240sx EGR tutorial

ONLY for ADVANCED technical discussion about the 240sx!
Posts: 3198
Joined: Thu Oct 30, 2003 1:30 am
Car: 1991 240sx

240sx EGR tutorial

Postby vancouverbc » Wed May 27, 2009 12:03 am

Return to tutorial index

EGR operation explained

The EGR's purpose is to send small amounts of exhaust gas into the air intake to lower combustion temperatures at certain times. The EGR system is comprised of the EGR valve, BPT valve, and EGR solenoid. The EGR valve is the valve that allows the exhaust to enter the intake when the BPT valve sends a vacuum signal. The BPT valve has a small tube at the bottom that senses the exchaust gas pressure. Whe there is exhaust pressure lifting up on the valve , a vacuum signal is sent to the EGR valve. The EGR solenoid allows the ECU to shut off the vacuum signal when it does not want exhaust in the air intake.

Cleaning the EGR

You will need carburetor cleaner and metal pipe cleaner or coat hanger or electrical wire to clean the carbon. The picture below of EGR shows how the exhaust flows through the EGR . It also shows the orifice where exhaust flows through small tube to bottom of BPT valve. These passages should be cleaned. The area where the exhaust flows into the intake should be cleaned as well. You may also want to clean the BPT filters.


When you race engine you will be able to feel the egr diaphragm lift if it is working. The EGR does not operate during idle.

Purple arrow points to vacuum hose in following picture. Suck on hose to create vacuum . This should cause egr diaphragm to lift. You can also feel a vacuum in this hose when you race engine.

the egr solenoid is given power from ecu when ecu wants egr off. ie during idle. The ecu stops sending power to egr solenoid when it wants egr on.

Removing the EGR

The EGR is fastened to intake with 3 12 mm bolts. You will need hinged ratchet wrench to get one of the bolts . Some people have to get the bolt red hot(gas lines in the area so not advised) to get it out as you are not getting much leverage.

The end that connects to exhaust manifold is more problematic. Get some mapp gas and get connection red hot to break rust bond. The size of nut is a mystery. Try not to strip nut . If you do, try pipe wrench. Try a crescent wrench first.

EGR theory

EGR Links

EGR plug part number


EGR smog

EGR plug smog

Advanced theory

amen @ clean the passages too
you can use a hanger, and it's only carbon, trust me there's a s*** ton more on the tops of your pistons i'm sure hahaha use carb cleaner, brake cleaner will work but is not o2 sensor safe, so use carb cleaner

egr valve dilutes your cylinder head temp by recirculating exhaust gas back into your intake. you're thinking "exhaust gas is hot, how the hell does it lower my cylinder/head temps?"..temperature wise it is "hot" but in comparison to your combustion chamber it's not. just like your anti-freeze would burn the s*** outta your skin...but it cools your motor, same thing. but anywho, the unburned fuel and other mixed gases in it helps cool your cylinders and reduce the chances of spark knock aka DETONATION. the hotter the cylinder temp, the more nitrous oxide (harmful gas aka NOX) is produced. therefore your egr valve and your catalytic converter work hand in hand to lower your NOX readings. for driveability and emissions purposes egr valve is a good thing. for performance purposes,where emmissions don't matter, delete egr and replace with intercooler and good tune =]

if you've ever looked at a nissan throttle body, it has coolant flowing through it. it does that to raise the intake air temp so your car doesn't run as lean. lean = power but lean also = heat, the extra fuel aka RICH cools the cylinder wall. running rich is safer than running too lean. anywho the car running lean heats up the cylinders and thus create NOX. on a performance motor , you want the air the engine ingests to be cool/dense, that's why there's intercoolers, and cold air intakes etc etc. anywho, hope you learned something :P

random pics

Tools to get at 12mm egr bolt

Modified by vancouverbc at 3:27 AM 5/27/2009

Modified by vancouverbc at 3:29 AM 5/27/2009

Modified by vancouverbc at 3:31 AM 5/27/2009

Modified by vancouverbc at 3:47 AM 5/27/2009

Modified by vancouverbc at 3:55 AM 5/27/2009

Modified by vancouverbc at 4:14 AM 5/27/2009

Modified by vancouverbc at 4:24 AM 5/27/2009

Return to “240SX Technical Forum”