Over the past few years I have watched the NOx level slowly rise in this car until this year when it has outright failed both low & high speed tests here in GA.
Both CO & HC remain where they historically like to be, lower end of the spectrum.

I have a meter that registers the O2 sensor operation and it registers normal fluctuations.

I checked the temp before, on & after the CAT -
pipe before = 146 C
center of CAT = 212 C
right after CAT = 200+ C.
Are these temps high enough or are they indicating a dying CAT (it is original).
Not sold on the idea of a bad CAT since CO & HC are OK.

No vacuum leaks, all new tubing last summer & no whistling anywhere.

Possible exhaust leak, it is loud under acceleration but I have not found an obvious leak yet.

Ran Seafoam through it (not much crud), filled up w/high test, ran the heater, gave it a good run before being checked but the numbers are about 200 points too high.

Anything I am missing? Have not checked fuel pressures yet but both pumps are a recent R&R.
--
1999 E320-200K 1994 F150 (awaiting a new engine) 1989 560 SL-180K 1994 945T (daughter's)-312K 1986 242Ti (awaiting a B230FT transplant) 1968 GT500KR (under slow restoration) 2007 HD Nightster (son's ride)

Does your car have an EGR system? If so, I'd blame it. The sole purpose of an EGR system is to reduce NOx output by dropping combustion chamber temperature.

The EGR valve on my 90 740T (b230ft engine) is attached to the block with the same bolts that secure the oil trap.

The easiest test is either the OBD self-test (this is present in 1990 LH2.4, not sure you have it), or just sucking on the vacuum line to the valve. Nothing should come out, but your idle should drop significantly if the valve and tubing is clear and working.

Seafoam was a great idea, distilled water might not hurt either (I use both, alternating between the two) because piston deposits are a big cause of too-high compression and high chamber temps.

I'd say more but my laptop battery is dying.

Good Luck!

My 1995 940 NA failed NOx horribly. The local Volvo specialist said I needed a new air mass meter and catalytic converter. Turned out all that was wrong was dirty contacts on the plug to the air mass meter. A little cleaning of the contacts and some dielectric grease brought the NOx from over 3000 to 27!

John

1995 945 NA, 1995 965

So I just spent the morning going over the engine & exhaust. There were a few loose bolts on the manifold & turbo which I have tightened. The downpipe is back in place. I also cleaned the distr cap & rotor.

I also looked at the fuel delivery system and think I may have found my problem. I am not getting any pressure reading for the tank pump, I hear it but when the car is running, there is no pressure before the main pump.

Tell me if I am wrong, no lifting pump pressure will relate to lower fuel pressure at the injectors which can result in a lean mix & higher NOx. I'm thinking there is no ONE problem I have but a series of compounding small ones.

I do not have time to do the pump right now (& can't get one 'til next week anyway) so will try another emission check to see what my efforts, so far, have amounted to.

It may be my imagination but the car does sound a bit quieter (but not as quiet as I would have thought). This may, however, be a result of this. It looks like the engine mounts might be blown (hydraulic). There is very little, if any, space between the crankcase & crossmember. If the engine is actually in contact with the crossmember, it may account for the increased cabin noise.
--
1999 E320-200K 1994 F150 (awaiting a new engine) 1989 560 SL-180K 1994 945T (daughter's)-312K 1986 242Ti (awaiting a B230FT transplant) 1968 GT500KR (under slow restoration) 2007 HD Nightster (son's ride)

Dear rjk2,

Hope you're well. When motor mounts are new, there's at least 3/8" (10 mm) space between the underside of the oil pan, and the cross-members. When that gap narrows to 1/8", it is time to replace the mounts. If the engine rests on the cross-member, there surely will be more noise in the cabin.

If the in-tank pre-pump has failed, you'll also get noise from the main pump, which strains to deliver enough fuel, especially under strong acceleration.

Hope this helps.

Yours faithfully,

Spook

With a full tank, the lift pump does nothing for fuel pressure.

So, I had good run yesterday and put the car up right after, case temp for the CAT was 230 C (445+ F) dead center.

I had checked for obvious leaks right after start-up around the exh mani & turbo but could not find any.

I let it cool then pulled the downpipe. There is some telltale leakage around the pipe union where it joins the CAT. I don't have time to pull the mani but will make sure all bolts are snug & reinstall the downpipe. If I improve the situation, the noise level (which only manifests under power) should improve.

I wonder if the cracks around the exh mani goilet could be opening up enough to allow air to enter.
--
1999 E320-200K 1994 F150 (awaiting a new engine) 1989 560 SL-180K 1994 945T (daughter's)-312K 1986 242Ti (awaiting a B230FT transplant) 1968 GT500KR (under slow restoration) 2007 HD Nightster (son's ride)

I agree with the exhaust leak as this can affect things. Your cat temperature seems way to low, but I'm guessing you are talking temp on the outside casing. Cat's operature at more like 800 - 900 F, if I recall correctly. Mike

Yes, those are outside casing temps.

I know they will not show actual internal operating temps, that is why I was wondering if anyone knew what range the external temps would generally be.
My gut tells me, even though they indicate there is something burning in there, the temps look low for as high a temp as should be on the inside. I just do not know what the delta-T would be, or if there even is one. The highest reading I got was dead center on the bottom of the CAT casing.

So if anyone has checked the casing temp of a new CAT. I would be very thankful if you were to share.

Dear rjk2,

Hope you're well. Check the exhaust manifold gaskets. It wouldn't surprise me if that closest to the firewall was the culprit. The slow rise in NOx suggests slow deterioration of gasket, etc. Has the noise from the exhaust leak gotten worse?

Another place to check is the down-pipe and the gasket between it and the turbo.

Hope this helps a tad.

Yours faithfully,

Spook

Thanks spook, yes exhaust noise level has risen noticably over the past 6 mos according to my daughter. A cursory inspection turned up nothing with the pipes.
Sunday gives me time to tear into the manifold.