Where's the EGR on Motronic 3.2L?

[getluky]

Hey all,

I've been taking an automotive technology course at the local community college this summer, and it's been fantastic. It's really helped me understand a lot of fundamental concepts and vocabulary that I was missing. I've also been taking the opportunity to poke around my pcar and learn about the way it works.

After I showed my professor my last smog results (which were passing, but very close to the max on HC and NOx, and fairly high in CO), he thought the HC might correspond to a leaky injector that might be causing a fouled plug on #5 (Compression was normal on a quick test). The high NOx, he figured might be attributable to a blocked EGR... but as far as I can tell, there's no EGR on Motronic engines. It looks like the CIS systems had both EGR (and air injection / air pump / smog pump for the HC, I guess), but Motronic got rid of them?

How is NOx usually reduced on these engines? Is there some alternative system to EGR? I don't have records on the car prior to 2001 or so, so i'm not sure if the cat is original or when the O2 was last replaced.

I read a bit about CO getting set manually, but I didn't hear what level it should be set at. Any opinions on that?

The fuel injector is a separate issue, and i'll post about it later after doing some searches on the boards.

[TRE Cup]

there is no egr on motronic 3.2 motors !

[SC-targa]

Originally Posted by getluky

Hey all,

It looks like the CIS systems had both EGR (and air injection / air pump / smog pump for the HC, I guess), but Motronic got rid of them?

How is NOx usually reduced on these engines? Is there some alternative system to EGR? .

78-79 California SC's with CIS injection did have a cat, EGR & an air pump. 49 state models had just the cat & the air pump. ROW SC's models with CIS used an air pump from 78-83.

From 1980 on, US 911' SC's became 50 state models. Instead of the 2 way cat, they now used a 3 way cat with an O2 sensor feedback loop that eliminated the need to EGR and air pumps. Your 3.2 uses a similar emission system, but with a more accurately metered electronic fuel injection system.



Regards,

Jerry Kroeger

[getluky]

Jerry: Thanks, that's a good explanation. My book did talk about 3-way catalytic converters, although they usually had an inlet for air from the air pump, which I don't believe the 3.2 has. Since the NOx reduction is supposed to happen in the reducing catalyst within the 3-way cat, does that mean that high NOx emissions are an indicator of a clogged catalytic converter?

The diagram you posted is really interesting, but I wish I could read the labels on the bottom. It looks like there's a low, mid, and high band on the right graph - what do those correspond to? It almost looks like NOx doesn't drop off over the mid and high bands even with the catalytic converter.

[TRE Cup]

USUALLY the cat is bad on motronic cars when Nox is high and other values are close to spec