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EGR valves

4X4HIGH

4X4HIGH

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Who knows about them and how to properly test a positive back pressure EGR valve? I have searched and found some info but it is contradicting with other info.

Here's what i know from my testing tonight. I first removed the vacuum hose from the EGR valve (EGR still attched to the engine) and hooked up my vacuum pump and when i pumped it i could see that the valve opened (from everything i've read and have been told this should not be able to do be done with this style of valve), i then pulled the EGR solenoid and tested that it's working by hooking a 9 volt battery across the terminals and the solenoid clicks and i'm able to draw a vacuum through the solenoid, i then started the engine and once again hooked my vacuum pump to the EGR valve but now with the engine running the EGR valve will not open when i try to apply a vacuum to it. With the engine running i was able to manually push the diaphram up and the RPM's changed by about 100 RPM's which tells me that ALL passages are clear. The only thing i don't know now is if i'm getting a reference signal to the EGR solenoid when it is commanded to open (how can i test for this)? Also because of my initial test of applying vacuum to the valve (still attached to the engine) and the valve being able to open do i even have the correct valve? I did replace this valve once by vehicle specific application several years ago.

I may not even have a problem but i want to make sure the system is working properly since my NOx was slightly higher than the MAX allowable for emissions testing purposes. If the EGR system is working properly then i need to install a new CAT ($225.00 installed) no more friendly $99.00 Hi-Flow CATS in California. :mad:
 
Well here's a question...does it trigger the check engine light?

You probably already know this? ECM commands EGR to solenoid, solenoid opens, valve opens.Vacuum in engine decreases (EGR open is a vacuum leak) and the MAP sees the pressure change. If the pressure change does not occur, the check engine is SUPPOSED to trigger.

My manual isn't handy, I can check it tomorrow, but I'm not even certain which type was used on these trucks, or if both were, depending on application or engine.
 
No SES light and no driveability issues. I'm just trying to get my NOx within a reasonable and allowable number so it will pass an emissions test. It appears this valve is supposed to be a positive back pressure valve BUT from some info i found on the internet is leading me to believe (from the testing i've done) that it might be a negative pressure valve that is on my engine. :crazy:

I have one last test to peform tomorrow before i actually pull the valve and inspect/test or replace it.
 
According to the GM repair manual the negative backpressure EGR valve will hold vacuum, if the vacuum bleeds off then the valve is bad.

I could try and explain the backpressure part but there's no point without pictures and diagrams. Sufficed to say it's not causing your problems.

As for the EGR solenoid; the pink wire is switched power the gray wire is the ground that is controlled by the computer. The computer should apply ground above idle. I've seen some that require input from VSS before applying EGR, it all depends on the chip.

To check solenoid operation connect a test light to the gray wire and the other end to battery power and see what happens. You may have to drive it with the test light connected. If the computer never switches the ground then you need to get a hold of the chip burner guy and have him check the EGR tables, he may have disabled them.

The other thing to check is actual EGR function by applying 15 inches or more of vacuum to the EGR valve with the engine idling. It should kill the motor or at least make it idle absolutely horrible. If it doesn't then there is a restriction somewhere and/or the wrong EGR valve or wrong EGR restrictor installed in EGR valve.
 
bigblock72 said:
According to the GM repair manual the negative backpressure EGR valve will hold vacuum, if the vacuum bleeds off then the valve is bad.

I could try and explain the backpressure part but there's no point without pictures and diagrams. Sufficed to say it's not causing your problems.

As for the EGR solenoid; the pink wire is switched power the gray wire is the ground that is controlled by the computer. The computer should apply ground above idle. I've seen some that require input from VSS before applying EGR, it all depends on the chip.

To check solenoid operation connect a test light to the gray wire and the other end to battery power and see what happens. You may have to drive it with the test light connected. If the computer never switches the ground then you need to get a hold of the chip burner guy and have him check the EGR tables, he may have disabled them.

The other thing to check is actual EGR function by applying 15 inches or more of vacuum to the EGR valve with the engine idling. It should kill the motor or at least make it idle absolutely horrible. If it doesn't then there is a restriction somewhere and/or the wrong EGR valve or wrong EGR restrictor installed in EGR valve.
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Well, i believe this year blazer is supposed to have a positive back pressure EGR valve and those can't be tested with a vacuum pump (HOWEVER, i was able to use a vacuum pump and the diaphragm did open and held BUT with the engine running it won't do it). From the reading i've done this is typical of a NEGATIVE back pressure EGR . :confused:

I did think about the chip not being set-up for EGR function and i have an e-mail into Brian @ TBIchips to see if there is a way for him to check if that was deleted from the chip or not even though i told him i need ALL emissions related stuff functional. I'll have to wait to hear from him to know about that. My other thought was to disconnect the EGR solenoid wire so that the EGR valve can't open if commanded to do so and shouldn't that throw a code 32 if it did not open and the ECM didn't see any change?
 
Yes, disconnecting it should trigger the light as well.

I believe it's possible to disable the check engine light but leave EGR functional, but Brian will tell you.

He could probably email you the .bin and you could look at it yourself in tunerpro or something similar.
 
4X4HIGH said:
Well, i believe this year blazer is supposed to have a positive back pressure EGR valve and those can't be tested with a vacuum pump (HOWEVER, i was able to use a vacuum pump and the diaphragm did open and held BUT with the engine running it won't do it). From the reading i've done this is typical of a NEGATIVE back pressure EGR . :confused:
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According to GM these either came with a negative backpressure EGR (under 8600 gvw) or an electronic vacuum regulator solenoid (over 8600 gvw). They don't show a positive back pressure as an option. You are right about it not opening with the engine running (didn't think about that when I mentioned testing it, it was late) as the manifold vacuum will hold it closed.

If the solenoid isn't receiving a signal from the computer then it has to be either a bad computer or the EGR is disabled in the PROM. Just make sure you do everything you can to test the operation of the EGR solenoid and computer, it'll sure save some hassle with the chip.
 
I did a little further testing this morning and here's what i did. I ran a vacuum hose directly from the throttle body to the EGR valve bypassing the solenoid and once the RPM's are above 2000 or so the valve will start to move and playing with the RPM's will change how the valve reacts so i'm pretty confident that the valve is working. The only unknown at this point is whether or not the ECM is sending a signal to the solenoid when EGR is commanded. I will now unhook the electric to the solenoid and drive it which should force the ECM to throw a code 32 since the 02 isn't reporting to the ECM what the ECM is looking for. I will post back later today once i've accomplished this "test".
 
Brian got back to me and here is what he said.

I made the EGR valve open up more and will send the updated programming out today. Please send the old chip back once you get the new one and that should help you out with your NOx. Also, make sure your not using platinum plugs in that motor. For some reason, I have a lot of problem with NOx and platinum plugs for some reason.

Now i want to know if the ECM varies voltage to the EGR solenoid to allow it to only open so far depending on the voltage supplied. The reason i wonder this is his response that said " I made the EGR valve open up more "

I disconnected the EGR solenoid wire and drove about 8 miles under varied conditions and that did not turn on the SES light and i also checked by grounding the A & B terminal to verify that no code was set. So now i don't know if i have a problem with the ECM or not.
 
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My understanding of the EGR process is that the solenoid is pulse-width modulated, same as injectors I believe. Opens/closes the solenoid rapidly to attain the result desired.
 
dyeager535 said:
My understanding of the EGR process is that the solenoid is pulse-width modulated, same as injectors I believe. Opens/closes the solenoid rapidly to attain the result desired.
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Only the over 8600 gvw trucks used an electronic vacuum regulator solenoid that used a duty cycled signal from the ECM. The EVR systems also used a conventional EGR valve, whereas the under 8600 gvw systems used a simple solenoid with a negative backpressure EGR valve.
 
How can i test if i'm getting a signal to the EGR solenoid? Is it as easy as unplugging the solenoid wire and using a test light between the terminals (ECM side) to see if the light will light at any time while driving? If not do you know how to test up to that point?
 
4X4HIGH said:
How can i test if i'm getting a signal to the EGR solenoid? Is it as easy as unplugging the solenoid wire and using a test light between the terminals to see if the light will light at any time while driving?
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Yep, just make sure the pink wire has keyed power then connect the test light to the signal wire and go for a drive.
 
I checked and with key on engine off i get 11.77 volts at the pink wire.

Am i supposed to put a test light between the pink and gray wire to see if EGR is commanded?
 
bigblock72 said:
It's not after 5:00 what are you doing working on your own stuff?:D
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Sometimes it's nice owning your own business, except when you have time to work on your own junk because there isn't any business coming in the door, which also means no money, which also means no paycheck. ;)
 
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