EGR System Test

Lycaon1349

Registered User
does anyone know how to test the EGR pressure sensor or have any information on the voltage specs? i failed emissions on NOx and before i go taking the car apart to change the EGR i want to check to make sure everything electrical is working properly. also if anyone has any other suggestions on testing other EGR system components or common problem areas to cause high NOx itd be appreciated, thanks
 
What is your vacuum reading at warm idle? Is the vehicle stock?

A large buildup of carbon can cause high NOX readings as well.
 
its running totally normal though, no high idle or anything indicating vacuum leak
You can have a vacc leak thats enough to miss emissions and not have any running problems. Had a (get this) check engine light on wifes minivan from the vapor circuit (caused by a small vacuum leak). The only problem and it was a big one, was fuel consumption. It was about 15mpg on the road... after I fixed it... 21+ :eek: Other than that, there were no start or running problems.
 
does anyone know of a common culprit for the vac leak or is it likely that my egr is actually clogged? i dont want to have to tear apart the car to change out the egr if i dont have to. also just to ask again does the propane trick work with a vacuum leak thatd be that small, or would a SMALL vac leak even be enough to mess with the emissions?
 
It's not common for these cars to plug the EGR.

Common tricks for finding vacuum leaks don't really work on these cars unless the leak is extreme. The EEC reacts so fast to changes in fuel (propane) that you won't normally get an rpm fluctuation that you can observe.

Go to a shop and have a smoke test done. A smoke test is definitive and 100% accurate. Just make sure the supercharger bypass is open during the test.

As for the EGR, it is easy to check once you have it off the car, on the car I don't think there is any good way to check it.

Before I would worry about all that I would start with new plugs, clean the MAF, replace 02 sensors if they are old, and have someone check your cats with an infrared heat gun. That will tell you right away if you have a non-functional cat.

In my experience you don't usually need a functioning EGR to pass emissions testing, regardless of what you are told.
 
The EGR only operates under throttle to reduce NOX by reducing combustion temperature. Spring pressure keeps the EGR closed at idle. If you want to check your EGR valve it is pretty simple with it still attached to the engine. Just remove the vacuume line and plug it. Connect a handheld vacuume pump to the EGR. Start the engine and apply vacuume to the EGR. The engine's idle will start to change to try to compensate for the vacuume leak created by the EGR valve opening. The more the EGR opens, the worse your idle will get. If your idle does not change or only changes slightly, then you have a clogged intake port or exhaust tube. When they removed lead from gasoline in the 70's, the gas lost its ability to keep combustion temperatures down and with the increase of temperature came the dreaded "run on" and also "spark knock" or detonation. With the EGR bypassed or not functioning properly, your engine is more likely to detonate under acceleration, and of course, your NOX goes up. More NOX is created when your combustion temperature rises so let your car cool off prior to taking your emmissions test, especially if your EGR is by-passed or not functioning. The catalytic converter also removes NOX and need to be hot in order to remove NOX from your exhaust gas so don't let your car cool off too much. I would think you would need a fairly large vacuume leak for your car to fail emissions considering everything else was working properly. If your car is not running hot and the EGR is functioning properly, then I think you most likely have a spent converter.
Mark
 
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