emissions problem....1989 GMC Sierra

Not sure what you guys can tell me, but wanted to pose the question.....

I tried to get my truck inspected today and found that it wont pass the NOx portion of the emissions testing. The truck doesnt smoke at all from the tail pipe and the oil pressure is around 30 on the dash gauge. No check engine light is on and it runs and drives really good with plenty of power, even with 253k miles on it. It does have a catalytic converter on it too.

What is the possible problem with the emissions?

EGR or you are running really lean. See http://www.troublecodes.net/articles/smog.shtml.

You need a vacuum pump to test the EGR and the EGR solenoid.

//2000CAYukon

The EGR valve will hold approx. 25 in. Hg.....after about a minute it will start loosing an inch every 30 seconds. It doesnt seem to have a large leak and seems to hold a good pressure. Also, the link you provided said that the EGR and Exhaust Gas Oxygen Sensor work kinda together. Not sure if there is a way to test the EGOS, but for $20 at AutoZone, should I just replace it? Also, the link stated the CAT converter.....how do I know if it is working properly?

Would putting a couple cans of Berrymans B12 and a few gallons of super unleaded gasoline in the tank help?

I also want to know....if my alternator isnt pushing enough voltage, would that affect my problem at all. I know it is going bad, I checked it today and it is pushing 11 volts max and my dash gauge reads really low.

Much longer, with not many more parts.....I will have a new truck, geeezz.

The EGR valve will hold approx. 25 in. Hg.....after about a minute it will start loosing an inch every 30 seconds. It doesnt seem to have a large leak and seems to hold a good pressure.


If it not holding a vacuum, I would replace it. The factory manual says to apply around 20 in vacuum and then start the truck. The vacuum should go zero after start. However, it should still hold a vacuum.

You should also hook the vacuum pump up to the TBI side of the EGR solenoid. It must also hold a vacuum.

Also, the link you provided said that the EGR and Exhaust Gas Oxygen Sensor work kinda together. Not sure if there is a way to test the EGOS, but for $20 at AutoZone, should I just replace it?


How old is the 02 Sensor? I would recommend AC Delco here for a replacement.


Also, the link stated the CAT converter.....how do I know if it is working properly?


Not sure how to test them. 100,000 miles is pretty good for a converter.


Would putting a couple cans of Berrymans B12 and a few gallons of super unleaded gasoline in the tank help?

Hooking up a scanner here could help. It would tell you if it is running lean (bad 02 or mechanical issue) or not.

On your air cleaner, there is a valve that allows hot air from the passenger side exhaust manifold when the engine is cold. Make sure this valve closes when the engine is warm and not allowing hot air into the air cleaner.

Mine is bad so I wired it shut to keep all the hot air out.

//2000CAYukon

I also want to know....if my alternator isnt pushing enough voltage, would that affect my problem at all. I know it is going bad, I checked it today and it is pushing 11 volts max and my dash gauge reads really low.

Much longer, with not many more parts.....I will have a new truck, geeezz.

11 volts is too low; however, I don't know if this is causing your emissions issue or not. Another part that needs replacing :grinno:

//2000CAYukon

I will replace the O2 sensor....not sure what age it is, although I can say that is came out of the manifold real easily (not like an old one would have). As far as how many miles is on my converter....not sure, but the odometer reads 253k miles and last years readings for emissions were great and it passed with flying colors. I will check the air cleaner valve at the exhaust hot air side and see if it is working properly as well as the vacuum pressure on the TBI side of the EGR and let you know what I find.

I have to wait until my next pay day (2 weeks) before I can start buying parts. I tried taking the alternator apart and putting a kit in it, but fubared it up......so I cant even start the truck right now.

I will replace the O2 sensor....not sure what age it is, although I can say that is came out of the manifold real easily (not like an old one would have). As far as how many miles is on my converter....not sure, but the odometer reads 253k miles and last years readings for emissions were great and it passed with flying colors. I will check the air cleaner valve at the exhaust hot air side and see if it is working properly as well as the vacuum pressure on the TBI side of the EGR and let you know what I find.


How does the 02 sensor look? Is it black or more light brown in color?

I still think the EGR valve needs to be replaced if it does not hold vacuum.


I have to wait until my next pay day (2 weeks) before I can start buying parts. I tried taking the alternator apart and putting a kit in it, but fubared it up......so I cant even start the truck right now.

I can relate. I rebuilt my alt probably a year and 1/2 ago. It lasted a year and then I started having wierd problems. Replaced it with a life time warranty unit from my local parts store. Should have done that the first time.

Post back when you make some progress.

Good luck!

//2000CAYukon

Ok....I just checked the EGR solenoid and it does NOT hold a pressure with the truck not running (cold). I am trying to look it up to get a price on it, but there are listings for all kinds of EGR solenoids.....it has two ports coming off of it. The top port is plugged off and the bottom port goes to the EGR valve and there is a elect. plug on the opposite side. It is a very small part that will fit in the palm of your hand. I checked both ports for vacuum, and niether would hold any pressure at all, I made sure to plug the alternate port before pulling a vacuum. Did I perform these actions properly?

What is this part "exactly" called.....control relay, position sensor, vacuum modulator valve, vacuum solenoid or pressure sensor?

The O2 sensor tip was very light in color, not really even brown....more on the "whiteish" side.

Ok....I just checked the EGR solenoid and it does NOT hold a pressure with the truck not running (cold). I am trying to look it up to get a price on it, but there are listings for all kinds of EGR solenoids.....it has two ports coming off of it. The top port is plugged off and the bottom port goes to the EGR valve and there is a elect. plug on the opposite side. It is a very small part that will fit in the palm of your hand. I checked both ports for vacuum, and niether would hold any pressure at all, I made sure to plug the alternate port before pulling a vacuum. Did I perform these actions properly?


One port is connected to the TBI, the other to the EGR valve. The port on the TBI side should hold vacuum with the engine off. The ECM controls when the solenoid opens to allow vacuum to go to the EGR valve. If the TBI side is not holding vacuum, it is bad and needs replaced.


What is this part "exactly" called.....control relay, position sensor, vacuum modulator valve, vacuum solenoid or pressure sensor?


www.acdelco.com calls it "SOLENOID,EGR VAC REG VLV" or EGR Vacuum Regulator Valve Solenoid. The AC Delco part number is 214-329. You can buy this at any AC Delco Parts store or online at www.rockauto.com


The O2 sensor tip was very light in color, not really even brown....more on the "whiteish" side.

Sounds like the 02 looks normal.

//2000CAYukon

I purchased an EGR vacuum solenoid, O2 sensor, spark plugs, gas cap, belt and a new alternator. I installed all of these items, stopped to put gas in the truck on the way to re-inspect it and put some B12 in the tank with the gas. Well, it passed inspection this time......but BARELY. It only lacked a few points from failing again, literally. I am happy I got my inspection and I can "legally" drive it now, but something still isnt right. I guess my only other option is to replace the cat converter before I have to get it inspected again.

I did a vacuum check on the EGR valve itself and it will hold a good 20 in. without leaking......so I am assuming the egr valve is good.

I purchased an EGR vacuum solenoid, O2 sensor, spark plugs, gas cap, belt and a new alternator. I installed all of these items, stopped to put gas in the truck on the way to re-inspect it and put some B12 in the tank with the gas. Well, it passed inspection this time......but BARELY. It only lacked a few points from failing again, literally. I am happy I got my inspection and I can "legally" drive it now, but something still isnt right. I guess my only other option is to replace the cat converter before I have to get it inspected again.

I did a vacuum check on the EGR valve itself and it will hold a good 20 in. without leaking......so I am assuming the egr valve is good.

Was it HC the problem or was it still NO giving you the problem?

//2000CAYukon

NOx