Failed CO emissionss--high NOx

[kerrye]

5.74 grams per mile. Limit is 4. (used to be 9 when I first bought the truck). It's passed fine the last few tests. The only difference this year is that I retarded the timing. I had been having pinging and discovered the timing was set way too advanced. It probably had been that way since I had the headgasket done. Will advancing the timing reduce NOx emissions?
If not, does any know any standard cures for high NOx numbers?

 

[Pin_Head]

No.
The primary responsibility of controlling NOx is the EGR system. The valve may not be opening all the way or the passages may be partially obstructed.
The 3 way catalyst further reduces NOx in both the quantity and chemical sense.

 

[kerrye]

I have had the check engine (p401?) code. But it's been that way as long as I've had the truck (6 yrs?) and it didn't cause high NOx in the past. But that might be it. Been reading the threads and see I need to check the in/out temperatures on the cats. Truck had new cats and 02 sensors put on by the PO right when I bought it so it would pass emissions.

 

[Timpanogos Slim]

I have a buddy who built an old detroit muscle engine with compression that was just too high, and adding EGR prevented pinging by lowering the ignition temperature.

But, our engines don't have that problem.

 

[kerrye]

Looks like my cats are working--350 degrees in and 550 degrees out at idle after a short drive in the city.

 

[kerrye]

Is there an 80 series emissions guru in denver?

 

[Timpanogos Slim]

If you have P0401 your EGR is malfunctioning. In Utah you would fail emissions on that alone.

Try following the test procedures in the FSM.

 

[kerrye]

I've got another thread with this specific question but does anyone here know if the EGR won't hold vacuum, that it's a definitive test for a failed valve that needs to be replaced? I think it is because I can't see how it could work without holding vacuum but I just want to get confirmation before I fork over $200 for a new valve.

 

[ToyotaDon]

Yes, the valve should hold vacuum, and cause the engine to stumble or die when it does. The EGR system's main function is to reduce NOx, by lowering combustion temperatures.

Timing will affect NOx as well, and if you have pinging/detonation, you are pretty sure to be creating NOx.

Just curious, do they have a four-wheel drive dynamometer they're using? We only have two-wheel in CA, so the full-time vehicles don't get measured for NOx.

 

[kerrye]

Thanks. I'll replace it. Yes, they do have a special AWD dynamometer line just for us.

 

[Pin_Head]

The port at the top that is above the diaphragm should hold vacuum well enough for the valve to operate. The factory service manual has a good diagram in it. It can probably tolerate a small leak. It is hard to know if it is really bad without observing the opening and shutting of the valve.

 

[kerrye]

Won't build any vacuum at all with the engine running or off or with the other hose squeezed off. I think the diaphragm inside the EGR must have a big hole in it.

 

[Pin_Head]

How do you know it won't build a vacuum? Are you relying on engine vacuum? Have you looked at the FSM? Which hose are you testing? The one on top operates the valve. The one on the bottom supplies exhaust gas to the EGR modulator. You need to suck on the top hose or put a vacuum gauge and pump on it. It helps to also verify that the valve moves up and down when you suck on it. If the engine stalls when you pull a vacuum on it, this is good evidence that the valve is opening properly.

PS the temperature increase of the catalyst is due to CO and HC oxidation, not due to NOx reduction, so it is not an indication that they are working for NOx.

 

[kerrye]

Put a Mity Vac on the top port passenger side. Won't build any vacuum at all.

 

[Pin_Head]

I didn't notice that you started a new thread.

If the vacuum pump works and doesn't leak, then it looks like your EGR valve is shot. If possible, remove the stud from the head. It makes removal easier.

 

[kerrye]

Which stud? Looks like it has a couple of bolts and a big union nut holding it on to the manifold and pipe.

 

[Pin_Head]

Two studs hold the flange to the head and there is a large compression fitting nut that joins the pipe to the valve. If they look like bolts, it is probably because of the rust.

 

[blkprj80]

I think you mean intake PinHead.
If you can extract the studs after you take the nuts off, it is a lot easier for sure. Keep an eye on the gasket.

 

[hadmatter]

Kerrie,
Curious to know if replacing the egr valve solved your problem. Our truck barely squeaked by emissions in December due to NOx reading. Truck has been throwing the egr code for 6-mo or more. I've read all the threads, dreading the investigation process of finding the source.

By the way, I recognize the camper in your aviator, think we used to be neighbors, if your 80 is red? - I used to live in Baker also, on Cherokee st.

 

[LFD2037]

If your throwing an egr code, and they test for emissions, your going to fail.