Failed CA Smog

To start: 1990 Renix, 5 speed, 4:56 gears, 33 inch tires, new cat and exhaust manifold. O2 sensor is two years old. All grounds have been refreshed.
Had to smog it this year and ended up failing with these numbers:



Looks like its running rich, so I pulled the fuel rail to check for a leaking injector. No leaks. Checked the O2 sensor next and found that it's not receiving 12 volts on the orange lead but is getting 5 volts from the ECM. I checked the sensor with the engine running and at idle, it read a steady 5 volts, only swinging to two volts once. I'm going to replace it and try to figure out where I'm losing the 12 volt feed from.

Where does the 12 volt source originate from? If I need to run another wire to bring 12 volts to the sensor, where word the best source be?

There is a relay on the passenger side fender well. I think it's the rear one. I think my engine had to be running to get 12v to the sensor.

I wouldn't replace the sensor knowing there is no 12V heating voltage to it.

Front relay is O2 sensor heater relay.

Might need a cat also, when is the last time you did plugs wires dist cap rotor bug and coil?

Check the vacuum line to the fuel pressure regulator for signs of gasoline. There should not be any. Do a fuel pressure test, while connected turn of the engine, and see if it holds about 30 psi, or not. If not an injector(s) is leaking.

TPS may be bad, check both sides, ECU and TCU sides, against specs, see the "Renx Files" I wrote a while back, and or curiser54's thread on testing the TPS, be sure to test both sides!!!

Your gearing, tires, and a non OEM header?, may keep it from passing too?

It is obviously running rich. Keep on the trail of the O2 sensor wires, like you are doing too!!!

IIRC someone else had only 5 Volts on the 1990 O2 heater wire. I think that may be what 1990 used? But I am not sure yet. I think they finally passed with just 5 V on it, but I forget the final details. It may have been a bad O2 heater drawing the 12 V down to 5 V? Check the O2 sensor heater while the wires are disconnected, it should be about 8 ohms, not zero ohms from the orange wire input (not the wire harness side, but thhe sensor side) to ground.

MaxxXJ said:

Might need a cat also, when is the last time you did plugs wires dist cap rotor bug and coil?

Click to expand...

OP said the CAT is new.

Ecomike said:

OP said the CAT is new.

Click to expand...

I posted at 4am... I was a lil sleepy still I guess

Well. time for an update. Did read a bunch of old thread looking for answers (thanks cruiser and Ecomike!!) Spent the morning trying to figure out where the orange wire might be screwed up and why i wasn't getting 12 volts. Found the O2 heater relay and cleaned up the connections. Cleaned out the whole relay bank...there was definitely 23 years worth of crud in there. Rechecked the harness connector and had 12 volts at the heater feed, 5 volts from the ECU. Resistance at the ground wire is 0.3 ohms. Looking good so far. Guess refreshing the relay connections did the trick? Replaced the O2 sensor with a new Bosch I picked up at NAPA and hooked up the volt meter. The sensor is doing what it is supposed to do, swinging between 2-4 volts and settling near 2 volts at 2000 RPM. Success!

Mike, I changed the TPS last week when preparing for the smog test. I had an erratic idle that would bounce up to 1000 RM, down to 500 then settle at 750. I have a manual tranny, so I set it for 0.83 volts. Made the idle better, smoothed it out. Its idling MUCH better now with the new O2 sensor though. I never suspected the O2 sensor being bad because I replaced it last time I smogged it. I had a crack in my exhaust manifold (which made me fail) so I changed the manifold and O2 sensor at the same time. Makes me wonder why it failed so fast. I've only driven this thing about 6000 miles in the last two years. Oh, and I am running the same gears and tires as last time too.

I checked my fuel pressure, started at 34 psi, leaked down to 32 and held there. Pulled the rail to make sure I didn't have a leaky injector, all is well.

The cat is new, less than 4000 miles on it. Last smog it still had the original cat. Changed it after it started making noise, found half of the insides were broken and loose inside and it still passed smog! The cap, rotor, and wires have about 10,000 miles on them.

Going for a retest in the morning, I'll post up the results.

Look for intake leaks and or exhaust leaks upstream of the O2. Even if you pass with the new cat and O2 sensor, leaks will mess with the O2 sensor signal and kill your cat early. I had a slight leak at the intake manifold gasket that messed with my idle RPM. It seemed to vary due to heat/cool expansion/contraction.

I just went through all this a few months ago. Ecomike and Cruiser are invaluable! I learned a lot and I think my XJ is running better than it ever has in the 6+ years I have owned it.

88trailcrawler said:

Look for intake leaks and or exhaust leaks upstream of the O2. Even if you pass with the new cat and O2 sensor, leaks will mess with the O2 sensor signal and kill your cat early. I had a slight leak at the intake manifold gasket that messed with my idle RPM. It seemed to vary due to heat/cool expansion/contraction.

I just went through all this a few months ago. Ecomike and Cruiser are invaluable! I learned a lot and I think my XJ is running better than it ever has in the 6+ years I have owned it.

Click to expand...

Excellent idea to check the tightness of the intake manifold bolts.

MaxxXJ:

Now you know why I did these 2 write-ups.

Renix Ground Refreshing
The Renix era XJs and MJs were built with an under-engineered grounding system for the engine/transmission electronics. One problem in particular involves the multiple ground connection at the engine dipstick tube stud. A poor ground here can cause a multitude of driveabililty issues, wasted time, and wasted money replacing unnecessary components.
The components grounding at the dipstick tube stud are:
Distributor Sync Sensor, TCU main ground, TCU "Shift Point Logic", Ignition control Module, Injectors, ECU main ground which other engine sensors ground through, Oxygen sensor, Knock Sensor, Cruise Control, and Transmission Sync signal. All extremely important stuff.
The factory was aware of the issues with this ground point and addressed it by suggesting the following:
Remove the nut holding the wire terminals to the stud. Verify that the stud is indeed tightened securely into the block. Scrape any and all paint from the stud’s mounting surface where the wires will attach. Must be clean, shiny and free of any oil, grease, or paint.
Inspect the wire terminals. Check to see that none of the terminals are crimped over wire insulation instead of bare wire. Be sure the crimps are tight. It wouldn’t hurt to re-crimp them just as a matter of course. Sand and polish the wire terminals until clean and shiny on both sides. Reinstall all the wires to the stud and tighten the nut down securely.
While you’re in that general area, locate the battery negative cable which is fastened to the engine block just forward of the dipstick stud. Remove the bolt, scrape the block to bare metal, clean and polish the cable terminal, and reattach securely.
Another area where the grounding system on Renix era Jeeps was lacking is the engine to chassis ground. There is a braided cable from the back of the cylinder head that also attaches to the driver’s side of the firewall. This cable is undersized for it’s intended use and subject to corrosion and poor connections at each end.
First off, remove the cable end from the firewall using a 15mm wrench or socket. Scrape the paint off down to bare metal and clean the wire terminal. Reattach securely.
Remove the other end of the cable from the rear of the head using a 3’4" socket. Clean all the oil, paint and crud from the stud. Clean the wire terminal of the cable and reattach securely.
A suggestion regarding the braided cable:
I prefer to add a #4 Gauge cable from the firewall to a bolt on the rear of the intake manifold, either to a heat shield bolt or fuel rail bolt. A cable about 18" long with a 3/8" lug on each end works great and you can get one at any parts store already made up. Napa has them as part number 781116.
A further improvement to the grounding system can be made using a #4 cable, about 10" long with 3/8" terminals at each end. Attach one end of this cable to the negative battery bolt and the other end under the closest 10mm headed bolt on the radiator support just forward of the battery. Napa part number 781115.
For those of us with Comanches, it’s very important to remove the driver’s side taillamp assembly to access the ground for the fuel pump. Remove the screw holding the black ground wire. Scrape the paint from the body and corrosion from the wire terminal. Reattach securely.
　
　
If you want to upgrade your grounds and battery cables in general, contact Jon at www.kelleyswip.com. He makes an incredible cable upgrade for a very reasonable price.
　
Revised 12-04-2012

I suggest unplugging EVERY electrical connection in the engine bay you can find, whether engine related or not, and spraying it out with a good electronics cleaner, visually inspecting the terminals making sure they haven’t retracted into the plastic holder, and then plugging it back together. There’s a critical 10-pin connector for the front lighting system located in front of the air cleaner and behind the left headlight assembly. Don’t miss that one. Also be sure that the connectors to the ballast resistor mounted near the air cleaner housing are clean and tight.
ALL of the relays should be removed, the terminals wire-brushed until shiny, and the receptacles sprayed out with contact cleaner. Then plug them back in. I do this on every Renix Jeep I purchase or work on for someone else.
Revised 07/23/2012

Went for my smog retest this morning and these were the results:



Pass!! Thanks for all the suggestions folks. And once again, thanks to cruiser and Ecomike for all the great info.

awesome. it's amazing how clean a renix will run when everything is working properly.
my renix xj's have always smogged cleaner than the ho's i've had.

Congrats!!!

cruiser54 said:

Excellent idea to check the tightness of the intake manifold bolts.

MaxxXJ:

Now you know why I did these 2 write-ups.

Renix Ground Refreshing
The Renix era XJs and MJs were built with an under-engineered grounding system for the engine/transmission electronics. One problem in particular involves the multiple ground connection at the engine dipstick tube stud. A poor ground here can cause a multitude of driveabililty issues, wasted time, and wasted money replacing unnecessary components.
The components grounding at the dipstick tube stud are:
Distributor Sync Sensor, TCU main ground, TCU "Shift Point Logic", Ignition control Module, Injectors, ECU main ground which other engine sensors ground through, Oxygen sensor, Knock Sensor, Cruise Control, and Transmission Sync signal. All extremely important stuff.
The factory was aware of the issues with this ground point and addressed it by suggesting the following:
Remove the nut holding the wire terminals to the stud. Verify that the stud is indeed tightened securely into the block. Scrape any and all paint from the stud’s mounting surface where the wires will attach. Must be clean, shiny and free of any oil, grease, or paint.
Inspect the wire terminals. Check to see that none of the terminals are crimped over wire insulation instead of bare wire. Be sure the crimps are tight. It wouldn’t hurt to re-crimp them just as a matter of course. Sand and polish the wire terminals until clean and shiny on both sides. Reinstall all the wires to the stud and tighten the nut down securely.
While you’re in that general area, locate the battery negative cable which is fastened to the engine block just forward of the dipstick stud. Remove the bolt, scrape the block to bare metal, clean and polish the cable terminal, and reattach securely.
Another area where the grounding system on Renix era Jeeps was lacking is the engine to chassis ground. There is a braided cable from the back of the cylinder head that also attaches to the driver’s side of the firewall. This cable is undersized for it’s intended use and subject to corrosion and poor connections at each end.
First off, remove the cable end from the firewall using a 15mm wrench or socket. Scrape the paint off down to bare metal and clean the wire terminal. Reattach securely.
Remove the other end of the cable from the rear of the head using a 3’4" socket. Clean all the oil, paint and crud from the stud. Clean the wire terminal of the cable and reattach securely.
A suggestion regarding the braided cable:
I prefer to add a #4 Gauge cable from the firewall to a bolt on the rear of the intake manifold, either to a heat shield bolt or fuel rail bolt. A cable about 18" long with a 3/8" lug on each end works great and you can get one at any parts store already made up. Napa has them as part number 781116.
A further improvement to the grounding system can be made using a #4 cable, about 10" long with 3/8" terminals at each end. Attach one end of this cable to the negative battery bolt and the other end under the closest 10mm headed bolt on the radiator support just forward of the battery. Napa part number 781115.
For those of us with Comanches, it’s very important to remove the driver’s side taillamp assembly to access the ground for the fuel pump. Remove the screw holding the black ground wire. Scrape the paint from the body and corrosion from the wire terminal. Reattach securely.
　
　
If you want to upgrade your grounds and battery cables in general, contact Jon at www.kelleyswip.com. He makes an incredible cable upgrade for a very reasonable price.
　
Revised 12-04-2012

I suggest unplugging EVERY electrical connection in the engine bay you can find, whether engine related or not, and spraying it out with a good electronics cleaner, visually inspecting the terminals making sure they haven’t retracted into the plastic holder, and then plugging it back together. There’s a critical 10-pin connector for the front lighting system located in front of the air cleaner and behind the left headlight assembly. Don’t miss that one. Also be sure that the connectors to the ballast resistor mounted near the air cleaner housing are clean and tight.
ALL of the relays should be removed, the terminals wire-brushed until shiny, and the receptacles sprayed out with contact cleaner. Then plug them back in. I do this on every Renix Jeep I purchase or work on for someone else.
Revised 07/23/2012

Click to expand...

Mine passed but the NOX was kind high.. I need to trace out what's causing that...

MaxxXJ said:

Mine passed but the NOX was kind high.. I need to trace out what's causing that...

Click to expand...

High NOx is caused by high combustion temps, check the colling system operating temps, the EGR valve, and solenoid system, check for a clogged injector, and run injector cleaner (add to the gas tank) and some Gumout through the intake to clean the carbon out of the engine.

Also check for a small crack or air leak on the intake by the head.

scottmcneal said:

Also check for a small crack or air leak on the intake by the head.

Click to expand...

Very good point, a vacuum leak into only 1 or 2 chambers (versus all) could make them run lean and hot causing the NOx, that is one I have overlooked!!! And 4.0s are notorious for loose manifold bolts!