O2 sensor issues?
#46
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From: Connecticut
Year: 2000
Model: Cherokee (XJ)
Engine: 4.0
You keep saying 'parasitic drain'. Parasitic drain is something unwanted that isn't supposed to be there. If you are measuring the current to the O2 heater, that is supposed to be there, and it is supposed to be enough to heat the O2 sensor, not sure what that is but 1-4 Amps DC seems reasonable.
#47
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From: syracuse ny
Year: 1997
Model: Grand Cherokee (ZJ)
Engine: 4.0, new lifters valve job with new springs and exhaust valves, preload set with shims
#48
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From: arizona
Year: 1990
Model: Cherokee (XJ)
Engine: 4.0
I think what that does is make the ECU think there's a fuel pump relay there. I would check the entire fuel pump wiring system to see how the PO got the fuel pump to work w/o the relay (as well as making sure it doesn't work when in key off (because fuel pump relay power is hot all the time, so he couldn't have simply bypassed the relay at that point)).
This is in addition to figuring out why that ignition yellow is hot all the time. It seems there are at least 2 issues underfoot.
This is in addition to figuring out why that ignition yellow is hot all the time. It seems there are at least 2 issues underfoot.
Going to dig out the relay holder and the ignition control unit so I can see whats going on under them. Broken wire, short, etc.
Something for Monday. Will post findings asap.
#49
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From: arizona
Year: 1990
Model: Cherokee (XJ)
Engine: 4.0
#50
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From: arizona
Year: 1990
Model: Cherokee (XJ)
Engine: 4.0
You keep saying 'parasitic drain'. Parasitic drain is something unwanted that isn't supposed to be there. If you are measuring the current to the O2 heater, that is supposed to be there, and it is supposed to be enough to heat the O2 sensor, not sure what that is but 1-4 Amps DC seems reasonable. The concept is that the O2 sensor has a heater built in it to preheat the sensor so it works before the engine warms it on it's own to 600F, which can take a while. If you're not getting a code that says "O2 sensor heater circuit open" then it is doing what it's supposed to do.
If it did that would make things easier by sending me in a general direction.
But then that's what a voltmeter helps with. Don't know which would be easier.
The titania o2 sensors do not produce a voltage like the newer Zerconia sensors. The titania (Pre 90"s Jeep), sensors are heated from battery voltage through the relay.
That's why, due to the drain on my battery with key off, I though the sensor I have been getting were of the Zerconia type.
But in reality I do have a wiring issue that's causing my battery drain.
http://tomco-inc.com/Tech_Tips/ttt20.pdf
Last edited by randy61; 05-19-2019 at 12:30 PM. Reason: correction
#51
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From: Connecticut
Year: 2000
Model: Cherokee (XJ)
Engine: 4.0
If you go to Key On, but do not Start, does the fuel pump run continuously or shut off after 3 seconds?
So the relay shuts down...
...except there's no relay.
Can you repeat that but listen to see if a relay clicks on or off? Perhaps the guy cannibalized one of the other relays (and that's a pretty short list) or put another one in someplace.
#52
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From: arizona
Year: 1990
Model: Cherokee (XJ)
Engine: 4.0
With o2 relay NOT installed and jumper sharing o2 and FP relay #85 terminal the FP relay does click.
#53
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From: Connecticut
Year: 2000
Model: Cherokee (XJ)
Engine: 4.0
To be clear, fuel pump runs without the fuel pump relay as long as the jumper wire is in.
If the oxygen sensor relay is NOT plugged in or the jumper wire is NOT in place the fuel pump will not run.
If the oxygen sensor relay is NOT plugged in or the jumper wire is NOT in place the fuel pump will not run.
#54
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From: Connecticut
Year: 2000
Model: Cherokee (XJ)
Engine: 4.0
I am trying to understand how the fuel pump could work without the relay, but the fuel pump relay socket appears to be behaving normally. I have concluded that it can't be done (me understanding, that is).
And the behavior when the O2 Relay is out seems a little inconsistent but maybe that's me, so let's hold on that for a minute.
These are 85 connectors but in the schematic they use the single digit nomenclature. Does the jumper connect GRY-YEL and ORG-T (2) or YEL and ORG (5)?
And the behavior when the O2 Relay is out seems a little inconsistent but maybe that's me, so let's hold on that for a minute.
The jumper wire between the fuel pump relay and the o2 sensor relay is only sharing the relay grounds, which is why the fuel pump will run without the fuel pump relay installed.
#55
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From: Connecticut
Year: 2000
Model: Cherokee (XJ)
Engine: 4.0
Because it seems to me that you cannot simultaneously get grounds and power. It would have to be either the 2 combination (grounds) or the 5 combination (power).
Great puzzle.
And leaving the jumper wire intact and removing the fuel pump relay the fuel pump kept working because the pump was getting power from the o2 sensor relay.
#56
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From: arizona
Year: 1990
Model: Cherokee (XJ)
Engine: 4.0
Are you confused because I made what seemed like a contradiction, or because of what this thing is doing?
I ran another test so I could make a summary.
Fuel pump relay out the fuel pump runs and the o2 relay clicks on then off.
o2 sensor out the fuel pump does not run but the fuel pump relay clicks on then off.
Both tests were with the jumper wire in place on 85 to 85.
This time I made a point to put my finger on each relay during the test.
What I found strange is that when the relays clicked on then off they made another single click. It's like they clicked on then off then on again and stayed on.
I ran another test so I could make a summary.
Fuel pump relay out the fuel pump runs and the o2 relay clicks on then off.
o2 sensor out the fuel pump does not run but the fuel pump relay clicks on then off.
Both tests were with the jumper wire in place on 85 to 85.
This time I made a point to put my finger on each relay during the test.
What I found strange is that when the relays clicked on then off they made another single click. It's like they clicked on then off then on again and stayed on.
Last edited by randy61; 05-19-2019 at 05:07 PM. Reason: correction
#58
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From: Connecticut
Year: 2000
Model: Cherokee (XJ)
Engine: 4.0
#59
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From: arizona
Year: 1990
Model: Cherokee (XJ)
Engine: 4.0
#60
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From: arizona
Year: 1990
Model: Cherokee (XJ)
Engine: 4.0
According to the diagram it looks like the jumper wire is connecting the grounds on each of the FP relay and the o2 relay.
Orange-T is ground from FP relay, (relay pin 85) to ECU
Grey-Yellow is ground from o2 relay, (relay pin 85) to ECU
And, the yellow goes from both relays (pin 86) to the ignition switch
Maybe there's a ground issue and ignition switch not allowing an interruption in the power to relay.
Tomorrow I will dig up the relay mount and the ignition module for a look-see.
Orange-T is ground from FP relay, (relay pin 85) to ECU
Grey-Yellow is ground from o2 relay, (relay pin 85) to ECU
And, the yellow goes from both relays (pin 86) to the ignition switch
Maybe there's a ground issue and ignition switch not allowing an interruption in the power to relay.
Tomorrow I will dig up the relay mount and the ignition module for a look-see.
Last edited by randy61; 05-19-2019 at 07:40 PM. Reason: correction