As usual, my '93 Caravan has failed emissions due to high NOX readings.

I've owned this van 2 yrs, this will be the third inspection its had in my ownership.

First inspection, oxygen sensor WAS bad, replaced it and had a new (universal) cat installed......passed inspection.

Second inspection, failed again, replaced cat under warranty......passed inspection.

Now during this whole time, the van seemed to be running a little 'rich'. I finally fixed that issue recently.

Which brings us to the third inspection which it has failed again for the same reason with almost the same numbers.

Did I kill the convertor (again) running it 'rich' until recently? Do I need to step up to a better (not universal) convertor?

Or, do I need to look somewhere else for the problem?

This is really chapping my butt because the thing runs so good. Before this, I had a '91 Ramcharger that was a gas sucking, oil burning pig, and it passed emissions with flying colors.

Aside from replacing the cat again, I'm at a loss here.

NOx is caused by high combustion chamber temps. Lean mix,faulty EGR,cooling system issues,etc. Nox should be reduced by the cat. Yes the cat could have been killed by the rich mix(CO poisoned)Yes I've had poor luck with "universal" cats.

Oh yeah, forgot to mention, this thing DOES NOT have an EGR valve on it. Got into it with the guy at the inspection station about it too. The block off plate has a factory looking number on it, and the vacuum line routing decal underhood doesn't even show the EGR.

All I can tell you about the cooling system is that it doesn't overheat.

I kinda went with the (cheaper) universal cat because I didn't know if this van would last another year (when I first got it).

Thanks for the reply.

Put in a few gallons of e-85, that will bring the NOX down real nice, it will even help with HC and CO.

3.0 V6? How was your HC #'s? You say it was running rich so I would think it would have failed on HC too.

I had a Spirit with a 3.0 that I used to get to pass by gassing up with premium before testing. Premium burns slower so it's a little cooler burn which lowers your Nox. The downside is that it will drive up your HC so you have to be low in that dept.

Kevin

The cheaper cats do not last very long, to the point in California the CARB outlawed the sale of cheap Cats and had them pass a test before they can be sold to a person in California.

Oops, forgot to mention its the 2.5 four banger......

No E85 around here (that I know of), so, scratch that.

I can do premium though.

Interesting tidbit about CA outlawing cheap cats, didn't know that.

No E-85, eh? Why couldn't you buy a couple gallons of denatured alcohol and get the same effect? I realize it's 100% grain alcohol rather than corn alcohol but...?????

Denotured will work just the same. Don't leave a bunch of it in the tank for a long time, it is more corrosive than ethanol.

Yep....a couple of bottles of Heet and about 5 gals of premium do the trick on my non-cat cars every year.

Well, I didn't try the heet, but, I put about 10 gallons of premium in. I drove the van 50 miles and took it straight to the emissions testing.

It failed AGAIN. But, for a different reason. HC and CO was way up.

NOX dropped to well within the legal limit.

Could it still be the convertor?

I'm about ready to throw a match on this thing.

for the weekday crowd.........

Post the numbers
RPM, Measured numbers (all of them) and limits.

Something has happened. Fired it up this morning, and it was chuggin' and left black soot on the driveway. It was fine before.

Let me check a few things before I post readings.