Fuman Shoo

Once again, I failed the NOx portion of the test (1400). Since my vehicle is a test only, the mechanic can't instruct me as to what the problem is and offer to correct it.

Thus far, I have changed the spark plugs and wires, changed the catalytic converter, seafoamed the hell out of the engine and in the fuel tank to clean the injectors, and did the obligatory oil and air filter change. Yet, the failed tests. Also, I should note that I have had no error codes and no problems with the 02 sensors, (especially since the jeep has been running lean).

The technician did mention that the engine was running hot (overheating). Also, I have noticed that I am running a tad low on coolant after having added coolant a couple of weeks ago, but no puddles on the ground.

My question is this, can my NOx problem be as simple as flushing my engine coolant and adding a coolant leak stop product to stop any (if at all) leaks? Should I inverst in a new thermostat even though my temp gague hovers at dead center line at peak engine operation? I've noticed that the gague WOULD tip just past center if I am stopped after getting up to optimum temp, but would go back down to centerline once I begin moving again.

Outside of this smog issue (and that annoying knocking coming from the left front end of the suspension), this Jeep has been running exceptionally well.

If a new thermometer is recommended, is this an easy fix; meaning, can I go out and do this quickly? Also, what are known issues with changing thermostats?

Any advice would be tremendously appreciated.


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DeMarcus D.
1993 Jeep Grand Cherokee...$700
134,000 miles and counting...Priceless
Living under California's arcane smog regulations...

solderjunkie

NOx is reduced typically by EGR or lower exhaust temps.

If your ZJ is a 5.2 liter, fix the non-functioning EGR.

If it is a 4.0, fix the lean-running problem to get the exhaust cooler (lower cylinder temps = lower exhaust temps).

RRAM

I know not about a 4.0l but I have never ran into a thermostat that was hard to change. I would not recommend using a stop leak in your coolant system. Find and fix the problem. Hopefully you do not have a head gasket problem and having water going through the engine.

KT01

Same problem, and no idea how to cure it. I have a '93 Cherokee, a 1 week old CA cat installed and NOx is 1351 at 2150rpm... emissions otherwise measure outstanding! The NOx with my old cat were 900 at 2150rpm, and 700 at 1500rpm (both about 2x the limit). At 1500rpm the NOx measures 14 now, so the new cat is clearly working at low rpm. So what happens at higher rpm? Advice anyone?

Fuman Shoo

When's the last time you replaced your O2 sensor? Considering you have a 1993, if you haven't replaced it since you bought it new or if bought used, don't know when the original owner replaced it, just go out and buy a new one. The 1993 4.0L GC only has one O2 sensor to change. Mine cost $52. If you have an Autozone parts store near you, you can rent the O2 sensor wrench/tool for free. It's only a $15 deposit that you get back when you return it. Otherwise, it's about $10-$15 to buy it.

The only thing I did to get my NOx to pass was to have the "on-engine" fuel injector/fuel system cleaning at Jiffy Lube. The benefit of the Jiffy Lube treatment is that they put a cleaner in your gas tank while simultaneously introducing a cleaner into the engine (that they claim is better/safer than Seafoam: especially on your cat). If you do that treatment, it will cost you ~$60. Then throw some 91 octane gas in the tank and drive it hard on the freeway for a few miles.

Also, make sure you have driven the Jeep hard just before you take it to the smog testing shop.

can'tstopjeepen

Don't put stop leak in a 4.0!!! I flushed the system on my old 91 xj and so much of that stuff came out of the motor it was gross. It plugged up everything on it.

KT01

Thanks Fuman! I'll check out the O2 sensor. I added the "guaranteed to pass"stuff into my tank, but might go for the Jiffy Lube deal to make double sure. Hope I'll have good news soon.

Fuman Shoo

That "guaranteed to pass" stuff didn't work for jack! You're better off just going with the Jiffy Ube service since they put an additive into your tank as well.