I have an 89 rs 305tbi auto that has been failing emissions with high numbers across the board. It seems to have a slight miss at idle so I started chasing vac leaks, new pcv, and new tbi base gasket, new cap rotor, plugs wires... So on to the EGR.

In theroy if i disconect the vac line to the old egr and put it on the new egr not yet installed and increase rpms I should see the valve move, right?

When I do this i get no movement and I guess i'm trying to figure out if it's the valve or selenoid.

For sake of emissions can i run a vac line to the valve right off the TBI unit? Thx guys for any input.

 

First of all, the EGR valve reduces NOx(oxides of nitrogen) emissions only. It does this by feeding a ported amount of inert (exhaust) gas back into the intake airstream to lower combustion temperatures. As far as testing the valve and solenoid, understand first that the solenoid on this series of EGR is only an enable/disable type of control. The ECM activates it, thus venting vacuum on the EGR circuit, to disable EGR function during certain operating conditions. Otherwise, when the solenoid is deactivated, the EGR valve is controlled by ported engine vacuum. The EGR valve is generally a pressure modulated type and will only open when there is adequate exhaust pressure. Therefore, it may not open with the engine revved in park. The pressure modulation valve works by venting vacuum. Therefore, to test for normal EGR system function, with the engine warm so that EGR is allowed by the ECM, T-in a vacumm gauge to the EGR line at the valve and monitor vacuum while driving. You should see 7" H2O at cruise. If not, try bypassing the EGR solenoid. If you get vacuum with the solenoid bypassed, you probably have a leaking solenoid. You can verify this by testing for power and ground at the solenoid to be sure it's not being activated. If you do not get vacuum at the valve in either of these tests, check the line back to the TB for proper connection. It needs to be ported vacuum, meaning it shows vacuum only with the throttle open.

I'm going to venture a guess that since most states don't monitor NOx anymore, your car isn't failing due to the EGR valve. But rather, since you say that you idle is uneven, the car is failing on HC(hydrocarbons). Hydrocarbons are liquid carbon, or raw gasoline that has made it through the engine without being burned. A few things can cause HC to run high. The most common cause that I see on factory vehicles is too lean fuel mixture. The lean condition causes lean misfire and as hard as it may be to believe, when mixtures get too lean, the fuel actually doesn't burn at all. Other causes for high HC are timing too advanced. The engineers relied on hot exhaust manifolds to burn off excess HC. When timing is too advanced, the exhaust manifolds run cooler and fail to burn off HC. The catalytic converter was designed principally to process HC and CO. If your catalyst is not working at full capacity, HC may be too high to pass the test. However, if engine tune is not good and HC is very high, even a healthy cat will not be sufficient to bring the levels into compliance. In this case, engine performance needs to be addressed.

 

That was great,thanks. I live in GA and they test HC, CO, and NO. All my readings are high with the CO being way out of range. So if I understand you correctly I could by pass the selenoid by running a vac line from the ported vac on the TBI directly to the egr. Thanks again.

 

Yes, that would work. Still may want to perform the vacuum test to verify the valve is working. CO being high is unusual for a factory stock EFI vehicle. How high is it? 2-3% can be caused by a failed cat but any higher starts to look like a fuel management issue. A few common suspects are O2 sensor, MAP sensor, ECT sensor. It is more common on factory stock EFI vehicles to see a lean condition, with high HC. This is aggravated by aging injectors, lowered compression from engine wear. We can compensate for high HC by adjusting timing. It's a cheat since we readjust after the test for best performance. What are the standards in Georgia? Oregon's are CO: 2%, HC: 220ppm, NOx: not tested, CO2: 10% min.

 

Well I wen t for a retest today with a new erg (that I would later learn was bad) hc ppm was 121 allowed is 148, co % was .12 and allowed is .94 so all good there but NO ppm was 1897 and allowed is 1047.

Now I was running a 5 to 1 mix of 89 octaine and denatured alcohol. I was stumped so I went home check vac to and from the selenoid and all was good. So I pulled the new egr and found that it didn't hold a vacuum at all so I put another new one in.

Now my big question is in park if I slowly increase the rpm I can feel the egr pulsing, under this situation how much should the valve be opening?

I thank you and more importantly my wife does to cuz the sooner I get this solved she can put me to work on house projects!

 

As I said earlier, the pressure modulated valve won't open with just vacuum. It has to have exhaust pressure then it will open with vacuum. The test for this valve is to T in a vacuum gauge to the vacuum line at the valve. If the modulator is working correctly, you will see vacuum as high as 7"H20 at cruise. If the modulator is not holding vacuum, you will see much less vacuum or none at all. Other issues can cause NO to run high. Where is your timing set? Too much advance will push combustion temps high. Are you running the original AC Delco plug number or an aftermarket brand? You must run the original plug and may need to go one heat range cooler to bring NO down. Of course, are your EGR passages clear? They may be restricted with carbon build up.