I also had some difficulty getting an 87 244 with 235,000 an the odometer thru emissions testing last year. It was a car I had just bought on ebay so I didn't know anything about its history. It ran very well but failed miserably on CO2, HC and Nox originally. I tried everything I could before eventually replacaing the CAT. We get free retests for 30 days until a car passes and the test station is right on my way to work so I would just make a change and then try again. Turned out the original cat that was on the car had the guts removed - it was just a hollow tube - but it ended up being a great learning experience for me as I was able to see the results of the various changes. By the way, after installing a new cat I passed but my mileage decreased by 3mpg. Went from 23 to 20 in my daily mixed drive of about 50 miles.

Here's some of what I learned from my experience- all without a cat installed.

Disconnecting and plugging the vaccuum advance did alter the Nox, but only slightly.

Running on E-85 (ethanol) the HC went to almost nothing - no effect on Nox.

Fixing vaccuum leaks had a big effect on Nox.

As I understand it - Nox is the result of excess air present at combustion - in other works it is "burnt air". If your HC and CO2 are ok but your Nox is high then your cat is not the culprit - your culprit is something causing too lean of a condition at combustion.

I would look for a vaccum leak - could be the injector seals, the throttle body gasket, the intake manifold gasket - these would also likely cause a high idle - how fast are you idling?

I'd also test the O2 sensor - very easy to do with a voltmeter - just peel back the insulated cover for the single wire - don't disconnect it - and touch the + lead of the voltmeter to the contact - ground the - lead of the voltmeter and if the o2 sensor is good you should see the voltmeter swing back and forth between about .3 and .8 volts. If the o2 sensor is bad it will not swing much or swing slowly around .4-.5 volts.

Hope this helps!

Jim

! more thing to check is the airbox thermostat.
joe

Hello. Thanks to all who replyed. I have questions about your replys and to those catching this fresh please see my original post(3/27/07 9:44CST)for my situation. Just how much will removing and plugging up vacuum line to fuel pump regulator lower NOx ? I need to knock down NOx by over 500. I am going to try this trick as it is easy to do as it was to remove & plug up Vacuum line to ignition controler. Now as far as adjusting timing to or close to zero my question is as I do not have a timing light/gun : which way - clockwise or counterclockwise should I turn distributor to achieve this ? Many thanks to all with this. I hope to go for another(3rd !)re-test tommorrow.

i had the same problem here in NJ for 1988 240,many attempts to find a problem no avail. car is running to lean. remove and plug up the vaccum line for the fuel pressure regulator. worked like a charm and the car ran much better. Good Luck.
Joe

check your header pipe for hairline cracks or air openings.
check your header pipe to manifold gasket for seal and nut tightness.
check you exhaust manifold for any cracks however tiny

any air introduced post exhaust manifold but before cat WILL radically alter NOX levels and there is no amount of tweaking that can be done without first fixing the source of air infiltration into the exhaust gases.

This will sound crazy, but I knew a guy with an '88 240 with the same problem. Someone suggested to him that he add about 8 oz. of rubbing alcohol in the gas tank, then drive to the test. He tried it and passed "with flying colors". I don't actually understand the science behind it.

This advice, of course, is completely unofficial. Actual results may vary, void where prohibited by law, etc. etc.

Hope it goes smoothly.

--
Guid ('92 745 233k, '91 940 SE 257k,)

You have the Volvo/Chrysler ignition used on 240s from mid '81 thru 1988. It's been found that the V/C Ignition can contribute to High NOx, and that plugging the vacuum line to the ICU can reduce NOx levels, with little or no effect on normal operation. Note that this is not a guaranteed fix, but worth a try if your other numbers (and cat) are good.

This is my canned post on the subject. It might work for you as it has for several others, especially with a new cat. I didn't write the tech info -- I just happened to find it on a 'net search in 2004.

For a technical description, see the original post here, and the first success story here.

Other positive responses are posted in this thread and this one,
and one more here.
Yet another one .
And another on 2/04/06.
Here's the latest, from 3/12/07.


--
Bruce Young
'93 940-NA (current), 240s (one V8), 140s, 122s, since '63.

You can set the timing to 0 or near 0 this will drop NOX way down.