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Old 08-21-2020, 12:31 AM   #76
ZVOLV
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O2 sensors don't oscillate on a cold start. Once the sensor and coolant temp is warm enough, the ECU goes into closed loop and you see oscillating voltage as the ECU oscillates the mixture.

O2 sensors create their own voltage.

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Old 08-21-2020, 01:45 AM   #77
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Maybe that’s the problem then. On a cold start it oscillates, then settles around 0.8-0.9. When I revved it, it stayed closer to 0.95 with some occasional drops.
I went ahead and ordered a new one earlier.
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Old 08-21-2020, 02:46 AM   #78
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I unplugged the 2-pin connector for the O2 sensor and noticed absolutely no difference in the way it ran. Is that normal or am I just being hopeful that this just might be the problem?
That is because this two wire connector is just for the heater. Power and ground. Once the O2 sensor is warm, it doesn't need the heater. The heater is just there to warm up the sensor on a cold start and get



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Maybe thatís the problem then. On a cold start it oscillates, then settles around 0.8-0.9. When I revved it, it stayed closer to 0.95 with some occasional drops.
I went ahead and ordered a new one earlier.
That's not right.
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Old 08-21-2020, 04:22 AM   #79
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Originally Posted by ZVOLV View Post
O2 sensors don't oscillate on a cold start. Once the sensor and coolant temp is warm enough, the ECU goes into closed loop and you see oscillating voltage as the ECU oscillates the mixture.
An accurate voltage reading occurs when the engine is idling at normal operating temperature, thanks for pointing that out Zvolv

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Old 08-21-2020, 10:46 AM   #80
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That is because this two wire connector is just for the heater. Power and ground. Once the O2 sensor is warm, it doesn't need the heater. The heater is just there to warm up the sensor on a cold start and get





That's not right.
Yes, Iím aware. I checked the diagrams after checking it.
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Old 08-22-2020, 04:11 AM   #81
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Yes, Iím aware. I checked the diagrams after checking it.
curious to see how it develops, good luck

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Old 08-22-2020, 10:41 AM   #82
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I'm really hoping this O2 sensor fixes it once and for all, it would make sense that it's been failing for a while. It shouldn't be running so rich when revving though. My plugs certainly don't look like it's running as rich as the O2 sensor shows.
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Old 08-22-2020, 01:24 PM   #83
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Check your wiring between the LH and the O2 also, while you're at it.
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Old 08-22-2020, 01:26 PM   #84
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Check your wiring between the LH and the O2 also, while you're at it.
Will do!
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Old 08-22-2020, 01:32 PM   #85
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On the off chance I'm being dumb, use the obd to cycle the injectors and give a listen w the screwdriver at the base of each one.

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Old 08-22-2020, 04:00 PM   #86
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On the off chance I'm being dumb, use the obd to cycle the injectors and give a listen w the screwdriver at the base of each one.

Marty
I did, they are all clicking the same. None sound weaker and they all 4 work.
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Old 08-24-2020, 05:59 PM   #87
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No surprise, the new O2 sensor didn't fix it. Great!

I tried unplugging the large vacuum hose that goes to the climate control (just to make sure there aren't any leaks in that area) and after capping it off, it started kinda hard and the CEL came on for a few seconds. Weird. Anyway, I'm not sure what to do next... this car has really been testing my abilities. I've never had such a hard time diagnosing a seemingly simple problem.
I'm about to pull the cam cover now and swap out the valve shim on the cylinder 1 exhaust valve. That should loosen up the clearance to match up with the rest of them. I should have done that before, but oh well... at least it's easy to access.
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Old 08-25-2020, 02:11 AM   #88
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No surprise, the new O2 sensor didn't fix it. Great!

I tried unplugging the large vacuum hose that goes to the climate control (just to make sure there aren't any leaks in that area) and after capping it off, it started kinda hard and the CEL came on for a few seconds. Weird. Anyway, I'm not sure what to do next... this car has really been testing my abilities. I've never had such a hard time diagnosing a seemingly simple problem.
I'm about to pull the cam cover now and swap out the valve shim on the cylinder 1 exhaust valve. That should loosen up the clearance to match up with the rest of them. I should have done that before, but oh well... at least it's easy to access.
Have you done a voltage test of new o2 at normal operating temperature(do not waste time checking cold) ? It's important to verify which systems are working properly.
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Old 08-25-2020, 11:16 AM   #89
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Have you done a voltage test of new o2 at normal operating temperature(do not waste time checking cold) ? It's important to verify which systems are working properly.
I'll test this today. I went ahead and adjusted the valve clearance on the #1 exhaust valve, and it was definitely WAY too tight (0.010").
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Old 08-25-2020, 10:23 PM   #90
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Looked over the voltage at each pin on the ECU just out of curiosity, and most everything looks good. Just had a couple concerns...

Pin 5 was the most concerning. It's a signal ground, and it should have battery voltage with the key on and engine off. My car is showing 37.6 mV... that's a bit low. Typo maybe, or is this supposed to be 12v?
Pin 18 (injector control) should be battery voltage key on engine off, and only 190-200 mV engine on. It's showing battery voltage at idle. The pinout says when engine speed increases, the signal should as well. It goes down when I rev it. Again, maybe it's different for my '91 turbo, but worth mentioning.
Pin 25 (load signal) was a little high with the key on, engine off at 350 mV. It shows 250-300 mV.
Pin 32 is low (32 mV, should be 12v), but I have the cold start injector unplugged so I'm not worried about that one.

Today when I started the car, it ran like absolute garbage. Even worse than before... it has a hard time starting now before idle "normalizes" (relative term with this car). CEL actually comes on for a few seconds, then turns off. Really odd. I'll have to check for codes tomorrow just in case it stored anything.
I also checked the O2 sensor signal at the ECU, and it started around 0.5V (engine was warm earlier in the day, but it had been sitting for a few hours) then slowly went up as I ran it longer. By the time I went on to test other pins, it was around 0.7V.

This is the pinout I referenced: https://ipdown.net/jetronic.info/tik...s+and+Diagrams

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Old 08-25-2020, 10:38 PM   #91
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If, after warm up, the O2 sensor is not swinging something upstream has failed. The engine is running RICH. Now, what would cause that?
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Old 08-25-2020, 11:13 PM   #92
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If, after warm up, the O2 sensor is not swinging something upstream has failed. The engine is running RICH. Now, what would cause that?
Yeah, I'm pretty sure it's running rich. I'll have to get it to operating temperature and check once again just to be sure, but just from how it smells, it's running rich.
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Old 08-25-2020, 11:22 PM   #93
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Put some dish soap around each joint in the exhaust system upstream of the O2 sensor, and blow air through the tailpipe with a shop vac's exhaust port. You might have an exhaust leak bathing your O2 sensor in fresh air. Are you sure there isn't a huge gash in the back of your exhaust manifold somewhere?
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Old 08-26-2020, 12:13 AM   #94
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Not that I can see. I’ll check it out and see if I can find any leaks, but I don’t hear any.

Now, it’s worth mentioning that for some reason, someone welded an additional O2 sensor bung on the top of my downpipe. No idea why it’s there, all I could think is that it was a wide band sensor for an AFR gauge, but I’m not totally sure.
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Old 08-26-2020, 02:48 AM   #95
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Not that I can see. I’ll check it out and see if I can find any leaks, but I don’t hear any.

Now, it’s worth mentioning that for some reason, someone welded an additional O2 sensor bung on the top of my downpipe. No idea why it’s there, all I could think is that it was a wide band sensor for an AFR gauge, but I’m not totally sure.
I assume you know you can do a signal wire o2 voltage test at the connection under the hood ? I would try it there also, since the readings are not in the correct range.
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Old 08-26-2020, 11:14 AM   #96
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I assume you know you can do a signal wire o2 voltage test at the connection under the hood ? I would try it there also, since the readings are not in the correct range.
Yes, that's how I tested it before.
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Old 08-26-2020, 02:07 PM   #97
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Tested the O2 voltage just now, it looks good at operating temp. It fluctuates between 0.2 and 0.8 as it should. False alarm on that problem!

Driving it today, it felt better than before. I think the sluggishness may be an issue of cam timing. As far as the low, twitching vacuum gauge, I have no idea what is causing that. It also does it in boost when it’s at full boost (10-12 PSI).
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Old 08-26-2020, 04:55 PM   #98
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Have you tried a known good MAF?
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Old 08-26-2020, 04:58 PM   #99
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I’ve tried 3, and one was definitely bad. I’ll have to borrow my cousin’s MAF just to test it.
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Old 09-03-2020, 07:30 AM   #100
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bmdubya, check out the last few posts in VolvOrr's thread. See if any of it applies to your situation. I saw in an earlier post that you're using an iPD cam. You might need at least an adjustable gear, or in a worst case a different cam.

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