|Whenoptimal air/fuel mixture is attained (14.7:1), the combustion process createsseveral different nitrogen oxides (NOx) because the combustion chamberis operating at over 2000° F . To reduce the NOx emission, the combustionchamber temp must be lowered. So the Exhaust Gas Recirculation (EGR) valve(generic diagram 1.) recirculates the now inert exhaust gas backinto the combustion chamber to lower the total volume of combustable mixture.This results in a slight loss of power. Too much EGR flow will result inpoor fuel economy, rough running and increased emissions. Too little flowcan possibly cause internal engine damage from overheating.|
The EGR valvehas a control hose that goes to the intake plenum and allows the EGR valveto open at wide-open-throttle, allowing some exhaust gas to mix with theintake stream. The exhaust gas conections to the EGR valve are 3 metaltubes. One goes to the driver exhaust manifold and the others to the bottomof intake plenum on each side (red dots in 2.).
To test theEGR valve operation, start the engine and then disconnect the control hose(light blue dot in 2.). The EGR valve should open and engine shouldslow or hesitate. If disconnecting the hose makes no difference, eitherthe hose is leaky/ blocked or the EGR exhaust gas pipes are blocked.
The basic failureof an EGR valve is the diaphram that senses intake maifold vacuum and opens/closesthe valve. With a clean hose on the control input, suck on the hose andput your tongue against the open end of the hose. It should hold the lowerpressure, stick to your tongue, for at least a minute. You can do the sametest with a vacuum gauge of course, if you have one. If the valve won'thold low pressure, then it won't close completely at idle and your enginewill idle poorly.
Supposedlyreplacement can be accomplished with the engine in the car. We did Shahram'swhile his engine was out of the chassis getting the turbos replaced. Itwas still difficult this way.
1. Spray everythingaround the EGR valve with a penetrating lubricant, also the fitting onthe drivers side exhaust manifold. I recommend Blaster brand.
2. Disconnectthe vacuum line from top of the EGR valve (light blue dot in 2.).
3. Remove thewater line fom the driver side of the valve's location (yellow dots in2.)(3 x 10mm). Get a bucket before cracking the line, just about every bitof water left in the heads will come out of this tube. Remove the 3 rubberhoses from the metal water feed tube up top (3 x hoseclamps).
4. Remove thebolts on the EGR valve (6 green dots in 2.) (6 x 12mm).
5. Remove thefitting on the exhaust manifold (1 x 23mm?), Not sure on the size, I justused a crescent wrench to remove it.
6. Follow theexhaust tube from the EGR valve to the underside driver side of the intakeplenum. Disconnect it there (2 x 10mm). Remove the bolt holding the lineto a bracket on the rear side of the head (1 x 10mm) to loosen the feedline. Pull the line upwards from the EGR valve & rotate/slide the valveout of it's mounting position (3.).
7. Note theorientation of the exhaust feed tube on the EGR valve. Remove the exhaustfeed tube from the valve (purple dot in 2.). Put anti-seize compoundon both ends of the fittings. Install tube on new EGR valve. Torque to25-33 ft-lbs.
8. Clean offall old gasket material on all seating surfaces.
9. Rotate/sidethe new EGR valve into position. Start the threads on the exhaust manifoldfitting. Bolt the EGR valve back to the engine (2 x 12mm). Use anti-seizecompound on the bolts. Torque to 15-20 ft-lbs.
10. Start thethreads on the driver side exhaust feed tube in all locations (3 x 10mm,2 x 12mm). Use anti-seize compound on all. Use appropriate replacementgaskets. After all are started, torque plenum bolts to 6.2-8.0 ft-lbs,EVG valve bolts to 15-20 ft-lb, torque bracket bolt to 8-10 ft-lbs.
11. Reconnectthe passenger side exhaust feed tube (2 x 12mm) with gasket. Use anti-seizecompound on the bolts. Torque to 15-20 ft-lbs.
12. Torqueexhaust manifold fitting to 25-33 ft-lbs.
13. Reconnectvacuum line to top of EGR valve (1 x hoseclamp).
14. Installthe water feed tube on driver side of EGR with new gasket (2 x 10mm, 3x hoseclamp). Torque to 10-15 ft-lbs.