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Could it be a bad 'new' Oxygen Sensor?

R

Redsnake

NAXJA Forum User
Location
Tulsa, OK
I replaced my Bosch O2 Sensor a couple weeks back as it had about 40K+ miles on it since the last change and I figured since my gas mileage had dropped a bit, and after doing any of the other things (distributor change, plugs, wires, new tires, air filter, etc....) this was the last thing that needed to be changed.

Flash forward to this week... and my Check Engine light has come on a couple times. Ran my code scanner and got codes P0148, P0138 & strangely... '00 8' and not sure what that is. I know that one of these is for the O2 sensor signals, but not sure the other two. This just started about 1 month after replacing the O2 Sensor w/another new Bosch Sensor.

Could I have just got a bad Sensor? I have the box the part came in, but not the receipt and doubt Autozone will exchange for me. I kept the 'old' O2 sensor so perhaps I should just swap that one back in and try my luck at exchanging and replacing.

Any suggestions? Could it be something else I need to check?

Appreciate the help.
 
Did you disconnect the battery before you put it in. Try that. Let the computer know you put in a new 02 sensor.
 
I did disconnect the battery prior to changing out the O2 Sensors.

I did not however replace the post/after-cat O2 Sensor as I got the impression that doesn't really do much other than tell the Computer that the Cat is good or bad.

I Only replaced the Pre-Cat O2 Sensor.
 
From what I've read, that's all that 2nd sensor does: either good or bad cat feedback--the ecu does not use those readings to further adjust A/F ratios.
 
P0138 O2 Sensor Circuit High Voltage (Bank 1 Sensor 2)

The sensor after the cat is reading lean. This doesn't necessarily mean it's bad, so don't start throwing parts at it. This sensor is reading a lean condition. Find out if the lean condition exists before you assume the sensor is bad. Find out why you have a fuel delivery error too.

P0148 Fuel Delivery Error

This is usually from fluctuating fuel pressure. Check fuel filter, fuel pump, and lines. Aftermarket parts can cause this.

How many miles on the truck?
 
221K miles on my XJ.

I haven't changed the fuel filter in a while... not sure how many miles, maybe 40K+ miles... so that should probably be done as well.

OE fuel pump. No aftermarket parts other than just maintenence stuff. Put in a new/rebuilt Distributor about 3-4 months back, new Mopar Performance Wires and NGK Plugs at that same time. Air filter is clean and I do regular Oil changes w/ Mobil 1 5W-30 and Motorsport filters.

I'll put a guage on my Fuel Pressure check valve and see what kind of numbers I'm getting. I don't have any missing or poor running problems... other than getting poor fuel economy. However, that'd be more of an idication of running rich, not lean.

Any suggestions for how exactly I test to see if I'm running lean? Do I need to pull the plugs and check those? When I did a plug change the plugs I pulled gave me indications that the 4.0 liter was running pretty good. No carbon or white/burnt like deposits.. just normal wear.
 
I think I would change the fuel filter. Did you know that there is a "combination" filter and regulator inside the tank of late 90's cherokee's. What year do you have?

Check the fuel pressure. It should be atleast 45 PSI, no more than 55 PSI if I'm not mistaken.

Also, try a couple of bottles of sea foam after the filter replacement. This will help clean your lines and injectors. Do you know how to add sea foam through the intake? I'd do that too. A sticky injector could through this code too.

Repoet back.
 
Mine is a '96 and I was unaware of any other fuel filter, than the one inline of the fuel lines just forward of the fuel tank. I will change that one out.

I have not run any sea-foam in the fuel lines, but did run a can thru the Intake about 3 months back. I'm sure it helped clean out my intake and valves and what-not, however I gave them a good manual cleaning about 18 months back when I had to pull the intake to replace my busted OE header w/a new APN one. I cleaned them up while I had it all apart.

Header08-05-06014.jpg


Header08-05-06019.jpg


I'll run a can of Sea-Foam thru the gas tank and lines along w/a fuel filter change. That should help clean up any fuel problems... assuming I don't have a busted injector or something else.

Does anyone know where I could get a Fuel Pressure Gauge to mount to my Fuel Line Schrader Valve? I have one that I can attach (hose mounted) but would like a permanently mounted one.
 
http://www.gbodyparts.com/product_info.php?products_id=478&osCsid=228c71200e75c466162389d21ab03f2d

This will fit.

I bought one about 3 years ago form another company that specialized in Buick GN parts also. I can't remember the name, but it had 3 feet of steel braded line and a bracket so I could mount it on the hood or something like that. I never did, but it did come in handy once when I was having low fuel pressure under boost. 17 pounds of boost with not enough fuel is a VERY bad combo! I could tape it to the windshield while I tested, then I'd coil the line back up and secure it back under the hood when I was done. I will try to find the one I bought like that. It was $39.
 
Yeah... 17 lbs of boost and not enough fuel = BOOM!!! Love GNs ... always been a Mustang man myself... but Jeeps are fun too. :) Hard to take my old Cobra off-roading, or for that matter keeping it on the road in bad weather. Thanks for the info.
 
PO138 high voltage means the 12-14 volts heater wire is shorting to the 0-1 volt signal return wire from the O2 sensor back to the PCM. Those wires have a bad habit of getting loose and burning the insulation off by making contact with the exhaust.
 
Ecomike... thanks for that tip. I'll take a look at that. Just for reference... are you referring to the Pre or Post Catalytic Converter O2 Sensor? or Both? Thx
 
Redsnake said:
Ecomike... thanks for that tip. I'll take a look at that. Just for reference... are you referring to the Pre or Post Catalytic Converter O2 Sensor? or Both? Thx
Click to expand...

P0138 has to be a post cat. A burned wire could definately be the cause. Otherwise if your FP is fine then I'd replace it.
 
stealth908 said:
P0138 has to be a post cat. A burned wire could definately be the cause. Otherwise if your FP is fine then I'd replace it.
Click to expand...

Definately the O2 sensor after the cat, post cat!

O2 sensor wires after O2 sensor replacement are frequently not placed, tucked away properly, and easily get hung up on something that burns them or rips them up. Mine got eaten by the drive shaft and then slung over the exhaust manifold where the exhaust heat finished the job the drive shaft started. The Differential vent hose got loose and started the whole process. Mine is a Renix, 87, a little different than yours, but it does happen on the newer ones too. Kind of a common road hazard thing, especially if you run over bush, brush or other road hazards that can grab onto the dangling wires.
 
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