for protection, since a cold engine is more likely to misfire in a damaging way. If your sensor is bad, the ECU is seeing a cold engine even though it may have warmed up. It will keep running in open loop (default rich mixture) setting until it gets a signal it likes from the ECT sensor.

The sensor that controls the gauge is its own thing, doesn't affect the engine at all.


The biggest problem is, those sensors are pricy.

 

[BlueCruiser84]

That is how I was imagining it to work, but I wanted an explanation from someone else to confirm.

The thing is, since it has gotten warm around here every time I start it up it has had a s***ty idle; It acts like it is dropping a cylinder, runs super rich, and fouls plugs rather quickly. Every once in a while when the gauge temperature gets up to normal it will smooth out, idle normally, and generally run awesomely (is that a word?) The majority of the time, however, it runs like crap.

I'm thinking maybe a bad/corroded connection that is affected by the hot air temperature. This is the first summer I have had the 80 and I bought it right at the beginning of winter so I hadn't had much hot weather experience with it. I think this may also explain the somewhat intermittent nature of the issue.

I just ordered one from Cdan, 'bout 50 clams, but in the meantime I am going to clean up the connections and the sensor itself and see if that changes anything.

 

[Eicca]

If the truck isn't actually warming up then I'd suspect the thermostat. Happened in my stupid Ford truck, the T-stat would never close, so the thing would never warm up and ran like junk.

 

[BlueCruiser84]

The truck warms up great and the gauge sits right in the middle.

 

[Eicca]

Do you have a factory service manual? There's a test you can run on the ECT with a multimeter to determine if it's crapped the bed or not.

 

[Tenzig Norgay]

I had a ECT sensor fail, it would go intermittently and cause the ECM to shut down the fuel pump. This was is my 4-runner however, I could see it happening with a LC eventually

 

[Eicca]

I had a ECT sensor fail, it would go intermittently and cause the ECM to shut down the fuel pump.

Why would it do that? That sounds to me like nothing but a big safety problem.

 

[Tenzig Norgay]

I don't know the exact reason, but I suspect Toyota did it for safety reasons, and this was in an 88 4-runner, so It may be different. I figure if the engine was overheating, perhaps burning and on fire, and the ECT sensor had an extremely high reading, the computer would shut down the fuel pump. Sounds like a good reason to me.

I know this was happening in my situation for sure. After replacing the fuel pump my mysterious random killing symptom was still occurring, so I hooked up a test light to the fuel pump. When the pump was running my test light was on, If the light goes out that means power to the pump was shut down. Every time the engine would kill, the light would go out at that exact moment. Out of shear blind luck, I decided to replace one sensor, the engine coolant temp sensor(it may be the engine temp sensor in the runner, may make a difference). Its been fine for 7 or 8 years, maybe 40,000 miles, and i haven't changed anything but shocks since then.

I think its normal for the sensors to eventually go bad, everything eventually does. I have always wondered if this same senario could happen with the Land Cruiser, but as of yet I haven't heard of it and everyone keeps calling me dumb when I bring it up, but someday. I don't know the electrical terminology, but I don't why a sensor couldn't fail in either a closed or open state, on one end the sensor would be telling the ECM cool, and on the other end the sensor would be telling the ECM overheating. What really matters is how the ECM of that particular vehicle responds, and I can't answer that. So yeah, I guess I am at least ignorant, maybe not dumb.

 

[Eicca]

I don't know the exact reason, but I suspect Toyota did it for safety reasons, and this was in an 88 4-runner, so It may be different. I figure if the engine was overheating, perhaps burning and on fire, and the ECT sensor had an extremely high reading, the computer would shut down the fuel pump. Sounds like a good reason to me.

Yeah but if it cuts out while driving, say on the freeway, there goes your power steering and brakes! I think if it was on fire the driver would know to pull over and shut it off... Just seems crazy unsafe to me.

Still, I'd recommend testing the sensor with a multimeter as per the FSM and go from there.

 

[Tenzig Norgay]

That happened twice to me on the way back home one day, where I garaged it till it was fixed. It was definitely scarry, and now I see what you mean by unsafe. Before that, the symptoms occured mainly on start up.

 

[ToddD]

Bumping this old thread...

I have a temp sensor that is all over the board. Engine actual temp was 199 and the sensor was jumping around, 175, 195, 180, 185, 198, etc... I have a super rich running condition and this is going to be part of that issue.
I know there are 3 sensors in the head but which one is it? I can't seem to figure it out...
Thanks

 

[feralyouth]

I had a ECT sensor fail, it would go intermittently and cause the ECM to shut down the fuel pump. This was is my 4-runner however, I could see it happening with a LC eventually

I know it’s been along time, but my LC runs at 585-615 when at op temp and in gear. The seemingly random my rpm’s drop to 400s, sometimes if I let it ride, rpm’s creeps back up to normal. It usually happens after exiting the freeway or on warmer days. I’ve had one stall. Does this sound like what you experienced?