I just need to know whether the temp sensor on the back of the water pump and the one next to the oil pressure sending unit are interchangeable.
I think the one on the side of my engine is malfunctioning but the only spare temp sensor I have is the one from a water pump.

 

they are different (size/plug)

 

No they are not interchangable. There are a totally different sensor for a totally different purpose. They don't even look vagely similar in shape or size.

 

Ok, now I'm a little confused. I checked the plug that's next to the oil pressure sensor and it's OK. But the temp sensor on the water pump is completely torn off from the connector! I thought the one by the pump is the one that relays the temp to the gauge and the one by the oil pressure sensor is the one that relays to the ECU. Am I backwards? My gauge works perfectly.
I believe the sensor that sends info to the ecu is bad because my car is having a really hard time starting on cold mornings. Almost like it wants to start a few times but just barely can't get enough fuel. I heard that when the sensor doesn't work it defaults to hot starting conditions. Is there any way to rig it so that the sensor is tricked into thinking the car is cold? I'm thinking that with complete resistance (connector torn off) the gauge believes the car is hot. With zero resistance (wires jumped to each other) the car will think it's cold and will respond correctly. If I'm wrong please tell me. I have to get to work early (cold) tomorrow!
Am I right? Anyone? ... Beuller?

 

Yep, completely backwards.

That would be because of the "completely torn off from the connector" bit. The ECU is not getting a temp signal so it's assuming the engine is warm. You need to fix that.

 

Thanks NZconvertable. I still need one more question answered from my earlier post- is there a way to use the broken connector to trick the ECU into thinking it's cold? I see two leads hanging out of the broken off connector and I was thinking that if they aren't touching each other and therefore telling the ECU it's hot, will making contact with the two by bridging them trick the ECU into thinking it's cold?
At work I tried it by getting a metal clip and making contact with the two and the responded sort of like I remember it doing a while back on cold days- starts up and revs to approx. 2,000 rpm, then settles down to 1,500 and then to 750. I need to know because I have to go to work early and I won't be able to get my spare plug until I go back to Cruces on Tuesday.

 

There are three temp sensors. The one by the oil pressure sensor only controls the instrument gauge. The one on the water pump is a variable resistor that provides input to the ecu. You need to fix this, sounds like. The last one (water temperature switch) is at the base of the radiator. When closed (cold) it allows the ecu to energize the air bypass solenoid. You may have to check this one too.

Happy motoring.

 

beautiful

Seriously though, thanks for your help guys I really appreciate it.

 

A suitably sized resistor wired across the terminals could mimic any temp you choose, but fooling the ECU into thinking the engine's cold would be pointless because it'll run like crap when it's warm The engine spends far more time warm that cold, so why make the situation worse than it is?

DO NOT DO THAT! A short-circuit like that will quite possibly fry the ECU. Don't EVER short circuit anything unless you know exactly what you're doing!

Stop messing with it and fix the problem properly before you damage somthing. You're much better of just leaving it disconnected until you do. An engine that runs badly when cold is better than one that runs crap when warm or doesn't run at all.

 

Which sensor is the one that tells the ECU to trim fuel for hot/cold? The one wire sensor? or the two wire sensor? Will reversing the leads on the two wire sensor with the square plug cause the hard-start condition?

 

The two wire, usually green in color, somewhat rectangular in shape.

Reversing the leads/wires makes NO difference.

Hard starting is usually caused by a low compression engine. Isn't yours recently rebuilt????????

And for the original author of this thread: If the wires are off the sensor, then the ECU sees that and fails the water thermo sensor signal to a 180 degree temperature. So even if the air temp/water temp is 32 degrees, the ECU sees the temp as 180F.

Unfortunatly that causes PROBLEMS. During the cold start procedure, the ECU does NOT use the afm for fuel delivery. It uses engine rpm (less than 500rpm), water thermo sensor temperature and a 12v signal from the *starter circuit* (key HELD to Start).

If everything is functional, it will see the water temp at 32 degrees on that cold day and deliver a pulse width of maybe 21ms to the fuel injectors. But if the wires are off the sensor, then the ECU sees 180F and will make the pulse width of the injectors during starting, something like 7ms.

The 7ms makes for a difficult start on a cold 32 degree day and a stone cold engine. Later in the day if the car gets started and the water is now up to temp, then the rest of the starts during the day will be easier.

Unless you let the engine cool off too much then your back to square one.

I fudged on the water temp and the pulse width a smidge because I'm too lazy to open the book or go to the car. The real default temp might be 179F. Big deal.

 

No, it's definately not a compression problem. It was working about 45 mins before I disconnected them and cleaned the wires with some electrical contact cleaner then put some dielectic grease on the connections.

I figured I turned them around or something.