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Failed Emissions


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I have a 92 El Dorado that just failed emissions for the 3rd time :angry:

I have changed the plugs and wires

Had a fuel rail repaired

Had my EGR Valve Cleaned

Does anyone have any other sugestions before I have my cat changed?

Any help is greatly appreciated.

The following were the readings:

Reading Standard

Hydorcarbons (HC) 1.93 1.00 Fail

Carbon Monoxide (CO) 14.00 12.00 Fail

Oxides of Nitrogen (NOX) 1.94 2.50 Pass

Thanks in advance.

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Do you have any computer codes that have set? O2 sensor codes or EGR codes or fueling imbalance, or misfire codes, are related... Any check engine lights flashing?


CO is a result of incomplete combustion due to insufficient air in the air/fuel mixture. The level of CO emissions (usually measured as a %-age of the total) is almost entirely dependent on the balance of the air/fuel ratio. The lowest emissions being consistent with excess air. In this condition, further weakening the air/fuel ratio has no effect on CO levels.

When the mixture is fuel-rich, the CO emissions will be high. Variations of ignition timing will have only a marginal effect on CO levels.



HCs are measured in ppm (parts per million). Their presence in the exhaust stream is a result of unburned or partly burned fuel, and engine oil. Unburned fuel originates from areas of improper combustion in those areas of the combustion chamber which are difficult for the sparkignited flame front to reach. HC emissions are also caused by blow‑by, where unburned air/fuel mixture escapes past the piston rings into the crankcase. Current engine design restricts the amount of escape to the atmosphere by recirculating engine fumes back into the intake manifold. Unlike CO emissions, HC emissions increase during both rich and lean air/fuel conditions. When the air/fuel mixture is rich in fuel, the combustion may be incomplete, therefore allowing the presence of unburned HCs in the exhaust stream.

HC emissions increase in proportion to ignition advance, except at very lean air/fuel ratios. Factors such as poor mixture distribution, ignition misfires and low engine temperatures, will all cause significant increases in HC and CO emissions


If you are getting an E048 code its related to EGR. The EGR system has to flow good. Try rodding out the two ports that you see in the throttle body when you open it and look in on the 4.9 engine. CHECK all EGR vacuum hoses for cracks and leaks. Its possible you are not getting good EGR flow.. Clean out the passages, the two tubes you see in the throttle body are the same tubes that are under the EGR valve, I squirt GM upper engine cleaner in the tubes, use round wire brushes and blow those tubes out with compressed air (with the EGR off and a RAG over the two holes under the EGR), replace the EGR gasket when you clean it or the tubes

NOx emissions rise and fall in a reverse pattern compared with HC emissions. As the mixture becomes leaner, more HCs are burned. But the free oxygen present combines with nitrogen, especially at high engine temperatures and at high pressures in the combustion chamber.

NOx emissions also increase in proportion to ignition advance, regardless of variations in the air/fuel ratio.

NOx emissions can be significantly reduced by the technique of EGR (exhaust gas recirculation). Since NOx formation is encouraged by high combustion chamber temperatures and pressures, EGR works to divert exhaust gases from the exhaust manifold into the intake duct, either through internal passages, or via external stainless steel piping. This addition of exhaust gases cools the incoming charge. The process is controlled by either a vacuum-operated EGR valve, or as in some late‑model vehicles, by an electrically-operated EGR valve.

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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Clean two EGR tubes inside of the throttle body (under the plates) with a coat hunger. Do not worry about debris falling down. Plugged tubes will affect emission very much.

The saddest thing in life is wasted talent

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Dont know what type of test they are doing but....

In Nashville, they do a idle sniff test to pass. You drive in...they insert wand for 60 seconds or so. Pass or fail. No dyno or anything like that....Newer cars they hook up a scanner..

So, this is for older cars..

In my case, with my '93 SLS (w 4.9). It could never pass @ idle. What I did....I would rev and hold the engine @ 2800 rpm for 90 seconds or so when I was next in line. This would get the cat good and hot and working.

Sure, it caused some strange looks from the state emissions tester dudes.....who cares....I could get the car to pass everytime doing this trick. Good for another year.

I have done this on other GM cars too. Fire up the cat and it will pass.

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What about the codes? Fixing what the codes tell us needs it will just about guarantee that the car will pass emissions.

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Thanks for the responses.

I do not have any codes or a check engine light present. I originally had an EGR code and that is why I had it cleaned. The emmisions came down dramatically. However, I am still a little high.

To be honest, I really don't know if the shop cleaned the tubes in the throttle body. I know they did the EGR cleaning. I'll have to check.

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