If someone with a LT1 could please help me.

Open the hood.. put a vacuum pump on the EGR valve, crank the engine and start it.. apply vacuum.. does the engine try to bog down and die?

Please let me know.

Thank so much in advance..

 

Yes, it should try to die.

http://shbox.com/1/4th_gen_EGR.html

 

Thanks Rob.
Does our EGR need a certain amount of backpressure first in order to actually move the diaphram using a vacuum pump?

I have a negative backpresure type N.

Ok. I took the EGR off, took it to the parts house, and was about to purchase a new one when the guy behind the counter informed me that since it is a negative backpressure valve, just applying pressure will not make it open..

He asked me to get a helper ( the wife ) and have her sit in the car, with the e-brake engaged and with the brake pedal pressed.. then put it in drive and tap the gas pedal to put a load on the engine.. if I felt the EGR valve move, then I would know that the system in itself was working correctly.

Well, that test failed.. I and still do not know why I left my theory of the vacuum test at the parts house counter.. I feel like i should have just bought the damn thing..

I am correct when I assume that if I apply vacuum to the EGR vacuum port, and it does NOT hold vacuum, and it does NOT effect the idle.. then the EGR diaphram is non functionable?

 

I have not tried that exact test. The testing info in the link is what the factory manual shows for testing. Maybe I should have not answered yes to your question so quickly. I was thinking of the pushing in of the diaphragm test. I might try to do your test tomorrow, if I have time.

 

Please Rob. if you have time. Thank you sir.

 

Anyone else tonight wanna help out a fellow member that is in a pinch?

 

I think there may be an easier way of proving the problem is the egr valve. You've already proven that the egr valve isn't sticking by pressing it while the engine is idling. Next step is to run a vacuum line from the egr to a known vacuum port on the engine. I would just run the line so that it can reach where the fuel pressure regulator is plumbed. Leave the regulator attached, start the engine and let it run a minute or two until it idles smoothly. Then switch the line to the egr. If there is no difference in idle quality the egr valve is bad. If there isn't then check the wiring and plumbing going to the egr for problems.

This method gets around any low back pressure issues associated with the type of egr.

Two things-have you checked for any stored codes and are you certain that your vacuum pump pulls a vacuum?

 

Thanks everyone.. I just said the hell with it and purchased the new EGR valve..

Installed.. It holds vacuum... sorry I made a huge deal about this.

FACT = Negative backpressure EGR valves, installed on our LT1, with engine running, will at the very least hold a vacuum via the vacuum port using a vacuum pump.

Thanks again Rob and bw_hunter (again!!)


close this thread.

 

It is a no-brainer to say that the EGR valve has to hold vacuum (otherwise, it could not operate). I was unable to address this until today. I did test on my own car at idle and applying vacuum directly to the EGR valve. The engine immediately started to stumble and run rough (as expected). When releasing the vacuum, the idle cleared up.

 

Thanks Rob.
I should have stuck to my guns when I was going to buy it in the first place.
The older gentlemen behind the counter that used to teach some kind of community college shop class chuckled when he saw me in there with my vacuum gauge and EGR..

He said I would love to take your money and sell this to you.. but your problem likely falls somewhere else..

If I would have just went with my gut.. reinforced by what you guys say.. i would have had a better running car with inspection sticker one day earlier!!

 

Next time you see him, you can point out his error.

 

This is the plan.

 

Actually, the error was yours, taking diagnostics advice from a parts counter guy...LOL

 

Yes. I understand this. It was a very humbling experience. :-S

 

Chuckle... Don't beat yourself over it. Before the recession and high unemployment I would have said that parts guys do parts work because they aren't diagnosticians. Now you have college professors working at McDonalds so anything is possible. I guess the bottom line is to do your own diagnosis, getting help where you need it, and decide your own path forward. You don't have to ignore the parts guy, just don't attach a ton of importance to what he says....

Glad it's fixed......