Do I need a Positive or Negative EGR valave?
 

I have a 91 z28 that was originally equipped with a 5.0L enginge.
I did a swap about 3 years ago and put a 5.7L engine in the car.

My brother changed the egr valve when the 5.0L was still in the car but he isnt sure if he replaced it with the correct part.

When I did the swap I put a new egr valve on and it needs to be replaced already. I'm thinking it may have failed so early because the incorrect part may have been on there?
Do I want a negative or postive back pressure egr valve? What would my car originally have been equipped with?

The other thing is, I have a borla exhaust system in which I have different plates that I can insert to control how much exhaust is forced into the muffler. I usually use the plate that forces no air into the muffler. I dont really know anything about negative or positive back pressure and how an egr valve actually works but if I dont have any exhaust being forced into the muffler I'm guessing I would have less back pressure than if I did force some exhaust into the muffler. Could that affect how my egr valve works and possibly be why my egr valve failed so soon?

I recently changed my plugs, wires, cap and rotor and the car is running fine. It's probably idling the best it ever has even though the egr valve isnt working properly

Re: Do I need a Positive or Negative EGR valave?
 

They were originally negative, but most of the aftermarket ones are positive. Doesn't really matter as long as it opens. How did it fail?

Re: Do I need a Positive or Negative EGR valave?
 

The guy at a local garage told me it wasn't holding a vacuum.

Re: Do I need a Positive or Negative EGR valave?
 

That doesn't mean it's bad. You need to apply vacuum to it when the engine is running at about 2000 RPM and see if the diaphragm moves.

Re: Do I need a Positive or Negative EGR valave?
 

Yes, it does matter what kind of EGR valve you replace it with.

It should be a negative back pressure EGR valve. If you apply vacuum to it with the engine off, it should open and stay open. Start the engine and the vacuum will bleed off and it should close.

Re: Do I need a Positive or Negative EGR valave?
 

This is only true for a stock NP valve. At 20+ years old, there's no way to know for sure. A PP valve will work and is what most aftermarket ones are.

Re: Do I need a Positive or Negative EGR valave?
 

The guy at the garage said he tested it and it wasnt working properly...that is also why i failed my emissions test.

Seeing as how I would have little back pressure the way my exhaust is set up, should I try and get a postive or negative back pressure egr valve?

How important is the egr valve? My car is running so well right now I almost dont want to change it?

Re: Do I need a Positive or Negative EGR valave?
 

It only effects it at part throttle. You can use a Standard Motor Products EGV-393 which is a positive pressure replacement. Rock Auto has them, among others.

Re: Do I need a Positive or Negative EGR valave?
 

Are there certain brands I should stay away from or is an egr valve an egr valve?

My dad will be by autozone and advance auto parts tomorrow. Autozone carries Duralast and Advance Auto carries BWD.

Or should I go the ebay route and try and get a gm egr valve?
Are ACDelco parts what gm used?