Exhaust Gas Recirculator (EGR) Sensor

Mechanically Disabling the EGR Valve

Originally, I suggested blocking off the EGR valve to improve power and increase gas mileage then I changed my mind and enabled it. Well, after about 3/4 of a tank of gas - it's disabled again. It just hurts performance and all around driveability too much to enable it! Disabled, it provides about a 5% increase in both hp and gas mileage from what I can tell. The engine runs better and has better acceleration without the egr.

The EGR (exhaust gas recirculation) valve's job is to introduce exhaust back into the intake manifold to reduce emissions at the expense of power and gas mileage. The previous link does a good job of describing its operation.

This seems to be utterly stupid especially because exhaust gases are added after the fuel/air mixture is determined. It seems to be defeating the purpose of a proper air/fuel mixture!

Now, my goal is to increase fuel efficiency so that I use less gas - consequently reducing the pollution to the atomosphere. So far with all the mods (including this one), I've increased my highway mileage dramatically and increased the engine's power!

The EGR valve at the back of the engine.

The EGR valve is located at the back of the throttle body. It has a pipe that runs from the exhaust manifold over the head next to the firewall to the EGR valve. Ideally, you would like to disconnect and block off that pipe but you'll find that it is seized and rusted in place. A big nightmare to get it off. The alternative is to block off the EGR to throttle body passage - that's a lot easier. Just takes an easily made blocking plate made out of a piece of sheetmetal you have lying around. If you can't make your own EGR blocking plate, the Detail Zone sells inexpensive blocking plates (link courtesy of jkmustang - thanks!).

The exhaust pipe from manifold to EGR valve

Gasket on top, sheet metal blocking plate on bottom

There's two bolts (10 mm head) that hold the EGR valve onto the throttle body. The top bolt is easy to get to but the bottom is very awkward. Disconnect the throttle body position connector from the driver's side of the EGR valve to give yourself room. I used a box end 10 mm wrench to unscrew the bottom bolt.

Undo two bolts and slip in new gasket and blocking plate

I purchased a new EGR valve gasket for $4.00 and used it as a template for making a blocking plate. Put the new gasket against the throttle body and the blocking plate on the EGR side. Bolted it all together. Took less than an hour! The engine runs quieter and smoother. I have a little more power and will find out if the gas mileage improves with the next tank of gas.

Some Final Words

Aaron K. sent me an email with some good questions, here's my response:

  • You can't remove the EGR components otherwise the ECU will think something has failed - we are fooling the EGR system here.
  • It's pretty much impossible to remove the pipe from the exhaust manifold to the EGR valve - it will be rusted solid in the exhaust manifold
  • After every modification that affects the fuel/air mixture like this one - you must reset the ECU by removing the negative terminal of the battery. Wait 5 min, reconnect and then over the next 15 miles of driving (idling won't work!), the ECU will relearn the new air/fuel mapping.
  • You don't have to turn the key to the on position when resetting the ECU. Just disconnect the negative terminal as outline previously.

Option #2 - Fooling the ECU using an EGR Simulation Circuit

If you don't feel like using a block off plate then you can build this EGR simulation circuit. Just to clarify, you can defeat the EGR either with a block-off plate or using this circuit. There's no need to do both. The EGR simulation circuit fools the ECU into thinking that the EGR is working when in actual fact, it is disconnected, shut off and no exhaust gases can get into the intake manifold.

There are two parts to the EGR system and here's how they work electrically:

  • EGR solenoid

    The +12V EGR solenoid is mounted on the passenger fender well and controls the vacuum to open the EGR valve. If you disconnect the electrical connector, the ECU detects that it is disconnected and generates an error code. You can replace the EGR solenoid with a 100 ohm 1/4 watt resistor. This will fool the ECU into thinking that the EGR solenoid is still connected.

  • EGR position sensor

    The ECU expects that in the closed position, it will receive a minimum 0.5V signal from the EGR position sensor. In the open position, when the EGR solenoid is energized, it expects a +5V signal. In testing, I found that it takes almost no vacuum to energize the EGR valve to the full open position. I have a vacuum hand pump tester and I had just started to pump to create vacuum, the needle barely moved and the EGR valve was open.

    The key then is to take the EGR solenoid's drive signal from the ECU and use it to falsely generate an EGR position sensor signal that the ECU expects to see.

    In the preceding circuit, I used an inexpensive $0.25 PNP transistor, 2N3906 to fool the ECU into thinking that the EGR valve was in the correct position. When the EGR solenoid is off (+12V at Brn/Pink wire), the transistor is off (acts like an open switch between the transistor's C and E pins). The transistor appears to be not part of the circuit and we're left with a simple voltage divider. The 30k/3.3k ohm voltage divider creates a 0.5V signal to the ECU's EGR position sensor input which is what the ECU expects.

    When the EGR solenoid is energized (on), there is 0V at the Brn/Pink wire. The transistor turns on and this acts like a short between the transistor's C and E pins (like turning on a switch). The 30k ohm resistor is shorted and +5V goes to the ECU's EGR position sensor input which is what the ECU expects.

    On my Ranger, the EGR Solenoid connector is quite long and taking it apart, I found an extension has been added that holds a current limiting resistor. I added the 100 ohm resistor inside the extension. I did have to run a wire from the EGR solenoid connector on the passenger side of the engine compartment to the EGR position sensor wiring on the driver's side firewall.

    EGR solenoid connector with room for resistor.

    I went to the wreckers and purchased a EGR position sensor and tore it apart and used it to hold the transistor and components but it turned out to be quite a difficult job getting it open and not worth the effort. I suggest just cutting the wires on the wiring harness connector and wiring the components directly or finding an alternative connector to use for both the circuit and wiring harness.

    Here is the EGR Position simulator circuit in the modified junkyard position sensor.

    Here is a picture showing the EGR and wiring with the fake EGR circuit.

    Total cost of modification: less than $2.00! I've removed most of the EGR components and run this EGR simulation circuit for two weeks now and it works like a charm!

    NOTE: If you do this, make sure that your battery is disconnected. You do not want to accidentally apply +12V from the EGR solenoid to the +5V EGR postion sensor circuitry of the ECU. You will FRY your ECU!

Final Words

I received an email from James- ASE Master Tech and he says:

Just thought I'd give a little info on the EGR page in the 2.3 article. You wrote that by you blocking your egr you gained power and economy. If your egr is working properly, then you should not have noticed ANY gains. The egr only operates during cruise conditions. It does not operate at idle because idle quality would be greatly affected. It does not operate at full throttle because Ford knew you want full power when you put the pedal to the metal. The reason they do it at cruise is because it has very little effect on performance when you are cruising down the freeway at a light load. when you smash down on the accelerator, the egr shuts off. In my 94 ranger the egr uses a DPFE (Delta Pressure Feedback EGR). In that, there is an orifice inside the tube that goes from the manifold to the throttle body. There is a silicone tube on each side of this orifice that goes up to what looks like a map sensor with two lines going to it. When the egr starts to operate, there is a pressure difference within the tube on either side of that orifice. This is how that 'map' sensor verifies that the egr has proper flow. In addition, when that sensor sees flow of the egr at cruise the computer knows that it is an inert gas and backs off fuel to keep a proper AF ratio, lower NOX, and save fuel. So if you noticed any power increase from blocking off your EGR it was not working properly. It most likely had a sticking valve that was allowing exhaust gasses back into the intake at all RPM. This would greatly affect power.

It's good to hear an alternative "argument" about blocking off the EGR valve. Unfortunately, I don't have the truck anymore to follow up and check the EGR valve.

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Copyright February 2011 Eugene Blanchard