'87 F150 4x4 with a 302.

Started off with KOEO codes 31o & 31c, which indicated a problem with the EGR Valve Position Sensor. Verified the sensor was bad, was giving wildly erratic resistivity measurements when the plunger was moved in and out.

Replaced it, and am now getting KOEO code 84o, and after running the engine, code 33c. These indicate a problem with the solenoid that controls vacuum to the EGR Valve.

There is vacuum to the solenoid, though not measured with a gauge. The vacuum line from the solenoid to the EGR is fine. There is proper voltage to the solenoid. Since I couldn't figure out a definitive way to check the solenoid, I replaced it, but the problem persists.

What should I check next?

-Kennon

 

Finally figured out how to test the solenoid. First, with the electrical connector off it should measure 20 to 70 ohms between the pins. The old one didn't, but the new one did....at least until I tried the 2nd test.

The info I found said to attach jumper wires to the pins, using an inline 10 amp fuse for the hot side, then tap the wires on the battery terminals and I should hear it click. And also if I was blowing through the vacuum connections I should be able to feel it opening and closing. It clicked once and then simultaneously blew the fuse and burned up the solenoid.

So with the second new solenoid installed and connected, I ran a jumper from the negative connector and tapped it on a ground. I couldn't hear any clicking, but when I hooked a tube to the vacuum connector to blow through, I could tell it was working. Then I hooked up the vacuum, and with the motor running I could ground out the connection and the engine would die.

But it's still throwing the Code-84. So it looks like in addition to the original solenoid being bad, the computer may be bad also.

-Kennon

 

I`n not aware of your testing procedure but the vref volts are only 5 volts. Care should be taken to not fry the computer with 12 volts if it is only suppose to be 5 volts. It takes a hand pump to move the valve,I don`t think u can suck on the tube hard enough to move it. Take the egr off and clean it first.

 

Usually when the computer goes bad you can`t pull codes also.

 

Aktech why are we always working on EGR? Anyway what he said. Solenoids ore pretty simple on off magnet deals so if you have voltage and resistance your probably good. You can touch jump a lead from the 5 v to the solenoid and from the solenoid ground to ground and that should activate the solenoid. And switch the vacuum. A hand pump is the way to go for the valve. You can also remove it and make sure its clean and moves freely and the vacuum plunger (sorry its late can't think if the right name ) isn't leaking.

 

Perhaps I did not explain clearly, the code-84 indicates a problem with the solenoid that controls vacuum to the EGR Valve, not the EGR valve itself, nor the EGR valve position sensor.

Since code-84 is an engine-off code, it cannot be a vacuum problem, so must be an electrical problem.

The final test I mentioned, which verified the solenoid is good, was to run a wire from the pin-33 side of the solenoid connector which made it possible to manually ground out the circuit. In other words, to manually do what the computer is supposed to do. When I grounded it, the engine would die, indicating that the solenoid was properly switching to supply vacuum to the EGR Valve, and that the EGR valve was indeed opening.

-Kennon

 

Yea there should be a sticky on how to test it,how it works,what it does,etc...

 

Sounds like you tested it correctly. Now you need to make sure the computer is sending a close signal, the solenoid is closing and the signal is getting back to the computer. I would start with simple continuity tests on the wires and wiggle tests on the connectors ( including a visual inspection of the pins.