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02 Pegged at .9V

TempleUWS6

TempleUWS6

Member
Joined
Feb 18, 2014
Location
Celebration, FL
So my 91 944Ts 02 sensor was bad, would slowly drop down to .00xV after start up and stay there till ECU would store 2-3-2 and 1-1-3. Bench tested the old one and it won't budge under the propane torch; new one builds to .9 and drops under a second. Put in a brand new Bosch 13957 and now it does the complete opposite, slowly climbs to .9xxV and stays till the same codes come on. So the car is running rich and that's probably what killed the other 02 (NTK brand crap anyway). So where should I start to figure out why it's running so rich? Why am I not seeing any cross counts?

It starts fine, idles fine, revs up nice. I haven't been driving it much at all, since it is in dire need of a trans mount replacement.
 
my o2 sensor died and made my car run really rich and gave me those same codes. It still ran and reved up nice, though obviously rich. I replaced mine with bosch part number 13913 and it's been running fine since
 
My o2 sensor disintegrated and made my car run so rich that at times I couldn't do more than 20mph. Replaced with the cheapest that Rockauto has to offer and it's fine.
 
Do a snap throttle and see what happens.

Introduce a fat airleak and see what happens

Maybe try bench testing them with burning propane.

Could be the sensor or a true reading.
 
ZVOLV said:
Do a snap throttle and see what happens.

Introduce a fat airleak and see what happens


Maybe try bench testing them with burning propane.


Could be the sensor or a true reading.
Click to expand...

TempleUWS6 said:
Bench tested the old one and it won't budge under the propane torch; new one builds to .9 and drops under a second.
Click to expand...

Hank Hill approved.


air leak dips the reading.

Could the ECU be running off the fuel mapping it had established with the dead 02? Even though I've deleted the stored codes, should I disconnect the battery to flash the ECU?
 
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TempleUWS6 said:
Hank Hill approved.


air leak dips the reading.

Could the ECU be running off the fuel mapping it had established with the dead 02? Even though I've deleted the stored codes, should I disconnect the battery to flash the ECU?
Click to expand...

I doubt that is the trouble if you don't have a 113 set, but in your '91 all you need to do is momentarily lift fuse 6. Easier than taking the battery clamp off and it won't disturb your radio presets.
 
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If it starts, idles fine, seems to run fine, I would be checking the fuel pressure and ECT out put. Constantly rich means the ECU can't trim the fuel enough, or, it thinks the engine is cold and is adding excess fuel.
 
Power probe 4. Under $200.

Very good clean safe easy way to apply power to components for testing.

There is also of course the scope. Both mine are broken, but recently I was thinking of using one to graph o2 sensor voltage and set it up to do some math and calculate lean vs rich bias.
 
ZVOLV said:
Power probe 4. Under $200.

Very good clean safe easy way to apply power to components for testing.

There is also of course the scope. Both mine are broken, but recently I was thinking of using one to graph o2 sensor voltage and set it up to do some math and calculate lean vs rich bias.
Click to expand...

Damn. I have a power probe 3... Once you get something, they always come out with a new and improved one.
 
Trade it in to a tool truck dude for credit towards the probe IV.

I still want a $1200 Pico scope for myself. I can graph o2 sensor data on scan tools but the graph is pixelated and slow.

Your pegged at .9v reading sounds like it could really be a true reading. That's why the ECU is tossing the mixture codes. It's not seeing it evenly swing between min and max.

Leaking injectors is possible. Coolant temp sensor. Faulty MAF. Faulty ecu.

I just fixed the rich on my 86 740 from what I think was leaky injectors. Two leaked externally. Now my car is failing emissions not for being on the rich side but for being lean now! I think it's the accordion intake hose leak.
 
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cosbySweater said:
Replace the O2 sensor with a AutoZone unit, if it doesn't work return it and say it was bad and get your money back. Easy as that :)
Click to expand...

use bosch part number 13913, I paid $37.99 for it at o'rilleys and it's genuine. You'll have to splice the harness with the old one though (comes with a Ford connector.) When i had them look up a Volvo branded part the price was ridiculous
 
Where's that thread where the guy here claims that the o2 sensor breathes thru the wires!? Turns out he was partially right but not in this application.
 
I had a similar issue in my 1986 740 GLE. O2 was pegged at .9v for a test or two. But later on when I went back to it, the sensor was oscillating just fine. I still haven't got it thru smog. It keeps failing. This time I am gonna fix a torn intake hose.
 
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