Chris69

I'm having some problems with the '81 (idling rich). Fresh carb, and everything else checks out... 'cept the 02 sensor and dwell readings. Dwell is great for about 8 minutes (35-ish, give it some juice and it goes rich, 25-ish), and pretty consistent. After about 8 minutes dwell goes lean while creeping up to 50+ while idling. Increase the RPM's and it goes a bit rich then jumps back up to 50. Disconnect the 02 sensor and dwell normal again. Voltage on the sensor varies, averaging only .01 at 1500 rpm's. I haven't done a bench test with a torch (guess I should). Tell me if I'm thinking right here... Problems began after installing coated headers and the 02 sensor is pretty far downline compared to what it was on the shorties. The coated headers don't seem to get very hot and cool off quickly. I'm thinking the sensor is not staying hot enough to work right. Does all this sound about right? Is replacing the sensor with a 3 wire 'heated' version a good idea in this case? Help!! :confused:

Racer16k

I mounted mine on the driver side collector. It's a one wire sensor. I have TBI instead of carb but I haven't had any problems yet.

Chris69

I had Jet-Hot install the bung in the driver's side collector before they coated it. I checked a couple other forums and saw a few references regarding this, and a heated sensor seemd to take care of the problem for them. Almost sounds too easy... :yesnod:

Dalannex

Sounds like you're on the right track to me. I figure that a heated sensor is a win win situation either way. They are supposed to be far more accurate than the original.

-Justin

Racer16k

Maybe the heated one would make all the difference. It couldn't hurt to try it.

stickboy

sounds like a heated sensor is what you need :cheers:

Chris69

Ok, spent the morning converting the oxygen sensor to a three-wire heated type. Picked up a companion weather pack connector, pins and seals, and made up the harness side (no splice job, so do I get one bubba-get-out-of-jail free card? :lol: ). Cranked it up, waited for the temp to come up, and no more eye-burning exhaust!! Took it for a spin, and the power difference is amazing when the F/A mixture is right! Woohooooo...

:party:

UKPaul

Chris,
Thanks for this post :thumbs: I've got a set of coated Headers to fit with an O2 fitting in the collector. I was told when I got the Headers that the std sensor would be OK in the new position but, as things never seem to go smoothly, I've been wondering if I needed a heated sensor.... and now I know :)
Soooo, where did you get the sensor & connector for it? Is it an "off the shelf" item, do C4's or C5's use them (we're not exactly awash with chevy parts here, so I'm trying to find the easiest way of getting one)?
TIA
Paul

CHEESERAL

Sounds like you fixed the problem Chris. Now all you have to do is buy a second heated O2 sensor and make a wire conversion kit so I can install it on my car while it's still up in the air. Don't worry, I'll give ya a few bucks for your trouble, lol. Glad to hear you got that worked out and I'm serious about doing that to mine, my sensor is in the same place.

Dalannex

The old oxygen sensor is a 2 wire. What do the two wires do? One is voltage supply, the other a voltage return or what? And, when you hook up a multimeter to get the voltage readings to find out how rich or lean you are running, how do you hook it up, which wire do you check I mean? And, how do you wire up a 3 wire oxygen sensor? Is it just the 2 existing wires same as normal, then another one that goes to 12v+ or what? I'm wondering all this because I think I may be having a similar problem. I was getting an oxygen sensor code, so I put a new one in, then started the car and got an ECM error, so I unhooked the battery to clear the code, now I need to restart it once I get my trans. back together and see what it does. But, if the 3 wire O2 sensor is easy to install I may just do that.

:spam :grouphug: :auto: :U
(the smilies are because my 4 year old son was standing here wanting me to put smilies in my post, then he picked out the ones I was supposed to use. :D )

BSeery

Chris - what year/make/model did you get the heated O2 sensor from ?

Chris69

The sensor is a three-wire Bosch (13077). It cross-references many Chevy applications, including the ZR-1. I got the stuff at Pep Boys. The connector is just the compatible weather pack style, also at Pep Boys. You have to buy the pins and the rubber seals separately. I just clipped the old 2 wire connector off, plus ran an ignition switched 12V wire. The original 2-wire is simply a signal and ground. The 1-wire sensors uses the housing for the ground (same thing, but guess you get a reliable ground in case the sensor threads get corroded). When I put the pins on the harness wires, I soldered them in place. In the case of the '81, the old 02 sensor was installed right after the collector on the factory shorties, so I feel sure it was getting much hotter than having it installed on the full length header collector, especially being coated inside & out. I almost think you'd be better off installing the 02 on the reducer since the uncoated metal probably gets hotter there (just a guess). The Jet-hots I have really do cool down very fast, so the majority of the problem should come when idling. I'm not saying this is the cure-all for everyones' problem, but it sure seemed to help in my situation, and the more I searched in the net, the more info I found regarding headers and sensor problems.

Here's more news though... All went well, as I described in the previous post, then we went on a 2 hour cruise, a 2-hour cruise.... Yeah, I know.. :lol: Anyway, guess what, it started running rich again. Got home and threw the dwell meter on and sure enough, full lean at idle (meaning it's trying to fix a rich condition). Yeah, I cussed... the carb acted like it was flooding again (just received it back after a warranty rebuild... for flooding). I put my other carb on the car, and everything is great again. Just so you don't think it was the carb all along, the original problems I had were with both carbs. I'm geting pretty quick at swapping out Qjets! What blows my mind is how well it ran when I disconnect the 02 all together. Not a stumble at idle and very responsive. So what gives here?! :smash:

Dalannex

Go drive it again and let us know. :D I am wondering if a guy doesn't maybe need a 4 wire sensor if he's going to go with a heated sensor. Our cars (or mine anyway) has a 2 wire sensor. I know that what that means is that one is a voltage lead, and one is an isolated ground lead to the ECM, no to be confused with a ground to vehicle ground. Cars with one wire oxygen sensors use vehicle ground as signal ground. I assume there is a reason GM used an isolated ground, such as variables in resistance to vehicle ground or voltage spikes through the ground or something. When you have a 3 wire sensor the wires are one for voltage to the ECM, and two for + and - for the heated element, leaving the signal ground to come off of vehicle ground, not isolated ground. This leads me to believe that if we decide to change to a heated oxygen sensor we need to go with a 4 wire, and to decipher which wire is for what so that they can all be hooked up correctly. (can you tell I spent the afternoon at the parts store and the library studying????? :jester :yesnod: ) Anyway, i picked out a sensor in the book at my local parts store that is for some kind of Cadillac, Buick, and something else, that is a 4 wire, and is $50 bucks. I now need to go to the library and find out which wire goes to which on that particular car, and how they are positioned in the plug, or which wire is which on the sensor, which could be hard information to come across. I also need to find out if the stock sensor is a titania element or a zirconia element. There are big differences in the way that they detect oxygen levels, and the signal they send. I think it is a zirconia element. Zirconia conducts exygen ions, where as titania is a resistance thing. I think we have zirconia, but I'm not sure of that. I have some more homework to do on that. I'll let everyone know what I come up with.

Here's a question for you all.....is an oxygen sensor on a GM (like my 81' corvette) just a standard spark plug thread? I need to get a tap to clean out the hole for mine, but need to know what it is. Thanks.

-Justin

UKPaul

Chris,
Good post, I can get ZR1 parts here no problem :D
Justin,
Hi :)
One part of the electrics I haven't really looked at is the O2 sensor. I think 12V is supplied to it & gets earthed via the ECU which monitors the voltage drop to get the O2 levels? I'll try & get home at lunch to check the manual & measure the sensor thread for you. Could a 3 wire sensor use 2 wires as ours currently do, but use the 3rd for a +12v supply to the heater element which is then earthed through the body of the sensor? That would be nice & simple.

I got it wrong! My sensor fitting (now I've had a look at it) is in the aluminised reducer, not the collector. D'oh. We could take a different approach here: as stainless is a poor heat conductor (compared to steel), we could get a reducer made in stainless with a sensor fitting. The reducer would then take less heat from the sensor through conduction, but would take longer to heat up (it wouldn't rot out either!). It'd be nice to know just how much below the ideal temp the sensor is at idle. Before buying my Headers I was worried about the sensor being relocated & both Dynomax & Summit assured me that relocating it to the reducer would be OK. If there's only a few degrees in it, then drilling out the fitting & inserting a helicoil may solve it. Helicoiling a stripped plug thread in an aluminum head causes the plug to run hotter, as less heat is transfered through the stainless helicoil than it was through direct contact to aluminum, so we may be able to use this to our advantage. I know it sounds like clutching at straws, but I've had to change heat grades of plugs due to helicoils in the past, so the temp difference must be significant. I could be coming at this from the wrong angle if it's not the heat that's stored in the sensor that's crucial, but the heat that's stored in the metal around it?
As I've got 2 reducers with O2 fittings I could helicoil 1 & try each in turn to see if I get any difference. This approach appeals to me as a fitting a Helicoil will take me 5 mins, but buying a heated sensor will cost about $90 & will involve wiring it in - & there's far to many wires on my firewall as it is :lol:
Don't hold your breath though.... I've got to fit a new tranny before I even look at fitting the Headers.
:cheers:

Chris69

Justin... I was confused about the 4-wire sensor when researching this (the 4th wire being for chassis ground), and one guy mentioned that it would be a good idea, but probably not necessary. Later model cars too, so don't know what the difference might be. I did check the harness wire to make sure it was a good ground and it seemed to be, but don't know where that wire went. There was another ground wire spliced into, near the firewall. Makes you think it's just a common ground.

I did drive the car for about 45 minutes last night, in traffic and open roads, and it worked fine. I ain't counting my chickens yet, but I think it's all working fine now (I'm whispering this, though). :p:

UKPaul

Chris,
The wires to the stock O2 sensor are a purple one from term 9 on the ECU (O2 Hi) & a tan one from term 14 (O2 Lo). The O2 Lo wire is shown as being grounded (possible through the sensor itself?) & joins another couple of wires, one of which is a chassis ground & the other being the ECU ground (term U).
Justin,
I haven't got a spare O2 sensor so had to measure the thread in my new reducer (I'm never confident when measuring internal thread sizes!). It looks to be a M18 fine thread (1.5 pitch).

The manual stated that in some conditions the sensor could cool down enough on idle to cause the system to go into open loop. Doesn't bode to well for moving the stock sensor further downstream :(
:cheers:


[Modified by UKPaul, 2:36 PM 3/11/2003]

mrvette

Guys, O2 sensors come 3 ways....one,three, or 4 wire....they are alll compatible SENSOR wise...the only thing is now the unit is wired....

the one black wire unit is obviouls....goes to computer, with signal ground referance being engine ground through the pipes....computer has a systems ground which at the earlier times was considered good enough, as in reality IS, assuming you have good computer/instrumentation grounding....
to measure it's performance...your dash instrumentation goes to to the black wiere and engine ground...or your DVM + lead to the black wire , and engine ground for - lead....you should read +.5 volt and see it swing from =.1 to.9 volts when proper operation when driving say down the highway ....
NOW for temp controll issues, like in a header collector that never sees 600f degrees unless under steady highway cruising on a warm day...you need to have at least a 3 wire unit...black to computer as normal....ONE of the white wires goes to engine ground...the other goes to a switched +12 source...like the ignition hot wire...or maybe fuel pump hot wire....either one is fine....
this assures the internal resistance heater will make it get up to 600f fast and consistantly all the time....so the crystal sensor element will light off , and act as a feedback.....otherwise it's 'sluggish' in response...and the computer is NOT happy....

NOW, later on, for some reason it was determined in newer cars the insutrumentation ground in the exhaust pipe was not so good, SO they ran a sensor ground referance up to the computer, this for just the SENSOR , NOT the heater....

I used a Bosch 13190 sensor...intended for Chrysler useage...same thing, electrically, but it's cheap price and connector matchup made it an obvious choice....
I think I paid only about 35 bux for it....brand new of course...

GENE

UKPaul

Gene,
Excellent post. What we've got is a 2 wire sensor with one wire to the computer & the other is the reference ground to the computer (also joined to the computer ground & a physical ground connection). The manual circuit diagram seems to imply that there's also a ground through the exhaust pipe via the sensor, as you describe. And yes, the sensor doesn't start working until 600F is reached & it will give readings of up to 1v.
Now, the sensor that you've used has a black wire (which we need to connect to the computer O2 Hi terminal) but you imply that it also has 2 white wires: one for ground & one for a switched +12v. If they're both white then how do we know what one is the ground & what is the live? :confused:
Thanks,
Paul

Dalannex

Paul, thanks for checking the thread for me. Now I can stop and get a tap for that. :cool: I'm guessing that the black wire is the sensor voltage to the ECM, sensor ground is through the manifold, and the two white wires are for the heater + and - which probably wouldn't matter since it's just a heating element.

I thought at first that we must supply voltage to the sensor and get a voltage signal back to the ECM, but that's not the way it works. (although it seems logical to me) That is the way that it works on the titania element. The titania element will change the volatge supplies by the computer through resistance and send that back to the ECM. Zirconia produces it's own voltage to send to the ECM. (that's what we're running). :cheers:

-Justin





[Modified by Dalannex, 11:01 AM 3/11/2003]

Dalannex

Here's an update for anybody thinking of going with a heated sensor. Bosch makes a universal, that comes with instructions as to what wire on the sensor is for what, zirconia element and all. I'm not sure what it has for connectors, mainly becasue I will more than likely have to change them to match my car. I am getting a 4 wire, but I imagine they make 3 wire too if you want to go that route. Makes it easier than trying to decipher what wire does what on a different sensor.

-Justin