Getting through the emissions test

Wow, that is a good check list, thanks. I can tick most of the suggestions as done. ✔️
I have just changed the sensor for the recommended NTK one. There is no downstream sensor, that's where the mystery thermocouple lives which I broke today trying to get out. Since no one has ever been able to tell me what it's there for, I might just be about to find out.

The engine should be free from any carbon build up since most of the time it runs on LPG (propane) which burns the carbon off.
I'm not sure about a stuck injector as I don't know what the symptoms would be, but it might explain why it running rich. Suggestions welcome on that one.
Same applies to 'open loop' what are the signs to look for? The engine runs as sweet as a nut right through the range.

Having just broken the EGT I shall have to wait to find out what does or does not happen on the next trip out. I'll have to be careful as the car can't legally be on the road with a failed test. Here in Spain they just confiscate the car, no questions asked.

I did a run of about 10 miles today down the back roads and could not feel the slightest bit of difference from what it was like with an unbroken thermocouple. Now I'm wondering if has ever worked and just what it does. The mystery just gets deeper.

I'm going to change the cat and see what that does.

Might just check the fuel pressure as well.
Open loop is between just starting and meeting a number of sensor specs. One is temp. The other is O2temp and readings. Part is time and possibly any air temp?map? while these are not met it runs richer and off of a preprogrammed table. After closed loop it used the sensor data.

If your TPS is bad it may think it is getting more air so it adds more fuel.

Exhaust leak outside air comes in reading high o2 and adds more fuel.

Injector trouble shooting. Mechanics stethoscope to the back of the injector you should hear it clicking open and closed. No click might be stuck open. You might then pull that plug and see if it is wet or much cleaner than others.

Never look down on anyone unless you are helping them up - Jesse Jackson
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I've got it booked in to change the cat. I have decided I'm too old to be grovelling around on a hard floor.
Between now and then I'll change out the thermocouple for a new one I got a while back, but I have no idea if it's the right one. I just got the most common type in the hope it works. I'll have to take out the instrument panel as the little black box it connects to is up above the steering column.

The installation of this looks like it was an afterthought. The braided cable is held to the chassis with P-clips pop riveted on and the corrugated conduit is fixed with cable ties which is how it would have left the factory for Japan. My other Jeep is identical.

I will try to find if the emissions regs for Japan require this thermocouple to be fitted. My current thoughts are that it might be something to do with the changeover from open to closed loop.
How can you check if that changeover is actually happening?

Typically hook up obd and it comes up on screen open or closed loop.

Never look down on anyone unless you are helping them up - Jesse Jackson
Sadly my Jeep does not have an OBD socket. It relies on you counting flashes on the check engine light. It's pre OBD 1
I have accessed the box where the thermocouple connects way up on the bracket for the brake pedal.

It is a Stanley DVO75-41070. I can't find any info on the net. That is literally all I know. I still don't have a clue what it does.
I am going to change the thermocouple for one I have got whilst all the dash is ripped out.

The Jap emissions regulations are pretty much the same as ours. No mention of thermocouples.

Tried upload a pic and it still won't let me it just goes back to the log in page every time.

If some kind soul has 10 minutes spare can you see if you can find anything with that number? Thanks
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Wow, everything on the net comes back to one auction for that part in japan. I can find it in japanese and russian but no one knows what the part does, except it seems to be removeable with no issues.
My experience so far seems to indicate that the car operates quite well since I broke the thermocouple.
I also managed to find the one on a Jap auction site, Pace Auctions, but access has been restricted since 2022. It was only a picture though.

I am chasing this in the hope it might be linked to emissions and it might control the change from open to closed loop. It seems odd that you say it can be removed with no problems. Why did they fit it if it can be removed? Curiouser and curiouser as someone once said. I think it was either Alice or the White Rabbit.

Today I am going to continue to change the t'couple simply on the basis that I have a replacement. There might be a problem in joining the new cable to the plug/old cable that goes into the black box as joints in t'couple cables cause problem by creating another secondary measuring point due to the dissimilar metals. I used 'couples many years ago at work and remember that it could be a problem as it made the readings inaccurate.

Can superj please give me a link to the guy with the yj and the pictures? Thanks for the continuing help.
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Here is the plan for the new cat and 'couple..I have welded an M18 boss into the outlet end of the new cat , then there is a reducing bush from M18 to 1/4NPT, then a nut and olive fitting for the K type thermocouple.
I have now got the braided cable through to the inside of the car using the old conduits.. Next is to attach some blade connectors for the little black box.
Sadly after all this I'll never know if it works because no one knows what it's supposed to do. Such is life.


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I've followed the link above and from what I can make out is that even the Wrangler fraternity were struggling with this thing.

Mine definitely has no connection to any speaker or buzzer, I don't even have the little speaker. The chime module in mine,which is velcro'd to the fuse box goes off for key in, lights on etc.

Another mystery is why the same little black Stanley box might have two different purposes on different models. It has certainly got something to do with Japanese exports though.

In the pic showing the beeper there is a braided cable. This looks exactly the same as the wire from the thermocouple in the back end of the cat.
so I would suggest that the original poster traces it out and see if it links the t'couple to the Stanley box. If so, it is the same set-up as my XJ.
It somehow looks like an afterthought by the way it is installed.

It still remains a mystery what it does. I have made contact with Stanley and await their reply, but I'm not holding my breath because I don't relate Stanley to little black electronic modules.

me either.

Not much progress today but I have discovered that Stanley Electrical Co. Ltd is nothing to do with Stanley tools apart from being what they call a licensed partner.

Stanley Electrical started 100 years ago in Japan and seems to be a huge worldwide company, although I have never come across them. They specialise in lighting and lighting units for cars. Their website is worth a visit.

They have a place in Ohio where I think Jeeps are made, so I have emailed them for any info they might have. It seems sort of logical, to my mind anyway, that they might have supplied this thing in the first place.

More to follow.
Toledo is a few hours north of me. Not that it helps you find the part. If I recall it is just off I75

Another thought is to check fuel pressure. Bad regulator allows high pressure and will force more gas into the cylinder causing rich condition.
Never look down on anyone unless you are helping them up - Jesse Jackson
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Well, that's that one eliminated. I have checked the fuel pressure as per the manual and the readings are just about what the book says +/- 1 psi.
I listened to the injectors and they all sounded about the same.

I tried to time any tickover speed changes that might be caused by the change from open to closed loop, when starting from cold, but I did not notice anything, it didn't suddenly drop to 700RPM from say, 900 for example.

I am waiting to see if Stanley Electrical reply to my request for info on the mystery box. Some firms are very bad/slow at replying.
When we first got email at work (half a lifetime ago) I was taught that it was very bad form not to reply within 24hrs. I still stick to that today.

It's booked into a local garage to get the cat changed. The first time it's been into a garage since we bought it in 2005. As mentioned before I'm to old to be grovelling on the floor. One day I won't be able to get back up!!

I feel the same about emails but not alot of people seem to care about other people's time anymore.
Finally, I think I see light at the end of the tunnel. I have got the new cat and thermocouple fitted and had a reply from Stanley Electric, the outcome of which is that I need not have bothered with the EGT thermocouple. It turns out that it was only used to turn on a warning light if the cat got too hot. That requirement is no longer there and was just a requirement in Japan at the time. So there was no need to replace it.

The cat was well past replacement. It seemed that every internal component was loose and was sitting in the bottom of the casing. I knew it rattled a bit but had no idea that it was that bad, so it probably was not even capable of working, hence the failed tests.

Next job is to book it in again for another retest. Hopefully the end of this drawn out saga.

I have tried to upload another picture but having selected one the system will not upload it. Why? I have tried all sorts.
I am glad everything has gotten straightened out and everyone kearned something on an odd part.

Hopefully it passes with flying colors

Im glad you figured this out and could put it behind you. Yes a lot was learned and next issue you have a better idea on how it works so resolving it will be easier.

Study hard for your test!!! :-/

Wish i could tell why your pic doesn?t load? Are you on the web page or an app? I-phone or android?

Never look down on anyone unless you are helping them up - Jesse Jackson