My 240 was due for smog test this month (Oct). Took it to a TEST ONLY
station yesterday and failed for high NOX.I've read on the board that someone suggested to plug the vacuum hose to the control unit transducer. My question is, where is the control unit transducer on a 240? Thank you.

Jose,

Let's us know how the re-test with the plugged ICU line goes, if you would.

This may be a wasted post, since you don't say what year 240. But it applies from mid '81 thru '88. It's the Ignition CU, at the right front below the windshield washer tank. You'll see a white plastic tube with a 90° rubber tip that plugs to a round metal diaphragm.

A recent poster said he pulled the rubber tip off, taped the port, then replaced the tip—and passed. Below is my usual post on this:

>>I believe you have the Volvo/Chrysler ignition used on 240s 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 ECU can lower NOx production with little effect on normal operation.

I first posted it 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, put the old cat back on and passed!.
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Bruce Young
'93 940-NA (current) — 240s (one V8) — 140s — 122s — since '63.

Do you know if the Rex Regina system has a similar arrangement? I bought a new cat last year, and still can't pass NOx. I have replaced temp sensor, MAP sensor, Air filter and plugs with the effect of reducing NOx from 3900 to 1600 ppm, but I need to be below 900 ppm. So, I am thinking of re-replacing cat, and perhaps O2 sensor.

1993 940 B230F with Rex Regina.

Thanks.

Tom

Do you know if the Rex Regina system has a similar arrangement?

No. it was only used on the '80s 240s. From what I've read, high NOx is usually caused by high engine (Cylinder head) temps. Try searching here on "900 nox" or something like that. And look in the 700/900 FAQ forum.
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Bruce Young
'93 940-NA (current) — 240s (one V8) — 140s — 122s — since '63.

Bruce, sorry for the incomplete info. My 240 is 1988 model.
Thanks for the tip.I'll try this and see if my car will pass.