88 cherokee wont pass smog,

I took my jeep down last month and had it smog only to find out that it was already classified as a gross polluter. The result cam out like this

HC (PPM CO(%) NO(PPM)
Max GP MEAS Max GP MEAS Max GP MEAS
M1: 15mph 124 311 122 .75 2.05 .21 714 1807 2821
M2: 25mph 104 261 79 .95 2.25 .12 616 1607 2442

After the test I ended up replacing the motor because I was going to put a newer one in it anyways. So after I put a new block in and reused all the old parts and hoses and such my test came out to be almost the same except the

NO (PPM) where a little bit lower around 2000 and 2100, so it droped somewhat. Does anyone know what the prob could be based on the numbers in my test?

hows ur cat? u know cali is damn strict! stuff some 000 steel wool WAY up the tail pipe!! (act as a filter and put low octane fuel in the tank) never done it myself but many of peeps have told me it works!! ANYONE??

replace your cat converter and o2 sensor. looking at your numbers looks like the cat is not working. also replace the o2 becasue they become tired and lazy and will take out a cat by running it too rich.

the 02 sensor is new but i was tod that my cat was working fine. the guy at the auto shop showed me how he checked it with a heat meter and said that the cat was burning all the HC inside but im not sure. is there anything else that could cause my jeep to run rich?

look at the o2 content on the smog report. should be around 14 %. if it is low signs of a dead cat. a temp gun maybe showing the temp of what is coming out of the engine and not the cat

check for exhaust leaks, i had one a while ago, just a tiny hole can create a vacuum and draw air into the exhaust and screw with the sensor shoved us the tailpipe. also the forwardmost (for you the only) O2 sensor is notorious on xjs for failing or just not working right. good luck, gotta love the crap California throws at your cherokee.

Not that i condone this .. but it was easily found on google .. i dont have first hand experience with this but .. from what i hear .. it works ..
Be warned, you must get to a gas station and fill up in full FAST after this .. it WILL grenade your fuel system if you don't be careful ..



The smog test pass method :

What you will need:

-One gallon of Denatured Alcohol. DO NOT get a methyl/methanol based one it will eat away at your seals and or gaskets, get a ethyl/ethanol based one, I bought a gallon at Home depot in the paint section for about 14bucks.

-A gas container filled with gas (this is not required but its comes in handy after the test)

STEP ONE : Drive around for about 30mins or more to fully warm up your engine and expel all of the bad start up gases from your system. Run your gas tank down as low as you can safely do without getting stranded and get to the SMOG station.

STEP TWO: Once there DO NOT turn off your engine. I had a little more then two gallons of regular in the tank so ended up a 25-33% content of alcohol. Its been tried at many varying percentages, any where in between 25% to 100% I was aiming for 50% but I still passed. Its has been observed that the engine stumbles sometimes but mine seemed to have no change at all. I also poured in the alcohol with the engine running. You may want to drive it around the block to get it mixed up inside the tank.

STEP THREE : Pray that it passes.

STEP FOUR : When done with the test use that extra tank of gas to fill her up a bit and get to the nearest gas station ASAP and fill the tank full.

Looks like your HC and CO are passing, only failing on the the Nox (Gross Polluter).

NOx is generally controlled by your EGR valve. Check all the vacuum hoses, check that the valve actually moves under vacuum, and check the EGR solenoid function.

(Non-Renix 4.0's did away with the EGR).

Since I live in CA and I have 2 RENIX Jeeps here are the steps I take every 2 years when my number comes up.

1. Check and replace ALL vacuum lines that even look sketchy. Bulk vac line is cheap...you can even use sprinkler tubing, cheaper still.

2. Check the grommets on top ot the valve cover. A split in either one can ruin performance AND emissions. My rear grommet looked fine on the outside, but when I took it out, I found this:



Also, be sure that the hoses to/from your charcoal cannister are in good shape. These are often neglected and DO affect emissions.

3. Unless O2 sensor you've replaced the O2 sensor in the last 25-30,000 miles, do it. Luckily for us there is only 1 sensor.

4. Change the oil, plugs, and all the other tune-up hardware. Test the EGR function as said above.

5. Buy a BRAND NEW gas cap. Fill it up with fresh gas, go for a half hour drive to get everything blown out before you show up.

6....oh and wash that thing...it's Gross. LOL

I've heard stories of acetone (or a similar solvent) helping you guys stuck in Commiefornia get past the smog nazis.

*shivers at the thought of smog nazis contaminating the rest of the USA.

Had a similar problem with smog on a TBI Dodge 318. NOx was 2500PPM, limit was 1500PPM. Got her good and hot, threw in 2 bottles of Guaranteed to Pass, and made sure she dropped into 3rd gear on the chassis dyno. NOx dropped to 1410PPM and life is good

jeeptec said:

look at the o2 content on the smog report. should be around 14 %. if it is low signs of a dead cat. a temp gun maybe showing the temp of what is coming out of the engine and not the cat

Click to expand...

That makes no sense, you have it backwards. The Cat will lower the O2 concentration if it is working.

Follow the instructions here, and see if the system is running rich:

http://www.naxja.org/forum/showthread.php?t=1012701&highlight=oxygen+sensor+test

If there is no power to the O2 sensor heater it will run rich.

Sounds like your is running lean, with an EGR problem, but you have may other issues.

It would be helpful if we knew why you replaced the engine, what engine did you replace it with (New, used...?), and what other parts did you replace, and not replace, like a complete list!!!!

I replaced the engine cause the last one had 265k on her. So I pulled the motor from a 91 XJ and just used the block and kept all the rest of the parts from my old motor except the water pump,thermastat. Other then those 2 parts I swapped over everything else from my old motor. All the connections where the same so mad it a lot easier for me to hook up. The jeep runs great. It does like to run cold though. Not sure if that would make any difference. After I drive it and then let it idle the temp gauge will get up to around 160 degrees and maybe even 190 or so if i let it sit for awhile.

Has it ever passed smog since you replaced the engine?

The 91 is a HO engine, and there are differences between it and the Renix engines. The HO did not use and EGR! Did you reuse the Renix head?

master turner said:

check for exhaust leaks, i had one a while ago, just a tiny hole can create a vacuum and draw air into the exhaust and screw with the sensor shoved us the tailpipe. also the forwardmost (for you the only) O2 sensor is notorious on xjs for failing or just not working right. good luck, gotta love the crap California throws at your cherokee.

Click to expand...

so i have 1994 jeep cherokee 2.5 liter
smog people gave me a paper to test what was wrong they said the ppm is at 2024 ppm and i need it 500 ppm. they said check for vaccum and exhuast leaks. cant find any. next thing to check on my list iis the exhuast manifold. were would common vaccum leaaks or exhuast leaks be.
Has new cat, air filter, they said my oxygen sensor was okay. I have checked hoses and stuff for cuts and cracks, replaced a few to be sure, bought new plugs. have taken it in about six times. Cant take it no were else because they wont smog it, i have to go back to the same one.

Every two years right before smog:
sea foam intake, gas tank, and crank case.
then change plugs and oil, air filter, cap and rotor, o2 sensor, and check for exhaust leaks.
drive around on 91 octane and acetone for like a few days.
day before smog, dump 2 pints of acetone in the tank.
day of smog, drive it for 30 minutes, top off tank with 91 and turn my efan on to make sure it doesnt over heat....
when I first got the jeep years ago it would barely pass smog.
these days it passes with flying colors- and its had alot more abuse, deeper gears, bigger tires, etc etc etc . almost no emissions when I go this route. plus no matter what the jeep gets a nice fat tuneup every 2 years max.

one thing ive noticed too, not sure if it helps a ton, bigger tires just for the day to keep the RPMS down at the 15 mph and 25 mph test.


if you havent done it in 5 years, consider slapping a exhaust/intake manifold gasket on with some copper RTV on both sides. while its off, check the manifold for cracks. If you have exhaust leaks it will make your chances of passing much lower since the o2 sensor will read out of whack even if new.

Take the golf tee out of the vacuum line to your EGR