86 Suburban failed emissions with high NOx

[dcp]

My 86 C1500 Suburban 2wl drive 350cc failed emissions for the first time for high NOx. It failed on both the 25/25 and the 50/15 tests on NOx. The overall readings for the 25/25 test were:
HC 128 (142 allowed)
CO 0.11 (1.74 alllowed)
NOx 2396 (1881 allowed)
CO+CO2 11.1 (min 6)

The overall readings for the 50/15 test were:
HC 116 (145 allowed)
CO 0.11 (1.3 allowed)
NOx 2464 (2017 allowed)
CO+CO2 11.2 (min 6)
2 years before (I can't find the report for one year before) it passed but was close on the NOx, reading 1857 with a 1881 limit on the 25/25 test but it had 1276 (2017 allowed) on the 50/15 test. In between I had a rebuilt carburetor and new distributor/coil put in.

I'm wondering whether I should look to the fuel mixture or timing as a cause of increased NOx because of the above two items being replaced. However, the NOx was almost unacceptable two years before for the 25/25 test. I'm also puzzled by the 25/25 test two years ago almost failing for NOx but the 50/15 test passing with flying colors (1276 of 2017 allowed). Why would higher use of engine horsepower and slower speed give such a better result? Finally, I don't think catalytic converter on an 86 dealt with NOx, did it? Does it give a clue as to what the problem might be. Sorry for the long post. Its my first here and I wanted to give all the relevant details. Car was warmed up well for all tests since with 240,000 miles on the original engine rings need to warm up to seal well.
Thanks!

[chengny]

Couple of things to consider:

Do you have functional AIR pumps and is the associated piping intact? The hoses and manifolds that deliver the fresh air to the exhaust manifolds needs to be tight. BTW - These pumps are protected by dedicated air filters - located either in a common upstream canister or individually - behind the driven pulley.

If it has passed EPA in the past and is slowly beginning to struggle (to meet the limits) check the vacuum tubing. All of it, not just the line to the EGR diaphram. One good sized leak will disable the entire vacuum network.

Provide the vacuum system identifier (usually starts with Y and is located on the filter housing) and maybe someone can come up with a good drawing.

A.I.R. System vs. NOx

The AIR pump (Air Injection System Pump) or smog pump in your motor vehicle is a critical part of the emission reduction system. This A.I.R. pump is designed to pump in clean air and combine it with your engine's hot exhaust gas as it leaves the combustion chambers. The air injection pump is a critical piece of equipment that needs to be working properly in order to maintain proper emissions readings. The reason for the AIR pump system is because the hot exhaust gas by itself is not enough to complete the burning of the exhausted gas mixture. When the air pump system is working properly, it will allow the continued burning of the fuel mixture as it travels down the exhaust system and eventually out the tailpipe.
There are basically two ways how the actual air pump motor itself is powered.

• (1) Mechanical via a drive belt system
• (2) DC power via electric motor (sometimes used as secondary pumps)

1A currently is carrying the electrically DC powered AIR pump motors. These electric air pump motors are built to strict quality control standards and come with a limited lifetime warranty.
Symptoms of an electric AIR pump malfunction:

• Poor Idle
• Service Engine Soon (SES) light illuminates
• Trouble code from a computer scan displays code P0410
• Increased Oxides of Nitrogen NOx emissions
• Corroded electric motor
• Failed vehicle emission test
• Frozen motor

It is possible to diagnose some AIR pump problems. Consult your vehicle's repair manual and follow all precautions when performing any type of diagnosis. Operating your vehicle on a public road with disabled emission equipment could violate the law.
Our AIR pump motors are made to the same specifications as the originals. They will fit and function with no hassle. They come with everything needed to change out the old motor.
Whether your car or truck needs a new electric AIR pump or you are performing preventative maintenance, purchase a new AIR pump motor from 1A Auto today.
Remember that a properly working AIR pump assembly results in both increased gas mileage and reduced Oxides of Nitrogen (NOx) emissions.



EGR Valve vs. Nox

The Exhaust Gas Recirculation (EGR) system's purpose is to reduce NOx emissions that contribute to air pollution. The first EGR systems were added to engines in 1973, and today most engines have an EGR system.
As long as the EGR system is functioning properly, it should have no noticeable effect on engine performance. But if the EGR system is leaking or inoperative, it can cause driveability problems, including detonation (knocking or pinging when accelerating or under load), a rough idle, stalling, hard starting, elevated NOx emissions and even elevated hydrocarbon (HC) emissions in the exhaust.
WHY EGR?
Exhaust gas recirculation reduces the formation of NOX by allowing a small amount of exhaust gas to "leak" into the intake manifold. The amount of gas leaked into the intake manifold is only about 6 to 10% of the total, but it's enough to dilute the air/fuel mixture just enough to have a "cooling effect" on combustion temperatures. This keeps combustion temperatures below 1500 degrees C (2800 degrees F) to reduce the reaction between nitrogen and oxygen that forms NOx.


In which state are you trying to pass emissions? Seems to me that, other than CA, they don't require these trucks to pass a gas analyis. They are too old and they came out with nothing other than those air pumps as far as emission control. There were never any cats installed.

[dcp]

Thanks for the reply. Will check the items you suggested and try to come up with the vacuum system identifier as a drawing would help. Did have vacuum line issues before and had to replace some tubing. The state is Georgia and I have to make it two more years before I no longer need an emissions inspection (that is the only inspection we have here). I have to get it fixed or spend ~$700 to try each year to get a waiver. Thanks for the clarification on the catalytic converter not being present. Whenever they do inspections, the record always says catalytic converter present... One other aside: the truck runs great-no knocking or troubles accelerating. Of course it is very thirsty.

[hotrodpc]

It always cracked me up, the AIR pump always being reffered to as a "Smog Pump". In a sense I guess one could say it does pump air. But its actual purpose is to INJECT air, not pump it. It injects air right at the exiting of the exhaust gases leaving the combustion chamber, also why the holes are so close to the head of the exhaust manifold. At the right time, when the exhause gases leave the combustion chamber, that injected air causes the gasses to actually reburn again on their way out of the exhaust manifold. Actually a quite effective system of reducing emmisions. And everyone wanted to disconnect that little bitty smog PUMP that was robbing all the horsepower. Far from true. That pump might have absorbed 2 ponies. Where the performace is cut down is in the ports of the head, so all these years that people took off the smog pump and plugged the holes in the manifold, they really did nothing to imporve performance. Also by adding headers, you still have the smog bump in the heads, so there is very little gain and alot more terrible on the environment. Also reffered to AIR pump, many think its just that, an air pump. NO, its actually an A.I.R. Pump. A.I.R. for Air Injection Reactor. Sounds bad doesn't it??? As if we have some kind of nuclear energy device on our vehicle. But not true.

[hotrodpc]

Ready for lesson #2 on "Smog Pumps" or the Air Injection Reactor pump. If anyone has ever heard of a dual bed Catalytic converter, its just that. It has 2 differant spaces in it. The 2nd bed of the Cat, also had a hose from the A.I.R. pump that would also inject air AGAIN into the 2nd bed of the conveter, and it did the same thing as it does up front at the exhaust manifold. It causes yet another reburn of the exhaust gases before they leave the tailpipe. The whole idea of emmisions is so that exhaust gases are all burned up and no harmful emssions is left by the time they leave the tailpipe. One of these days I have a feeling, someone will come up with the technology and a person could actually breathe the emmisions out of the tailpipe. In a perfect combustion situation, you would actually have water running out of a tailpipes instead of gases or fumes. If you ever pay attention to tailpipes these days sitting at a stop light. You do actually see some water dripping from tailpipes on newer vehicles. It alway makes me wonder if that is not partially perfect combustion due to todays technology. Not saying that the car has 100% perfect combustion. Just wondering if a portion of the gases were not perfect combustion and the results of the drips. Its common in cold cars, being mositure in the tailpipe etc. But sometimes you see cars that you are certain, as hot as it is, and they just did not leave their house. You know that vechile is well warmed up. So what else could it be?

[Crmzendrgone]

Here is another bit of info. Chrysler has on some of the late model vehicles the radiator coated in a "chemical" if you will that gives it a green look but that coating actually cleans the air as it passes through the fins. Kinda like an ionic fan or whatever.

[chengny]

Here is a quick check to determine whether your air pumps are putting out. Pull the black rubber hoses from the top of the check valves, start the engine and let it warm up. If your Thermac system is still in place and working it will quickly cause the air temp sensor to make (the one that is mounted through the air filter housing - on the drivers side). Usually it is connected by a yellow and a brown wire. Once that switch closes - and provided your "computer" is good - the diverter valves will shift the airflow from the dump lines to the manifolds (via the check valves) . You should feel a good flow of cool (well ambient temp) air. There doesn't need to be much pressure - with no catalytic converters - the back pressure in those two big exhaust pipes (2 1/2" O.D. front to back?) should be negligible.

If the system is pumping air, reattach the hoses, and after a reasonable amount of time (maybe only a minute or so - but don't trust me - lick your finger tips) feel the chrome injection pipes. They should be nice and cool.

If they do not cool down, pull the check valves and make sure that they are clear and are actually functioning as "check valves". They are only in the system to prevent backflow of exhaust gases during the two modes when the diverters are dumping to the air filter housing (or to atmosphere in some applications).

Backing up a bit, if the, pumps are not pumping you can disable the diverter valves. They fail with the valve open to the injection piping.

That's all I know about these systems. I just recently decided to disable mine. Well they are actually still in place - to keep my headers cool during an upcoming cam break-in (but that's another story).

I have attached an isometric diagram that clearly shows the control circuitry and I have more info on how to troubleshoot this white elepahant if you require it.


Oh and BTW - all this useless info is based on the assumption that you have a FEDERAL (not CA) heavy duty emissions package. The serial no. should have an M as indicated in the example below. If not then please disregard everything.

1GTGK24 M 7GF716340

[hotrodpc]

Sounds like good info there Chen. I thinking as I was reading your post, those are called diverters valves, but reading on you got to that part. But yep, I agree.
As far as Federal and CA emmissions, yes there used to certainly be a differance. A huge differance. But If I am not mistaken, with auto's s clean as they are now, hasn't CA also adopted the Federal emmissions standards?? I do believe the emmisions are now 50 state, but the gasoline you buy in certain counties in CA is formulated differantly. Like higher in Ethanol content. CA emmissions also require the fuel dispenser (pump) boot over the nozzle in certain counties. It is amazing how much believe it or not, So Cal has drastically cleaned up their air in the last 25 years. If people do not beleive emmission on cars make a differance, So Cal is the proof that yes it does. A huge differance. I expect anytime now, which we sorta do anyway, lawn equipment is going to have emission standards, like no 2 stroke motors. Not 100% certain, but I am almost positive you can no longer buy a 2 stroke motorcyle in the US. All bigger CC 4 strokes now. It'll be a sad day, when my little weed eater is about 4 times it normal size for that biggo Cat Converter hanging offf the side of it.

[chengny]

As far as Federal and CA emmissions, yes there used to certainly be a differance. A huge differance. But If I am not mistaken, with auto's s clean as they are now, hasn't CA also adopted the Federal emmissions standards??

You know Rod, it just goes to show ya. Once you get something set in your mind it is hard to see things any other way. My point; I had always just assumed that it was the State of California that had the tighter emissions standards. I mean that they were the stricter of the two (Fed vs. CA) by comparison. Never thought for a moment that it could be the other way around.

I have dealt with the State of California Lands Commision many times during my seagoing career. They are something else - not as bad as the Alaska DEC. But they are in a league of their own (the Alaskans).

Even after a boiler light off, you are allowed only 15 minutes to clear your stack (under 4 Ringleman). If not - BAM - the shipping company gets a 50K dollar smoke ticket (and the chief engineer gets a lot of phone calls). Up in Valdez anyone, and I mean anyone, can report emissions violations by a tanker docked at Alyeska. They, on the other hand, will work with you as you try to get a clear stack.

What kills me though is California, the supertankers come into LA/LB to fill up the refineries so that everyone can drive their cars (everywhere).

All done, back to work.

[chengny]

One last thought - how come these guys pop in, ask an involved question like that and then sometimes never even report back with the results.

I take time to answer as best as I can, and I'm not really complaining (and I definitely don't need any more publicity than I already get) but it would be nice to know if it helped.

Now I'm really done.