Here is a thread written by krazybaddude for rebuilding the digital EGR valve off of a 1990 through 1994 Cavalier.
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EGR Clean/Rebuild for GM Digital 3-Solenoid</SIZE>
Some of you may have wondered, when buying a new EGR valve for your 1990-1994 3.1L, if there is a cheaper alternative than spending 200-400 dollars on a new EGR valve.
Well, there is. I have typed up a How-To, on how to disassemble, clean, check for correct operation, and reassemble your EGR valve. Chances are, that you can get your old, carboned, rusted EGR valve working the way it should be, without spending any money at all. The only reason that you wouldn't be able to restore it is if you have a dead electromagnet.
Step 1: Disassembly
Let's start by taking apart the valve. There will be 3 T-20 torx screws holding the base plate to the electromagnet unit. Remove these, and your valve will come apart like this
NOTE: Do not try to remove the screws on top of the individual magnets .... these will not come out, and do not need to come out)
From left to right. You have the Base, then the Base Plate Gasket. Then there is the Base Plate. Then you have 3 pintles, which slide into the holes on the electromagnet unit.
Step 2: Testing
(Word of caution, just to prepare you. You may receive a VERY SMALL shock, if you are touching the wires while connecting them, because of the fairly high amount of current being drawn to operate the electromagnets. Nothing major at all, but it may make you jump! )
First we will test the electromagnet assembly. I recommended to obtain a 4 wire egr harness from the junkyard for this step. It is possible to do this step without the wiring harness, but will be very time consuming, and frustrating, trying to get wires to stay on just the pins ..... However, if you must do it this way, i have provided a picture of the pins, and which pins correspond to which wire color:
The top two pins, sitting horizontally, from left to right, are blue and red.
The bottom two pins, sitting vertically, from top to bottom, are brown and pink.
If you are going to use this method, the bottom pin is the positive + (pink), and the top 3 pins are the 3 solenoids ground pins.
It is also NOT recommended to cut and remove your current wiring harness from the car, as the final product will be messy, and unattractive looking. (I'm sure most of you know this, but I had to say it anyway)
Take notice of the wiring harness. You will have a pink wire, a blue wire, a brown wire, and a red wire.
The pink wire will be the positive (+) for the next step. The blue, red, and brown wires each control one individual magnet. These are the grounds (-).
(For this step, you will need a fresh 9V battery, and a 9V battery snap is recommended as well, as it will aid in testing.)
Attach the pink wire to the positive side of the battery. (Note: it is recommend to have a 9v battery snap on hand, so you can twist the wires together, and attach the battery snap right to the battery)
Attach, one at a time, each ground wire (blue, red, and brown) to the negative terminal of the battery. Using a flathead (or Phillips) screwdriver, stick it inside of one hole at a time. When the screwdriver sticks to the bottom of the hole, you know that individual electromagnet is working properly. Repeat this step for each hole, and wire (besides the pink +). If you have no pull or very little pull, in any of the holes, you can stop there .. it is not possible to rebuild it. (Go the the junkers with your T-25 and 9V battery, and find a working one to rebuild. ) If you have a strong pull in all 3 of the holes, and the holes correspond to the wires, congratulations, your valve has successfully passed the magnet test, and you can move onto step 3!
Step 3: Cleaning
Now we begin the fun part! Cleaning all the carbon off of everything (well, almost everything. you'll see)
Let's clean the base first.
You want to clean all of the carbon out of chamber in the base, paying careful attention not to damage the gasket on the perimeter of the chamber. Just get it as clean as possible, within reason. Then flip this piece over, and clean the bottom of it.
The next part in your lineup is a thin gasket. This is called the Base-Plate Gasket.
DO NOT SOAK OR CHEMICALLY CLEAN THIS GASKET. You can carefully clean some carbon off of the raised(bottom) side, but that's about it. This gasket is porous, with gasket material in the pores, and on the topside of it, and any type of chemical or rough cleaning will remove this gasket material. (And as far as I know, GM does not make an internal gasket kit for the EGR...)
You can now move onto the Base-Plate
You can get this part as clean and shiny as you want, as there is no gasket material whatsoever on it.
Now its time to clean the pintles (sorry for the blurry pictures)
Everything on the pintles should be movable. The head should pivot on the bar. Both ends should slide up and down on the bar.
The only thing that should be solid, is the small bar coming from the body shaft of the pintle. You really want to get these as clean as possible, as they are the main moving part in the EGR and need to move very well. Soak them in carb cleaner or gas (or your preferred cleaning solvent) for a few hours, or even overnight if they are bad enough. You also want to clean the body shaft if it is corroded, carbon covered, or rusted.
Take a look into the 3 holes on the electromagnet assembly.
The walls should be very smooth, and you should see no rust or corrosion inside of these. Take one of your pintles, slide it into each hole individually, and press down and up on the pintle. It should slide in and out smoothly, and not bind up at all, in its travel. If it does, you can take some steel wool, roll it up, and clean out the inside of the hole. Make sure to spray some compressed air into the hole when done to ensure no metal flakes inside. (or blow into it if you want).
Well, that should be everything for the cleaning process.
You can now reassemble your valve. Basically just reverse the disassembly process. Slide the pintles into the holes on the electromagnet assembly. Orientation does not matter. Slide your base-plate over the pintles. Note: This base-plate only goes on ONE way. You can slide your screws in, from the top, and make sure that all of the holes line up like they should. Now take your base gasket, raised side up, material side down, and slide that over the pintles. Orientation of this gasket does not matter.
Now do the same thing with the base. This part will only go on one way as well. If you wish, you may use the screws to line up all the holes, but eying it up works pretty good too.
Well, it looks like that's it!
You can now do a final test, to make sure that the pintles move as they should. Using the same 9v battery and snap, perform the same magnet test as in step 2. For each wire/pintle, you should hear a click, and see the pintle move away from the hole on the bottom. If this condition exists for each pintle, then you have successfully cleaned / rebuilt your EGR valve. If you have a problem with the valve after it is reassembled, make sure that the valve passes the tests in step 2. If so, check pintle movement, and plate orientation.
Well, I hope this was informative. Good Luck
-Dan
Written by KrazyBadDude (Dan).