I failed the emissions test here in Ca. on my 87 240.
The readings on the CO were very low (.01) and high on the NO (1028 @ 1139 at 15mph and 25 mph respectively).
The HC reading was fine (30) and the car runs and idles perfectly. My NO readings are always on the edge with my bricks but this one's a bit our there and with the CO being so low I'm a bit puzzled.

Any help would be greatly appreciated.

K.S.

You have the Volvo/Chrysler ignition used on 240s from mid '81 thru 1988. It's been claimed that the V/C ICU's design can cause hi NOx, and that plugging the vacuum line to the ICU can lower NOx production with little effect on normal operation. Note that this is not a guaranteed fix, but worth a try if your other numbers (and cat) are good.

I first posted it (with technical details) on 5/21/04 (see original post here. ) At least one person has found that this solved his high NOX problem.

You can see his happy response at success story.
NOTE that he had failed with a new cat, then plugged the ICU vacuum line, put the old cat back on and passed!.

Another success was recently reported on this thread.

And yet another one here.

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

thanks, I did see those posts yesterday and they did pique my curiosity. I'm not sure if I have the Chrysler ignition but will check (did all 240's in those years have the Chrysler ignition?). My CO levels seemed very low so I was leaning towards vacuum or exhaust leak, do you have any thoughts on that one.
Tomorrow is my day to check things out so any and all suggestions are welcome.

thanks again.

K.S.

Yes -- all 240s from some '82s thru all '88s have the V/C ignition, although the white-capped Chrysler distributor disappeared by '84 or so.

I think vacuum leaks could contribute to NOx. I've found using propane while reading the O2 sensor voltage (signal lead disconnected from ECU) to work very well for leak testing. But IMO, plugging the ICU vacuum is worth a shot in any case. Here is my "canned" propane pitch:

I use Propane to test for vacuum leaks. It's less messy—and no more volitile—than carb cleaner or other sprays. Take the nozzle tip off a propane torch and replace it with some snug fitting rubber hose about 2 feet long. Practice with the valve to get a moderate gas flow (not a roaring blast).

With the engine at a warm idle, open the gas valve and poke the end of the hose around each injector for a couple of seconds. If the seals leak, you should hear an RPM change when the propane gets sucked in and burned.*

Do the same around any other suspected areas, like hidden vacuum hose ends and the intake manifold gasket itself.

To block the breeze from the fan, lay a piece of cardboard from the fan shroud to the engine

*If you use use a DVM to "read" the O2 sensor output voltage (O2 disconnected from ECU), you'll see the voltage rise instantly if any propane gets drawn in.

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

well, I did a little looking this morning and there's a definite exhaust leak where the front pipe attaches to the manifold (right where the O2 sensor is located) so that would definitely be sucking in air and giving a false O2 sensor reading. I guess after fixing that I should also plug the vacuum to the ICU?

thanks again.

k.s.