My '90 vette. just failed the smog test!
NOx is 4 times higher than the max allowed, it drops to about 2.5x at the higher RPM test level. The other thing is the CO is essentially zero, it was about 71x lower than the max level.
We have searched for vacuum leaks and found nothing.
The engine temp is essentially normal
The timing is actually 1.5 degrees retarted
Since the EGR is not active at idle and since it fails horribly at IDLE, it has to be somthing other than the EGR.
It has eight new fuel injectors.
It has a new coil, cap, plugs and wires.
It would seem that the source of the problem is a lean mixture, yet we find nothing to create a lean mixture. We are now thinking that may be the O2 sensor is out of wack. We believe the O2 sensor may be original with 100K miles. From what I have read, they tend result in a more rich mixture as they near the end of their life. If so, this is probably not the source either.
The check engine light if OFF
Any ideas?


[Modified by split63, 8:21 PM 2/28/2004]

 

Are you assuming the EGR is not active at idle or have you checked? The solenoid or the valve could be bad.

How does the car idle?

 

Well, the EGR gets vacuum as the throttle is opened. At idle the throttle is essentially closed and as a result there is no vacuum to the EGR.
My understanding is that the EGR only operates off idle. While it was idling I pulled off the hose and I could feel no vacuum, as I opened the throttle I clearly felt the vacuum increase with increasing throttle opening.

Thanks,


[Modified by split63, 8:38 PM 2/28/2004]


[Modified by split63, 8:39 PM 2/28/2004]

 

NOx is the only one I passed and I ended up having a bad egr valve.
I'm interested in seeing what happens in this thread because I've done a number of things and am hoping to pass :confused:

 

Another thing that is supposed to be off at idle is the gas vapor evaporator can.Is it working right?

 

I'm not seeing a connection to the high NOx and low CO emissions?
I looked the Canister over in search of vacuum leaks, but found nothing out of the norm.

 

Do you have a modified exhaust (bigger front or rear y-pipe)? If so, the engine is probably lacking enough back pressure for the EGR to function properly which results in high NOX levels.

 

The car is entirely stock. No modifications of any kind

 

My '85 Z51 completely stock/unmodified with 143,000 miles passed on the fourth try.

It received a new cat.. the original one must have hit some road rocks; the front half was cracked and the back half of the honeycomb was missing, it had long since passed through the tail pipes.

I put in some stock AC Delco spark plugs and cut back the electrodes for better buring efficiency.

Changed the oil with premium Mobil 1 10w-30; the engine needs valve seals and guides-- it smokes.

I also installed a new original type air filter.

Installed a new air pump because the old one squeeked.

I found that if my car was tested at around 197 to 205 degrees it did much better. It failed miserabily at 230 degrees.

Lots of Luck.





[Modified by Mark-44, 8:04 AM 2/29/2004]

 

One thing I found on my 88 was the vapor canister and all the vacuum lines were good but the solenoid controlling the canister had went bad in the open position so it was purging even at idle. You might give that a check.

Ethan

 

You've helped me, GKK.
My cat was hollowed! I wonder if this is causing the continued code? :yesnod:


[Modified by Vett-eight-nine, 11:45 AM 2/29/2004]

 

QUOTE]One thing I found on my 88 was the vapor canister and all the vacuum lines were good but the solenoid controlling the canister had went bad in the open position so it was purging even at idle. You might give that a check.[/QUOTE]

Where is the controlling solenoid located?[

 

You have verified the EGR is recieving the correct vacuum signels, but have you checked that it isn't hanging open or leaking? If exhaust gasses are entering the intake, you would have a lean mixture, which could cause high combustion temps (and NOX) and a lean missfire. I had the spring on an EGR weaken with age, and it caused similar problems. If there is a carbon build up on the valve or seat, gasses can pass when they shouldn't. Good luck, and...

RACE ON!!!

 

The solenoid is located right next to the canister, I will have to run out and look to tell you exactly what it is bolted to. You just need to follow the larger vacuum line from the throttle body (I can't remember if it is 5/16 or 3/8) back to the canister, it should go to a solenoid first then another hose goes from the solenoid to the canister. If I remember correctly it should be closed when it has 12 volts and open when the voltage is 0. I don't have a camera handy otherwise I would take a pic for you.

Good luck

Ethan

 

[QUOTE]You have verified the EGR is recieving the correct vacuum signels, but have you checked that it isn't hanging open or leaking? If exhaust gasses are entering the intake, you would have a lean mixture, which could cause high combustion temps (and NOX) and a lean missfire. I had the spring on an EGR weaken with age, and it caused similar problems. If there is a carbon build up on the valve or seat, gasses can pass when they shouldn't. Good luck, and...QUOTE]

I tend to believe that this would not be the case since when the EGR is open it lets Oxygen devoid exhaust into the intake. This reduces combustion temperatures and lowers NOx emissions. Since my NOx are very high, I can't see how this would be the cause.

At this point I'm considering three sources of vacuum leaks:
1. Bad PCV valve
2. Bad valve on the Fuel Vapor recovery tank
3. leaky brake boost line (unlikely, as the brakes work great)

 

Okay.

 

Ok folks, I think I found the problem. Although I have not retested the emissions yet, we found that the PCV valve was wide open. That was the vacuum leak. We bought a FRAM replacement, and the new one was much more closed at idle.
For those of you unfamiliar with the PCV valve, its designed to be slightly open when there is little blow-by(Idle), and more open when there is a lot of blow-by (WOT) . IT works very simply in that it hooks right to manifold vacuum. When the vacuum is high (IDLE) it seats an internal plunger, and very little air passes. As the vacuum degreeses (increasing throttle opening), an internal spring moves the plunger to the more open state.

The old one was so open at idle, that if I pulled the hose off the other valve cover and put my thumb over the hole, a vacuum would form. When I pulled my thumb off, you would hear and feel the vacuum. The entire crankcase had a vacuum on it.
When I put the new PCV valve on, I could no longer feel a vacuum passing through the crankcase to the other valve cover. I'm very confident that was the issue. That was one big vacuum leak. And of course the ECM masked the problem by lowering the idle and enriching the mixture. In fact, the engine ran fairly well, though it did not have all its power.

The old valve looked good too. It had no rust, and had a light coat of oil on it. You could hear and feel the plunger move inside.

Best of all, the new part was only $3.00

Thanks for your help all.


[Modified by split63, 4:24 PM 2/29/2004]