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QuickMustang
04-06-2009, 07:33 PM
Well I was tuning with my quarterhorse the other day and I noticed that my HEGO2 oxygen sensor wasn't switching right. It was rarely going over 0.5 volts and never went above 0.6. I also got a CEL that threw a code 176 (oxygen sensor reporting lean condition, left side). The CEL was only on for about 3 minutes and hasn't came on since. So I replaced my passenger (edit it was the drivers side) side oxygen sensor and the voltage still won't go over 0.5 V. I attached the datalog that shows how well HEGO1 is switching, but HEGO2 isn't going high enough. It is moving along with HEGO1, but just not going very high. Even at WOT, the voltage stayed around 0.5. So what else could be causing this besides the oxygen sensor? Or is it possible that I just got another bad O2 sensor?

Attached is the datalog and a graph of HEGO1(Blue) and HEGO2(red)

Thanks.

XR7 Dave
04-06-2009, 07:49 PM
So I replaced my passenger side oxygen sensor

Don't read well do you? :p I think we already told you that HEGO2 is the driver side.

QuickMustang
04-06-2009, 08:19 PM
Don't read well do you? :p I think we already told you that HEGO2 is the driver side.

No, I don't type well...I actually replaced my drivers side!

fturner
04-06-2009, 09:00 PM
Better check the ground lead that goes to the back of the drivers side head and make sure its tight.

Fraser

QuickMustang
04-06-2009, 10:17 PM
hmm...that's an interesting theory...Where does that ground run to? I'm not sure if I've ever had one there. I do know that I have a ground that goes from the drivers side motor mount to the battery. It is a 3 wire 02 sensor on my bird, so I assume it does rely on being grounded through the exhaust. Would having anti-seize on the 02 sensor keep it from having a solid ground?

Have you seen this problem caused by a bad ground before? Everything else seems to be perfectly fine with the car.

fastsc92
04-06-2009, 10:24 PM
are you sure it's not a 4 wire o2 sensor? It should be...

QuickMustang
04-06-2009, 10:57 PM
Well I know that all the parts stores list a 4 wire for the 91, but only a 3 wire for the 1990. My car is a 91 but the harness (on both sides) where the 02 sensors plug in to only have 3 wires going in to them, so I have 3 wire 02 sensors on both sides. That's also what the car had in it when I got it (it had blown headgaskets when I bought it though).

I was thinking about the bad ground theory. My exhaust is one solid welded piece, so if the passenger side is working fine(which the datalog leads me to believe that it is), then the drivers side would have to be grounded as well. If I'm off here, let me know.

Is it possible that I could somehow have the drivers side plugged into the passenger side plug and vice versa? It seems unlikely, but I don't know. Maybe I'll switch the 02 sensors tomorrow and see if that moves the problem to the other side. If that doesn't work, I'll throw the wideband in the driverside and make sure that my car isn't really running lean on that side. Any other suggestions, let me know.

RedSC93
04-06-2009, 11:56 PM
As the harness sits it wont reach the to each other, so its pretty impossible to have them backwards. If you need a new 3 wire o2 let me know, I have one I cant use because my is a 4 wire setup on my 93, its used but its a Bosch brand.

Jerry

QuickMustang
04-07-2009, 09:18 PM
Well I kind of figured out the problem and kind of made it worse. The drivers side 02 sensor was only getting .75 volts. The passenger side was getting 12. The wires for the 02 sensor going in to the plug on the passenger side at the rear of the engine compartment had 12 volts there. The Blk/light green wire seemed to be the problem(I found out later that it is the ground). I checked for continuity between the plug and the 02 sensor plug and there wasn't a connection.

So before I knew exactly what that wire is I did something stupid apparently because now the car doesn't run. The wiring diagram that I had wasn't accurate to my car. I jumped across two wires to get the 12 volts that I needed at the sensor and now the car doesn't start.

I don't really have a question about this because I know I can undo what I did and should be able to just ground the blk/lg and I think I'll be ok...I have more investigation to do tomorrow. Hopefully I didn't screw anything up. One of these days I'm going to learn to stop doing stupid things.

fastsc92
04-07-2009, 09:23 PM
ZAP!!:eek:

fturner
04-07-2009, 09:28 PM
The O2 sensors are wired direct to the EEC :eek: as it controls the heat circuit (12 volt) and has the sensor return line tied to it as well.

Hopefully you didn't take out the EEC or worse the QH.

Fraser

fastsc92
04-07-2009, 09:29 PM
that's exactly what I was thinking. One of the two are most likely toast.... Can you poll information from the EEC or do you get null values if the key is in the ON position?

fturner
04-07-2009, 09:35 PM
If the QH doesn't respond, then pull the QH out and see if the car starts ;). If it doesn't then unplug the driver's side O2 and try it.

If it still doesn't you might want to start looking for another EEC for your car. Make sure the codes match (well technically because of the QH, you could get any GSALC based EEC 91's or any of the GSALI based EEC's - 92/93 and just upload your GSALC code into it ;) ) but thats another story :D.

That ground lead should bolt onto the back of the driver's side head I believe. There should be 3 bolt holes there, and one is used to hold the fuel rail.

Fraser

XR7 Dave
04-07-2009, 09:52 PM
Sorry, been missing this thread due to whatever, but I think a major issue has been overlooked here.

1) 91 SC's have 4 wire 02 sensors.

2) In cases where 91 SC's do not have 4 wire 02 sensors, see #1.

You have a major problem that needs to be sorted out.

Also, the ground wire that Fraser is referring to is only on 89-90 SC's with 3 wire 02 sensors. 91+ SC's with 4 wire 02 sensors do not have a separate 02 sensor ground.

Ira R.
04-08-2009, 10:52 AM
The O2 sensors are wired direct to the EEC :eek: as it controls the heat circuit (12 volt) and has the sensor return line tied to it as well.

Hopefully you didn't take out the EEC or worse the QH.

Fraser

I hope he didn't take out the QH. They're out of stock until after May 1 according to the web site.

Ira

QuickMustang
04-08-2009, 12:21 PM
I hope he didn't take out the QH. They're out of stock until after May 1 according to the web site.

Ira

The QH is fine...So is the EEC. I can still read and write to the QH and the computer is still self-testing and giving me codes. (113 and 118, I must have tapped in to the temperature circuit accidently?). Somehow my wiring harness is not factory when it comes to that oxygen sensor. Looking at it again, I realized that my passenger side 02 sensor has 4 wires (both in the sensor and in the wiring harness to the sensor). The drivers side only has three wires in the harness going to the sensor plug

The plug at the back of the engine compartment on the passenger side isn't matching my wiring diagram either. The wires, according to the color codes, are switched between the b/lg wire and whatever color wide is supposed to go the "cold engine lock out", whatever that is? I think the b/lg wire is just the ground and that seems to be where the problem is in this whole thing. It is not coming back to the right spot on that plug at the back of the engine compartment. There is another wire where it is supposed to go, but I'm not sure what that wire is actually going to. What I did was cut that wire and jump the b/lg wire to it so the 02 sensor wire was going to where it's supposed to. Somehow that wire was needed, because when I cut it is when the car stopped running(it still tries to start it's just flooding). I'm thinking I can just cut it at the 02 sensor and ground it somewhere and fix the wire I cut. Hopefully that will solve my problem...

What is the forth wire on the 02 sensor for? According to my wiring diagram there are four wires that go to the 02 sensor but on the 02 sensor picture there are only three things labled; power, ground, and signal?

This has been like this since I owned the car and the car has ran great, which has me confused. How does that 02 sensor work at all when it's getting less than 1 volt?

XR7 Dave
04-08-2009, 12:31 PM
Wires that don't match should be replaced. Get the right wiring harness for the car. That it ran ok in the past doesn't make it right. I'm sure it can run "fine" with it as is if that is all you want it to do. The sensor return circuits are completely different on the 89/90 vs. the 91/93. I would not attempt to rig it up because you are going to end with bad signals or overloaded circuits.

fturner
04-08-2009, 12:39 PM
The four wires is ground, 12 volt power, hego signal from EEC (approximately 0.55 volts) and return sensor signal (fluctuates based on rich/lean).... I believe.

If your measuring 0 - 1 volt on the one line, then that is probably the sensor signal, and if the 12 volt is missing then the O2 sensor may not be getting heated up enough to give an accurate reading.

Fraser

fastsc92
04-08-2009, 12:41 PM
the sensors are heated so you'll have power, ground, signal return and heater. Or it might be that you'll have power, ground, signal return and heater ground. It's either one of those two.

:: Dang Fraser...this is the 4th post in two weeks that you beat me too it by mins....:rolleyes::p

fturner
04-08-2009, 12:46 PM
the sensors are heated so you'll have power, ground, signal return and heater. Or it might be that you'll have power, ground, signal return and heater ground. It's either one of those two.

:: Dang Fraser...this is the 4th post in two weeks that you beat me too it by mins....:rolleyes::p

Ok, I can look to see if your name is showing online and disconnect your account while I reply :p:D.

Fraser

XR7 Dave
04-08-2009, 12:46 PM
You guys are cracking me up. Get the right harness!! I'm sure someone here will give it to you for the cost of postage. The 3 wire system sends the sensor signal return through the engine block. The 4 wire system uses a dedicated sensor return. The two systems are not compatible.

fturner
04-08-2009, 01:17 PM
Ya know, you always end up with a party pooper somewhere :(

Just funnin :)

Fraser

QuickMustang
04-08-2009, 05:32 PM
Wires that don't match should be replaced. Get the right wiring harness for the car. That it ran ok in the past doesn't make it right. I'm sure it can run "fine" with it as is if that is all you want it to do. The sensor return circuits are completely different on the 89/90 vs. the 91/93. I would not attempt to rig it up because you are going to end with bad signals or overloaded circuits.

If running ok was all I cared about I never would have messed with it in the first place...I actually have a spare engine and it still has the harness on it. It looks like it's the right one. At least the oxygen sensor stuff is all right. I think that engine came from a 1992 SC. Would there be any differences in the harnesses between the 2? I don't want to replace the harness to solve the 02 sensor issues only to cause another set of issuesn if some other part of the harness is different...

QuickMustang
04-08-2009, 10:13 PM
Well I put it back how it was so I can drive it for now. Everything is acting just like it was before as I expected, but that means it's still running fine. It looks like I may have to pull the supercharger to swap out the wiring harness. I have an upgraded supercharger that I want to put on anyways, but I want to get a baseline so I can tell how much, if any, the supercharger helped. The drag strip is supposed to open on Friday so weather permitting I might be able to get some test runs in then. Then I can change the SC and harness out on Saturday assuming that the harness I have is correct.

If I can't make it to the dragstrip, does anyone have any ideas as to why the dragstrip part of BE doesn't work for me? Even a quick run with that would be a better baseline than nothing.

fturner
04-09-2009, 07:17 AM
MPH is critical for that to work... is it registering properly?

Fraser

QuickMustang
04-09-2009, 09:25 AM
Yea, MPH works fine...When I hit staged it just sits there...So it does work with your set-up then?

S_Mazza
04-09-2009, 10:17 AM
Fturner is right about the 4 wires. Heater power, heater ground. Signal power, signal return. I don't know the colors. The 3 wire sensors have a separate heater circuit, and the signal is grounded through the exhaust / engine.

It sounds to me like, if you don't even have 12V at each sensor, then you have a problem that goes beyond grounding. Maybe a mechanic was too liberal with the wire cutters.

fturner
04-09-2009, 10:29 AM
Yea, MPH works fine...When I hit staged it just sits there...So it does work with your set-up then?

Yup, have had no issues with it other than trying to avoid the cops :D.

Fraser

QuickMustang
04-09-2009, 12:20 PM
It sounds to me like, if you don't even have 12V at each sensor, then you have a problem that goes beyond grounding. Maybe a mechanic was too liberal with the wire cutters.


I think a mechanic was too liberal about swapping a section of the wiring harness with one that didn't belong on the car. I have 12 volts at the right place going to that section of harness, but the wires that run to the 02 sensor don't plug in the right location. Kinda screwed up, but at least I have the right one...Even when I get the full 12v for the 02 heater (temporary jumping from the battery), it isn't right. The signal from the 3 wire 02 sensor is slightly different as many have told me here...But it works to make the car driveable and it's been this way at least since I've owned the car and has always driven fine (probably rich on that side though). Hopefully I will be able to repair it properly this weekend...


Yup, have had no issues with it other than trying to avoid the cops .

Hmmm...that's strange...Do I have to have datalogging on or off? Is there some other setting I could miss? Very strange that it doesn't work for me...

QuickMustang
04-19-2009, 01:15 AM
Just to update this know that the work is done, replacing the wiring harness and the 02 sensor with a 4 wire solved my problem. 02 sensor is switching right and the car is running great...Thanks for all the help!!!

S_Mazza
04-20-2009, 11:48 AM
Excellent! Glad you got it fixed.