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Testing Jeep O2, Oxygen sensors

In order to run pin 30 of the o2 relay to pin 87 of the fuel pump relay is it a simple matter of disconnect the o2 pin 30 wire and reattaching it to the FP pin 87?

I don't imagine it would be wise to run a jumper as it will only create the same issue or make it worse.

And if that is correct and I did that, would the ECU be able to cut power to the heater when it's not needed?

Also would that mess with fuel trims?

Correct. No jumpers, just o2 30 to FP 87. That way the power is controlled correctly.

ECU can still pull power by activating the o2 relay, as long as 86 is getting ignition and 85 is going to the correct ecu pin. Even if not, this function is not super important. The o2 relay is only controlled to turn off under WOT throttle then it comes right back on after.

And nada, fuel trims should be just fine if the fuel pump isn't being cut accidentally.
 
Was going to do the o2 pin 30 switch to fuel pump pin 87 but before doing so I decided to do 2 voltage tests on the fuel pump relay pin 87. Got Power.

Because of that I tested all pins on all relays. Am thinking there is an short circuit somewhere or the ECU has issues.

Battery Terminal Disconnected

A/C relay
Pin 87a - 0v
pin 30 - 0v
pin 87 - 0v
pin 85 - 0v
pin 86 - 0v

Latch relay
pin 30 - 12.24v
pin 87 - 0v
pin 85 - 0v
pin 86 - 0v

fuel pump relay
pin 30 - 12.24v
pin 87 - 12.24v
pin 85 - 0v
pin 86 - 0v

o2 relay
Pin 87a - 0v
pin 30 - 12.24v
pin 87 - 0v
pin 85 - 0v
pin 86 - 0v

Battery Terminal Connected

A/C relay
Pin 87a - 12.02v
pin 30 - 12.02v
pin 87 - 12.00v
pin 85 - 12.02v
pin 86 - 11.64v

Latch Relay

pin 30 - 12.24v
pin 87 - 11.70v
pin 85 - 11.65v
pin 86 - 11.90v

Fuel Pump Relay

pin 30 - 12.24v
pin 87 - 12.24v
pin 85 - 0v
pin 86 - 12.02v

o2 Relay

Pin 87a - 0v
pin 30 - 12.24v
pin 87 - 12.02v
pin 85 - 11.65v
pin 86 - 12.02v

Also corrected the orange/black and green wire cross on the A/C relay. Nothing negative happened, A/C clutch and blower still works.
 
Battery Terminal Disconnected

fuel pump relay
pin 30 - 12.24v
pin 87 - 12.24v
pin 85 - 0v
pin 86 - 0v

How exactly is your meter hooked up?

If one of the 2 battery terminals is disconnected then there is no possible way that voltage can be on any pin.

The multimeter is measuring the voltage potential difference between the 2 leads. The Black Lead should go to ground, as that is what gives the multimeter it's ground reference. Once it can see "0v" then it can show you the difference on the red lead.

So with that in mind, are your readings still accurate?

It seems odd that almost every terminal has voltage.
 
How exactly is your meter hooked up?

If one of the 2 battery terminals is disconnected then there is no possible way that voltage can be on any pin.

The multimeter is measuring the voltage potential difference between the 2 leads. The Black Lead should go to ground, as that is what gives the multimeter it's ground reference. Once it can see "0v" then it can show you the difference on the red lead.

So with that in mind, are your readings still accurate?

It seems odd that almost every terminal has voltage.

Black test lead to negative COM input jack and the red test lead to positive V jack. Set the meter on DC voltage measurements 20v. It reads 0v when leads are not touching anything.

Negative lead to negative battery terminal positive lead to the relay holder pins.

The battery tested 12.24v Its a bit low because I have been doing so much voltage tests without running the engine.
 
In the post above I had the voltages backward for Battery Terminal Disconnected and Battery Terminal Connected. The following is the correct version.

How all of those relay socket terminals can be powered with the battery negative cable disconnected from the battery is a HUGE MYSTERY!

Battery Terminal Connected

A/C relay
Pin 87a - 0v
pin 30 - 0v
pin 87 - 0v
pin 85 - 0v
pin 86 - 0v

Latch relay
pin 30 - 12.24v
pin 87 - 0v
pin 85 - 0v
pin 86 - 0v

fuel pump relay
pin 30 - 12.24v
pin 87 - 12.24v
pin 85 - 0v
pin 86 - 0v

o2 relay
Pin 87a - 0v
pin 30 - 12.24v
pin 87 - 0v
pin 85 - 0v
pin 86 - 0v

Battery Terminal Disconnected

A/C relay
Pin 87a - 12.02v
pin 30 - 12.02v
pin 87 - 12.00v
pin 85 - 12.02v
pin 86 - 11.64v

Latch Relay

pin 30 - 12.24v
pin 87 - 11.70v
pin 85 - 11.65v
pin 86 - 11.90v

Fuel Pump Relay

pin 30 - 12.24v
pin 87 - 12.24v
pin 85 - 0v
pin 86 - 12.02v

o2 Relay

Pin 87a - 0v
pin 30 - 12.24v
pin 87 - 12.02v
pin 85 - 11.65v
pin 86 - 12.02v
 
How all of those relay socket terminals can be powered with the battery negative cable disconnected from the battery is a HUGE MYSTERY!

Well that's the answer right there. I'm assuming you are putting your black probe on battery negative right? If the Negative terminal is disconnected then the battery is no longer part of the circuit and should not be used as a reference, because as you can see it will give you odd readings.

It's measuring the difference between the 12v side that is connected, and the 0v side that is not connected.

Move your black probe to the disconnected negative lug or any body ground and you should see all of these mystery voltages disappear.
 
Well that's the answer right there. I'm assuming you are putting your black probe on battery negative right? If the Negative terminal is disconnected then the battery is no longer part of the circuit and should not be used as a reference, because as you can see it will give you odd readings.

It's measuring the difference between the 12v side that is connected, and the 0v side that is not connected.

Move your black probe to the disconnected negative lug or any body ground and you should see all of these mystery voltages disappear.

Yes, I put the negative test lead to the battery's negative terminal.
I did as you said and put the neg test lead to the negative battery cable and no more voltage readings.

Well, call me 'STUPID':looney: and I'll agree with you.
 
Ding ding, we have a weiner. So it looks like the o2 heater input was swapped to a 12v hot source at some point which is causing your battery drain.

At the very least, I would switch o2 heater pin 30 to an ignition source so it only works with key on, but ideally it should be run to pin 87 of the fuel pump relay so it's only on when the engine is running.

This should help your battery drain issue just a bit depending on how much else was changed. :roll:

Fuel pump relay has power to pin 30 and 87 with key off. So what's left? I only see three options. Either connect pin 30 to ignition source, go wideband, or rip out the harness and look for a shorted wire or some other PO fix. Maybe its the ECU???
 
Fuel pump relay has power to pin 30 and 87 with key off. So what's left?

Well then, let's go farther up the diagram.


It looks like pin 30 of the Fuel Pump Relay is a 12V Hot line, so no worries there. FP Pin 87 having power with key off is a problem though so lets check more pins.


87 should only get power if the relay coil is energized, so lets test the coil first. Pin 86 should only be an ignition line, so if 86 has power with Key Off then that is our first problem.

Part 2 is to see if pin 85 is being grounded with the Key Off. If you get continuity / low resistance from FP 85 to ground then there is either a short to ground in the wire or the ECU is goofing up.


If both coil pins are doing what they should, then the relay may be stuck. Unplug it and Check continuity from 30 to 87 and see what you get. Without power this should be open. For giggles, check 30 to 87a and you should have a closed circuit there.
 
Well then, let's go farther up the diagram.


It looks like pin 30 of the Fuel Pump Relay is a 12V Hot line, so no worries there. FP Pin 87 having power with key off is a problem though so lets check more pins.


87 should only get power if the relay coil is energized, so lets test the coil first. Pin 86 should only be an ignition line, so if 86 has power with Key Off then that is our first problem.

Part 2 is to see if pin 85 is being grounded with the Key Off. If you get continuity / low resistance from FP 85 to ground then there is either a short to ground in the wire or the ECU is goofing up.


If both coil pins are doing what they should, then the relay may be stuck. Unplug it and Check continuity from 30 to 87 and see what you get. Without power this should be open. For giggles, check 30 to 87a and you should have a closed circuit there.


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.
 
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?
 
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.




.
 
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.
 
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?
 
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.

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

How do you do that, am not sure.

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.
 
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.


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?
 
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.
 
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.
 
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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