OT: Failed Emission check

Slowpoke

Well-known Member
My van failed the 25 mph test with high NOX. The tech said it was most likely the EGR valve. So I run the engine, put a vacuum pump on the valve and I cannot pull a vacuum.. I manualy press in the diaphram and the engine stops. With the EGR off the engine, mouth vacuum pulls in the diaphram. There is only a single vac nipple, and no electronics on the valve.
Although there are two smaller holes on the EGR, there are no matching holes on the engine and the gasket has only two large holes, so the small holes are blocked off. . The EGR is same as ACDelco 214-5073. Can this be a back pressure valve? Apparently there is no check except to replace at $50+.
The same thing happened 2 years ago and it turned out to be a bad oxygen sensor. That was probably less than 500 miles ago. Can it happen again?

Thanks for your advice.
Slowpoke.
 
Scan it through the OBD. If you don't have access to a scaner,see if a part house near you will scan it for you. Are you running fuel aditive? Some fuel additives mess with exhust read out,cause bad reading on good system or vis versa.
 
(quoted from post at 04:07:19 02/28/15) My van failed the 25 mph test with high NOX. The tech said it was most likely the EGR valve. So I run the engine, put a vacuum pump on the valve and I cannot pull a vacuum.. I manualy press in the diaphram and the engine stops. With the EGR off the engine, mouth vacuum pulls in the diaphram. There is only a single vac nipple, and no electronics on the valve.
Although there are two smaller holes on the EGR, there are no matching holes on the engine and the gasket has only two large holes, so the small holes are blocked off. . The EGR is same as ACDelco 214-5073. Can this be a back pressure valve? Apparently there is no check except to replace at $50+.
The same thing happened 2 years ago and it turned out to be a bad oxygen sensor. That was probably less than 500 miles ago. Can it happen again?

Thanks for your advice.
Slowpoke.
aybe not valve malfunction, but whatever controls the vacuum line which controls the valve.
 
While I am not familiar with your van, do not know make, model, or year, I can offer some advice....
I have been to several schools on emissions. One thing that I learned is that the whole purpose of the EGR is to reduce NOx emissions. It serves no other purpose.
The line of reasoning is this:
NOx is formed from high combustion chamber temperatures. EGR reduces the peak temperatures in the combustion chamber thus reducing NOx emissions.
On most older engines, EGR is controlled by carb vacuum taken above the throttle plates, most commonly venturi vacuum. This actuates the EGR valve at mid to higher throttle openings when engine load is highest, and combustion temperatures are also their highest.
The second generation of EGR mostly used a pair of solenoids to control EGR opening. EGRC and EGRV were the official designations. These were controlled electronically by the PCM. These were later replaced by a single modulated solenoid also controlled by the PCM. The electronically controlled ones use some form of monitoring actual EGR flow or opening in a feedback type of circuit. The backpressure EGR valves monitor flow mechanically by balancing engine vacuum against exhaust backpressure.
Your problem sounds like the EGR is not functioning. You may be able to sneak it through an emission test by retarding the timing slightly. A slightly richer mixture would also help to keep the NOx down. But that might raise your HC and CO numbers.
 
Strange that the valve will open with mouth vacuum but not with the vacuum pump. Try the vacuum pump again with the valve off. See if it gets to a point that it looses vacuum somewhere toward the full open position. If it moves full stroke without loosing vacuum, you can assume the diaphragm is good.

Since the engine idled well with the valve closed, the valve is sealing closed as it should.

Since the engine dies when manually opened, the ports are not clogged.

The only thing left to check is the vacuum source to the valve. With the engine up to temp, put the park brake on or have an assistant hold the brake, put the transmission in drive, slightly crack the throttle. You should be able to feel the diaphragm move as the valve opens. Don't help it, just carefully feel for movement. If it doesn't move, check the vacuum circuit back to the source. Could be a bad temp controlled valve, a split hose, improperly routed, etc.
 
The valve will open with any source of vac either off or on the stopped engine. With engine running the valve can't be pulled open by mouth or pump.
Reconnected to engine vacuum source, if engine speed is increased to about 12-1500rpm only a very tiny movement of the diaphragm is felt. The control module that supplies EGR vacuum was replaced at the prior emissions check with 2 new units to no avail. It turned out to be the the oxygen sensor which was then replaced. The van has 66K miles and less than 500 in the last 2 years. Very strange and frustrating to have the same problem 2 years in a row.
 
No additives in fuel. I have an AutoXray scanner which did not detect the exact same problem on the prior emissions check. It said the vacuum control unit was bad. So I replaced it twice without any change, thinking maybe the first one was defective... I manualy tested the oxygen sensor which proved to be bad. I replaced it and passed the test.
Can the replacement be bad after only 500 miles?
AAARRRRGGGG!!!
 
If its not throwing any codes, you may try and squeek it thru with e85 . Run the fuel down to a quarter tank, then add enough e85 to get a little over a half tank, get it good and warm and run it thru. Had to do that with my old corvette. After the test, fill the tank up with regular fuel. May also block some of the radiator with a little cardboard to get the engine a little hotter when testing.
 
I had three bad valves right out of the box, so it can happen.
The probem I had was that the valve would stick in the open position and if you gave it a tap with a wrench or short bar it would then release.
 
My son has a Hyundai that he has replaced the Oxygen sensor about once a year for the last three years. Yes, it can happen again.
 
Does your EGR go to a thermal vacuum switch (TVS)? If your engine runs well enough 17-21 inches of vacuum and the diaphragm seals, it should open. I would check vacuum supply before replacing the valve. I believe it needs to be at operating temp for the TVS to work.
 
Try running a small braided ground strap from your exhaust system via an exhaust clamp to the frame or a good ground.
 

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