HELP,
I just had my 1985 500SEC tested, (it's a Georgia thing) and all test parameters were excellent (or even better) except for NOx which was 3900 with an allowed 975. There is no EGR on this car to fail, so what do I do now. The car runs great, gets good milage, HELP. Any suggestions or recommendations.

Is this a grey market car? I thought all the 85 V-8s had EGR. If you change the oil, temporarily lean the mixture and back off the timing a few degrees you should be able to pass the test.
Good luck

Ahem, Uhh, NO. Leaning out the mixture will cause the combustion process to be hotter, which *encourages* the formation of NOx. IF, and I say IF your HC reading is *very* low, try RICHENING the mix a little. Your HC will go up, but the NOx will come down. Changing the oil will help a little, usually more with HC, but it’s worth a shot.

I don’t know about the Federal versions of the 1985 cars, so I can’t comment on whether it should have EGR or not, but it seems likely that it should. If it is a gray market car, it may have been mickey-moused. My Euro Rust Bucket V-8 had the frequency valve (part of the 02 sensor feedback loop) jury rigged into the control pressure line coming from the warm up regulator. An aftermarket mixture controller controlled it. This set up will work to some degree, at least in theory, but by controlling the center plunger pressure (via the control pressure line) it will not have as fast of a response as a system with the proper fuel distributor and pressure bleed point. Talk about Mickey-Moused, this was on a 1978 car which didn’t even need a 3 way catalyst!

You might try some of those “emission passer” snake oil gas additives – I’d be curious as to whether you get any results from those products. I would venture a guess that they are something to make the fuel more volatile and therefore more easily fully combustible. Who Knows. Not Me. I don’t know anything this late at night .

Well, I too thought that motor would have an EGR valve, but it appears that it doesn't (on US models - I know the 500SELs we brought in and Federalized all had them). The US system with Lambda control and three-way catalyst I guess takes care of the NOX.

If your car is a US model then timing is your only hope. The effective mixture is controlled by the lambda system. Only base mixture is adjustable and it would only affect the cold running engine.

Unfortunately, you may have a catalyst problem. The small precats right at the exhaust manifold are the redux cats. They reduce (opposite of oxidize) NOX to N2 and O2. You should be able to pass, by retarding the timing significantly. It may not have any power but it will help passing a lot. Also try and do the test in the morning with the car as cool as possible (even better in the rain) don't run the A/C.

A thorough decarboning will reduce compression and make a big difference.

__________________
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician

Just trying to redeem myself here….

Well, as always, Steve is right on the money. I forgot to mention the timing issue. I guess that I should not try to help people that late at night. Also, I should have specified that my reply would apply *only* if it was a butchered up gray market car with the type system that I described. It sounds like the cars that Steve federalized were done properly – now doesn’t that surprise everyone? (That’s called being facetious, thank you )

And, Steve, I don’t know if you’ve come across a car where the aftermarket O2 system has the frequency-valve controlled bleed point tied into the control pressure line, like I described. In my (limited to one example) experience with that type system, the mixture is controlled in a relatively sluggish manner – it does not respond very quickly to changing loads, but seems OK in a steady state mode *unless* the basic mixture is outside of the unit’s capability for compensation. This is how/why I was able to fool it into compliance with an adjustment to the basic mixture setting. I do know that this will not work with a *properly* engineered system. I don’t know if it was common practice outside of California, but there are a lot of gray market butcher jobs here.

Another issue may be the *ability* to run the car through Georgia’s test procedure with the timing altered. Here in California, they check the timing & report it on the results. One time, on my 1980 U.S. spec 107, I had the timing set 4 degrees advanced (where it runs much better) and I forgot to ‘fix’ that problem before taking it for a smog check. The VERY first thing he checked was the timing; I immediately realized that I had forgotten to reset it to specs, so I said that before he went any further, I would reset it and come right back - but he said that the test was already “in progress” and he couldn’t stop. What a load of B.S.; the guy hadn’t even entered any of the vehicle data into the machine yet. I stood there as he went through the procedures, knowing full well that he was going to screw me. It passed the sniffer test just fine, but the guy FAILED me for the timing. To add insult to injury, he also reported “tampering” for the timing being off. Tampering is when hardware is physically *altered*, not if someone’s timing ‘drifts’ out of spec. What an SOB – He offered to reset my timing for $45 (!!). For the 5 minutes of work that he said would take ¾ hour of shop time. Plus *another* $40 for the retest. Unbelievable. I would have gladly paid him a reasonable amount to reset it on the spot – I mean everyone deserves to make a living, but $45 to set the timing? To make a long story short(er), you may want to find someone that is a little more consumer friendly than what I ran up against that one time. I wish harm to no one, but I have to admit that I was a *little* pleased to see that he was out of business a few months later. Karma?

Good Luck!

I appreciate the input. The car is a U.S. version, does not have an EGR and has no signs that it ever did. In fact the car and even the exhaust seems to be original. The timing is set at only 5 degrees, so low that the car runs fine on pump regular unleaded. (A little spark knock at heavy throttle only.) The mixture is just rich enough that there is a little sulphur smell at the initial return to idle, and the car barely has any soot in the tail pipe. (This part drives the other guys in my engineering department nuts.)

Sounds like a replacement cat to me. That is $500 I did not need to spend, especially when upgrading the exhaust to a high performance cat system is not a sure fix if we are not sure that the OEM part will work.

In response to the O2 aftermarket system, I have experience with the CIS systems and these control pressure feedback LAMDA units. If the operation is sluggish, suspect the O2 sensor or location. It must be CLEAN, and located either in the manifold or between the manifold(s) and the cat. It must be HOT to work. The OEM CIS feedback system actually controls from the bleed pressure port so there is virtually no difference in the response of the systems.

I am still open for any alternatives.