1988 Renix CA Smog Fail

Hey Guys, This is my first post.

I recently bought a 1988 Cherokee Pioneer with 190k. Auto Trans, 4x4, runs great......but doesn't pass smog here in California.

All levels are over their limits but the CO's are through the roof meaning its running really rich. Took it in for a diagnostic, and then got a second opinion and they both said egr, and cat had to be replaced. The second place said thought the injectors were leaking in 5 cylinders but i dont know if i trust them. The PO changed them 2 years ago.

Other things i could note is that the temperature sensor isnt rising above the first tick mark after 100 (but isnt overheating).

As for the EGR, i recall the tech saying when playing with the vacuum, the valve was closing but not opening (or maybe it was the other way around).

2nd tech i took it to said he didnt find anything weird about the electrical systems. I also cleaned the c101 connector as well as the stud ground by the dipstick tube just to be safe.



Im wondering if the cat should take care of the high CO levels enough to let me pass. Then i can register the jeep and figure out the rest.

Anything i can troubleshoot at home? My mechanical skill set is about a 2....i can change my own oil, differential fluids, air filters, pcv valve (on other cars), sparkplugs, radiator drain/refills, valve cover gaskets, distributer caps and rotors/wires, etc.

Things that will cause rich mixture:

O2 sensor
Coolant Temp Sensor (the one under the manifold on the engine block)
Vacuum leaks

Now, since you're tagged as a "gross polluter" you need to go to a Gold shield smog station. So spending some time and money to refresh everything is even more important. Your Jeep will run better too and you'll likely see mileage increase.

The O2 sensor for Renix models is relatively cheap...$50...and will usually be all you need.
Also, make sure all your drivers side vacuum lines are in good shape, with no cracks or breaks in CCV grommets and no duct tape holding things together.
The coolant temperature is monitored by 3 devices.
One is a SENDER on the back of the drivers side head...it is for the gauge, and only the gauge.
One is a SWITCH, on the radiator to control the e-fan through the e-fan relay...that's it.
One is a SENSOR, located under the exhaust manifold on the block. With smogging, the only important one is the SENSOR as it tells the computer to adjust the A/F ratio.

So with tight and right vacuum connections, a shiny new O2 sensor, a new gas cap, and a working coolant temp sensor you should be fine. Also, take that bad boy out on a nice long hot drive before you pull it in to the smog bay. One of the reasons I like my Renix Jeeps...no pesky CEL to tip off the state computer.

I'd check the exhaust manifold for cracks, and the exhaust system for leaks before the converter as well.

I bet you have a bad exhaust leak due to a cracked manifold, a bad cat, a bad o2, and some vacuum line issues.


you need to find all exhaust/intake/vaccum leaks. Might need a new exhaust manifold.
Do a full tune up too- plugs/cap/rotor/plug wires/oil change/fuel filter/air filter. Throw a ton of legitimate fuel injector cleaner in the tank too.

probably going to need to replace the o2 and cat.
Maybe CTS and TPS, clean all grounds.


Test/check the MAP as well.

jimmy310 said:

Other things i could note is that the temperature sensor isnt rising above the first tick mark after 100 (but isnt overheating).

Click to expand...

You need to confirm what your engine temp really is. This could be a sensor as noted by others. But, it could be a thermostat stuck open, preventing the engine from ever fully warming up. That could definitely make it run rich.

So, confirm the temperature of the motor when it's warmed up. Then replace either the temp sensor or the thermostat depending on what you find.

Try the guaranteed to pass fuel additive. My buddy did that on his renin xj after it failed, and then it passed.

Planetcat said:

Try the guaranteed to pass fuel additive. My buddy did that on his renin xj after it failed, and then it passed.

Click to expand...

I was going to mention that but I dont know jack about Cals smog check. In Oregon I can run through as many times as it takes to pass and only pay if it passes.

My 90' is borderline passing at times. I have found 2 bottles of the yellow bottle HEAT and good run on freeway to heat it up good and hot I pass with flying colors. Essentially alcohol is all that is in HEAT.

My Renix does have a reader port in the engine bay on passenger side by the bank of relays. Might find an old school mt2500 snap on scanner to read the values in real time only for temp sensor or 02 sensor.

mnoeltne said:

You need to confirm what your engine temp really is. This could be a sensor as noted by others. But, it could be a thermostat stuck open, preventing the engine from ever fully warming up. That could definitely make it run rich.

So, confirm the temperature of the motor when it's warmed up. Then replace either the temp sensor or the thermostat depending on what you find.

Click to expand...

I'll look into those things this weekend.

Im kinda in a bind and wanna go the new cat/denatured alcohol route just to get it registered....after that i plan on changing to an open cooling system anyways

I would put a new 02 sensor and some alcohol before trying a cat.

Paradise has the best answers so far IMHO.

I would like to add that you need to get the engine up to temp. Put a 195* thermostat in it also.

Last tune up with plugs, wires, cap and rotor?

ParadiseXJ said:

Things that will cause rich mixture:

O2 sensor
Coolant Temp Sensor (the one under the manifold on the engine block)
Vacuum leaks

Now, since you're tagged as a "gross polluter" you need to go to a Gold shield smog station. So spending some time and money to refresh everything is even more important. Your Jeep will run better too and you'll likely see mileage increase.

The O2 sensor for Renix models is relatively cheap...$50...and will usually be all you need.
Also, make sure all your drivers side vacuum lines are in good shape, with no cracks or breaks in CCV grommets and no duct tape holding things together.
The coolant temperature is monitored by 3 devices.
One is a SENDER on the back of the drivers side head...it is for the gauge, and only the gauge.
One is a SWITCH, on the radiator to control the e-fan through the e-fan relay...that's it.
One is a SENSOR, located under the exhaust manifold on the block. With smogging, the only important one is the SENSOR as it tells the computer to adjust the A/F ratio.

So with tight and right vacuum connections, a shiny new O2 sensor, a new gas cap, and a working coolant temp sensor you should be fine. Also, take that bad boy out on a nice long hot drive before you pull it in to the smog bay. One of the reasons I like my Renix Jeeps...no pesky CEL to tip off the state computer.

Click to expand...

Could any of you guys confirm or get me a part # and picture of the CTS. Anytime i search for it it shows me senders, and switches.

This is the one i see:

jimmy310 said:

Could any of you guys confirm or get me a part # and picture of the CTS. Anytime i search for it it shows me senders, and switches.

This is the one i see:

Click to expand...

You can test it......easily.

What about the questions Paradise asked?

cruiser54 said:

You can test it......easily.

What about the questions Paradise asked?

Click to expand...

I will be looking into those things first (o2 sensor, cts, etc.)

I saw the long o2 sensor sticking out of the exhaust manifold pipe. I thought i saw the coolant temperature sensor under there too, is that just above the oil pan about a foot away from the o2 sensor? I should also mention i saw a non insulated wire sticking out of the plastic wire loom. Perhaps this needs to be grounded and is the cause of all my problems?



Anyways the Spark plugs, wires, and distributer cap/rotor are about a year old.

I will probably be getting the coolant gauge sender as that may be faulty aswell. At the very least, they're cheap.

CTS is in the driver's side of the block about 1/3 way up. The one just above the pan is knock sensor.
I have the values to test the CTS but I never learned how to post photos on this forum.

Here

http://www.cherokeeforum.com/g/album/1725214

Looking at the picture the OP posted of the sensor it looks right. The one that goes in the radiator does not have a probe. It's flat on the radiator with no probe. The rad plug is also fatter. Unless you're not clear on the year ( and that one looks like it could go in the t-stat housing of a later 91+). The pigtail looks right.

Mine isn't shiny anymore. Expect that when you remove the one on the block, the coolant will start to drain, so don't do it hot and put a drain pan under it while you're swapping it out...and/or taking it with you to the store [suggested].



This is the switch on the radiator, wired to the relay on the inner fender.

I have been eyeballing this oem nos mopar cts sensor on ebay.


I take it the best o2 sensor for renix jeeps is the bosch one? (part # 12009)

That's a CTS.

I went through this about 3 years ago.

You can search for my thread, I went through quite a bit. Got ALOT of help from this forum and learned A LOT about my renix jeep.

I can't recall all the details. One bit of advise I would offer is to not just focus on passing, but on finding and fixing the real problems. You'll enjoy your jeep more and in 2 years you won't have to start all over.

Note from DJ
Standard Motor Products TX28 Temp Sender/Sensor goes in the block
88XJ Renix Block Coolant Temperature Sensor and
Intake Manifold Air Temperature Sensor
To Resistance Value
Fahrenheit—Celsius—Ohms
212*-----------100*--------------185
160*------------ 71* ------------ 450
100*------------ 38*-----------1,600
70*------------- 21*-----------3,400
40* -------------- 4*-----------7,500
20* --------------7* ---------13,500
0* -------------18*---------25,000
-40*------------ -40*-------100,700

Let’s see if I can explain some of the mystery of the temperature sensing devices involved with the Renix system.

There are a total of four different temperature sensing devices in all.

The first two are the coolant and manifold air temperature sensors. They are temperature to resistance converting sensors which are used by the ECU to control different operations related to engine management.

The coolant temper sensor was originally located in the side of the block below the intake and exhaust manifold and the MAT sensor should be located on the back side of the throttle body screwed into the intake manifold. These two sensors are covered by the table in the link in my prier post. Now if the previous owner moved the location of the coolant temp sensor to the thermostat housing they should have unplugged the original wiring from the original CTS position and extended the connections up to its new location and reconnected them there.

Temperature sensor number three will be located at the back corner of the head next to the firewall and the bake booster and the master cylinder. This sensor is used for transmitting information to the instrument cluster for either a gauge or hot engine light.

Number four is the one screwed into the engine side of the radiator on the driver side below the upper radiator hose.

Here is the information regarding this sensor.
NOTE: it is simply an ON-OFF switch which controlled the cooling fan relay.

Electric Cooling Fan
An electric cooling fan in addition to the engine drive fan is used on vehicles equipped with air conditioning or heavy cooling. Normal operation of the fan is controlled by the coolant temperature through a radiator mounted temperature switch. This switch is located on the lower left [or drivers] side of the radiator there is a bung hole (about an inch in diameter) this is the location of the thermal switch.

When the engine coolant temperature is below approximately 190*F or [88*C] the radiator switch is open and will not allow battery voltage to the cooling fan relay. The fan does not operate because the relay contacts are open. When the coolant temperature reaches approximately 190*F or [80*C] the radiator switch closes and allows battery voltage from the ignition switch to reach the relay coil and to ground, thus energizing the relay and allowing battery voltage to the cooling fan motor.

If A/C is selected regardless of coolant temperature, the ECU provides a ground for the A/C relay coil. With the A/C relay coil energized, the circuit is closed from battery voltage to the A/C clutch and to the engine cooling fan relay. Since the engine cooling fan relay has a permanent ground, the relay is energized and battery voltage is applied to the engine cooling fan motor from the ignition switch.

So if the previous owner was trying to use a resistance sensor to control the coolant fan relay, it will not work on the Renix system.

I hope this information helps, please keep us posted as to your progress or if you need more info.