1991 Roadmaster Wagon Fails Emission Test

[TxBuicks]

My 1991 Roadmaster Estate Wagon has failed the annual Texas emissions testing. Too many Hydro Carbons (HC) and Carbon Monoxide (CO). I read up and my understanding (which could be flawed) is the cause of these high numbers is that it is not burning all the fuel going into the cylinders, and thus passing the unburned fuel out the exhaust. Common remedies started with electronic tune up, such as rotor, distributor cap, and plugs. Well, I changed all that and it still failed. As a matter of fact, it was worse. Oh, I put a bottle of RXP in the tank before the second test. I heard it was supposed to help pass emissions testing. I wonder if it caused the HC or CO to go higher?

I only changed 6 out of 8 spark plugs because I could not determine how in the world anyone can change out number 2 and 4 cylinders (front passenger side), as they are beneath the A/C compressor. I would have to pay someone to get those. But, because the results were worse with the new plugs I'm thinking that wasn't the issue anyway.

So now, I'm calling upon the vast knowledge of the Buick forum collective for advice as to what to do next. I have a week to get it through inspection or I have to pay another $40. I guess I could let it sit for 5 years until the emissions requirement no longer applies, but I drive this car everyday.

Thanks.

Edited April 4, 2011 by TxBuicks (see edit history)

[Guest aussie buick]

I'm guessing this is running an efi Chevrolet engine? A car of that age would be due for new fuel injectors. A new catalytic convertor could also be on the cards, it's prime purpose is to burn hydro carbons, carbon monoxide and oxides of nitrogen into less harmful gasses. Change the injectors first as over fueling a new cat will kill it very quickly.

[TxBuicks]

Good point, aussie buick. It does have 175,000 miles on it. It is a trottle body 5.0 litre set-up. Probably original injectors, though. Wouldn't be that hard to change out.

[stealthbob]

O2 sensor is typically the main reason cars don't pass these tests...then the catalytic converter.

What has worked for me is to put gas line antifreeze in your tank before the test, it burns a little hotter and more complete but starting with the items above you should be fine.

I doubt you have that available though.....Its basically just Methyl hydrate or methanol.

[NTX5467]

The injectors in the GM TBI units are not hard to change. Might be best to take the TBI off of the engine, though. That particular part is no different than for a carburetor. You'll need to bleed the residual pressure from the fuel system FIRST, though. Once off the engine, the top of the TBI unit comes off to access the injectors. There is a gasket kit from GM, but each injector should come with some in them too. Then, a new base gasket will be needed.

RXP can work just as Ed says it will. It's main function is to remove residual carbon from the combustion chambers. The carbon deposits can be places where unburnt hydrocarbons can hide, then claim, so they need to go. They used to claim that it would clean things up in one tank-use, so you'd need to add it and then drive the car (hopefully on the highway) until it was time for more fuel.

My gut suspicion is that a new catalytic converter will pretty much fix things. There are several options, from universal to "exact-fit" aftermarket to OEM replacement. Aftermarket converters are only supposed to be effective for about 30K miles, but are significantly less expensive. If a universal one is used, there will be a "fit kit" that might be needed, too, which can make the "exact fit" version a better deal. Of course, OEMs will have the same life expectancy as the one which came on the vehicle when it was new.

The OTHER little things are to present the vehicle for inspection with a fresh oil change. Unburnt hydrocarbons can find their way into the engine crankcase via somewhat worn piston rings, then recycled into the combustion chamber via oil from the rings and/or valve guide/seals. Fresh motor oil minimizes that.

PLUS make sure the vehicle has been driven for at least 10 miles at highway speeds to ensure that the converter is fully up to operating temperature and full effectiveness. Converters which might not be fully-fired-off can result in a "fail" situation yet would pass if they were at full operating temperature.

If there are no "Check Engine" codes in the computer, indicating that all systems are operating without problems, then the new converter would most probably fix the "fail" situation, I suspect.

Just some thoughts,

NTX5467

[Guest wildcat465]

Roy, check the fuel pressure regulator diaphragm for leaking, it will let raw fuel into the intake and give you a high HC issue.

[old-tank]

Roy

Check for vacuum leaks, which the computer will (over) compensate for by delivering more fuel.

Also be sure the correct thermostat is installed and working properly...too cold and the computer will deliver more fuel.

Willie

[TxBuicks]

Thanks everyone for the suggestions. It sounds like it could be a number of things. I did an oil change just before the inspection, and I think the thermostat is working properly. The car idles smooth so I don't think I have a vacuum leak. I think the most likely cause at this point, and mentioned here most often, is the catalytic converter. That's it's job, to reduce the HC and CO. Although the rest of the car may not be running at peak efficiency, perhaps a new one will over compensate anyway. It still has the original one after 175,000 miles. I don't think it is plugged, but I think it is used up. I had a new one put on today and the shop said I should drive it for 50-100 miles before I try the test again, so I will teat it again tomorrow. I will post the results.

And I will see most of you in Salado this weekend. Thanks, again.

[Guest Jim_Edwards]

Thanks everyone for the suggestions. It sounds like it could be a number of things. I did an oil change just before the inspection, and I think the thermostat is working properly. The car idles smooth so I don't think I have a vacuum leak. I think the most likely cause at this point, and mentioned here most often, is the catalytic converter. That's it's job, to reduce the HC and CO. Although the rest of the car may not be running at peak efficiency, perhaps a new one will over compensate anyway. It still has the original one after 175,000 miles. I don't think it is plugged, but I think it is used up. I had a new one put on today and the shop said I should drive it for 50-100 miles before I try the test again, so I will teat it again tomorrow. I will post the results.

And I will see most of you in Salado this weekend. Thanks, again.

A smooth idle does not mean no vacuum leaks with a computer controlled ignition/emissions system. The computer will compensate for the leak unless from a broken or disconnected vacuum line and you may never know about it unless you closely watch gas consumption.

Issues with the EGR valve is often a cause for emissions tests rejections. Unless it has been recently replaced with that many miles on the car if its the original it's probably no longer functional.

Jim

[TxBuicks]

New catalytic converter solved the problem. The car is legal again! However, I learned that I had to pay for an entire inspection again ($40), because the state of Texas only allows one free re-inspection, which I did after I changed the spark plugs. I argued with the owner, which I've known for many years, and all he can say was that 'the computer won't allow him to waive the fee after the first re-inspection.' It's funny how people use the 'computer' excuse when it's in their favor. I told him to be careful, that he's about to loose a long-time customer.

On another topic, I will check the EGR and oxygen sensor. Might as well give it a complete tune up and get it ready for another 175,000 miles.

Thanks for all the advice. I knew I could draw on your expertice.

[NTX5467]

In reality "Big Brother" is alive and well in the computers of emissions testing stations, from what I understand. Seems like there used to be a way to put some earlier machines in "demonstration" (or similar) mode where what was checked and recoreded was retained locally (not in memory) and not transmitted to the State's main database. This way, they could check and "play" to see what might get acceptable readings. Apparently, no more.

You probably noticed that the Inspector had an ID tag he swiped before the test was begun? Plus that the VIN was scanned, too? This is part of the "data trail" for every state inspection in Texas and probably other states too.

Therefore, every time a vehicle is hooked up to an emissions test computer, it's recorded "somewhere". Hence, why the second "full fee" was required.

If there's an EGR issue, it should set a code and illuminate the "Check Engine" light. Probably a higher idle speed, too. In the world of EGR valves, each engine has a particular "flow rate" of EGR that it will tolerate. In the OEM side of things, everything is specific, but on the replacement side of things, there are usually colored washers which will need to be added to the new valve to make it work for particular engine sizes. You can suspect which one is more expensive and is more tailored for the particular engine and vehicle. Be that as it may.

As Jim mentioned, some vacuum leaks can be compensated for by the computer. In general, though, the difference in idle quality is minimal . . . BUT it's there, as you'll usually see when the leak is repaired.

Don't forget to clean the PCV valve, too.

Glad everything's fixed and legal again!

NTX5467

[stealthbob]

This emissions testing gets even sillier here in my area. They decided that they were only going to test cars that are registered in the "Smog Belt"..an arbitrary line that parallels the St Lawrence River. This means that quite literally we have situations where you have to do it but your neighbor doesn't. I'm about a 20 minute drive to this line and yes I'm on the wrong side of it. :mad:

[TxBuicks]

Stealthbob, Texas is the same way. Only certain, high population areas of Texas are required to have emissions testing as part of their annual safety inspection. Diesel powered vehicles and motorcycles are exempt from emissions testing, but are still required to have the annual safety inspection. Any vehicle 2 through 24 years old registered in these counties must get 'sniffed'. Mine, because of its age, was put on a 'treadmill' and operated at a lower RPM for a few minutes, then sped up to a higher RPM for several minutes, with a sniffer crammed up its tailpipe the whole time. Several years ago, I had a car with dual exhaust. When one tailpipe failed, they tried the other side and it passed. So they passed the car.

Edited April 7, 2011 by TxBuicks (see edit history)

[serb]

Just more examples of our government in action!

[Budd]

You probably noticed that the Inspector had an ID tag he swiped before the test was begun? Plus that the VIN was scanned, too? This is part of the "data trail" for every state inspection in Texas and probably other states too.

Therefore, every time a vehicle is hooked up to an emissions test computer, it's recorded "somewhere". Hence, why the second "full fee" was required.

You are correct -- and it's stored in what is called a VID (Vehicle Information Database) which is separate system from most Motor Vehicle registry and safety information systems (DMV, RMV, DOT-- whatever the entity is that governs the vehicle registration for a given State). A VID is a part nearly all (if not all) I/M programs administered by States and Provinces. Older vehicles (model year 1996 and older) usually require a two speed idle and/or dyno test while their emissions are sampled via exhaust gases. Newer vehicles have the option of OBD/OBDII only test, where the Analyzer can sample data directly from a vehicle onboard diagnostic port to verify conditions for a pass/fail result. Information concerning your vehicle and it's test result is either real-time transmitted to the Registration database, or is batch transmitted overnight. That's how your emissions test data becomes part of your vehicle record back at the DMV. VID's track zero personal information about you-- they are only concerned with the vehicle and it's emissions status.

Most Analyzer workstations allow a technician to perform a "pre-inspect" mode test where you can indeed see if the car can pass a test without repair, prior to conducting the official test. Not sure if that is available for the system in Texas, I am not familiar with that system.

Cheers,

Budd