egr solenoid

[lbagley]

95 5.7L

The EGR solenoid does not open to send vacuum to the EGR valve when the vehicle is running. The voltage at this time is at 13.4v

However, with the vehicle off and switch on, the "switch" opens and closes properly as I attache the connector. The voltage at this time is at 12.3v.

The Code returns a 32. Would the 1 volt difference matter, also what should the voltage to the EGR solenoid be?

Thanks for any help!

[AKWE-gt]

1. engine running 13.3V: running off alternator
2. engine off 12.3V: running off battery
3. switch is working correctly and egr is opening correctly
then maybe you have carbon built up in the egr passages under the valve.

[lbagley]

My testing was done with egr hose not connected to valve. The solenoid clicks open when only the switch is on, but will not click open when engine is on, regardless of whether the vacuum line to the egr valve is connected. The egr valve does funtion properly when I manually apply vacuum to it bypassing the solenoid.
Any additional input greatly appreciated.

[AKWE-gt]

i would have to say it's a bad solenoid then. at idle the egr valve is suppose to be and open under throttle. i would check the vacuum line first to make sure that wasn't the problem and then try replacing the solenoid. sounds like it isn't creating any vacuum to open the egr valve.
this site might help.
http://autorepair.about.com/gi/dynam...echtipidx.html

[Purerock Racing]

I have a 1994 Chevy Silverado, w/350 TBI. It's got 149k miles on it, and runs perfectly.
I recently went for my smog check and it failed. First time it failed in the 5 yrs I've owned it. High N0x levels

The only thing that has changed since the last smog check is a new catalytic converter. The old one fell apart inside, so I had a new one installed by Big O Tires/California Muffler shop locally where I live.

I've attempted to try to figure out what is wrong. I've already replaced my dist. cap, rotor, and installed new Bosch Platinum spark plugs (I've heard good and bad things about these). Plug wires look to be good. Went for a re-test. It still does not pass smog. The smog technician checked my O2 sensor, and said it's working fine. So now he said to focus on the EGR system. He said with a new cat, the engine should pass no problem.

The EGR valve is not stuck and can be moved manually with ease, and seems to be working. Vacuum test to the EGR also loos good. Now onto the other components. There's the EGR solenoid which monitors how much vacuum is allowed to the EGR valve. Could this be bad? How about the MAP sensor, what role does that play, and how do I check it. Thirdly, and this is odd part. The temp. sensors that basically tells the computer that the engine is at operating temps to allow the EGR system to function.

Could one or both of the temp sensor be bad? Would that effect anything? 2 people have told me, that even tho I have high NOx levels (high heat in the combustion chambers), that my motor is registering cold, and that the computer "thinks" the engine is cold all the time, thus disabling the EGR system from working properly. How could that be? You can feel the heat in the radiator hoses. Very hot. The gauge on my dash reads very cold all the time. Like (1) notch off the cold mark. It will not even go to 1/4 hot on the gauge. Do you think that has anything to do with it? I've read that the temp sensor in the ECM circuit is what allows voltage to the rest of the EGR system via the computer.

All vacuum lines appear to be good and I've checked for vacuum leaks and didn't find any.

Any advise you can offer would be greatly appreciated. I need to get this thing to pass smog so I can get my 2005 registration tags.

[joe92k1500]

I would aim toward a bad thermostat. I have seen them actually break or stay in the open position. This will keep the motor cooler than it needs to be, but it will feel hot to the touch. Give that a try, if it does not help, then aim for the coolant temp sensors. I am not sure on testing for the temp sensors. Pick up a haynes manual , or maybe someone else in here knows. Hope that helps.

[Purerock Racing]

Originally Posted by joe92k1500

I would aim toward a bad thermostat. I have seen them actually break or stay in the open position. This will keep the motor cooler than it needs to be, but it will feel hot to the touch. Give that a try, if it does not help, then aim for the coolant temp sensors. I am not sure on testing for the temp sensors. Pick up a haynes manual , or maybe someone else in here knows. Hope that helps.

I think those temp sensors open and close just like a thermostat, but allow current to flow to the EGR components rather than coolant. That's why they say that your EGR system is not suppose to work when you have cold start up. I'll try the thermostat first off. Several other friends of mine also have had these same trucks, and said there's ran cool also. But barely off the cold mark on the gauge is a bit extreme I think. Come to think of it, one time I was getting it smogged a couple years back, it failed the first time, so the tech. let the truck run for like 15 minutes to get it hotter, and tried it again. Guess what, it passed.

[Mikado14]

The temp sensors do not open or close. They are basically a thermistor whose resistance will vary with temperature. I believe that the 5.7 in '95 had 2 sensors, one for the guage and one for the ECM. However, I seem to be having a brain fart here due to old age, I work in an independent shop and can't remember which make vehicle but the ECM sensor might be a switch and yes, it could open and close but I doubt it, I believe the GM is a thermistor. Most will close around 160 degrees well below the opening and closing of a thermostat.

Check thermostat first then go to sensors.

[Purerock Racing]

Originally Posted by Mikado14

The temp sensors do not open or close. They are basically a thermistor whose resistance will vary with temperature. I believe that the 5.7 in '95 had 2 sensors, one for the guage and one for the ECM. However, I seem to be having a brain fart here due to old age, I work in an independent shop and can't remember which make vehicle but the ECM sensor might be a switch and yes, it could open and close but I doubt it, I believe the GM is a thermistor. Most will close around 160 degrees well below the opening and closing of a thermostat.

Check thermostat first then go to sensors.

------------------
yep, for sure. This morning and yesterday on the way home, the gauge read 100 degrees the whole time... maybe 110 at the most. That cannot be right. If that's true, then the EGR system will never function. I'll let ya know what I find.

[AKWE-gt]

ect is a thermistor resistance varies with temp. when the engine is cold the the resistance is high and when engine is warm the resistance is low. this means when the engine is cold it runs rich and when warm it leans out.
with high NOx levels usually the main problems are that the engine is running hotter and leaner than normal. so if your engine was running colder it should be running richer and shouldn't have high NOx levels.
when you applied vacuum to egr did it effect the engine? if not than you should check the exhaust passages maybe their clogged with carbon.
also you can put your hand on the solenoid to see if its working.

[Purerock Racing]

Originally Posted by AKWE-gt

ect is a thermistor resistance varies with temp. when the engine is cold the the resistance is high and when engine is warm the resistance is low. this means when the engine is cold it runs rich and when warm it leans out.
with high NOx levels usually the main problems are that the engine is running hotter and leaner than normal. so if your engine was running colder it should be running richer and shouldn't have high NOx levels.
when you applied vacuum to egr did it effect the engine? if not than you should check the exhaust passages maybe their clogged with carbon.
also you can put your hand on the solenoid to see if its working.

============
OK, I tried to see if the EGR valve was working while the truck was running in park and engine fully warmed up. I can barely notice any movement at all when I rev. up the engine to approx. 1/2 throttle. Just a very slight instance where the diaphram moved very slighty not enough to allow the valve to open enough to do anything. Actually it only moved very slightly right when I opened the throttle, then it closed again. I've read that some EGR systems don't work unless you are in drive. Not sure with GM. Should my EGR move signaficantly and stay open or hardly move at all? I have also applied manual vacuum to the EGR while at dile, and the motor nearly dies off, so I assume it's working and not clogged with carbon. Either the EGR solenoid is not working right, or the temp sensor is not allowing enough voltage to the solenoid to allow it to work...

[Purerock Racing]

replaced the thermostat just now, and it heats up to approx. 190 degrees. I can now see and feel the EGR valve working...off to re-test at the smog station...