Replaced oxygen sensor/no power
05-06-2007, 09:09 AM
#1
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Replaced oxygen sensor/no power
I own a 1985/2 944 with 149,000 miles on it. The car failed the emission test in CT.My CO was 5.11 and the limit is .64. I had the oxygen sensor replaced. Drove the car home from the shop and it drove great.
Went for a little ride and after the car warms up there is no power. Let the car sit over night and starts right up and runs great till it gets warm, then again feels like no power.
The rest of my numbers are HC was 230 should be 200 and NOx was 590 should be 1400.
Could this have anything to do with the Cat?
Car ran great before the emission test.
Thanks
Went for a little ride and after the car warms up there is no power. Let the car sit over night and starts right up and runs great till it gets warm, then again feels like no power.
The rest of my numbers are HC was 230 should be 200 and NOx was 590 should be 1400.
Could this have anything to do with the Cat?
Car ran great before the emission test.
Thanks
05-06-2007, 11:17 AM
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I am having a similar problem and have yet to solve it. I failed emissions (we have the IM240 dyno test). Passed on CO, failed on NOx and HC. I replaced the O2 sensor with the exact replacement, not the universal one many use. Failed again but now NOx is much lower than the standard, but CO and HC fail. Car runs great. I am in the process of leaning out the idle air bypass on the AFM. Going 1/2 turn at a time and driving around a while. I am looking for vacuum leaks also. I have a 951 so lots of places to leak.
Maybe my cat is toast, but that is my last resort. I also looked at the temperature sensor at the front of the head. It changes mixture as the engine warms up. Maybe yours is bad. They are about $25.
Maybe my cat is toast, but that is my last resort. I also looked at the temperature sensor at the front of the head. It changes mixture as the engine warms up. Maybe yours is bad. They are about $25.
05-06-2007, 11:32 AM
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Your cat is for CO only. NOx and HC (to a certain extent) take a diferent kind of catalyst setup to be eleminated. I know this because I am a catalyst chemist developing a selective catalytic reduction(SCR) system for my company. HC emissions are eleminated with a heavy platinum catalyst on a particulate filter. NOx is eleminated with a specific kind of catalyst (SCR) that requires ammonia injection or exhaust gas recirculation reduces it to a certain extent.
You will make more HC when your car is running rich.
You will make more HC when your car is running rich.
05-08-2007, 11:10 PM
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High NOx and HC with low CO is typical for a single cylinder misfire or leaky injector. The computer sees the raw fuel, thinks you are rich, and trims the fuel. How long before it runs crappy? It takes less than a mile to light the converter with a heated O2 sensor (OE in 85-2 cars). If the good to bad transition happens quickly, I'd bet this is your issue. If your car loses power as the water temp goes up, look for a sensor, wiring, or computer issue.
Two things you could try- unplug the O2 sensor and see if that changes anything. With the sensor unplugged, ground the O2 line from the ECU. Motronic will see the open as constant lean, grounded as constant rich. This may help you diagnose the problem.
Personally, I'd buy a fresh set of NGK V-power plugs and see if that helps. They have resolved a "mystery miss" in four of my cars over the years. Cheap too.
Hope this helps. Unless you know what you are doing, find someone to help with the O2 test. Motronic boxes are tough but there is always the chance you could damage something.
Hope this helps,
Bill
BTW-earlyaddict is both right and wrong about the catalyst. Motronic Lambda-sond uses a 3-way converter that first reduces NOx then oxidizes CO and HC. To do this, you have to have the right amount of oxygen- hence the O2 sensor.
Two things you could try- unplug the O2 sensor and see if that changes anything. With the sensor unplugged, ground the O2 line from the ECU. Motronic will see the open as constant lean, grounded as constant rich. This may help you diagnose the problem.
Personally, I'd buy a fresh set of NGK V-power plugs and see if that helps. They have resolved a "mystery miss" in four of my cars over the years. Cheap too.
Hope this helps. Unless you know what you are doing, find someone to help with the O2 test. Motronic boxes are tough but there is always the chance you could damage something.
Hope this helps,
Bill
BTW-earlyaddict is both right and wrong about the catalyst. Motronic Lambda-sond uses a 3-way converter that first reduces NOx then oxidizes CO and HC. To do this, you have to have the right amount of oxygen- hence the O2 sensor.
05-08-2007, 11:34 PM
#7
Drifting
It's good to live in Kansas.
I'll be taking the cat off the S2 here soon. Gotta love those extra couple of ponies you pick up!
And yes Mamoo, you can take the cat out so long as you don't have to pass emissions. Cars prior to 96 will run fine just cutting the cat out. Cars newer then 96 have ODBII and have an upstream of the cat O2 sensor, and one downstream of the cat; just to make sure the cat is functioning correctly. You can buy a Sensor simulator on the web for about 30 bucks that wires into the old sensor wires and tells the ECU that the cat is "perfectly fine and there".
I'll be taking the cat off the S2 here soon. Gotta love those extra couple of ponies you pick up!
And yes Mamoo, you can take the cat out so long as you don't have to pass emissions. Cars prior to 96 will run fine just cutting the cat out. Cars newer then 96 have ODBII and have an upstream of the cat O2 sensor, and one downstream of the cat; just to make sure the cat is functioning correctly. You can buy a Sensor simulator on the web for about 30 bucks that wires into the old sensor wires and tells the ECU that the cat is "perfectly fine and there".
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05-09-2007, 10:22 AM
#9
Drifting
Mamoo-
For you, since your 944 is prior to 96, you can simply cut the cat out and be fine. If you cut the cat out on a car later then 96, it will run the car lean as the 2nd O2 sensor is telling it to, but with the simulator, it tells the ECU that the "cat is fine".
All you have to do is remove the cat and enjoy the unoticeable hp increase...
For you, since your 944 is prior to 96, you can simply cut the cat out and be fine. If you cut the cat out on a car later then 96, it will run the car lean as the 2nd O2 sensor is telling it to, but with the simulator, it tells the ECU that the "cat is fine".
All you have to do is remove the cat and enjoy the unoticeable hp increase...
