No vacuum at EGR valve

[Cheburashka]

I have a 1995 4.0

Went to get smogged and mechanic said I need to have vacuum at the EGR valve when the accelerator is being pressed and I don't, so the valve does not open.

I removed the solenoid, put 12v on it and it does not click like I expected. Got a new one from O Reilly and it still doesn't click.

So now I'm at a loss of what to do. My valve is 100% working and I have vacuum at the inlet of the solenoid, but I can't get vacuum at the outlet of the solenoid.

Wonder if I bought a faulty solenoid or if these are not supposed to click.

 

[Cheburashka]

Also I haven't tested the DPFE with Forscan, but I will tomorrow. Should no just apply vacuum the the EGR to see a voltage change or block the solenoid off somehow?

 

[RonD]

EGR solenoid gets 12v with key on, computer grounds the solenoid to activate it, and it actually pulses the ground to send more or less vacuum to open the EGR Valve more or less

So 12v on red wire with key on, full time, other wire is ground from computer, brown/pink wire maybe

And as mechanic said, EGR system is not used on cold engine, and after warm up its only used when accelerating or cruising above 30MPH


EDIT:

DPFE sensor reads exhaust pressure not vacuum, the two hoses on it go to exhaust pipe between manifold and EGR valve
So just apply vacuum to EGR valve with engine idling, engine should start to stumble if so EGR valve is working

Do you have a code, if so what is it?

 

[Cheburashka]

Thanks for your help as always, RonD.

No CEL on, I do have a code but I think its stored from when I replaced a vacuum line.

I have tested the leads going to the solenoid and they do get 12V. I'm just surprised the solenoid does not click.

Do you know, on a warm motor, if you press the accelerator at idle, should the solenoid provide vacuum to the EGR or not? That is what I am not sure about.

My coolant temp is generally right below the center line, so it runs a bit cooler than ideal, I wonder if that is the issue.

 

[RonD]

No, no vacuum at EGR valve if you are not moving
EGR use is based on engine "Load" as calculated by computer

You can use one of the hoses and blow thru either of EGR solenoid's ports while activating it, it will pass air when activate and block air flow when off

Adding exhaust gases to intake air is done to "cool" the cylinders which reduces NOx production, a toxic gas
As most know when you drive up a longer grade, or haul a heavy load, engine temp will go up a bit because engine "load" is higher

NOx production spikes as cylinders heat up more when engine is under higher load
Exhaust gases lower the temp spike so lower NOx levels
As a by product it also lowers the chances of pinging/knocking on Regular gas because cylinder temps don't go up as much
People who eliminate EGR systems often have issues with pinging when using Regular 87 octane fuel, this has to do with engine model and computer/spark advance under load



Ford Temp gauge is calibrated for about 205degF at 1/2
Your thermostat should be 190-195degF rated
So just below 1/2 is what you should see in normal operation after full warm up

 

[Cheburashka]

Interesting, so the solenoid should be open when it is energized by 12V, and closed when it senses a pulse, correct?\\

So even if I am not moving, and I press the throttle, the EGR valve should not open?

Mechanic told me that the EGR valve should open when throttle is applied even if the car isn't moving.

 

[RonD]

Mechanic is incorrect

Solenoid valve is open all the way when it has 12v and a ground
The computer varies the ground so 12v drops down to 7v or 8v or 9v or ect........, this in effect partially opens the valve
Valve is close with no ground from computer

The computer will Pulse the Ground to partially open the valve to send partial vacuum to EGR valve so it partially opens, lol
This is based on engine load, no load means no ground to valve so valve is closed, there is very little load when you REV an engine any time its not connected to drivetrain
If you want to put it in gear with foot on the brake and then REV the engine a bit, you might get some action from EGR solenoid, but never tried myself

The variable Ground is called Pulse Width Modulation(PWM) used to control many many thing in vehicles these days
If you have day light running lights PWM is used to run the headlights at 60% to 70% brightness
Pretty much all solenoid valves use PWM
IAC Valve uses PWM

Most understand how a dimmer works or a volume control works these are often controlled the Positive side, but you can do the same with Negative side
Simple test, put volt meter on battery terminals to get 12v
lift probe on negative terminal
Voltage goes to 0
Now rapidly touch and lift same probe, voltage will probably hang out at 5v or so, depends on meter and how quick you are, lol
Thats PWM, and can be done on positive or negative wire in DC Circuits
Car makers use Negative side because the fewer 12volt wires running around a vehicle the better, less chances for shorts and blown fuses

 

[Cheburashka]

Alright, came back from vacation and back at it.

I am going crazy trying to figure out if anything is even wrong with my system. I did hook up a vacuum gauge and drove around but couldn't get the EGR valve to open at all.

That said:
Tested DPFE by applying vacuum to the EGR valve. Volts go from 0.9v to 4.0v, indicating that it is functioning correctly as it is sensing the pressure delta. Which means the corresponding lines and orifice are operational.
EGR valve tested and working
EGR solenoid... not sure how to test since it vents to atmosphere, but replaced with a new one for good measure. I have perfect vacuum at the solenoid.

Is there anything I am missing? How do I get the system to open the EGR valve while the truck is moving? I drove around for 20min and it never applied vacuum to the EGR valve. The whole time, DPFE reading was 0.8-0.9v.

 

[RonD]

EGR should open when engine is warmed up and under a Load i.e. accelerating or driving uphill because cylinders start to heat up and generate higher levels of NOx, a toxic gas
EGR cools the cylinders(slows combustion) so lowers the NOx production, this is the sole purpose of the EGR system, lowing NOx

Some year engines didn't need much EGR because they were already low on NOx production so could pass emissions testing without EGR being used, but in some states EGR was required equipment, needed or not
Calif. required EGR systems

DPFE sensor is there to tell the computer how far open the EGR valve is, its not a "control" for EGR system, it would only react when computer has opened the EGR solenoid(EVR) and sent vacuum to EGR valve, the DPFE would then register a difference in pressure between its 2 hoses on the EGR tube
So you can use the DPFE sensor reading vs vacuum gauge to see if EGR valve is ever being opened

 

[Cheburashka]

That makes sense. I'm going to drive around a bit more and log the DPFE readings. Thanks for the help, will report back.