Lou Posted February 18, 2021 Share Posted February 18, 2021 The great state of California and I once again disagree on how well my engine is running. Its an 82 CJ7 258ci with about 2500 miles since complete rebuild. Hesco MOPAR MPI kit added. And to me it seems to run great. But I failed smog due to high NO. All other tests (including HC and CO) passed. The strange thing is, the last time (two years ago) I passed no problem. Since then I have not made any changes. I did check faults and it was showing a code for the O2 sensor. Since I read that it is a common cause I thought I had my solution. Unfortunately when I went for a re-check it still did not pass. The smog guy asked if I drove the Jeep after replacing the O2 sensor to let the computer adjust operating parameters. But I had only driven it a few mile to the shop for a re-check. How far do I typically need to drive to get things to reset? The O2 sensor fault has not returned. Is there a way to know if the problem is gone without spending the money on another check? Lou Quote Link to comment Share on other sites More sharing options...
Administrators Moses Ludel Posted February 18, 2021 Administrators Share Posted February 18, 2021 Lou...Our youngest son had a similar issue with an XJ Cherokee smog test. The vehicle had passed recently for the previous owner. The Jeep parked for months, and the battery voltage got low. Low enough that the codes reset to default. He drove straight to the smog station and had your experience. The shop told him to drive for a few hours and come back. I did some research, and others say to wait/drive a week after a battery change-out before undergoing a smog test. I would drive your CJ for a few days and make sure the battery and cabling are in good shape with secure connections. High NOx is generally too much heat in the combustion process. Your EFI conversion does not require an EGR system, which directly targets NOx by lowering the combustion temperatures. If high NOx persists, I would look for an exhaust restriction, a defective catalytic converter, ignition advance issues or other traditional causes of high NOx. The 4.0L six that was your EFI kit's prototype did not need EGR to pass emissions. The 4.0L cylinder head, however, has improved combustion chambers that resist heat, knock and NOx formation. The 4.2L head does not, part of the reason for the kit's 91-octane fuel recommendation to prevent knock/ping. (You might try 91-92 octane fuel when you attempt your smog test.) I'm not suggesting you do the 4.0L cylinder head conversion, although many have done so. Try to pass emissions as is. If you suspect a defective catalytic converter or have a low-restriction cat, that could be the NOx issue. The kit is 50-State legal and others pass California emissions with a stone stock 4.2L and your EFI conversion. The catalytic converter is essential for this EFI system to meet smog. Let us know what develops around your smog test... Moses Quote Link to comment Share on other sites More sharing options...
Lou Posted February 19, 2021 Author Share Posted February 19, 2021 Moses, thanks. Interesting suggestion regarding the battery. It has been in the Jeep for quite some time, but I try to keep a tender on it when it sits for a while. On a side note, I recently had a simlar situation with y motorcycle. I accidentally stalled it while getting ready to head out ion a ride. Then it wouldn't start and I had a bunch of fault codes. Though I feared bigger problems, it turned out to be a weak battery. I had a code for a 5 volt sensor. Not enough voltage to that and it inhibits starting and a chain reaction of other DTC's. I'll do a load test on my Jeep's battery and see what shape its in. If I remove the battery for a load test and re-install or replace it, will I need to drive for a week before I smog? Lou Quote Link to comment Share on other sites More sharing options...
Administrators Moses Ludel Posted February 19, 2021 Administrators Share Posted February 19, 2021 Yes, Lou...Simply disconnecting the battery for a few minutes requires the PCM to start fresh. All stored trouble codes disappear. Time for the fuel trim and other functions to reset and stabilize...Touchy. Moses Quote Link to comment Share on other sites More sharing options...
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