I need some help troubleshooting the EGR system. My car was failing smog test on everything HO,CO,Nox. I changed the Cat and HO,CO where at passing but Nox was high. I checked the EGR to see if it was clogged it looked fine. I bypassed the EGR solenoid valve by going taking vacuum directly to the EGR. Tested the car and it passed good. Nox stayed at 445 for both 15mph and 25mph. So my question is, how can i know if the Solenoid is receiving a signal? I dont want to leave the car with vacuum always directly to the egr valve. Help plz.

 

A scanner might tell you when it's commanded to be on but it would be harder to actually know if it does turn on when commanded to. It's a modulated signal. It's dangerous to do without a dyno, but maybe you could run it on jack stands, just be really careful.

What cat did you put on there? Aftermarket cats don't always pass because they skimp on the precious metals (which are a hot commodity now, even more than before).

Also other causes are running too hot, too lean, advanced timing. Yopu don't say much about your car so it's hard to offer specific recommendations.

 

You could tee in a vacuum gauge to the hose from the solenoid to the valve. Run a long hose so you can put the gauge where you can see it while driving (because the EGR only operates in part throttle driving conditions). Then you will be able to verify the valve is getting vacuum. The other question would be if it is opening or not.

http://shbox.com/1/4th_gen_EGR.html

 

If the EGR solenoid electrical circuit is faulty, you will get a code in both OBD-I and OBD-
II. There is also a code for "no flow" on the EGR system in both OBD-I and OBD-II, but the OBD-I diagnostic is not very sensitive. The OBD-II diagnostic will usually pick up "no flow". Even if the electrical circuit is OK, there is a possibility that the EGR solenoid is stuck closed.

First, look for the EGR solenoid codes. Then key on, check the brown wire to the EGR solenoid for 12V. If you have 12V, ground the other pin, and see if the solenoid opens. You could do that with the engine running, and check to see if you feel the vacuum on the EGR side of the solenoid when it opens.

Another SUGGESTION: Add a "signature" with basic info about your car - year, model, engine, tranhy and any major mods. In this case, knowing the year would have allowed us to tell you the specific codes to look for.

 

94 z28. 6 speeds. Ok this is what i know. I have try trouble shooting the solenoid by yes doing what shoebox said, used a long hose with a vacuum gauge and i can see the needle of the gauge moving as i drive. So it tells me the noid is getting power and opening.

I have tryed what shbox.com has for checking the egr. Now can someone tell me if they know how those the backpressure works? I also read that if exhaust is tempered not enough backpressure can be created. what is backpressure? Also could it be coolant temp, MAp sensor, and other sensors are not giving in proper info! I really hope you guys can help.

 

To add a "signature" (the vehicle info most people have appended to all our posts), go to the red task bar at the top of the page, left click on "User CP" and pick "Edit Signature".

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As I understand it, you have no SES light for the EGR solenoid, nor for the EGR flow. That would appear to confirm that you have an EGR system is working properly. You have verified all the components are working correctly, and that exhaust gas will flow if you open the valve.

You bypassed the EGR solenoid, by running the vacuum line directly from the nipple on the side of the intake manifold, to the EGR valve. The vehicled passe the emissions check.

Think about what this caused.

The EGR system is "pulse width modulated" (PWM). That means the PCM does not simply open the vacuum solenoid to actuate the EGR valve. It pulses the solenoid, to produce a variable vacuum strength, which controls exactly how far the EGR valve opens. In bypassing the solenoid, you defeated the variable flow control of the EGR system, taking control away from the PCM.

Now its flowing 100% (a scanner will show you the % duty cycle the PCM is commanding) of the available exhaust gas.

But your PCM doesn't know that. Since the PCM thinks the engine is getting more air (and less exhaust flow), its still providing the fuel required for the greater air flow. This means your "bypass" is causing the engine to run a bit richer than the PCM would normally set.

In effect, you richened up the mixture with the bypass. NOx is formed by high combustion chamber temperatures, which are caused by running lean.

Bottom line in my mind is the engine is running lean, and producing too much NOx. You need to find out why its running lean. Quit monkeying with the EGR flow and the componens therein. Focus on why its running lean.

====== PS: ADD A SIGNATURE

 

OK i understand what your saying. So where would i start to look if the car is running Lean? the help you guys are giving is very help full thanks

 

When is the last time the O2 sensors were changed?

 

I've had the car for about 3 years and i have not changed them. But i really wouldn't know. Should i test the O2 sensors?

 

Not sure how you would test the sensors. Might be a good idea to get some scanning software, and a cable, and run a data log. Freescan works great for this purpose (free software download), and TTS DataMaster as well, although TTS stopped their free downloads temporarily, until they solve some windows 7 bugs.

 

that's a great idea except that does cables are expensive. you know of a way to make a home made cable?