Failed emissions test

Our 88 failed too and they figured the EGR solenoid had failed and changed it. Plugs, cap and wires got changed too. Same deal another fail, so by this time I had enough money in it to get a 2 year conditional as it was the first test when the computer wouldn't give the conditional!

My 88 4.0 was under recall for a bad O2 sensor. Free new O2 sensor and it passed the test. Got my money back from the other tests too, because I took it to a Jeep dealer for the test just to avoid silly things and they were too lazy to check.

It would be worth calling Chrysler and asking about recalls using your VIN.

My recall doesn't show up in the on line databases.

Carbon build up can also make it run hot, the carbon gets cherry and spark knock can happen. Any knocking under load?

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's

Christian Fry wrote:

As usual, Romain has nailed this one. NOx is caused by high combustion temperatures (not necessarily high coolant temp). EGR is the primary means of controlling it, so that has to work, if equipped. Timing has to be on the mark or even a little retarded. Any audible pinging is a no-no.

Jerry

The hydrocarbons were well placed, I have a bit of room to move there...

As for warming the car up, from what I understand it's to get the emission controls up and running - it can take up to 90 seconds on cars to have the computer in closed loop mode. After that, a few more unburned hydrocarbons and I'm happy, so long as I get the paper!

Here is the complete results:

40 km/h Limit Readign HC ppm 104 39 CO % 0.58 0.36 NO ppm 1126 1984

idle HC ppm 200 33 CO % 1 0.22

Hope that clears up any issues regarding other control systems. Seems everything is well in check except for that. Mechanic advised me it might even be plugs that are too hot, hence the reason for going with a cold engine...

Regards, Chris

I did the test again this morning cold, and the NO went down to about 1500. Apparently if it was -40 or so I would have passed...

Since the cold seems to have left us, my only other choice is to inspect/replace the suspect catalytic converter. Not bad, think I can get away with $100 or so for that one...

Chris

hydrocarbons

Data Retrieved:

NOx (Nitrous Oxides) is a chemical created when an engine's combustion chamber temperatures reach over 2500F. The combination of nitrogen and oxygen under these high temperatures create NOx. Below are four of the possibly conditions, that could cause a vehicle to emit an excessive amount of NOx. Cause #3 is the most common, however in cases were a vehicle has failed for both high NOx and high HC, pay close attention to problem #4 also. (Note: You should always insure the EGR is working fine before replacing the CAT.) (Rare)1.Bad cooling : If an engine's cooling fans are not turning on at the right temperature this could cause the engine to overheat and emit NOx. If your engine doesn't have an over-heating problem you can omit this problem. (Rare)2. The second reason for a NOx failure could be high engine compression. High compression in an engine's combustion chambers develop over time due to carbon build-up. This high compression causes high temperatures, which result in NOx emissions. Keep in mind though, this problem usually is seen in vehicles with over 200,000 miles. (Most Common)3. The third reason for your NOx failure may be due to a malfunctioning EGR valve and/or plugged up EGR ports and passages. EGR stands for exhaust gas recirculation. And that is exactly what this component does. The EGR system recirculates burned up exhaust gases back into the combustion chambers. Since these recycled exhaust gases have already been in the combustion chambers once, they have burned up most of their fuels, means there is now much less real fuel in the chambers to ignite. This keeps the chamber temperatures down and thus reduces NOx emissions. The EGR valve should be inspected to insure its proper operation. A working valve should be able to open its passage using manifold vacuum. Manifold vacuum is created during the engine's intake cycle. The high demand for air during this cycle creates a vacuum within the engine's intake manifold. This vacuum is then used to control several important functions within the vehicle, including controlling the EGR valve. Some vehicles even rely on this vacuum to control their heating and air-conditioning components. The EGR system is prone to collecting carbon build-up. Some vehicle manufacturers recommend cleaning this component an a regular basis.

(Common)4. And, finally, the fourth reason for a NOx failure is a bad Catalytic Converter. The Catalytic Converter, commonly referred to as the CAT is a component designed to continue the combustion process within itself and emit a more thoroughly burned and less harmful emission containing exhaust. It is normally placed between your engine's exhaust port and your car's muffler. It allows the engine exhaust to pass through while it reduces all emissions. A good CAT should dramatically reduce HC, CO and NOx. The CAT is a catalyst, it plays a very small part on how well your engine runs. It only begins working after the exhaust has exited the engines combustion chambers. And like many catalyst it is not designed to last forever. From time to time it will need replacement. How long your vehicle's CAT will last depends on how completely your engine burns the fuel before presenting it the to the CAT and also on the quality of the CAT. Factory CATs should normally last 5 to 10 years. Aftermarket CATs should work for at least half that (for the cost difference I would normally go with the aftermarket CAT). We see this failure more often in vehicles which have produced high emission numbers in more then one category. Note: When replacing your factory CAT it is very important to use a OEM factory specification replacement part. Not all CATs are alike. They are all built to suit their own vehicle's specific needs.

The most accurate way to find out if your vehicle CAT is working efficiently is by using an exhaust gas analyzer. Unfortunately this tool is fairly expensive and not designed for home use. You must visit a local smog station and have the smog technician inspect the CAT via the shop's gas analyzer.

Obvious symptoms of a bad CAT however could be any of the following:

a. major loss of power over 15-25 mph (CAT is plugged up and restricting exhaust flow)

b. very strong exhaust smell on a vehicle that runs great(engine running efficiently, but CAT not completing the burning process)

c. Loud rattle being heard from inside the CAT (CAT substrate broken up).

In this first insure the proper operation of the EGR valve and then move on to the CAT system. Testing the EGR and CAT systems require the use of special expert tools. A certified station will be able to accurately diagnose your vehicle's emissions failure and and help eliminate the chance of wasting money replacing parts or components which may have not needed replacement. Specially in the case of replacing some of the more expensive emission components.

I've found a website on line called

They havea lot of information about smog checks and live smog support.

"Christian Fry" wrote in message news:...

Data Retrieved:

An Oxygen Sensor can cure a NOx failure if the failure is due to a Lean Fuel Mixture condition. Lean fuel mixtures cause your engine to run extra hot. Heat is what causes NOx to be formed.

Fuel distribution to your engine's combustion chambers is controlled by your vehicle's ECU(Engine Control Unit) and fuel injectors. In order for your engine to pass a smog inspection, fuel delivery must be preciously controlled to produce the least emissions. If the injectors do not present enough fuel to the combustion chambers, this would cause low CO emissions and high NOx emissions (NOx emissions are created when the combustion chamber temps reach above 2500F). In a situation where the injectors present too much fuel, this would causes high CO emissions and low NOx emissions (Excessive fuel keeps the chamber temperatures down by cooling the chamber). In order for the ECU to estimate the right amount of fuel to distribute, it needs to know how much fuel is currently in the system. This way it can always maintain a proper ratio and keep emission levels at their lowest. Are you with me so far? OK. The component responsible for letting the computer know how much fuel is in the exhaust system at this moment, is the Oxygen Sensor. The Oxygen Sensor sends an electrical signal to the ECU, letting the computer determine exactly how much fuel it should continue to deliver to the combustion chambers. If for any reason the 02 sensor (oxygen sensor) does not send accurate information to the computer or it is "lazy" in sending the correct signals, the fuel delivery program can be altered. The computer may then present either too much or not enough fuel to the combustion chambers and therefore cause an emission failure.

It may be possible your engine's oxygen sensor is this not sending the proper signal to the ECU, causing the ECU to send the combustion chambers less fuel then is necessary to keep the chamber temperature down, resulting in High NOx and Low CO.

Keep in mind with a computer controlled engine such as this, there are several other components which also play a role in determining fuel ratio. Along with the Oxygen Sensor, several components such as the, TPS (Throttle Position Sensor), ECT (Engine Coolant Temperature Sensor) and the MAP (Manifold Absolute Pressure Sensor) sensors also send vital engine information to the computer which is used to determine proper air to fuel ratio. If any one of these components are defective they can alter the fuel delivery program. A smog service station would be able to diagnose each component and report it's condition.

You can find more information on NOx from a website I found recently called

They have live e-mail with a smogtech.

Alec Vega

Mike Romain wrote in message news:...