'93 5sp H.O. - Still won't pass emissions, but some improvement....

Here's the link to my first post: http://www.naxja.org/forum/showthread.php?s=&threadid=13786

Ok, I replaced the O2 sensor, changed the oil, cleaned the K&N filter and replaced the spark plugs. It passed the HC and CO2 readings but were just a bit below the limits. It failed on the NOx readings. Here's the results from the second attempt:

CO2 3.6178 (Limit is 4.0000)
HC 21.9671 (Limit is 25.0000)
NOx 9.0997 (Limit is 9.0000)

Like I mentioned, this was my second trip back to the emissions center. The first time they ran it on the dyno today, the tester cancelled the test right at the end because the temp gauge showed 230. He said he didn't want to fry the engine -- I can respect that! I did have a problem with the fact that the big fan they put in front of the test vehicle (to move air into the radiator) was 6 feet away from the jeep. I also only heard 3 shifts when he ran it up to 60 mph so I was sure the RPM was way to high. I complained to the manager and he ran it through himself a second time and put the fan much closer. He also shifted appropriately to keep the RPM more realistic with my 4:56 gears. This kept the engine temp gauge at about 215-220. That's the temp my jeep usually runs. This second run is where the above results came from.

I did some research about NOx failures and most suggest checking the EGR operation. I'll be damned if I can find an EGR valve on my '93 H.O. engine - anyone know if it even has one?

Second, I figure that changing the thermostat would be another thing I could do to ensure that the engine temp is being managed correctly. (I have an electric aux. fan and it was running during the emissions test).

A friend suggested that maybe my "knock sensor" was bad and/or the timing wasn't advancing correctly. I have noticed that the engine does ping and clatter alot when trying to accelerate from 2nd gear to 3rd and so on. I thought this was just the 81 octane gas I run in it. Does my rig have a "knock sensor" and where would it be located? I know that the Renix (non H.O.) engines have one screwed into the block just above the oil pan. There's nothing there on mine.

Could there be something wrong with the distributor? Something to check inside it? I already cleaned the contacts on the rotor and cap.

Thanks again!
Troy

Does the 91-up even halve a knock sensor? I thought ChryCo deleted that when they deleted the Renix system...

Excessive NOx is caused by high combustion chamber temperatures. High chamber temperatures are typically caused by either inefficient cooling (you've not done a system flush recently, have you? You'd be surprised how little crud it takes in there to really foul things up...) or possibly by poor scavenging - but that should have been fixed by your cleaning your air filter, assuming everything else is fine.

Is the catalytic converter original? If your CO and HC are up slightly, that could be suspected of being slightly plugged, which would also effect exhaust evacuation by creating backpressure and therefore keeping hot exhaust gas in the system (more than would be passed back in by the EGR valve, which you don't have anyhow.) Something to think about... Since the 4.0 is generally a very clean-running engine (my 88 and 89 do very well - I just had to get them both smogged last month) I'd look at the "support systems" for the possible failures. The results from my last few smogs have been quite impressive, even if the techs have not.

5-90

The HO engine does not have a knock sensor and it does not have an EGR valve.

You are SOOO close to passing, I'd be tempted to throw in a couple of cans of alcohol to convert the gas into ethanol and see if that'll clean it up enough to pass.

Just don't use rubbing alcohol like my friends wife did. It's mostly water.

5-90,

Thanks for the reply! I'm thinking the next plan of attack is to replace the t-stat and check the flow through the system. I'm fairly certain that the radiator is in good shape as it's only a few years old.

I'm also thinking you may be correct about the cat converter. It is original equipment. I found some information on the web about removing the O2 sensor and using the port to connect a vacuum/pressure gauge. The info says that this is the best way to see if there's any blockage of the exhaust. It says that at idle, the gauge should read less than 1.5 psi and less than 3.0 psi at 3,000 rpm. Anyone else done this kind of test?

Does anybody know why my engine would have this ping/clatter problem under load in the lower gears? Is it simply the octane I'm using or could there still be some sort of problem with the ignition controls?

Thanks again!
Troy

Usually hi NOx levels are due to a lean burn condition and hi combustion chamber temperatures which can cause pre-detonation (enging pinging). You might consider checking the MAP sensor for proper operation and having the fuel injectors cleaned to ensure proper spray patterns and flow rates. Proper operating fuel injectors and MAP sensor should remove the lean condition and alleviate the hi combustion chamber temperatures.

With it being that close I would suggest going to a auto parts store and getting some of the emissions pass stuff. It is like five dollars a can I think. Ihave used it maybe five times and it has gotten me by in several different vehicles. Not a long term fix but may get you through emissions until you get it fixed permanately