I've posted here before about cooling issues in my 1994 940 non-turbo (now
186K miles). The leaks now seem to be fixed, no check engine codes,
but the car still can't pass the CA smog inspection due to high NOx
readings. Here's the summary:

HC (ppm)

15 mph MEAS: 12 AVE: 28 MAX: 59
25 mph MEAS: 6 AVE: 16 MAX: 50

CO (%)

15 mph MEAS: 0.05 AVE: 0.07 MAX: 0.50
25 mph MEAS: 0.03 AVE: 0.06 MAX 0.47

NO (ppm)

15 mph MEAS: *719* AVE: 265 MAX: 556
25 mph MEAS: *835* AVE: 221 MAX: 717

All seems good besides the high NO, which points to hot running engine... I'm planning to get the EGR ports cleaned (need to take the intake manifold off -- whenever I get time this week... before the current reg expires). A suggestion I've gotten from the SMOG Check place was to change the O2 sensor -- hard to say without a crystal ball if that's what causes it, but it doesn't seem unreasonable ($100 replacement sensor). Another thing that catches my eye is that one of the studs attaching exhaust manifold is broken (the outermost one on cylinder #1) and it seems like there could be a small exhaust leak past the exhaust manifold gaskets.

Wonder what would be a reasonable order to have things fixed, should I try to get the exhaust manifold fixed (tricky because of the broken bolt) or throw a new oxygen sensor on it as the smog people suggested?.. Good Volvo mechanics are a little scarce and far between in the area where I live, so I'm inclined to try trial and error before giving up and trying to find someone who can fix things for me...

Here are some general tune-up things that I've done so far: new oil/filter, new Volvo spark plugs, properly gapped (checked wires, OK), new 92C Volvo thermostat, new air cleaner, new coolant, run a can of BG 44K fuel system cleaner, sprayed a can of seafoam down the intake, replaced MAF sensor by a spare (used) just to check things, all seems fine. The car runs fine, it does seem to be a little noisy (leaking exhaust?? hard to tell). No overheating, but the temp gauge is right in the middle so it could be running a little hotter than it should be. Cooling system flushed several times and seems to work OK (some remaining rust in the engine from prior neglect, I'm sure).

Vlad