EGR and BPT operation

[Tungsten]

I have some questions for those who are running performance exhaust systems.

 

When I had a somewhat stock exhaust, I would hear some snapping/ticking sound on acceleration, which was coming from the BPT valve.

I don't know if it's supposed to make any noises but it did yet the engine worked fine and there were no codes coming up or anything like that.

Actually, that was from an exhaust leak so that's all good now.

 

Now when I switched over to a 2.5" exhaust, which reduced the back pressure significantly, the snapping/ticking sound is no longer there. Does that mean the BPT valve no longer responds to back pressure?

If the BPT valve is no longer operational then what happens to the EGR valve? Does it stay open or closed? Would cutting the EGR off be a good solution? Would cutting the EGR make it burn too rich or too lean?

 

I'm trying to figure something out here...

Edited July 9, 2011 by Tungsten

[ejin4499]

I have some questions for those who are running performance exhaust systems.

 

When I had a somewhat stock exhaust, I would hear some snapping/ticking sound on acceleration, which was coming from the BPT valve. I don't know if it's supposed to make any noises but it did yet the engine worked fine and there were no codes coming up or anything like that.

Now when I switched over to a 2.5" exhaust, which reduced the back pressure significantly, the snapping/ticking sound is no longer there. Does that mean the BPT valve no longer responds to back pressure?

If the BPT valve is no longer operational then what happens to the EGR valve? Does it stay open or closed? Would cutting the EGR off be a good solution? Would cutting the EGR make it burn too rich or too lean?

 

I'm trying to figure something out here...

If the bpt valve is no longer operational that means that no vacuum is being applied to your egr valve. Which means that it is never opening. This is not necessarily a bad thing and it wont throw a code on our trucks if its not working right.

The egr attempts to reduces NOX emissions by diluting the intake air mix down so the engine runs a little cooler. If its not working right and you take it to get your truck smoged you may not pass smog due to high NOX emissions. If its missing altogether you wont even pass the visual inspection if they have that in your area.

Edited July 9, 2011 by ejin4499

[MY1PATH]

Back pressure has nothing to do with the valve operation since it is controlled by mannifold vacuum.

However a theroy might be that when the valve opens it may have been opening faster when there was back pressure making a click sound when it was full open. Now that it opens slower it is quieter.

Lastly the engine will still get egr when there is less back pressure because the vacuum from the maniflod still pulls the exhaust in from the valve.

[Tungsten]

Alright, thanks for the info. I'm new to the EGR valve concept so I wanted to understand how it works.

 

Would the manifold vacuum decrease with a more free flowing exhaust?

 

I can push up on the diaphragm in the EGR valve and the engine seems to run into a rich flooding condition and starts struggling so I know the valve works.

However, the valve will not go up by itself when revving the engine.

 

How can I test that it works when I drive?

 

I was thinking about cutting the EGR out but the ECU may not like that and still run the engine too lean even with O2 sensor compensation.

Also, I'm in one of those nanny states that force you to go through emissions testing so I would rather have the EGR work than not.

[Slartibartfast]

Deleting it entirely could cause problems with the emissions test. That would be something to check beforehand. Also I think it would turn on a check light or put up a code, and IIRC you won't pass emissions with a code or a light on. (My area doesn't do smog checks, so this is secondhand info.)

 

From what I've read (Wikipedia), the EGR is controlled by vacuum from the intake (which you didn't tinker with, shouldn't be a problem). It channels some exhaust to the intake to suppress NOx emissions. So, lower back pressure would decrease the amount of gas going through the valve (same opening, less pressure), but I don't know if it would be enough to make a difference.

 

Also, EGR (again according to Wikipedia) is turned off at idle (where it would cause choppiness) and under high load (where it would decrease peak power). If you're trying to see it work, revving it may not be enough; it may require actual driving. Short of running test leads through the firewall/vents/out the window, or having a friend ride the front bumper with a voltmeter, I'm not sure how you'd test its operation. But, again, an exhaust job shouldn't change how the valve opens.

 

This is what I'm looking at: http://en.wikipedia.org/wiki/Exhaust_gas_recirculation

[Tungsten]

Here are some snippets from the FSM regarding the EGR system:

 

 

 

 

 

 

 

 

Edited July 12, 2011 by Tungsten

[Tungsten]

From my understanding, the EGR solenoid is basically an override to force the EGR system to OFF (by cutting the vacuum between BPT and EGR valves) during certain conditions like idle or high rpm. The BPT valve controls how much the EGR valve opens based on exhaust pressure. According to MY1PATH, that "exhaust pressure" line is actually the intake manifold vacuum. I can't see where that "exhaust pressure" hose goes in the diagrams so I will have to look. Will the manifold vacuum decrease with less back pressure in the exhaust? I already looked at that Wikipedia article but it mentioned nothing on back pressure transducers. Going from a 1.875" OD pipe (stock diameter) to a 2.500" OD pipe is a very big difference in pipe diameter.

 

EDIT 1: OK I checked it out today, the exhaust pressure line on the BPT valve is connected right where the EGR tube is, so it does indeed respond to the back pressure in the exhaust. Also, I noticed that the air filter in the valve was missing. The BPT controls how much the EGR opens based on the intake manifold vacuum, which it receives in the top port and shares with the EGR valve, and the exhaust pressure, which it receives in the bottom port. Basically, if my understanding is correct, the BPT valve uses the exhaust back pressure to modify (or reduce) how much vacuum the EGR valve receives, which determines how much the EGR valve opens. So in a case where there is too much back pressure built up, for example during a high load situation, the BPT valve releases the vacuum to the EGR valve to close or reduce the EGR valve to gain more power. In other words, the BPT valve is there to create a vacuum leak, which is why it should have a filter, to disable the EGR valve for more power.

 

If the BPT valve does not operate properly, for example if the diaphragm is torn or the valve is damaged, it is like having a vacuum leak to the EGR valve, which will cause the EGR valve to never open resulting in no EGR operation. On the contrary, if the BPT valve never opens, from less back pressure for example, it's like the valve does not exist. The BPT valve can be bypassed by disconnecting the small vacuum hose that's on it and plugging it; this is the hose that goes from it to the EGR valve and the override solenoid. Then the EGR valve will be controlled only by the intake manifold vacuum and the override solenoid but I have no idea if that may cause issues at certain speeds and/or loads.

 

EDIT 2: I think to test the EGR operation, I would have to connect a vacuum gauge to the "vacuum signal source" and see how much vacuum there is. If there is at least some vacuum then the EGR is operational and if there isn't any then the EGR system is non-functional.

 

EDIT 3: To disable the EGR valve operation, just yank the little hose going to it and put caps on the EGR valve and the hose. Or you can even pinch the hose off with a clothes-hanger and leave it pinched. To disable the EGR you have to pull the vacuum hose that goes to the top of the solenoid, that's where the manifold vacuum is.

Edited July 31, 2011 by Tungsten

[JamesRich]

From my understanding, the EGR solenoid is basically an override to force the EGR system to OFF (by cutting the vacuum between BPT and EGR valves) during certain conditions like idle or high rpm. The BPT valve controls how much the EGR valve opens based on exhaust pressure. According to MY1PATH, that "exhaust pressure" line is actually the intake manifold vacuum. I can't see where that "exhaust pressure" hose goes in the diagrams so I will have to look. Will the manifold vacuum decrease with less back pressure in the exhaust? I already looked at that Wikipedia article but it mentioned nothing on back pressure transducers. Going from a 1.875" OD pipe (stock diameter) to a 2.500" OD pipe is a very big difference in pipe diameter.

 

EDIT 1: OK I checked it out today, the exhaust pressure line on the BPT valve is connected right where the EGR tube is, so it does indeed respond to the back pressure in the exhaust. Also, I noticed that the air filter in the valve was missing. The BPT controls how much the EGR opens based on the intake manifold vacuum, which it receives in the top port and shares with the EGR valve, and the exhaust pressure, which it receives in the bottom port. Basically, if my understanding is correct, the BPT valve uses the exhaust back pressure to modify (or reduce) how much vacuum the EGR valve receives, which determines how much the EGR valve opens. So in a case where there is too much back pressure built up, for example during a high load situation, the BPT valve releases the vacuum to the EGR valve to close or reduce the EGR valve to gain more power. In other words, the BPT valve is there to create a vacuum leak, which is why it should have a filter, to disable the EGR valve for more power.

 

If the BPT valve does not operate properly, for example if the diaphragm is torn or the valve is damaged, it is like having a vacuum leak to the EGR valve, which will cause the EGR valve to never open resulting in no EGR operation. On the contrary, if the BPT valve never opens, from less back pressure for example, it's like the valve does not exist. The BPT valve can be bypassed by disconnecting the small vacuum hose that's on it and plugging it; this is the hose that goes from it to the EGR valve and the override solenoid. Then the EGR valve will be controlled only by the intake manifold vacuum and the override solenoid but I have no idea if that may cause issues at certain speeds and/or loads.

 

EDIT 2: I think to test the EGR operation, I would have to connect a vacuum gauge to the "vacuum signal source" and see how much vacuum there is. If there is at least some vacuum then the EGR is operational and if there isn't any then the EGR system is non-functional.

 

EDIT 3: To disable the EGR valve operation, just yank the little hose going to it and put caps on the EGR valve and the hose. Or you can even pinch the hose off with a clothes-hanger and leave it pinched.

I'm not sure on this system but I fought an EGR problem on a chevy because of too little back pressure in the exhaust.

I think the BPT samples the exhaust back pressure to close the EGR when you let off the throttle. If the engine returns to an idle with the EGR still open it will stall.

When you let off the throttle you will get a temporary vacuum in the exhaust system. This tells the BPT to cut vacuum to the EGR so it will close. Removing the converter can screw up this operation by giving the exhaust system too little back pressure for the BPT to close and send vacuum to the EGR. Then you will probably get a check engine light. This is the problem I had with the chevy. New EGR and EGR solenoid, and lots of testing and still had problems. Put two new converters on the exhaust and problem was gone.

James