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  #211  
Old June 6th, 2019, 13:43
randy57 randy57 is offline
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Re: Testing Jeep O2, Oxygen sensors

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Bad ECU maybe.

I got a computer from a 1990 xj automatic 2 wheel drive from the junkyard and posted pictures of it along with my original.

Please take a look and comment on your thoughts regarding circuitry similarities and if it would hurt to plug it into my 90 automatic 4x4.

https://www.cherokeeforum.com/showth...2&goto=newpost
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  #212  
Old June 6th, 2019, 18:28
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Re: Testing Jeep O2, Oxygen sensors

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All the relays have continuity between 30 and 87a. 30 and 87 is 0L. Its not the relay because I have switched them around and used several others that all tested good.

I checked continuity between FP pin 85 and pin A5 on the ECU plug and o2 relay pin 85 and pin A7 ECU plug. Got continuity on both.

Bad ECU maybe.
How about checking if either 85 pin is grounded with the key off.

Do both 86 pins only have power with key on?
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  #213  
Old June 6th, 2019, 20:20
randy57 randy57 is offline
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Re: Testing Jeep O2, Oxygen sensors

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How about checking if either 85 pin is grounded with the key off.

Do both 86 pins only have power with key on?

Voltmeter set to DC volts, red test lead to pin 86 on o2 and FP. Black test lead to body ground. Got 12v with key on.

Voltmeter set to DC volts, red test lead to battery positive and black test lead to pin 85 on o2 and FP. Got 12v with key off.




.
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  #214  
Old June 6th, 2019, 20:49
randy57 randy57 is offline
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Re: Testing Jeep O2, Oxygen sensors

Voltmeter set to DC volts, red test lead to pin 86 on o2 and FP. Black test lead to body ground. Got 12v with key on.

Zero volts with key off.
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  #215  
Old June 6th, 2019, 21:03
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Re: Testing Jeep O2, Oxygen sensors

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Voltmeter set to DC volts, red test lead to pin 86 on o2 and FP. Black test lead to body ground. Got 12v with key on.

Zero volts with key off.
Ok, so 86 is getting ignition as it should.

85 is a bit harder to understand. Generally the black lead will always be body ground for reference just to make sense of your input on the red wire. To check if a pin is grounded I test it with the red lead, and you should get something very close to 0v.

Another check is continuity to see just how grounded it is.

So if the coil is only getting ignition, then it shouldn't be able to activate with key off anyway.

With the o2 relay hooked up to the fuel pump like stock, do you get power correctly on the heater wire finally?
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  #216  
Old June 6th, 2019, 22:58
randy57 randy57 is offline
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Re: Testing Jeep O2, Oxygen sensors

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Originally Posted by NickInTimeFilms View Post
85 is a bit harder to understand. Generally the black lead will always be body ground for reference just to make sense of your input on the red wire. To check if a pin is grounded I test it with the red lead, and you should get something very close to 0v.
Can you elaborate more please.

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Originally Posted by NickInTimeFilms View Post
Another check is continuity to see just how grounded it is.
How do you do that, am not sure.

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Originally Posted by NickInTimeFilms View Post
With the o2 relay hooked up to the fuel pump like stock, do you get power correctly on the heater wire finally?
You mean o2 relay to o2 holder?
o2 heater wires 1 large orange and on small orange together is hot key off and key on.
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  #217  
Old June 6th, 2019, 23:28
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Re: Testing Jeep O2, Oxygen sensors

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Can you elaborate more please.

"Voltmeter set to DC volts, red test lead to battery positive and black test lead to pin 85 on o2 and FP. Got 12v with key off."
Although this seems to make sense from a flow standpoint, matching red with positive and black with negative, it doesn't really give us what we're looking for.

We want to see if there is a 0v potential on 85, also known as ground. Well if the meter is reading 12v, then it isn't exactly showing us what we want to know.

Think of the red lead as the input. We want to check the circuit in question with the red lead as this is what the meter is displaying. So with your red lead on battery positive, it's showing you what the battery is at, when we what to know what the relay is at instead. We will move the red lead to pin 85 instead, since that's what we actually want to know.

Black lead generally always goes to a common ground point for easy understanding. This is our reference probe, and whatever it touches is considered 0v to the meter. So if we put the black probe on the positive battery post, 12v would be considered 0v, and poking the red lead at 12v would show 0v(no potential difference), while poking it to ground would show -12v, since ground(0v) is 12v lower then the reverence of 12v.

In short, Red is Input, Black is Ground reference.



Now, with that in mind, we still run into an annoying problem when checking grounds with the meter. The Meter will show 0v when nothing is connected, so how can we tell if it's actually nothing, or if we have a 0v ground? Usually when you are checking a circuit it won't be perfect so a very slight stray voltage will be detected, so if for instance we check pin 85 and it reads like 0.5v then we can tell the it has some sort of connection to ground.

The more prefered way is a resistance or continuity check. Since we can't see a voltage difference, we can instead measure how much resistance there is between the 2 ground points and infer a connection that way. A Reading of OL would mean an open circuit so no ground, where < 2Ω would show we have a pretty good ground path there.


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Originally Posted by randy57 View Post

You mean o2 relay to o2 holder?
The heater relay output voltage going to the o2 sensor, that big orange wire that started this whole thread, haha. Is it still stuck on all the time with the o2 relay properly hooked up to the fuel pump relay?
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  #218  
Old June 7th, 2019, 00:32
randy57 randy57 is offline
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Re: Testing Jeep O2, Oxygen sensors

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Originally Posted by NickInTimeFilms View Post
Although this seems to make sense from a flow standpoint, matching red with positive and black with negative, it doesn't really give us what we're looking for.

We want to see if there is a 0v potential on 85, also known as ground. Well if the meter is reading 12v, then it isn't exactly showing us what we want to know.

Think of the red lead as the input. We want to check the circuit in question with the red lead as this is what the meter is displaying. So with your red lead on battery positive, it's showing you what the battery is at, when we what to know what the relay is at instead. We will move the red lead to pin 85 instead, since that's what we actually want to know.

Black lead generally always goes to a common ground point for easy understanding. This is our reference probe, and whatever it touches is considered 0v to the meter. So if we put the black probe on the positive battery post, 12v would be considered 0v, and poking the red lead at 12v would show 0v(no potential difference), while poking it to ground would show -12v, since ground(0v) is 12v lower then the reverence of 12v.

In short, Red is Input, Black is Ground reference.



Now, with that in mind, we still run into an annoying problem when checking grounds with the meter. The Meter will show 0v when nothing is connected, so how can we tell if it's actually nothing, or if we have a 0v ground? Usually when you are checking a circuit it won't be perfect so a very slight stray voltage will be detected, so if for instance we check pin 85 and it reads like 0.5v then we can tell the it has some sort of connection to ground.

The more prefered way is a resistance or continuity check. Since we can't see a voltage difference, we can instead measure how much resistance there is between the 2 ground points and infer a connection that way. A Reading of OL would mean an open circuit so no ground, where < 2Ω would show we have a pretty good ground path there.

The heater relay output voltage going to the o2 sensor, that big orange wire that started this whole thread, haha. Is it still stuck on all the time with the o2 relay properly hooked up to the fuel pump relay?
That was a great explanation Nick. Thank you


We get 044 ohms on pin 85 o2 relay and FP relay.
There still is power going to o2 with battery connected key off.

I guess I am still grappling with "the o2 relay properly hooked up to the fuel pump relay."

Hope I am not trying your patience. My patience is wearing thin, been pulling my hair out for the last 4 weeks. Wondering where I can et some C4.
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  #219  
Old June 7th, 2019, 00:52
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Re: Testing Jeep O2, Oxygen sensors

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I guess I am still grappling with "the o2 relay properly hooked up to the fuel pump relay."

Hope I am not trying your patience. .
Haha, this has turned into a fun little session as it's giving me a new viewpoint on using meters and testings things. It helps me learn too.

Well, do we know that the o2 heater wire is only going to the relay on pin 87a?

If wires weren't messed with there, then our only focus is o2 relay pin 30. This needs to be powered from the fuel pump relay pin 87. If it's getting power from somewhere else, then that needs to be fixed first.
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  #220  
Old June 7th, 2019, 01:14
randy57 randy57 is offline
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Re: Testing Jeep O2, Oxygen sensors

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Originally Posted by NickInTimeFilms View Post
Haha, this has turned into a fun little session as it's giving me a new viewpoint on using meters and testings things. It helps me learn too.

Well, do we know that the o2 heater wire is only going to the relay on pin 87a?

If wires weren't messed with there, then our only focus is o2 relay pin 30. This needs to be powered from the fuel pump relay pin 87. If it's getting power from somewhere else, then that needs to be fixed first.
o2 heater wire is only going to the relay on pin 87a.

I removed the relay holder on a junkyard 90 xj for two reasons.
1. So I could verify my relay holder wiring was in factory order. And mine were not messed with.

2. So I could clean it up real nice, being that I couldn't access mine for soaking contacts in vinegar and salt and rinsing with water and baking soda and soldering it in place of my original holder.

So we are good there. And I don't think it is getting power elsewhere.

I checked continuity between FP pin 85 and pin A5 on the ECU plug and o2 relay pin 85 and pin A7 ECU plug. Got continuity on both.
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  #221  
Old June 7th, 2019, 01:17
randy57 randy57 is offline
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Re: Testing Jeep O2, Oxygen sensors

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So we are good there. And I don't think it is getting power elsewhere.
Actually couldn't there be a open short or power shorting to a ground maybe???
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  #222  
Old June 7th, 2019, 13:19
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Re: Testing Jeep O2, Oxygen sensors

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o2 heater wire is only going to the relay on pin 87a.
Yes but what about o2 pin 30. That is the input supply and can only be active with the fuel pump relay. Fix pin 30 = fix your drain.
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  #223  
Old June 8th, 2019, 11:20
randy57 randy57 is offline
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Re: Testing Jeep O2, Oxygen sensors

I ran the engine today
I have a new 02 sensor and it still runs the same as with the bad o2.
Although the heater is on all the time the o2 voltage should be switching low to high.
The voltage slowly decreases as it worms up but never gets below 4v or so.
It doesn't go rich/lean either. Stays on lean all the time but runs very rich.
This is all at idle.
Before I started this thread the engine would try to quit at stop lights.
Not sure if that's due to a bad cat. The temperature difference between the front and back of the cat is only about 75 degrees. Hotter in the rear of that cat.

I still have to correct the o2 heater from staying on but I shouldn't be getting the above issues.

Any thoughts?
Thnaks.
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  #224  
Old June 8th, 2019, 20:05
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Re: Testing Jeep O2, Oxygen sensors

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Although the heater is on all the time the o2 voltage should be switching low to high.
The voltage slowly decreases as it worms up but never gets below 4v or so.
It doesn't go rich/lean either. Stays on lean all the time but runs very rich.
This is all at idle.
Ok, so when the sensor is cold it will read 5v, which is lean.

As the sensor warms up it should start reading accurately, which will almost always be rich. The computer is waiting for the voltage to drop to about 1v so it can attempt closed loop. Rich/lean only updates when in closed loop.

If your sensor never sees a rich condition then there could be an exhaust leak, any cracks in the manifold?
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  #225  
Old June 8th, 2019, 21:49
randy57 randy57 is offline
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Re: Testing Jeep O2, Oxygen sensors

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If your sensor never sees a rich condition then there could be an exhaust leak, any cracks in the manifold?
Nothing that I can hear. I've heard exhaust leaks before in other vehicles but not this one. That doesn't meant that there isn't a small one.

Also got some new data I found today.

Tested power at fuel pump connector. Key off got no power. Key on got power. With the jumper wire out from between pins 85 on the FP and o2, there was no power to the fuel pump connector with either key on or off.

Checked power to O2 with key off, key on and start. Like before, I had 12v with key off, and it dropped to 0v with the key on while the fuel pump was priming. Once the fuel pump stopped priming after 2-3 seconds, the voltage went back to 12v. Started the engine and the O2 voltage dropped to 0v again. Something new engine running o2 gets no power.

The way I see it, there is something wrong with the F22 14OR circuit because pin 87 on the fuel pump relay should not have any power with the key off.

Suspecting there is a short in the F22 14OR circuit causing pin 87 to be hot. This in turn is causing the O2 to pull voltage from the battery.

Also, with the fuel pump relay and O2 relay sharing the ECU ground, the computer cuts ground to the O2 relay for the heater to turn on, but the relay is still energized from the fuel pump relay ground.

Likely, the O2 heater will never work until the o2/FP jumper wire mystery is solved.

Any idea as to a work around for that?
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