pwhatley

I have a 1987 4000S and it recently failed the
state emissions test because of a high NOx reading. I was told it could be because of a faulty EGR valve. I checked with the dealer and they didn't list a EGR valve for this car. Also
I couldn't locate one based on the Haynes manual.
The metal tube located near exhaust manifold is capped off. I adjusted the idle downward,took the car for a re-test and almost had the NOx down to
the maximum standard(its 1440 and my reading was
1548). Do anyone know if the 4000S has a EGR system or an equivalent? What else can cause a high NOx reading? Thanks.

eharleq

The idle speed is supposed to be fixed for the test (EPA). The high nitrogen oxides comes from having the timing too far advanced. Put a timing light on the pup and change it back after the test. I would put new plugs and wires on the car, too.

Supposedly there is an egr valve, mine (86.5) is also capped off and I can't find anything that looks like it.

pwhatley

Thanks. I'll give it a try.