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| Duke sensor questions, IAT and O2 Sensor (Page 1/2) |
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82-T/A [At Work]
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MAY 29, 12:40 PM
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Hey guys, just a couple of questions on my daughter's 1985 Iron Duke / 5-Speed:
1. - I must be going crazy. I ordered a new sensor from one of each available on Rock Auto, and that included an Intake Air Temperature sensor. I thought nothing of it because the spare 1988 Fiero motor that I had (and pulled parts from) did in fact have an IAT installed in the intake. But I'm looking in the service manual, and at the intake for my daughter's 85, and I see nowhere that we could even install an IAT sensor. Does the 2.5 in the 84-86 model year not have an intake air temperature sensor? I searched and found nothing, and I see no mention of it at all in any of the diagrams or emissions controls in the service manual?
2. - Something that I thought about kind of late. I know that the O2 sensor that we have on our Fieros is a non-heated one... basically 3-prong. What I understand that to mean is it only works when it's within a certain temperature range. When / if it cools off enough (which can happen at idle), the O2 sensor will in fact not get used and the ECM will revert to "closed loop" mode. This may be undesirable and contribute to fluctuating or improper idle. The service manual even mentions this. Can I simply install a newer O2 sensor, one of the ones that's heated, from say... I dunno... a 1994 Oldsmobile Cialis or whatever? I assume this means it'll be a 4-prong, and then I just need to swap out the harness and run a positive to the O2 sensor from say, the power distribution block (switched power)?
Thanks!!!
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cartercarbaficionado
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MAY 29, 12:58 PM
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| quote | Originally posted by 82-T/A [At Work]:
Hey guys, just a couple of questions on my daughter's 1985 Iron Duke / 5-Speed:
1. - I must be going crazy. I ordered a new sensor from one of each available on Rock Auto, and that included an Intake Air Temperature sensor. I thought nothing of it because the spare 1988 Fiero motor that I had (and pulled parts from) did in fact have an IAT installed in the intake. But I'm looking in the service manual, and at the intake for my daughter's 85, and I see nowhere that we could even install an IAT sensor. Does the 2.5 in the 84-86 model year not have an intake air temperature sensor? I searched and found nothing, and I see no mention of it at all in any of the diagrams or emissions controls in the service manual?
2. - Something that I thought about kind of late. I know that the O2 sensor that we have on our Fieros is a non-heated one... basically 3-prong. What I understand that to mean is it only works when it's within a certain temperature range. When / if it cools off enough (which can happen at idle), the O2 sensor will in fact not get used and the ECM will revert to "closed loop" mode. This may be undesirable and contribute to fluctuating or improper idle. The service manual even mentions this. Can I simply install a newer O2 sensor, one of the ones that's heated, from say... I dunno... a 1994 Oldsmobile Cialis or whatever? I assume this means it'll be a 4-prong, and then I just need to swap out the harness and run a positive to the O2 sensor from say, the power distribution block (switched power)?
Thanks!!! |
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my 84 does not have the provision for an iat and I haven't seen any 85s that have them either but I might be missing something with those
also I have 1 prong 02 sensors on both of my fieros so I'm not sure how to help other than you could probably install a heated one using some retrofit kits for a more popular car
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82-T/A [At Work]
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MAY 29, 01:37 PM
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| quote | Originally posted by cartercarbaficionado:
my 84 does not have the provision for an iat and I haven't seen any 85s that have them either but I might be missing something with those
also I have 1 prong 02 sensors on both of my fieros so I'm not sure how to help other than you could probably install a heated one using some retrofit kits for a more popular car
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No **** , I just realize I too have the single prong O2 sensor as well. I was getting it confused with the fuel pump connector which is roughly in the same place.
Ok, I'll have to look... I think a heated O2 can improve idle, and cold starts... at least to the extent that it'll help the car operate within range more quickly.
As far as I know, a heated O2 does not negatively affect numbers at all, just helps it operate more quickly where as the old one has to be heated up via the exhaust in order to operate properly.
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82-T/A [At Work]
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MAY 29, 01:47 PM
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Ok, so I did a little bit more searching, there's apparently a simple kit that's offered: https://www.casperselectron...oduct&product_id=101
It allows you to use the factory harness and simply adds two more wires which deal with ground and positive for the heating element.
Here's a basic summation of what benefits it provides:
"The main benefit of using a heated oxygen sensor is that it can provide more accurate readings than a non-heated oxygen sensor. The reason for this is that the heated oxygen sensor is less affected by changes in ambient temperature. Another benefit of using a heated oxygen sensor is that it can help to reduce emissions from the vehicle."
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Patrick
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MAY 29, 02:14 PM
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| quote | Originally posted by 82-T/A [At Work]:
It allows you to use the factory harness and simply adds two more wires which deal with ground and positive for the heating element.
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It's actually adding three more wires, two of which are ground... one for the sensor and one for the heating element, and 12v for the heating element. I converted my Subie STi from a three wire O2 sensor (where the sensor grounded through the exhaust manifold) to a four wire sensor. In my research, I found that for optimal O2 sensor performance, the ground for the O2 sensor should be the same location as the ground for the ECU (which I believe on the Fiero is one of the bellhousing bolts/studs).
In regards to the IAT, they're not used on the '84-'86 dukes.[This message has been edited by Patrick (edited 05-29-2024).]
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82-T/A [At Work]
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MAY 29, 04:57 PM
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| quote | Originally posted by Patrick:
It's actually adding three more wires, two of which are ground... one for the sensor and one for the heating element, and 12v for the heating element. I converted my Subie STi from a three wire O2 sensor (where the sensor grounded through the exhaust manifold) to a four wire sensor. In my research, I found that for optimal O2 sensor performance, the ground for the O2 sensor should be the same location as the ground for the ECU (which I believe on the Fiero is one of the bellhousing bolts/studs).
In regards to the IAT, they're not used on the '84-'86 dukes.
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Nice, that makes perfect sense... and also answers so many other questions I have. I know the Fiero has the primary negative battery terminal attach directly to the cyl head post, along with a much smaller wire which then connects to the battery tray (I think)... so when / if the battery tray rusts out, you lose a ground point if not for the fact that the engine itself then also is grounded through some other points. But these flexible ground straps always end up getting ripped or destroyed when people work on the car... so it explains really well why so many people have running issues and poor sensor readings.
One of the things I've been doing as my daughter and I work on this car is try to identify all the places we can add ground straps from the engine back to the chassis as well, and not just the factory ones.
Thanks for the info on the O2 sensor, I'm going to do that.
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theogre
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MAY 29, 05:40 PM
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| quote | Originally posted by 82-T/A [At Work]:
Hey guys, just a couple of questions on my daughter's 1985 Iron Duke / 5-Speed:
1. - I must be going crazy. I ordered a new sensor from one of each available on Rock Auto, and that included an Intake Air Temperature sensor. I thought nothing of it because the spare 1988 Fiero motor that I had (and pulled parts from) did in fact have an IAT installed in the intake. But I'm looking in the service manual, and at the intake for my daughter's 85, and I see nowhere that we could even install an IAT sensor. Does the 2.5 in the 84-86 model year not have an intake air temperature sensor? I searched and found nothing, and I see no mention of it at all in any of the diagrams or emissions controls in the service manual?
2. - Something that I thought about kind of late. I know that the O2 sensor that we have on our Fieros is a non-heated one... basically 3-prong. What I understand that to mean is it only works when it's within a certain temperature range. When / if it cools off enough (which can happen at idle), the O2 sensor will in fact not get used and the ECM will revert to "closed loop" mode. This may be undesirable and contribute to fluctuating or improper idle. The service manual even mentions this. Can I simply install a newer O2 sensor, one of the ones that's heated, from say... I dunno... a 1994 Oldsmobile Cialis or whatever? I assume this means it'll be a 4-prong, and then I just need to swap out the harness and run a positive to the O2 sensor from say, the power distribution block (switched power)? |
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85 duke Does Not have "IAT"/MAT. Your Idle issue Is Not the O2 sensor "getting cold" & does Not need a Heated O2.
"1 wire" O2 sensor Does Not "get cold" @ idle on nearly all vehicle using them. More so on the Duke that has it ~5 Inches from the Exhaust ports that will make the O2 reach operation temp of > 600°F In Seconds from when the engine starts. That even in the Winter as reported by ECM scanners. If a Duke needs > 1 to 2 minute absolute max w/ engine start from very cold to see O2 Ready then have wiring problems, bad O2 sensor or bad ECM.
"1 wire" O2 sensors actually have 2 wire, Yes Two wires, but 1 is a Fake "Ground" to the block. Heated "3 wire" setup is the same for O2 sensor part.
Others have 4 wires, 2 heat, 2 O2
⚠️ Do Not compare to new models! Many New vehicles have Heated O2 for different reasons including required by EPA to run in "Close Loop" as fast as possible & stay close loop even on E85 fuel. That's just to run the Engine. Other O2 sensors when used are to "Enforce" the Catalyst is there & working. Those Sensor are In or after the Cat.------------------
Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.
(Jurassic Park)
The Ogre's Fiero Cave
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Patrick
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MAY 29, 05:49 PM
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| quote | Originally posted by theogre:
"1 wire" O2 sensors actually have 2 wire, Yes Two wires, but 1 is a Fake "Ground" to the block.
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Do you actually mean through the base of the sensor to the exhaust manifold?[This message has been edited by Patrick (edited 05-29-2024).]
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theogre
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MAY 29, 10:51 PM
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| quote | Originally posted by Patrick:
Do you actually mean through the base of the sensor to the exhaust manifold? |
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No. Return path for O2 is a Tan "ground" bolted to the engine. Often is on, w/ other wires, a "Stud head" bolt attach the transmission bell to block.
Base of O2 sensor just uses the E-manifold & block to find that wire.
Electrically Is similar to the "fake ground" on ICM for HEI & DIS. See https://web.archive.org/web...rocave/heiground.htm
Any problems w/ that wire means headaches often faking a bad sensor or wire directly to it. If cleaning/fixing that then do all "grounds" in the bay then coat w/ silicone or brake grease.
The Weather Pack plug for the sensor on car side often gets iffy too. You need a tool to remove the "pin."
Your dealing w/ a sensor that runs 0 to 1 volt & micro-amps of current & hate the tiniest of bad wiring. Way worse then 5 volt sensors like TPS, ECT, etc that wired all "pins" direct to the ECM.
If you think that's bad... Wide-band O2 have same 0-1volt out & those systems hate any error by iffy wiring even more then "standard" O2 systems.
Before you ask, GM & many others use same "1 wire" setup likely because of cost to make them. Teflon insulated "heat proof" wire cost more to start & just harder to make w/ 2 wire on the sensor so cost even more.[This message has been edited by theogre (edited 05-29-2024).]
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Patrick
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MAY 29, 11:23 PM
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| quote | Originally posted by theogre:
Return path for O2 is a Tan "ground" bolted to the engine. Often is on, w/ other wires, a "Stud head" bolt attach the transmission bell to block.
Base of O2 sensor just uses the E-manifold & block to find that wire.
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Okay, I admit to be being a little confused by this. I've previously been led to believe that single wire O2 sensors ground out through the base of the sensor. Period. How can you explain the following?
Oxygen Sensor Mod for Single Wire Sensors
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On the very early cars with O2 sensors, there was only a single wire for the signal voltage, and the ground went through the screw-in connection in the exhaust.
While this might have been a fine connection when the car was new, I recently measured the resistance from the connection point to chassis ground at the ECU, and it as 1100 ohms !!
Now, if the ECU had an extremely high input impedance, the 1100 ohms wouldn't matter much, but the ECU on the 1980 thru 1985 seems to be mostly passive components and resistive voltage dividers, as such I appears that 1100 ohms is enough to offset the calibration of the ECU.
The fix to correct this is simple and about $9. Attach some braided engine grounding strap from the chassis direct to the O2 sensor using a hose clamp.
The result is a good quality ground for the O2 sensor, enabling more stable and accurate operation.
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One thing I'd do differently than the poster above is that I'd relocate that ground connection to the same bolt/stud as the ECU ground.
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