Four Oxygen Sensors?!

cad614 · 09-17-2001, 09:51 AM

Decided I was going to replace my oxygen sensors today so I called up the local auto parts store. I didn't realize I had four of these things! Two behind the catalatic converters ($40 each) and two in front of them ($65 each)! So I'm looking at over $200 for some freakin oxygen sensors!

Tell me this isn't right.

------------------
'95 GT Convertable

Smokedawg · 09-17-2001, 10:01 AM

I didnt realize they had that many. I only have 2!

------------------
347 Stroker Motor: Balanced, Cobra Transmission, Extrude Ported and Polished Upper and ported Lower, GT40 Milled Ported and Polished Heads, B303 Cam, BBK 1 5/8 Headers, 30lb Bosch Injectors, Holley AFPR, March Underdrive Pulleys, Perma-Cool Fan, 3-Core Radiator, Accel Performance Coil, Accel 300+ Racing Wires, Ram Air, K&N Filter, 73mm Vortech MAF, 70mm TB, FlowMaster Exhaust w/BBK Offroad H-Pipe, Hurst Shifter, 3:55 Gears, Ram Clutch, Cross Drilled Rotors, AC and Smog del, rear seat del.

Mach 1 · 09-17-2001, 10:07 AM

The OBDII cars have 4. Two before the converter, and two after. THis is how they can monitor if the converters are working. They measure the difference between the front and back sensors.

But, a 95'isnt OBDII?

------------------
1993 GT/AOD
'93 Mustang GT

cad614 · 09-17-2001, 10:23 AM

Well I didn't bother to look under my car yet, I was just going by what the Autozone guy told me. He looked up my car, found the engine and asked if I needed the front or the rear sensors. I was shocked I had 4, so I figured I'd post here in hopes that someone knew what was going on.

PKRWUD · 09-17-2001, 01:35 PM

I am not aware of any 5.0 Mustangs having 4 HEGO's. That didn't happen until 1996, when the 3.8L and the 4.6L both got a double dose.

Might want to try a different auto parts store.

Take care
~Chris

------------------
Retired Moderator
MustangNet

My site: JimPorterRacing

RACECAR spelled backwards is RACECAR

HEY !!! Are you ASE Certified ??? If you are, ask me about iATN. The best tool you'll ever have, and it's free !!!

Daves 95GT · 09-18-2001, 12:40 AM

you have a 95 gt. you only have 2 HEGO sensors. the guy at the parts store is a nut. no mustang EVER came with 4. the two sensors on the front of the converters on 1996 and later cars are oxygen sensors. the two behind the converters on 1996 and later cars are called CMS sensors(catalyst monitoring sensors). this is one of the differences between OBD1 and OBD11 thier job is to read the gases after ther cat. converter to determine the leven in which the converters are functioning. if a converters isnt performing properly, it will set a check engine light, and this is most of the time a hard fault. but no, your 1995 mustang gt is not equipped with 4 oxygen sensors. by the way, why are you replacing them? did you have an intermittent check engine light? if not, then there is not any reason to replace them. it is a common misconception that they need periodic replacement, and they do not. as long as they are switching and giving correct readings, they are fine. if they are contaminated , they will trun the check engine light on once the car has warmed up. a lot of fuel additives will contaminate them, but you will see a light if it does.

[This message has been edited by Daves 95GT (edited 09-18-2001).]

cad614 · 09-18-2001, 08:03 AM

Wow, thanks for the info guys. I thought I only saw 2 of them last time I looked, but couldn't remember for sure.

Daves 95GT - I'm replacing them because that seems to be the general opinion of this board. I'm approaching 80k miles on my car, and I'm averaging 15mpg. There's no check engine light, but after doing a complete tune up and still getting 15mpg, I figure something needed to be fixed.

This is the first time I've heard anyone say that they don't need to be replaced, does anyone else agree?

------------------
'95 GT Convertable

Chevyguy · 09-18-2001, 10:43 AM

I know Bosch etc advertizes that you should replace your O2 sensor periodically, but is that like the 3000 mile oil change myth??

My Stang is almost at 114K on the original Os's I was planning to put new ones in soon, of course I had the H pipe off the car back during the trans swap, would have been a piece of cake then

eh oh well

So I'm curious too, how long do those sensors really last, I had assumed they "wore out" over time. I replaced the sensor on my Lumina twice, at 100Kand 200K miles, never really noticed anything, but they only cost $20 and only one.

------------------
Frank W
90 5.0 LX coupe Daily driver. Silencer removed, K&N filter. Flexalite fan, 3 core radiator. FMS flywheel and Clutch, FMS blue wires Energy Suspension end links
88 Notch 2.3L 5 speed Parts/beater car My two Notchbacks

74 Chevy Laguna Type S-3 305 Finally fixed getting a 454 to put in garage
<A HREF="http://www.chevellepages.com/folingo" TARGET=_blank>www.chevellepages.

John · 09-18-2001, 08:32 PM

Hey chevyguy i wouldnt call 3000 mile oil change a myth. The person who owned my car definately didnt do reg. interval changes. When i did my came and intake swap 2 wks ago the buildup of "ashed oil" was unspeakable. The chunks were so big they covered my oil holes under the intake and restricted drainage. I use mobil 1 and still change every 3000. My baby has 155,000 miles on her and no major engine probs. John

------------------
89 Notch: ASP Pullies,
K&N Air,Transgo shiftkit,Trans. cooler,FMS 3 core , FMS 4:10's, 1.5" cowl, cold air kit, hooker shorties(jet hot coated), O/R H-Pipe, ASP solid mounts, Energy Sus. Trans. Mnt. BBK 70mm TB, MSD 6al, Dual elec. fans, 5.0 Firepower Kit, Scorpion 1.6 RR's, Flowmasters, 73 mm MAF, cobra intake and crower #512 cam,

PKRWUD · 09-18-2001, 09:20 PM

MYTH?!?!?

Frank, I just lost all respect.

Have you heard about all the newer, cheap japanese engines that are for sale? In Japan, the standards for maintaining a vehicles registration are so extensive that it's not practical to keep a vehicle for more than 5 years. Most are less than 3. They then dismantle them and sell the parts overseas. There are dozens of places that sell nothing but imported japanese engines with low mileage, and they're very inexpensive. As it turns out, that's because most of them are trashed. The running logic there seems to be "why change the oil if I'm going to junk it @ 75k miles". I have removed oil pans from these engines, with less than 75k miles, and only 3 or 4 years old, and there was a "shell" formed by the crusty, sludged up oil. It had to be pryed away just to see the crank. The bearings in these engines looked like they had been used for 300k miles. Everything was extremely worn and/or damaged, and gave the impression of being from a 300k mile work truck.

Anyway, it's not a myth.

As far as not changing the O2 sensors until the check engine light comes on, that's about the worst advice I've seen today. That's just like not checking the oil until the engine light comes on. When the O2 sensors return signal isn't what it should be, the ECM will let you know, but it's not black or white, pass or fail, good or bad. They deteriorate as they age, and while they deliver a signal to the ECM that the ECM determines to be acceptable, it's not accurate. Tha average recommended O2 sensor life span, for a stock drivetrain, is 30k miles. Start screwing with the ECM by installing a lower temp t-stat, or setting the TPS voltage at .999, and you can cut that expectancy in half. It could still take 100k miles or more before the ECM decides it's bad, but by then you've paid the price with bad fuel mileage and accelerated engine wear. Older vehicles have an O2 sensor replacement warning lamp that is tied into the odometer, because it was too difficult for the ECM to determine accurately the condition of the O2 sensors and when they would need to be replaced. If yours have more than 60k miles on them, I would go ahead and replace them.

Take care
~Chris

------------------
Retired Moderator
MustangNet

My site: JimPorterRacing

RACECAR spelled backwards is RACECAR

HEY !!! Are you ASE Certified ??? If you are, ask me about iATN. The best tool you'll ever have, and it's free !!!

Chevyguy · 09-19-2001, 08:03 AM

Don't worry guys, i'ts not like I don't change my oil at all. The "Myth" I was referring to is that everyone needs to change oil at 3000 miles, it's really closer to 5,000 for average driving. I dump mine between 3,000 and 4,000, but I dont race my car and mostly do highway driving.

Certianly changing your oil never hurts the engine, and the piece of mind is probably worth it.

BTW my 305 never built up a drop of sludge etc in over 60,000 hard miles oil changes between 2,000 and 5,000 miles.

Interesting comments about the O2 sensor, looks like I'm getting a pair soon

------------------
Frank W
90 5.0 LX coupe Daily driver. Silencer removed, K&N filter. Flexalite fan, 3 core radiator. FMS flywheel and Clutch, FMS blue wires Energy Suspension end links
88 Notch 2.3L 5 speed Parts/beater car My two Notchbacks

74 Chevy Laguna Type S-3 305 Finally fixed getting a 454 to put in garage
<A HREF="http://www.chevellepages.com/folingo" TARGET=_blank>www.chevellepages.

cad614 · 09-19-2001, 12:05 PM

Arrrghhh!! Now I'm really ticked off! I went to the other parts store toady and they wanted $110 each! Obviously I didn't want to pay that much so I headed to the Ford house thinking they might have a better deal. I couldn't beleive my ears when he told me they were $90 for the front two and $70 for the back two!! What the $^&@ is going on?!! I crawled under my car and managed to find two sensors in front of the conveters, but that was it, just like everyone said.

So what am I supposed to do now? I don't want to spend $200 like the one store wants, and I'm sure not giong to buy from someone who thinks I have two more than I actually do. I think I'm just going to try to clean the existing ones and hope it works out. If that dosen't work I can always get an off-road h-pipe and a computer chip. This is nuts.

PKRWUD · 09-19-2001, 01:08 PM

Hey man, relax until Friday. Tomorrow is the last full day of summer. Try and enjoy it!

Take care
~Chris

------------------
Retired Moderator
MustangNet

My site: JimPorterRacing

RACECAR spelled backwards is RACECAR

HEY !!! Are you ASE Certified ??? If you are, ask me about iATN. The best tool you'll ever have, and it's free !!!

09-17-2001, 09:51 AM	#1
cad614 Senior Member Join Date: Apr 1999 Location: San Angelo, TX Posts: 377	Four Oxygen Sensors?! Decided I was going to replace my oxygen sensors today so I called up the local auto parts store. I didn't realize I had four of these things! Two behind the catalatic converters ($40 each) and two in front of them ($65 each)! So I'm looking at over $200 for some freakin oxygen sensors! Tell me this isn't right. ------------------ '95 GT Convertable

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Help - Oxygen Sensors	Sicy Stang	Blue Oval Lounge	19	10-13-2003 12:46 AM
longer oxygen sensors?? help!	coolguy620	Windsor Power	3	03-28-2002 01:21 PM
Do I have bad oxygen sensors?	dashapht	Windsor Power	5	09-26-2001 06:11 PM
Whats the best way to tell if your running lean or rich?	K.C. 5.0	Windsor Power	9	09-10-2001 03:04 PM
Will bad oxygen sensors show as a engine light?	Ryan95gt	Windsor Power	8	04-17-2001 01:52 AM

09-17-2001, 10:01 AM	#2
Smokedawg Tires Fear Me... Join Date: Jan 2001 Posts: 867	I didnt realize they had that many. I only have 2! ------------------ 347 Stroker Motor: Balanced, Cobra Transmission, Extrude Ported and Polished Upper and ported Lower, GT40 Milled Ported and Polished Heads, B303 Cam, BBK 1 5/8 Headers, 30lb Bosch Injectors, Holley AFPR, March Underdrive Pulleys, Perma-Cool Fan, 3-Core Radiator, Accel Performance Coil, Accel 300+ Racing Wires, Ram Air, K&N Filter, 73mm Vortech MAF, 70mm TB, FlowMaster Exhaust w/BBK Offroad H-Pipe, Hurst Shifter, 3:55 Gears, Ram Clutch, Cross Drilled Rotors, AC and Smog del, rear seat del.

09-17-2001, 10:07 AM	#3
Mach 1 Registered Member Join Date: May 1999 Location: Georgia Posts: 3,866	The OBDII cars have 4. Two before the converter, and two after. THis is how they can monitor if the converters are working. They measure the difference between the front and back sensors. But, a 95'isnt OBDII? ------------------ 1993 GT/AOD '93 Mustang GT

09-17-2001, 10:23 AM	#4
cad614 Senior Member Join Date: Apr 1999 Location: San Angelo, TX Posts: 377	Well I didn't bother to look under my car yet, I was just going by what the Autozone guy told me. He looked up my car, found the engine and asked if I needed the front or the rear sensors. I was shocked I had 4, so I figured I'd post here in hopes that someone knew what was going on.

09-17-2001, 01:35 PM	#5
PKRWUD Junior Member Join Date: Mar 1999 Location: Ventura, California Posts: 8,981	I am not aware of any 5.0 Mustangs having 4 HEGO's. That didn't happen until 1996, when the 3.8L and the 4.6L both got a double dose. Might want to try a different auto parts store. Take care ~Chris ------------------ Retired Moderator MustangNet My site: JimPorterRacing RACECAR spelled backwards is RACECAR HEY !!! Are you ASE Certified ??? If you are, ask me about iATN. The best tool you'll ever have, and it's free !!!

09-18-2001, 12:40 AM	#6
Daves 95GT Registered Member Join Date: Sep 2001 Location: frisco tx, usa Posts: 11	you have a 95 gt. you only have 2 HEGO sensors. the guy at the parts store is a nut. no mustang EVER came with 4. the two sensors on the front of the converters on 1996 and later cars are oxygen sensors. the two behind the converters on 1996 and later cars are called CMS sensors(catalyst monitoring sensors). this is one of the differences between OBD1 and OBD11 thier job is to read the gases after ther cat. converter to determine the leven in which the converters are functioning. if a converters isnt performing properly, it will set a check engine light, and this is most of the time a hard fault. but no, your 1995 mustang gt is not equipped with 4 oxygen sensors. by the way, why are you replacing them? did you have an intermittent check engine light? if not, then there is not any reason to replace them. it is a common misconception that they need periodic replacement, and they do not. as long as they are switching and giving correct readings, they are fine. if they are contaminated , they will trun the check engine light on once the car has warmed up. a lot of fuel additives will contaminate them, but you will see a light if it does. [This message has been edited by Daves 95GT (edited 09-18-2001).]

09-18-2001, 08:03 AM	#7
cad614 Senior Member Join Date: Apr 1999 Location: San Angelo, TX Posts: 377	Wow, thanks for the info guys. I thought I only saw 2 of them last time I looked, but couldn't remember for sure. Daves 95GT - I'm replacing them because that seems to be the general opinion of this board. I'm approaching 80k miles on my car, and I'm averaging 15mpg. There's no check engine light, but after doing a complete tune up and still getting 15mpg, I figure something needed to be fixed. This is the first time I've heard anyone say that they don't need to be replaced, does anyone else agree? ------------------ '95 GT Convertable

09-18-2001, 10:43 AM	#8
Chevyguy Backyard Mechanic/Chemist Join Date: Feb 2001 Location: Acton MA USA Posts: 435	I know Bosch etc advertizes that you should replace your O2 sensor periodically, but is that like the 3000 mile oil change myth?? My Stang is almost at 114K on the original Os's I was planning to put new ones in soon, of course I had the H pipe off the car back during the trans swap, would have been a piece of cake then eh oh well So I'm curious too, how long do those sensors really last, I had assumed they "wore out" over time. I replaced the sensor on my Lumina twice, at 100Kand 200K miles, never really noticed anything, but they only cost $20 and only one. ------------------ Frank W 90 5.0 LX coupe Daily driver. Silencer removed, K&N filter. Flexalite fan, 3 core radiator. FMS flywheel and Clutch, FMS blue wires Energy Suspension end links 88 Notch 2.3L 5 speed Parts/beater car My two Notchbacks 74 Chevy Laguna Type S-3 305 Finally fixed getting a 454 to put in garage <A HREF="http://www.chevellepages.com/folingo" TARGET=_blank>www.chevellepages.

09-18-2001, 08:32 PM	#9
John Registered Member Join Date: Dec 1998 Location: Ft.Myers, FL. Posts: 150	Hey chevyguy i wouldnt call 3000 mile oil change a myth. The person who owned my car definately didnt do reg. interval changes. When i did my came and intake swap 2 wks ago the buildup of "ashed oil" was unspeakable. The chunks were so big they covered my oil holes under the intake and restricted drainage. I use mobil 1 and still change every 3000. My baby has 155,000 miles on her and no major engine probs. John ------------------ 89 Notch: ASP Pullies, K&N Air,Transgo shiftkit,Trans. cooler,FMS 3 core , FMS 4:10's, 1.5" cowl, cold air kit, hooker shorties(jet hot coated), O/R H-Pipe, ASP solid mounts, Energy Sus. Trans. Mnt. BBK 70mm TB, MSD 6al, Dual elec. fans, 5.0 Firepower Kit, Scorpion 1.6 RR's, Flowmasters, 73 mm MAF, cobra intake and crower #512 cam,

09-18-2001, 09:20 PM	#10
PKRWUD Junior Member Join Date: Mar 1999 Location: Ventura, California Posts: 8,981	MYTH?!?!? Frank, I just lost all respect. Have you heard about all the newer, cheap japanese engines that are for sale? In Japan, the standards for maintaining a vehicles registration are so extensive that it's not practical to keep a vehicle for more than 5 years. Most are less than 3. They then dismantle them and sell the parts overseas. There are dozens of places that sell nothing but imported japanese engines with low mileage, and they're very inexpensive. As it turns out, that's because most of them are trashed. The running logic there seems to be "why change the oil if I'm going to junk it @ 75k miles". I have removed oil pans from these engines, with less than 75k miles, and only 3 or 4 years old, and there was a "shell" formed by the crusty, sludged up oil. It had to be pryed away just to see the crank. The bearings in these engines looked like they had been used for 300k miles. Everything was extremely worn and/or damaged, and gave the impression of being from a 300k mile work truck. Anyway, it's not a myth. As far as not changing the O2 sensors until the check engine light comes on, that's about the worst advice I've seen today. That's just like not checking the oil until the engine light comes on. When the O2 sensors return signal isn't what it should be, the ECM will let you know, but it's not black or white, pass or fail, good or bad. They deteriorate as they age, and while they deliver a signal to the ECM that the ECM determines to be acceptable, it's not accurate. Tha average recommended O2 sensor life span, for a stock drivetrain, is 30k miles. Start screwing with the ECM by installing a lower temp t-stat, or setting the TPS voltage at .999, and you can cut that expectancy in half. It could still take 100k miles or more before the ECM decides it's bad, but by then you've paid the price with bad fuel mileage and accelerated engine wear. Older vehicles have an O2 sensor replacement warning lamp that is tied into the odometer, because it was too difficult for the ECM to determine accurately the condition of the O2 sensors and when they would need to be replaced. If yours have more than 60k miles on them, I would go ahead and replace them. Take care ~Chris ------------------ Retired Moderator MustangNet My site: JimPorterRacing RACECAR spelled backwards is RACECAR HEY !!! Are you ASE Certified ??? If you are, ask me about iATN. The best tool you'll ever have, and it's free !!!

09-19-2001, 08:03 AM	#11
Chevyguy Backyard Mechanic/Chemist Join Date: Feb 2001 Location: Acton MA USA Posts: 435	Don't worry guys, i'ts not like I don't change my oil at all. The "Myth" I was referring to is that everyone needs to change oil at 3000 miles, it's really closer to 5,000 for average driving. I dump mine between 3,000 and 4,000, but I dont race my car and mostly do highway driving. Certianly changing your oil never hurts the engine, and the piece of mind is probably worth it. BTW my 305 never built up a drop of sludge etc in over 60,000 hard miles oil changes between 2,000 and 5,000 miles. Interesting comments about the O2 sensor, looks like I'm getting a pair soon ------------------ Frank W 90 5.0 LX coupe Daily driver. Silencer removed, K&N filter. Flexalite fan, 3 core radiator. FMS flywheel and Clutch, FMS blue wires Energy Suspension end links 88 Notch 2.3L 5 speed Parts/beater car My two Notchbacks 74 Chevy Laguna Type S-3 305 Finally fixed getting a 454 to put in garage <A HREF="http://www.chevellepages.com/folingo" TARGET=_blank>www.chevellepages.

09-19-2001, 12:05 PM	#12
cad614 Senior Member Join Date: Apr 1999 Location: San Angelo, TX Posts: 377	Arrrghhh!! Now I'm really ticked off! I went to the other parts store toady and they wanted $110 each! Obviously I didn't want to pay that much so I headed to the Ford house thinking they might have a better deal. I couldn't beleive my ears when he told me they were $90 for the front two and $70 for the back two!! What the $^&@ is going on?!! I crawled under my car and managed to find two sensors in front of the conveters, but that was it, just like everyone said. So what am I supposed to do now? I don't want to spend $200 like the one store wants, and I'm sure not giong to buy from someone who thinks I have two more than I actually do. I think I'm just going to try to clean the existing ones and hope it works out. If that dosen't work I can always get an off-road h-pipe and a computer chip. This is nuts.

09-19-2001, 01:08 PM	#13
PKRWUD Junior Member Join Date: Mar 1999 Location: Ventura, California Posts: 8,981	Hey man, relax until Friday. Tomorrow is the last full day of summer. Try and enjoy it! Take care ~Chris ------------------ Retired Moderator MustangNet My site: JimPorterRacing RACECAR spelled backwards is RACECAR HEY !!! Are you ASE Certified ??? If you are, ask me about iATN. The best tool you'll ever have, and it's free !!!