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Emission help

azjeeps tj&xj

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Ok, I have a stock 88' XJ with a 4.0L w/auto. The motor is stock from what I know, but the head was rebuilt recently. Took it in for emissions today and it passed everything except the Carbon Monoxide measured in grams/mile. It read 63.34 and the standard (max) is 25.00. I am taking it as it is running rich. Now the 88' runs the best between the two (other is a 90'), but the 90' past with no problems this last year.

I just checked the TPS and it read 3.86V, where it should be 4.2V. Now the input voltage was only 4.68V and it should have been 5.0V. So I figure it was within the 82% that it should be for being closed. I adjusted it to 4.18V to get closer to the 4.2V, but not sure if that will fix the problem.

I looked at the purge system, and all the lines look good, and the idle is fine, and I don't hear any vacuum leaks.

Now I only get one retest for free, after that it is another $30 to test. I am also thinking about switching the MAP sensor with the one from my 90', even though I did test it and it tested good, but all that does is show if voltage is getting through. Another option I was thinking about was just taking the injectors, regulator, and rail from the 90' and putting it on the 88' and see if that helps.

So does anyone have any ideas on what to do to get this thing back on the road?
 
A commonly overlooked source of running rich is the air charge temperature sensor on the intake manifold. It can be checked with an ohmmeter.
 
azjeeps tj&xj said:
Ok, I have a stock 88' XJ with a 4.0L w/auto. The motor is stock from what I know, but the head was rebuilt recently. Took it in for emissions today and it passed everything except the Carbon Monoxide measured in grams/mile. It read 63.34 and the standard (max) is 25.00.

This is typically the sign of a shot catalytic converter - if all the other numbers are within spec, look to the cat first. How low were the other numbers in relation to their limits?

More:

I am taking it as it is running rich.

Not necessarily. It could be running at the correct mixture, but without the cat working it won't pass a tailpipe test. I've been through this on a few vehicles, and with one exception (again, more on that in a few) it's always been the catalytic converter in these cases.

I just checked the TPS and it read 3.86V, where it should be 4.2V. Now the input voltage was only 4.68V and it should have been 5.0V. So I figure it was within the 82% that it should be for being closed. I adjusted it to 4.18V to get closer to the 4.2V, but not sure if that will fix the problem.

Likely not, but it doesn't hurt to have it within spec either.

I looked at the purge system, and all the lines look good, and the idle is fine, and I don't hear any vacuum leaks.

A good sign.

Now I only get one retest for free, after that it is another $30 to test.

My experience is only with California, so this may not apply - but does Arizona offer a pre-test? Here you can get the vehicle tested off the record, as it were (i.e., the results aren't reported to the DMV), and doesn't carry the Gross Polluter baggage that you'll be saddled with if you fail two tests in a row.

Another option I was thinking about was just taking the injectors, regulator, and rail from the 90' and putting it on the 88' and see if that helps.

Sounds like overkill for being over on CO only, IMHO.

Do the following:

- Clean the throttle body, intake, and Idle Air Controller with Sea Foam or similar. Be prepared for clouds of smoke after you restart; there are a good few threads here detailing how to do this, so I'd recommend a search. BTW, the local Pep Boys / Kragen chains now carry the stuff.

- Fill the tank and put the remainder of the can of Sea Foam into it.

- [/B]DRIVE THAT TANK TO EMPTY AND COMPLETELY REFILL[/B]. Once you've done that, run half a tank of 'clean' gas through the system. I can't repeat this enough: don't go to an emissions test with fuel system cleaners in your tank. You're almost guaranteed to fail if you do, and running clean gas through it helps to make sure that nothing's left in there that may cause problems.

If you still fail after this, post back here and we'll try to work on it some more. You say your vacuum lines are good, so assuming that's the case we're already ahead of the game.
 
casm said:
This is typically the sign of a shot catalytic converter - if all the other numbers are within spec, look to the cat first. How low were the other numbers in relation to their limits?
I was up in the air on this, granted I did have one Jeep that passed all of the sniff test, but failed on the visual. I wasn't sure, but upon looking at the numbers again, the Hydrocarbons are high for my liking (standard is 3.00 g/m and it read 2.95 g/m). I just compared it to my 90' and it read 1.03g/m. Which this now makes more sense, as the little guide they give you for failing list that if HC is high or HC and CO, then it list spark, timing, ignition, vacuum leak, and cats.

I think I just answered my own question while responding back. All I had to do is look at the 90's smog check and the 88's a bit closer.

So I will replace the cat and probly the O2 sensor (neither hurts it). I will post up the results in a few days, first I have to get the money for the parts :doh:


casm said:
- Clean the throttle body, intake, and Idle Air Controller with Sea Foam or similar. Be prepared for clouds of smoke after you restart; there are a good few threads here detailing how to do this, so I'd recommend a search. BTW, the local Pep Boys / Kragen chains now carry the stuff.
I don't think I need to do this. The head was rebuilt last year, and I put it on. And I am a bit anal on having things clean when I work on them, so I cleaned everything on the whole top end. And I like using Marvels Mystry Oil for the clouds of smoke, but it kills the cats :jester:

casm- thanks for opening up my eyes. I can normally figure everything out, but when it failed my jaw just dropped and my mind froze. Especially since it runs better then my 03' TJ, and has less leaks.
 
OK, I replaced the CAT, and swapped the O2 and MAP sensor from the other XJ, and did a small adjustment to the TPS. It passed with flying colors....here are the results....

before: read ......Standard
HC: 2.95g/m ..... 3.00g/m
CO: 63.34g/m ...25.00g/m
NOX: 1.90g/m ....4.50g/m

Now: read ........Standard
HC: 0.84g/m .....3.00g/m
CO: 10.89g/m ..25.00g/m
NOX: 0.96g/m ...4.50g/m

90' XJ readings (running bored TB, header, flowmaster):
HC: 1.03g/m .....2.00g/m
CO: 8.81g/m ...20.00g/m
NOX:1.85g/m ....4.00g/m
 
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