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3rd & 4th Generation (19921996 & 19972001) Toyota Camry Discussion for years: 1992-1996 & 1997-2001 Topics of discussion range from fuel economy, safety, modifications, performance all involving America's favorite family car, the Toyota Camry.

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#1 Old 02-28-2011, 10:51 PM
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egr modulator

I know theres alot of information on here but really couldnt find what i need.

how does it actually work in relation to the egr valve? theres a bottom port and 2 vacuum port and one port i believe just vents to atmosphere??

now does the bottom port recieve the exhaust gas pressures.. than as the gas pressures moves the diaphram does the exhaust goes to the 2 vaccum port p and r? im lost. id like to understand this thanks..
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#2 Old 03-01-2011, 06:54 AM
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ok i got a 99 4cyl camry.im holding the egr modulator. when i use compressed air into the bottom port. the modulator moves up.so im assuming the hose from the egr to the bottom port of the modulator is exhaust gases?pushes the modulator up. than from there port p and r is vaccum from the throttle body. how does p and r transfer the vaccum to Q into the egr valve vsv? what the point of toyota implenting a egr modulator? whats the benefit?
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#3 Old 03-01-2011, 08:22 AM
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Hi. I think I know part of the story. But I could be way off. The process starts with the computer. The computer attempts to control the combustion process by reducing the amount of oxygen in the air/fuel mixture. Too much oxygen increase the rate of combustion which produces too much NOx gases which is bad for the environment. By introducing exhaust gases into the air/fuel mixture, the combustion process is slowed down and less NOx gases are produced.

The computer sends a signal to the EGR VSV to actuate the EGR system. It closes a vent hole on the EGR VSV which has an effect of starting a vacuum which opens the flapper in the EGR valve which lets the exhuast gases flow from the exhaust mainifold into the air intake.

The EGR modulator has the effect of fine tuning the openning of the flap with in the EGR Valve.
The EGR modulator adds more vacuum or less vacuum to the openning of the EGR Valve flapper based on the exhaust back pressure it is sensing. ( there is a hose or pipe connecting the EGR Modulator to the exhaust. It's at the bottom of the EGR modulator).

When the computer determines the the exhaust gas isn't good for the engine performance, it stops the vacuum by openning the vent hole in the EGR VSV. The vacuum causes the flow. The vacuum loses it force ( or sucking power) when you put a hole in it ( or open a vent hole).

1996 V6 Camry 164K

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#4 Old 03-01-2011, 09:35 AM
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Hi. I've got a 1999 Camry 4-cyl with the infamous P0401 ODC code. So far, I've replaced the EGR valve and the Vacuum Control Valve. The only thing I haven't yet replaced is the modulator. In any event, I'm looking for a schematic of the emission control system for this model Camry.

Something like this, (but specific to a 1999 Camry 4-cyl)

http://i263.photobucket.com/albums/i...ntsDiagram.jpg

Can anyone help me, please? Thanks.

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#5 Old 03-01-2011, 04:06 PM
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good reading here:
DIY: 1MZ, EGR, code P0401 & P0402 diagnostic & repair


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#6 Old 03-01-2011, 06:18 PM
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Olesparkie, I found this for the 1999-2001 model year. It's for the 5SFE engine.

1996 V6 Camry 164K
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#7 Old 03-01-2011, 06:25 PM
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natedawg617, I'm also curious about the P, R, and Q ports and what pulls what open. Let me know what you find. Thanks.

1996 V6 Camry 164K
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#8 Old 03-01-2011, 06:38 PM
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Toyota has published a technical paper which does a pretty good job of explaining the EGR system. You can download the pdf here: http://www.autoshop101.com/forms/h61.pdf

They've published a whole series of articles like this and I've found them pretty useful on a few occasions. http://www.autoshop101.com/ (then click on "Technical Articles")
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#9 Old 03-01-2011, 08:56 PM
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just wanted to explain to me in simplest form i guess not.. anyone else?
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#10 Old 03-01-2011, 09:16 PM
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there is no easy explanation. it is an ancient design, partially mechanical (valve mechanism), partially electrical (switch) and vacuum based

Throttle Body ports P & R stay closed (no vacuum reading) at idle just like the throttle plate stays closed (at least it should).
port R opens to full engine vacuum blast after 2,500rpm while port P opens little by little earlier than that.

Port Q connects to EGR modulator (other side of modulator connects to VSV), while bottom of modulator connects (backpressure) to the side of EGR valve.

the VSV itself has 3 connections (one hose to modulator, other hose to EGR valve opener and the third one is a vent to atmosphere.

the last piece of puzzle is ECU which grounds circuit to VSV based on its sensor readings coming from engine.
On top of that engine vacuum changes depending on engine speed, backpressure also changes with engine speed.

Once ECU decides to actuate the EGR system it grounds the electrical VSV which vents the control signal (vacuum) to atmosphere, this causes EGR valve opener to react with relation to modulator input (based on engine RPM) and backpressure

easy, eh? I can't fully understand it myself, even though I grasped it for a moment a year ago...

it's an ingenius design (when things work and are new) and an idiotic nightmare design for troubleshooting when things start going wrong.

best explanations I know of:
1.
http://www.motor.com/magazine/pdfs/082009_04.pdf

2.
http://www.motor.com/magazine/pdfs/092009_04.pdf

3.
http://www.motor.com/magazine/pdfs/102009_04.pdf

Happy Reading


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Last edited by fenixus; 03-01-2011 at 09:26 PM.
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#11 Old 03-01-2011, 10:00 PM
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Thanks Fenixus. That's a great desciption.
One question. Is port Q the one that connects the EGR modulator to the EGR VSV ? I couldn't tell from your desciption.

The one thing that I read in the article that Agni referenced above was that the ECU will inhibit the EGR flow when it has the potential to cause adverse effects on the engine performance. The ECU uses the EGR VSV to accomplish this. The ECU decides to inhibit the EGR flow when the coolant temperature is below 130 degrees, when the rpm's are above 4200, or when the engine load is below some factor (not sure what this is).

I couldn't tell from the article whether the EGR VSV's only purpose was to inhibit the EGR flow or whether this was just one of it's functions.

1996 V6 Camry 164K

Last edited by coffee-3000; 03-01-2011 at 10:06 PM.
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#12 Old 03-01-2011, 10:42 PM
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i'm sorry, I think I made a goof
Port Q is not on Throttle Body as I remembered it hehe, it is actually the passenger side of EGR modulator named as Port Q and this port is in fact connected directly to VSV for EGR, you are correct.

what you said is correct, ECU cuts off EGR flow under conditions you mentioned.

I had a thread where some of those troubleshooting issues were covered, JohnGD was supplying me with info while I was trying to figure out some idle issues and intermittent power loss problems upon acceleration. It was a very long thread (20 pages?) but somewhere in it it was all discussed. will link it in a sec.

[SOLVED] 2000 camry gen4 5sfe short and long term fuel trims

I ended up replacing all 3 EGR parts, modulator just in case as it has a filter and backpressure port has a diaphragm which is impossible to clean and can get sticky/clogged.
I destroyed EGR valve in process of cleaning (bolt broke off holding it down to exhaust pipe), was sticky anyways, got new one.
I replaced VSV for EGR as testing it on car was showing some intermittent problems with energizing, but when I tested it off car (jumpered to battery) it worked fine, so I sold old one on ebay hehe. came up that I had a bad ground point behind the intake runners.

going further I replaced all EGR hoses except thick back pressure hose which I will be replacing next week regardless, just to be sure.

also regarding EGR VSV. again I was wrong (this system is crazy and illogical at first glance):
"The VSV’s vent filter (...) prevents EGR operation whenever it vents off EGR control vacuum." from article #1.

also when pulling vacuum on the EGR valve port (on top) it actually opens it and not closes it (which makes sense with quote above).

and 1 more quote to make it more clear:
"The top of the vacuum modulator conceals the vent filter for the internal vent(...). The two vacuum inputs are ports P and R. The modulator’s output is control vacuum coming out of port Q."


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Last edited by fenixus; 03-01-2011 at 11:08 PM.
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#13 Old 03-02-2011, 07:33 AM
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Thank you all, kindly!
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#14 Old 03-02-2011, 08:02 AM
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Quote:
Originally Posted by fenixus View Post
port R opens to full engine vacuum blast after 2,500rpm while port P opens little by little earlier than that.
Hi Fenixus. Sorry to beat a dead hose. Can I ask you one more question based on your understanding of this ? Does the ECU intiate the entire process ? That is, does the ECU detect that the engine has reached 2,500rpm and instruct the EGR VSV to communicate with the EGR modulator to pull air from the throttle body through port R ? The air now coming into the EGR modulator through port R causes . . . ( I'm lost here also)

Or . . . is it the rushing air through the throttle body that causes port R to open at 2,500rpm.
In this case, the ECU wouldn't be intiating the entire process.
It would be the increased air flow through the TB.

It gets more confusing the more you think about it.

Here is a photo for reference.

1996 V6 Camry 164K

Last edited by coffee-3000; 03-02-2011 at 08:30 AM.
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#15 Old 03-02-2011, 10:17 AM
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hey no probs, I still remember something from those things, however my V6 EGR knowledge is limited. better refer to motor.com articles or TN thread by Nervous I linked before.

anyways, on i4 (5s-fe) the vacuum on port P & R is the engine vacuum so it appears there regardless of what ECU does, depends strictly on throttle plate position (which changes together with engine speed RPM, engine load and backpressure). same about control vacuum signal present on Port Q of modulator, it depends strictly on engine conditions (vacuum and backpressure).

All the ECU can do is to send electrical signal to VSV (grounding it or opening the circuit) so it changes the flow of vacuum control signal (vacuum vented to atmosphere or loop closed) and in this regards, yes ECU controls the EGR system.

gen4 i4 2.2L uses MAP sensor to monitor the EGR system efficiency, however on V6 there is a temperature sensor in EGR valve itself that does same job (in other way).

my '02 V6 1mz-fe (non-VVT-i) has even something else, the EGR on it is not vacuum based, I haven't figured it out yet to be honest.

Quote:
Originally Posted by coffee-3000 View Post
Hi Fenixus. Sorry to beat a dead hose. Can I ask you one more question based on your understanding of this ? Does the ECU intiate the entire process ? That is, does the ECU detect that the engine has reached 2,500rpm and instruct the EGR VSV to communicate with the EGR modulator to pull air from the throttle body through port R ? The air now coming into the EGR modulator through port R causes . . . ( I'm lost here also)

Or . . . is it the rushing air through the throttle body that causes port R to open at 2,500rpm.
In this case, the ECU wouldn't be intiating the entire process.
It would be the increased air flow through the TB.

It gets more confusing the more you think about it.

Here is a photo for reference.


'02 Solara SLE V6 1MZ-FE/A541E@ 142k
'00 Solara SE 5S-FE/A140E @ 92k

"We are what we repeatedly do. Excellence, then, is not an act, but a habit." - Aristotle
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Last edited by fenixus; 03-02-2011 at 10:25 AM.
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