Name that part 1998 explorer 5.0

[Turkeybiscuits]

Was working under the hood to condition my timing belt-- I came across this grey wire that was cut off. On the end was a plastic conduit that was singed and slid right off when I pulled it up. The wire is leading back to a metal housing which has an upper radiator hosing being fed into it. See attached pic. It looks like a sensor of some sort sticking out of the top of the housing. There is no check engine light on. The temp gauge works fine, heating and cooling work perfect. Any idea? I cannot find the other end of the line where it was cut off from. This is a 1998 explorer 5.0 auto limited. First one to know for certain what it is gets a free beer--if you come to woodstock, ga : )

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[deadernie]

There's two coolant temperature senders. One for the gauge and one for the ECU. It's one of those two.
Hook up to a OBD scanner and make sure you're still getting a temp reading.

 

[Turkeybiscuits]

There's two coolant temperature senders. One for the gauge and one for the ECU. It's one of those two.
Hook up to a OBD scanner and make sure you're still getting a temp reading.

Ding ding ding!!! You are on the money. I looked it up further based on your response and it appears to be the coolant temp "Sending" unit. Gonna do a little testing on it tomorrow to see what's not jiving.

Any idea where the wire is suppose to go? Is it a lone wire that would go somewhere or would it be part of a multi-wire conduit? Again--it looked like it was in some sort of plastic conduit. Maybe I need to dig around and find the other burnt end.

 

[deadernie]

If I can get the three feet of snow off my EX I'll take a peek and see if I can see where it goes. Unless somebody else can say.

 

[koda2000]

Yes it's the temp sender/sensor wires. Does the TEMP gauge on the dash work? if it does it's the ECU temp sensor wires. W/out this sensor working you will run too rich and waste a lot of gas.

BTW, you don't have a timing belt. I assume you are referring to you serpentine accessory drive belt. What do you mean by "conditioning"? If you belt is slipping you need to replace it and possibly your belt tensioner.

 

[Turkeybiscuits]

Yes it's the temp sender/sensor wires. Does the TEMP gauge on the dash work? if it does it's the ECU temp sensor wires. W/out this sensor working you will run too rich and waste a lot of gas.

BTW, you don't have a timing belt. I assume you are referring to you serpentine accessory drive belt. What do you mean by "conditioning"? If you belt is slipping you need to replace it and possibly your belt tensioner.

Regarding the belt, yes it's the serp. belt. I use the Prestone Belt Conditioning spray. When I first got it, the guy before put on a new belt but for some reason it was slightly squeeky during idle. The spray alleviated it nicely.

Regarding the sensor: You know, that brings up a great point. I'm getting about 11mpg right now at best. I coast down declining roads and am light with the gas pedal. I've chucked fuel injector cleaner, it has new spark plugs, new air filter, checked tire pressure, and I am barely getting anything higher. I do have 32" all-terrains on it but that shouldn't drop me 4 mpg under the factory rated city mpg. It's also not lifted or modified, nor do I carry any cargo or trailers.

Please let me know if you find where it goes. In the meantime I'm getting a new fuel filter (it's at 156K right now and has the factory filter still on it!) and a bad o2 sensor replaced this evening.

 

[koda2000]

Regarding the belt, yes it's the serp. belt. I use the Prestone Belt Conditioning spray. When I first got it, the guy before put on a new belt but for some reason it was slightly squeeky during idle. The spray alleviated it nicely.

Regarding the sensor: You know, that brings up a great point. I'm getting about 11mpg right now at best. I coast down declining roads and am light with the gas pedal. I've chucked fuel injector cleaner, it has new spark plugs, new air filter, checked tire pressure, and I am barely getting anything higher. I do have 32" all-terrains on it but that shouldn't drop me 4 mpg under the factory rated city mpg. It's also not lifted or modified, nor do I carry any cargo or trailers.

Please let me know if you find where it goes. In the meantime I'm getting a new fuel filter (it's at 156K right now and has the factory filter still on it!) and a bad o2 sensor replaced this evening.

The coolant temp sensor connects to the PCM/ECU and tells the computer the temperature of the coolant/engine. When the engine is cold (or the ECU thinks it's cold) its like running with the choke on in a carbureted engine. On a computer controlled fuel injected engine it's called open vs closed loop mode. When the ECU thinks the engine is cold it gives it more fuel until it senses that the engine has warmed up. This will severely effect your fuel economy.

Those wires look cut, as the ends are straight and cut very cleanly. My 2000 V8's have this sensor, but it's in a different location and I believe they only have a single wire on the sender and the sensor. I'll take a look to be sure and see if I can see where they go, but they probably are concealed w/in a wiring harness.

You can try looking here for a free wiring diagram for your specific vehicle, which my be helpful. Use ID rrcc and PW rebsco to log in and go to the auto repair reference section.

http://search.ebscohost.com/

Edit: I tried to look at the sensors on my 2000 5.0L, but I can barely see them let alone see their wires.

Under engine controls #2 wiring diagram for the '98 Explorer 5.0L, the coolant temp sensor has a light green and red wire and a grey and red wire. Is that what you're seeing?

 

[Turkeybiscuits]

The coolant temp sensor connects to the PCM/ECU and tells the computer the temperature of the coolant/engine. When the engine is cold (or the ECU thinks it's cold) its like running with the choke on in a carbureted engine. On a computer controlled fuel injected engine it's called open vs closed loop mode. When the ECU thinks the engine is cold it gives it more fuel until it senses that the engine has warmed up. This will severely effect your fuel economy.

Those wires look cut, as the ends are straight and cut very cleanly. My 2000 V8's have this sensor, but it's in a different location and I believe they only have a single wire on the sender and the sensor. I'll take a look to be sure and see if I can see where they go, but they probably are concealed w/in a wiring harness.

You can try looking here for a free wiring diagram for your specific vehicle, which my be helpful. Use ID rrcc and PW rebsco to log in and go to the auto repair reference section.

http://search.ebscohost.com/

Edit: I tried to look at the sensors on my 2000 5.0L, but I can barely see them let alone see their wires.

Under engine controls #2 wiring diagram for the '98 Explorer 5.0L, the coolant temp sensor has a light green and red wire and a grey and red wire. Is that what you're seeing?

That was very helpful---I got into the ebsco account and looked at the diagram. That should be it however the only wire I see is gray as pictured. I got a mechanic buddy coming over this evening to take a look and see if we can find where the other end is. It bugs me that it was cut but wouldn't it also throw a code? I have a check engine light now that is for the bad o2 sensor, however that was the only code it read. After we install it, I'll let the motor run to see if the temp gauge goes up normally.

As a side note---what would be the purpose of someone cutting the wire? The guy I got it from was very upfront about everything that was done to it as well as the work it needed, maybe it gave him a check engine light, he cut it, and it managed to reset the engine light? I'm thinking maybe the guy before him did it and he just never saw the wire. It was tucked in deep before I pulled it out.

 

[koda2000]

That was very helpful---I got into the ebsco account and looked at the diagram. That should be it however the only wire I see is gray as pictured. I got a mechanic buddy coming over this evening to take a look and see if we can find where the other end is. It bugs me that it was cut but wouldn't it also throw a code? I have a check engine light now that is for the bad o2 sensor, however that was the only code it read. After we install it, I'll let the motor run to see if the temp gauge goes up normally.

As a side note---what would be the purpose of someone cutting the wire? The guy I got it from was very upfront about everything that was done to it as well as the work it needed, maybe it gave him a check engine light, he cut it, and it managed to reset the engine light? I'm thinking maybe the guy before him did it and he just never saw the wire. It was tucked in deep before I pulled it out.

I can't image why anyone would cut the wire. If someone wanted to disconnect the senor, why not just unplug it? If you can't find the other ends and reconnect it, you'll need to run new wires. It looks like the LT GRN/RED wire goes to the PCM, but in looking at the other wire (the one that's supposed to be GRY/RED) I can't determine if it goes to a common ground or what. The diagram shows it going to a junction of some sort.

It's strange, the wires shown in your pics don't look like normal automotive wiring. They look more like speaker wire. Maybe someone rewired the sensor??? Normal automotive wire is always color coded and usually individual wires.

Sensors work in a specific range of voltage. The CEL is set when the PCM sees that a sensor is functioning outside of its specific electrical range. I would think a disconnected sensor would set the CEL, but perhaps that particular sensor reads zero volts if the coolant is cold (?). In any event, not having that sensor reporting to the PCM will drop your fuel economy at least 4 MPG.

 

[Turkeybiscuits]

I can't image why anyone would cut the wire. If someone wanted to disconnect the senor, why not just unplug it? If you can't find the other ends and reconnect it, you'll need to run new wires. It looks like the LT GRN/RED wire goes to the PCM, but in looking at the other wire (the one that's supposed to be GRY/RED) I can't determine if it goes to a common ground or what. The diagram shows it going to a junction of some sort.

It's strange, the wires shown in your pics don't look like normal automotive wiring. They look more like speaker wire. Maybe someone rewired the sensor??? Normal automotive wire is always color coded and usually individual wires.

Sensors work in a specific range of voltage. The CEL is set when the PCM sees that a sensor is functioning outside of its specific electrical range. I would think a disconnected sensor would set the CEL, but perhaps that particular sensor reads zero volts if the coolant is cold (?). In any event, not having that sensor reporting to the PCM will drop your fuel economy at least 4 MPG.

Since 4 MPG is almost 40% of my fuel economy, you better bet I need to replace it. I'll see what my mechanic bud says about the whole situation. You guys have been very helpful, I'll update it later this evening with our findings.

P.S. I gave it a test run before putting in the O2 Sensor---the temp gauge does not work. It was working when I first bought it so it looks like it broke sometime the last time I drove it. Great.

 

[koda2000]

Since 4 MPG is almost 40% of my fuel economy, you better bet I need to replace it. I'll see what my mechanic bud says about the whole situation. You guys have been very helpful, I'll update it later this evening with our findings.

P.S. I gave it a test run before putting in the O2 Sensor---the temp gauge does not work. It was working when I first bought it so it looks like it broke sometime the last time I drove it. Great.

Either that, or the wires are for the temp gauge sender...

 

[1998Exp]

1) If the wires connecting the coolant temp sensor to the PCM were cut, you'd definitely get a trouble code for that (P0115, 116, 117, or 118).
2) For what it's worth, I looked at the thermostat housing in my '98 5.0 engine, and the location of your 'mystery sensor' is a blind hole. The sensor that serves the PCM is threaded into a fitting from which the coolant it taken to the heater, located a couple inches behind the thermostat. The other sensor, which serves the gauge, is a couple inches to the right of the first one.
3) The above, combined with the fact that the wires that you show are definitely not OEM, lead me to think that your 'mystery sensor' was an improvisation, most likely installed at some point to work with an aftermarket temperature gauge. If your temp gauge works and there is no trouble code for the temp sensor , I would just leave this 'mystery sensor' alone.

That was very helpful---I got into the ebsco account and looked at the diagram. That should be it however the only wire I see is gray as pictured. I got a mechanic buddy coming over this evening to take a look and see if we can find where the other end is. It bugs me that it was cut but wouldn't it also throw a code? I have a check engine light now that is for the bad o2 sensor, however that was the only code it read. After we install it, I'll let the motor run to see if the temp gauge goes up normally.

As a side note---what would be the purpose of someone cutting the wire? The guy I got it from was very upfront about everything that was done to it as well as the work it needed, maybe it gave him a check engine light, he cut it, and it managed to reset the engine light? I'm thinking maybe the guy before him did it and he just never saw the wire. It was tucked in deep before I pulled it out.

 

[deadernie]

The sending unit for the gauge has one wire connecting to it the temp sensor for the ECU has two wires going to it.

If the OP has a OBD scanner it would be pretty to see if the sensor for the ECU is working.

 

[Turkeybiscuits]

The sending unit for the gauge has one wire connecting to it the temp sensor for the ECU has two wires going to it.

If the OP has a OBD scanner it would be pretty to see if the sensor for the ECU is working.

I got my mechanic buddy to come over and check out the sensor. Even he was baffled that the wiring didn't look stock and it was basically speaker wire. We replaced the bad O2 sensor, change the fuel filter, and ran the car for about 15 minutes. The temp gauge went up. I previously though it was out but I forgot how long these motors take to warm up (plus its about 40 degrees here in GA at night.).

He's thinking that wire needs to be hooked up into something. However I've verified there is no other code being shown now that the bad O2 sensor has been changed. As previously suggested, I may just leave it alone and hope that the new fuel filter and O2 sensor help alleviate the MPG issue. I also took at the MAF and cleaned it as well as cleaned out the intake hose from the inside-out.

Sadly there is some pi$$ poor wiring work done from the previous owner. The electric fan has an exposed fuse and relay setup on the right hand side of the engine bay. There was electrical tape and loose wiring that was so bad that part of it was unraveling. The relay was dangling freely with nothing to protect the contacts from water so that's next on the to do list. It further shows that the mystery sensor could've been modified by the same guy.

Additionally, I have one major item left to fix which is an oil pan leak (which could end up being the rear seal). That will be done by Friday then I'll cruise around to clock the new MPG and check for any other check engine code to come up. I'll also know if the oil leak is still continuing. Fingers crossed. I would like to know if anyone else has the 5.0 and can verify there are no wires where my mystery sensor is located. If there most say no, I won't bat an eye at it again.

 

[1998Exp]

You have an electric fan on the radiator? That's certainly not stock, as the 5.0L engine used a mechanical one. That may explain the 'mystery sensor'. Electric fans need a temperature sensor to turn them on and off, so that's probably what they improvised, and then abandoned by cutting the wires. Does your fan have any sort of sensor at all, or is it running non-stop?

...
Sadly there is some pi$$ poor wiring work done from the previous owner. The electric fan has an exposed fuse and relay setup on the right hand side of the engine bay.

 

[koda2000]

You have an electric fan on the radiator? That's certainly not stock, as the 5.0L engine used a mechanical one. That may explain the 'mystery sensor'. Electric fans need a temperature sensor to turn them on and off, so that's probably what they improvised, and then abandoned by cutting the wires. Does your fan have any sort of sensor at all, or is it running non-stop?

Oh, that's an excellent guess. That would explain the location of the mystery part, the non-stock wiring and that fact that someone cut the wires. Maybe it's a thermal switch to turn the fan on and maybe it wasn't working, so the PO just cut the wires. On my 2000's and 2001 5.0's the sender and sensor are located on the intake manifold. I think those wires can be ignored.

I hope the new O2 sensor improves your fuel economy. It should help. I find during the winter months I get around 15'ish in town and maybe 19 hwy. During the summer I get around 17 in town and 22'ish hwy.

 

[deadernie]

I'm betting it's a temp sensor for the electric fan. As said earlier the electric fan isn't a stock piece. Does the electric fan ever come on?

You've confirmed the temp gauge is working but do you know if the them sensor for the ECU is working?

 

[Turkeybiscuits]

I'm betting it's a temp sensor for the electric fan. As said earlier the electric fan isn't a stock piece. Does the electric fan ever come on?

You've confirmed the temp gauge is working but do you know if the them sensor for the ECU is working?

I'll need to hook it up to a reader. Will places like Autozone have the ability to see this on their scanners or will I need to go out and buy one?

As for the fan: I'll look at it tonight to find out which wires are for what.

 

[deadernie]

Possibly. There are code readers that read codes only and there are scanners that can view freeze frame data and live data. So depending on which tool they're using it's possible.

Harbor freight has one that views freeze frame data for $80 (maybe cheaper if you can find a coupon) and most places have the tool loan program also.

 

[Turkeybiscuits]

Major Update:

So did some digging with my mechanic buddy--- the wires from the top of that temp sensor were from what appeared to be an attempt to wire them into the relay for the electric fan. There is an odd setup to the electric fan, there are two power wires (one from lower fan, one from upper, that are spliced together that then hook to the relay. The relay his hooked to a 40 amp fuse. The fans are always on and are triggered by the ignition. The wires from the temp sensors were likely a way to get the fans on/off without needing them on all the time. I re-wired the relay and crimped all the wiring so it looked clean. The wiring and relay run very warm which my concern was if a 40 amp fuse was too much for 1 relay and two fans drawing. So far I've driven it 100 miles now and no blow fuse and nothing is running 'hot'.

I'm also happy to report my gas mileage is now 15 mpg city/hwy. I cleaned the MAF, changed fuel filter, cleaned the throttle body, and added some injector cleaner. When we replaced the o2 sensor, I did all the above then unplugged the battery for 15 minutes which reset the check engine code. Happy to report no codes and it runs very smooth. There still in the oil pan gasket that needs replacement from the minor oil drippings which I'll take care of this evening. My buddy brought his scanner tool and hooked it up to the computer, he said all readings looked normal so nothing is running lean. My guess was the bad o2 sensor was causing it to run lean? Or maybe the dirty maf?

Either way, case closed. Thanks for the help. I also went under the body with some all-purpose lube and hit up any/everything that was squeeking while driving, also lubed every door and hinge in sight including the trunk glass hinges and door. Night and day difference, something I'd recommend if you have any body noises.