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GM Tech (Cam)
GM Tech (Cam), Chevy Technician
Category: Chevy
Satisfied Customers: 15181
Experience:  GM Grand Master Technician 2007. 14 years experience.
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On my 1996 chevy camero z28 5.7l fails on gh NOx emissions.

Customer Question

On my 1996 chevy camero z28 5.7l fails on high NOx emissions. while checking EGR valve operation, the valve holds vacuum when using a vacuum pump off the car and when the engine is off. If I lift up on the EGR valve at Idle the engine stumbles and die. While driving under a load the duty cycle applies 8" or more vac. to the EGR valve , but the valve does not lift. My concerns are possible back pressure problems.
Submitted: 1 year ago.
Category: Chevy
Expert:  AMEDEE replied 1 year ago.

Hello and welcome! My name is ***** ***** I can assist you with your question. How do you know you have back pressure problems? Have you checked exhaust back pressure? If so how did you check this and what are the readings?

Customer: replied 1 year ago.
I'm Just Suspecting possible back pressure problems., since nothing else makes sense.
Expert:  AMEDEE replied 1 year ago.

Does the engine run ok? Does it have plenty of power under a load?

Expert:  AMEDEE replied 1 year ago.

And how do you know the EGR valve is not opening?

Customer: replied 1 year ago.
Number one its failing Nox Emissions, and two, by using a scan tool I can activate my EGR solenoid by switching on my duty cycle, to see if the EGR valve opens, though pulsing the solenoid and vacuum applied it does not lift while engine is idling or car lifted and back wheel turning.
Expert:  AMEDEE replied 1 year ago.

That itself.. even it was the problem, has nothing to do with back pressure. If you had too much back pressure, the EGR valve would open up too early.

Expert:  AMEDEE replied 1 year ago.

The EGR valve should not get full manifold vacuum.

Expert:  AMEDEE replied 1 year ago.

And just because it fails the NOX readings does not mean the problem is "only" the EGR valve or EGR system.

Expert:  AMEDEE replied 1 year ago.

There are other things that can factor into high NOX

Customer: replied 1 year ago.
Again the valve is not opening while vehicle is under a load. I also changed one catalytic converter ( lefty side) only so far.
Customer: replied 1 year ago.
Isn't the EGR valve suppose to lift with vacuum applied while engine is at idle?
Expert:  AMEDEE replied 1 year ago.

No, the EGR valve does not operate at idle.

Expert:  AMEDEE replied 1 year ago.

The EGR valve should not operate under heavy throttle applications either.

Expert:  AMEDEE replied 1 year ago.

The problem is not your EGR valve.

Customer: replied 1 year ago.
Again, if I apply vacuum using my vacuum pump to the EGR valve while the engine is idling isn't the engine suppose to stall or die if the ports beneath EGR are cleared. So what is the problem seeing that it is not the EGR valve?
Expert:  AMEDEE replied 1 year ago.

Above in your first post you said the engine does stall out when opening up the EGR valve at idle.

Expert:  AMEDEE replied 1 year ago.

So, yes, the engine should stall out when the EGR valve is opened up at idle. This means the EGR ports are clean.

Expert:  AMEDEE replied 1 year ago.

Again, the EGR valve and system is not going to be the issue.

Customer: replied 1 year ago.
I did say when the valve is open the engine stalls. this is when I put my finger in the valve and lifted it up, it stalled. but not when vac. is applied.
Expert:  AMEDEE replied 1 year ago.

Ok, then yes, that is a problem. it sounds to me like the EGR ports are plugged up

Customer: replied 1 year ago.
You said ports are clean, now ports are clogged. the intake port can't be plugged or clogged. So what do you mean exactly? please help me to understand. I'll await your best answer.
Customer: replied 1 year ago.
Are you done answering?
Expert:  AMEDEE replied 1 year ago.

Hello and sorry for the delay! Now that I understand your question better because you explained it to me in more detail, it sounds like the EGR ports are restricted. Start by cleaning the EGR ports and then retesting the system. Let me know.

Customer: replied 1 year ago.
I am Sorry Amedee, I do not think you truly understand my question or know anything about how to solve this problem. You have not been specific enough to me about which port (intake or exhaust port), you cannot say ports if you said the ports are clear. We know the intake port is clear if the engine stalls and die when forced open with my finger, so I am a dissatisfied customer and I won't be needing your services anymore.

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