1986 GT EGR Solenoid Valve Operation & Testing

[86Stripper]

I have a 1986 GT Automatic on which I'm working on the EGR system. It sets a Code 31 for the EGR sensor so I'm in the process of taking everything apart to clean and test. Everything is fairly clean as the car has only a little over 100,000 KM (about 60,000 miles) and runs really well except for the Code 31 and a backfire when I let off quickly at the end of the quarter mile on a dragstrip run. If I let off slowly no problems.

The car has a really poor aftermarket exhaust that looks like it was made at a muffler shop with cheap Thrush 17658 mufflers and tailpipes with Magnaflow tips. It is loud. The pipes appear to be 2.25" throughout. No cats and no H crossover. Just straight pipes back from each side. The smog pump is connected via the original pipe to the approximate location of the original in just the passenger side exhaust pipe. The O2 sensors are very close to the stock header output and look pretty close to the stock location.

I have a number of questions regarding the operation and testing of the EGR system.

1. Is the EGR valve a back pressure type (negative or positive back pressure) that will not operate properly with this type of exhaust system? Does it need some back pressure? I'm interested in any comments from those that have had problems with Code 31 and aftermarket exhaust with no cats with or without the convertor air pipe operational.

2. Has anyone had any experience with bench testing the EGR solenoid (E53E-9J459-AA) that controls the EGR valve? I've tried to test the solenoid and I'm not sure I'm doing it properly. Pictures of the valve are enclosed below. When I connect 12 volt supply to the two contacts there is no audible click like the thermactor TAB and TAD solenoids. Should there be?

3. When I connect a vacuum pump to the supply port on the valve (bottom side) and a vacuum guage to the output port (top side) and 12 volts to the contacts and then try to pump vacuum through the valve the valve will not pump up and hold vacuum. However, as the vacuum drops it seems to slow down at around 5-6 In and then drop slowly from there. The valve will not hold vacuum at all without 12 volts across the contacts and drops quickly to zero rather than stalling at 6 In. I went out to the autowreckers and picked up three spare valves of the same number and vintage (Tempo and Topaz of late 1980s seem to have them). They all seem to have about 45 ohms resistance across the contacts. I believe this indicates the solenoid coil is okay. One of the valves from the wreckers will hold vaccum at 6 In. when powered by 12 volts. When the 12 volts is disconnected the valve makes an audible sound and releases the vacuum through the port at the very top of the valve under the cap through the filter. The valves that do not hold vaccum at 6 In. will also will release vacuum quickly with sound when the 12 volt supply is disconnected. There are actually three ports in this valve, bottom supply on the side, top side output to the EGR and top output to atmosphere through the filter under the cap. All are about the same size. It appears this valve does more than just apply and release vacuum to the EGR valve. It looks like it also regulates max vacuum to the EGR at about 6 In.

a) Am I testing this valve correctly,

b) does this valve regulate vacuum to the EGR at about 6 In.,

c) is it supposed to hold vacuum or not and which valve (holding vacuum or not) is operating properly, or

d) are they all defective or all okay?

The backfire is another issue I'm working on. I'm in the process of cleaning and testing all the parts for this but have not gotten very far yet other then dropping the solenoid valve on the floor and breaking the lower supply port off one of the valves. Expensive, but luckily I was able to locate one on eBay and it is on its way. Once I get it I'll test that system.

Hope this all makes sense.