Misfire just after start-up then runs fine.

Lowrange2 said:
All 4 wires were the same size.
Click to expand...

On the sensor, or the wiring harness side?

The black wire with the green tracer had 4 volts. I should have snapped a picture.

The wire had 4 volts disconnected from the sensor as well as plugged into the uninstalled new sensor.
Click to expand...

Then you still have a problem. Check the relay, the contacts on the relay may be bad and you may be getting a voltage drop at the contacts.

I assume we've been discussing the upstream O2 sensor in the down pipe closest to the manifold... I didn't even look for the down stream sensor.
Click to expand...

Yes, it is the one that the computer uses to control the fuel feed rates.
 
Ecomike said:
On the sensor, or the wiring harness side?

On the whole harness. Harness comes out the same conduit that houses the injector harness and runs down to the O2 sensor. All the wiring is the same gauge.

Then you still have a problem. Check the relay, the contacts on the relay may be bad and you may be getting a voltage drop at the contacts.

I don't doubt that I still have an issue. I did start the Jeep and didn't have the same issue but it didn't do it all the time anyways. It did most of the time. I'll know for sure tomorrow when she drives it. If it still continues this will be the first place I go.

Yes, it is the one that the computer uses to control the fuel feed rates.

That's the impression I was under.
Click to expand...

Now, what exactly is this relay called? The relay is on the passenger side firewall? I don't see a relay called out on the diagram other than the Ballast resistor relay that seems to be attached to the fuel pump circuit? That makes no damn sense.
 
Even if it no longer miss fires, it may let the engine run too rich at idle eating excess fuel!

O2 sensor or oxygen sensor relay is the name. May say O2 heater relay? Under the hood in the relay box. There should be a fuse too, but the relay is the one that gives low volts. Fuse is all or nothing.

The drawing is wrong.
 
Last edited:
Ecomike said:
Even if it no longer miss fires, it may let the engine run too rich at idle eating excess fuel!

O2 sensor or oxygen sensor relay is the name. May say O2 heater relay? Under the hood in the relay box. There should be a fuse too, but the relay is the one that gives low volts. Fuse is all or nothing.

The drawing is wrong.
Click to expand...

Ok, I'll keep that in mind tomorrow.

I'll check voltage at the relay and continuity from there to sensor.

A correct diagram would make this much easier.

Anyone have access to this?
 
I just got word that the Jeep drove better this morning that it has in a long time.

No misfiring.

I'll check the wiring again this evening with a different meter.
 
FYI. 1998 O2S.

The 1998 XJ doesn't have O2S heater relays like the 00/01. Power to the heaters is a direct shot from fuse F24 in the PDC to the O2S's, see image below.

O2S heaters are powered from the battery bus (12 VDC) from pin 87 of the ASD relay. ASD relay must be activated to power the O2S heaters.

The O2S heaters are grounded at ground point G101, see image below.

The body harness O2S heater power (12 VDC) wires at the O2S connectors for both upstream and downstream O2S's are Dark Green/White tracer. The ground wires for both are Black.

The O2S heater pigtail wires that mate with the body harness wires are: White to Dark Green/White (12 VDC), Black toBlack (G101 Ground).

The O2S signal wires (to PCM) are: Body harness - Black/Dark Green tracer (PCM Signal), Brown/Yellow tracer (Sensor Ground in PCM). The O2S pigtail wires that mate with these wires are: Gray to Black/Dark Green, and White to Brown Yellow.

O2S heater fuse location:

1997-1999XJPDCannotated.jpg


O2S Ground location - G101:

G101.jpg
 
Sidewinder CC said:
FYI. 1998 O2S.

The 1998 XJ doesn't have O2S heater relays like the 00/01. Power to the heaters is a direct shot from fuse F24 in the PDC to the O2S's, see image below.

O2S heaters are powered from the battery bus (12 VDC) from pin 87 of the ASD relay. ASD relay must be activated to power the O2S heaters.

The O2S heaters are grounded at ground point G101, see image below.

The body harness O2S heater power (12 VDC) wires at the O2S connectors for both upstream and downstream O2S's are Dark Green/White tracer. The ground wires for both are Black.

The O2S heater pigtail wires that mate with the body harness wires are: White to Dark Green/White (12 VDC), Black toBlack (G101 Ground).

The O2S signal wires (to PCM) are: Body harness - Black/Dark Green tracer (PCM Signal), Brown/Yellow tracer (Sensor Ground in PCM). The O2S pigtail wires that mate with these wires are: Gray to Black/Dark Green, and White to Brown Yellow.

O2S heater fuse location:

1997-1999XJPDCannotated.jpg


O2S Ground location - G101:

G101.jpg
Click to expand...

Nice, those colors match the wiring I had last night.

I still only got 4.2 volts on the wire that should have 12 volts.

I'll check the fuse and track down the issue.

I still never got direct continuity to ground in any of the wires.

I need to verify 12 volts to the Dark Green/white wire
and ground on the black wire.
 
Lowrange2 said:
Nice, those colors match the wiring I had last night.

I still only got 4.2 volts on the wire that should have 12 volts.

If you are looking for O2S heater power (12 VDC) at wire (Dark Green/White) of the body harness, don't forget that the engine has to be running inorder to activate the ASD relay, which powers the O2S heaters.

You may want to deatch the O2S connectors and move the body harness connector to the top siide of the engine bay to make it easier to work on. Start the engine, using your voltmeter, (+) probe to the body harness Dark Green/White wire pin socket and the (-) meter probe to the Black wire pin socket. You should see battery voltage (12 VDC +). If you are still getting 4.2 Volts, probe from the 12 Volt supply pin socket to the engine (ground). Still no 12 Volts? Shut the engine down and remove the battery negative post connector and using your Ohmmeter, read from the Black wire pin socket to the engine (ground). You should read continuity (less than .5 Ohms). No good? remove the ground wires at ground point G101 and clean each wire terminal end and reattach. Try for continuity again.

I'll check the fuse and track down the issue.

I still never got direct continuity to ground in any of the wires.

You should have continuity from the body harness Black wire pin socket to the engine (ground), see above. You probably won't see continuity from body harness wire Brown Yellow pin socket to ground, that's the O2S return (ground) in the PCM, unless you disconnect the appropriate PCM connector and read from pin to pin in this circuit.

I need to verify 12 volts to the Dark Green/white wire
and ground on the black wire.
Click to expand...

Read above.
 
mines doing the same checked everything replaced new o2's checked harnesses voltage is fine fuel pressure fine checked while driving with gauge etc... starting to think it the computer because if the check engine light is on it runs fine. if the check engine light is off it does exactly what he stated in his first post im gonna go over the o2s another time then swap the computer quick unless anybody has other ideas.
 
dam mine might just be different im gonna re check all the wiring and fuses relays with power probe after work hopefully i missed somethign but its ****ign weird hoiw it runs perfect with cel on it does come up with code o2's high if checked everything
 
That does not sound like a computer problem. When the light comes on, if it is an O2 code, the computer has switched to a mode where it ignores the O2 sensor. That means it runs smooth while wasting fuel that will eventually burn out the CAT converter. Sounds like a bad O2 sensor, or bad wiring or missing heater voltage....

Crfrider said:
mines doing the same checked everything replaced new o2's checked harnesses voltage is fine fuel pressure fine checked while driving with gauge etc... starting to think it the computer because if the check engine light is on it runs fine. if the check engine light is off it does exactly what he stated in his first post im gonna go over the o2s another time then swap the computer quick unless anybody has other ideas.
Click to expand...
 
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