Hello 2GNT!

We've noticed quite a bit of community effort being devoted to disabling the stock 420A exhaust gas recirculation (EGR) system, for off-road applications, and suppressing EGR related check engine lights (CEL) as well. EGR related error codes are a nuisance, though relatively harmless. Without regular ECU scanning, however, one harmless error code may hide more important codes.

We have developed a posssible solution to this issue, though we're not guaranteeing that it works, nor are we guaranteeing that it will become integrated into the SymTech product line if it does. We have decided to share the concept with the community; we want to hear your thought and opinions. We're even prepared to send the first prototype to a community member for testing. Here is some more technical information about the prototype:

The "EGR bypass plate" bypasses the cylinder head exhaust gas source, and instead routes fresh air through the EGR valve. Two stainless steel mesh filters (not pictured), which filter particles as small as four (4) microns, ensure only clean air is introduced into the EGR system. The bypass passageways and filters provide roughly the same amount of gas flow through the EGR valve as the stock 0.300" orifice plate. The prototype is completely made from 6061 aluminum, with stainless steel mounting hardware. Future prototypes may be made from stainless steel to somewhat insulate the EGR tube from heat.

One should not need to use a gasket between the valve and the bypass plate, though we recommend using one between the byplass plate and the cylinder head.

Here a few pictures for your review:









One possible reason this prototype may not work is that fresh air is not pressurized, like exhaust gas. What are your thoughts?

Love the craftsmanship!

Good point about atmosphere air not having the same pressure exhaust gas but I am not sure if that has an effect on the EGR flow detection.

If I had my emissions gear on my motor I would volunteer to proto test for you. With the different behaviors in the EGR systems we have seen on the board a small test group may be in order.

Very cool, and like Dave said, love the craftsmanship!

This would be awesome if it really fixes the problem. You raise a good point with the positive exhaust pressure issue, but my understanding is that the ECU only checks for air flow.

However, this technique would basically introduce a vaccum leak into the system, whereas the the positive exhaust pressure would create more of a "closed loop" system. If the ECU checks for changes to idle RPM or idle vac pressure when the EGR is activated, it may be able to detect that the EGR system is not operating correctly. You may have to play with the size of the air holes or possibly only limit it to one side.

I think another thing to take into consideration when testing are the different ECU's. It is highly likely that a 95 ECU will not react the same way to this as a 99.

I have a 99, and I would be more than happy to test this product for you. I currently do not have my EGR equiptment on the car, but could easily modify my EGR pipe (I run PF) and reinstall it with your plate.

Originally posted by Ebster1085
However, this technique would basically introduce a vaccum leak into the system...

Not any more of a leak than a functioning EGR system. The valve is still in place so as the EGR transducer opens & allows vacuum to pull the EGR valve you get the same results except the air is not exhaust.

The difference though is that exhaust gas has some pressure behind it versus atmosphere.

Excellent idea.

Here is food for thought. I have an EGR valve that's gone a slightly different route, with a hole drilled into the back (of approximately the same diameter as your bypass passageway) with mesh for filtration, and then a metal gasket that blocked flow from the head into the EGR. I found that this causes an insufficient flow CEL on a 1999, but not on a 1995. The 99 is smart enough to see that the flow is reduced, though by the diameter of the orifice you would think that it is enough. It's probably *exactly* the point you mentioned, that the exhaust gas is presurized thus providing more flow, and a small opening to atmosphere can't creat the same amount needed. So if that happens to be the case with your setup, I would suggest making that hole as big (and as stealth) as possible.

Ebster - I don't see this as a source of a vacuum leak. Remember that the intake mani will only be open to atmosphere when the EGR solenoid activates and opens the EGR valve (the valve is not open all the time, and as I understand it would not be open under WOT/boost).

Originally posted by ez
Excellent idea. Here is food for thought. I have an EGR valve that's gone a slightly different route, with a hole drilled into the back (of approximately the same diameter as your bypass passageway) with mesh for filtration, and then a metal gasket that blocked flow from the head into the EGR. I found that this causes an insufficient flow CEL on a 1999, but not on a 1995. The 99 is smart enough to see that the flow is reduced, though by the diameter of the orifice you would think that it is enough. It's probably *exactly* the point you mentioned, that the exhaust gas is presurized thus providing more flow, and a small opening to atmosphere can't creat the same amount needed. So if that happens to be the case with your setup, I would suggest making that hole as big (and as stealth) as possible. Ebster - I don't see this as a source of a vacuum leak. Remember that the intake mani will only be open to atmosphere when the EGR solenoid activates and opens the EGR valve (the valve is not open all the time, and as I understand it would not be open under WOT/boost).

ez, there are a few key differences between your design and ours. The first is that the hole you drilled is introducing air into the EGR valve after the orifice plate. This is fine if you precisely calibrate the hole and filter, but otherwise the results will be unpredictable.

Also, you mentioned that the hole you drilled is the size of our prototype's bypass passageway; but remember that the prototype has two of these passageways, not just one. We calculated the size of these holes based on the area of the orifice in the orifice plate and the open area of the mesh filter. Their combined areas, minus the closed areas of the mesh filters, are greater than the opening in the orifice plate. Insufficient EGR flow should not be a problem.

Originally posted by Ebster1085
Very cool, and like Dave said, love the craftsmanship! This would be awesome if it really fixes the problem. You raise a good point with the positive exhaust pressure issue, but my understanding is that the ECU only checks for air flow. However, this technique would basically introduce a vaccum leak into the system, whereas the the positive exhaust pressure would create more of a "closed loop" system. If the ECU checks for changes to idle RPM or idle vac pressure when the EGR is activated, it may be able to detect that the EGR system is not operating correctly. You may have to play with the size of the air holes or possibly only limit it to one side. I think another thing to take into consideration when testing are the different ECU's. It is highly likely that a 95 ECU will not react the same way to this as a 99. I have a 99, and I would be more than happy to test this product for you. I currently do not have my EGR equiptment on the car, but could easily modify my EGR pipe (I run PF) and reinstall it with your plate.

Originally posted by CODE4
Not any more of a leak than a functioning EGR system. The valve is still in place so as the EGR transducer opens & allows vacuum to pull the EGR valve you get the same results except the air is not exhaust. The difference though is that exhaust gas has some pressure behind it versus atmosphere.

Ebster, CODE4 and ez expressed our sentiments exactly. Remember that the EGR valve has a calibrated orifice plate built in. In order for there to be excessive EGR flow, some component of the EGR system (i.e. the valve, solenoid or differential pressure sensor) would have to be faulty. As long as the stock electronics are controlling the EGR system, the main concern is avoiding insufficient flow.

Also, we have considered the very likely possibility that this fix will be less successful with newer cars. We already have one tester with a 1999 model year vehicle, so we may either produce more prototypes or ask him to return the original piece so others can test it.

Thsi is the same idea I brought up what? 4 years ago on Tuners.....go search for the original thread you were still a wiseman/moderator back then.

The concept has been tested and works on my 97.

If i dig i am sure I still have the Alum plate i made in the attic of the garage.

Wouldn't this present a timing issue? IIRC, the computer compensates for the low-oxygen exhaust gas by advancing the timing when it tells the EGR sensor to open, and detects the appropriate resistance in the circuit saying the valve is open. At least when I was scanning to make a base MS map, that's about what I was seeing, anywhere from 5-10* advance. This is my only worry about any EGR bypass setups, as opposed to just letting the computer know the EGR isn't there (leaving it unplugged until emissions time for the '96+ years).

Originally posted by justins71
Wouldn't this present a timing issue? IIRC, the computer compensates for the low-oxygen exhaust gas by advancing the timing when it tells the EGR sensor to open, and detects the appropriate resistance in the circuit saying the valve is open. At least when I was scanning to make a base MS map, that's about what I was seeing, anywhere from 5-10* advance. This is my only worry about any EGR bypass setups, as opposed to just letting the computer know the EGR isn't there (leaving it unplugged until emissions time for the '96+ years).

What would be the difference in the 95 years? Stupid question maybe but im just curious.

Originally posted by Tuxdreamerx
What would be the difference in the 95 years? Stupid question maybe but im just curious.

Emissions aren't required on 95 and older vehicles.

Originally posted by daes_venge
Emissions aren't required on 95 and older vehicles.

Not true (at least in my area) - they just are tested differently. 96+ use OBDII scanning to test sensor/operation conditions, whereas pre-96 use ASM (dyno) or 2-speed idle testing (both use tailpipe sniffer).

Only when you hit 25 y/o do you get to just do safety inspections.

I was thinking more along the lines of a straight up vacuum leak versus a pressurized vacuum leak.

For example, if you were to create an opening in the intake system during idle this would simply create a vacuum leak and would have an effect on idle RPM as well as idle vacuum pressure. But, if you were to pressureize this leak slightly, I assume the effect on RPM and vac pressure would be different.

If what you are saying is true, and the EGR flow test simply tests for sufficient flow, it is just a matter of trying to pull in enough fresh air through these orifices to recreate the flow made by the positive exhaust pressure.

As others have mentioned above, this concept has been discussed and put into use before, but what I want to know, being a 99 owner, is has anyone sucessfully done this method on a 98 or 99?

Originally posted by Ebster1085
I was thinking more along the lines of a straight up vacuum leak versus a pressurized vacuum leak. For example, if you were to create an opening in the intake system during idle this would simply create a vacuum leak and would have an effect on idle RPM as well as idle vacuum pressure. But, if you were to pressureize this leak slightly, I assume the effect on RPM and vac pressure would be different. If what you are saying is true, and the EGR flow test simply tests for sufficient flow, it is just a matter of trying to pull in enough fresh air through these orifices to recreate the flow made by the positive exhaust pressure. As others have mentioned above, this concept has been discussed and put into use before, but what I want to know, being a 99 owner, is has anyone sucessfully done this method on a 98 or 99?

You're neglecting to remember that this bypass plate goes in between the EGR valve and the cylinder head. The EGR valve still has control over how much air is added to the intake manifold; in other words, the bypass plate is not just a fancy vacuum leak.

Originally posted by Ebster1085
I was thinking more along the lines of a straight up vacuum leak versus a pressurized vacuum leak. For example, if you were to create an opening in the intake system during idle this would simply create a vacuum leak and would have an effect on idle RPM as well as idle vacuum pressure. But, if you were to pressureize this leak slightly, I assume the effect on RPM and vac pressure would be different. If what you are saying is true, and the EGR flow test simply tests for sufficient flow, it is just a matter of trying to pull in enough fresh air through these orifices to recreate the flow made by the positive exhaust pressure. As others have mentioned above, this concept has been discussed and put into use before, but what I want to know, being a 99 owner, is has anyone sucessfully done this method on a 98 or 99?

Did you read my post? Keep in mind EGR system should not be open at idle.

Originally posted by CODE4

Originally posted by Ebster1085 However, this technique would basically introduce a vaccum leak into the system...

Not any more of a leak than a functioning EGR system. The valve is still in place so as the EGR transducer opens & allows vacuum to pull the EGR valve you get the same results except the air is not exhaust. The difference though is that exhaust gas has some pressure behind it versus atmosphere.

It's interesting. I can see how (keeping it technical) orifice diameter and exhaust pressure could play a role in the flow values. After all, the ECU closes the IAC and is expecting a certain volume of flow from that system during test.

At the same time, we made one of these with a Dremel back in 2003 or 2004 for run4cvr's 96 that worked flawlessly. I ended up getting a CEL on my 97, but there was no way to ensure consistency with this project the way we did it.

Ours was a 3-plate system. A solid plate sealed the port on the head. A second port was slotted at the bottom. The third plate matched up (roughly) with the actual EGR valve.

The same principles applied. This sealed the head off, preventing dirty exhaust gas from passing through to the intake manifold while still allowing the EGR solenoids to be connected and installed. The ECU saw function and it saw flow. CEL circumvented.

Of course, it looked nowhere as stunning as this bit.

Originally posted by justins71
the computer compensates for the low-oxygen exhaust gas by advancing the timing when it tells the EGR sensor to open, and detects the appropriate resistance in the circuit saying the valve is open.

I've since come to like the EGR for just this reason. I forget when, exactly, the EGR activated, but I want to say it was during cruising (and not WOT). The EGR sort of leans things out a bit and the ECU might be advancing timing a little bit, which contributes to increased fuel economy.

Dunno if I'd remove it today.

Originally posted by DR1665
I've since come to like the EGR for just this reason. I forget when, exactly, the EGR activated, but I want to say it was during cruising (and not WOT). The EGR sort of leans things out a bit and the ECU might be advancing timing a little bit, which contributes to increased fuel economy. Dunno if I'd remove it today.

Yup, that's the idea, I took it off cuz it was a pain to use MS with unless you had a fast-acting EGOcorr, which then made my idle surge like hell! lol If you really wanted it and weren't using anything (MS wise) you could do dual-tables or something and have it sense the EGR, but not that important if you ask me, and anyway this is for stock ECU's so I'm kinda talking outta my ass here haha. I want to say that the EGR is open on cold starts, or at least pops open intermittently in order to heat the engine up more quickly. It's not on under normal operating conditions at idle, though.

This looks interesting. I know it would make my life easier.

Originally posted by DR1665
I've since come to like the EGR for just this reason. I forget when, exactly, the EGR activated, but I want to say it was during cruising (and not WOT). The EGR sort of leans things out a bit and the ECU might be advancing timing a little bit, which contributes to increased fuel economy. Dunno if I'd remove it today.

The core Megasquirt developers are actually working on a performance oriented implementation of an EGR system. EGR systems do have their benefits, but they also have a few drawbacks. I think that discussing the pros and cons of EGR systems, however, is out the scope of this thread, and the project overall. We're just interested in a solution for EGR related CEL's using the stock ECU.

justins71 brought up an excellent point about ignition timing advance when the EGR valve is open. The ECU does this to account for the slower burning combustion mixture inside the cylinder. The next question is: how much is the ignition timing adjusted, and do these adjustments significantly and negatively affect the engine? We may need EGT and AFR data to confirm any conjectures.

Originally posted by SymTech Labs

Originally posted by DR1665 I've since come to like the EGR for just this reason. I forget when, exactly, the EGR activated, but I want to say it was during cruising (and not WOT). The EGR sort of leans things out a bit and the ECU might be advancing timing a little bit, which contributes to increased fuel economy. Dunno if I'd remove it today.

The core Megasquirt developers are actually working on a performance oriented implementation of an EGR system. EGR systems do have their benefits, but they also have a few drawbacks. I think that discussing the pros and cons of EGR systems, however, is out the scope of this thread, and the project overall. We're just interested in a solution for EGR related CEL's using the stock ECU. justins71 brought up an excellent point about ignition timing advance when the EGR valve is open. The ECU does this to account for the slower burning combustion mixture inside the cylinder. The next question is: how much is the ignition timing adjusted, and do these adjustments significantly and negatively affect the engine? We may need EGT and AFR data to confirm any conjectures.

Maybe someone should crack the ECU and do what Mopar Performance did, have it ignore the EGR and downstream O2.

Originally posted by teklein
Maybe someone should crack the ECU and do what Mopar Performance did, have it ignore the EGR and downstream O2.

Yes, a cracked+customizable ECU would be the single greatest thing since MS. I won't ever buy a MS, but I would buy a tunable ECU :)

IIRC, there was only one guy who had the knowledge capable of cracking the ECU, and that's how the few Howell ECUs came to be. His name was never made public for legal considerations.

I love it when people come out with new products for the DSM community that has been researched and is a good product. Thank you!