Persistent Code 84. (1987 Ford Bronco II Auto)

[Nelson and Hudson]

TLDR: The engine has the vacuum source, but the computer is sensing that the EGR still isn’t opening correctly during the test.

(1987 Ford Bronco II Auto) I have been trying to get my smog test passed for the last year. Could someone help me identify the issue?

In 2023, when I first had to get smogged, it failed at first, but then passed.
Smog Check #1 — 2/18/2023

• Visual inspection passed, functional check passed, ignition timing passed, and fuel evap controls passed, but the emissions test failed, and the inspector noted: “Check EGR”.
• The raw numbers showed the 15 mph and 25 mph test results passed, so this first failure looks more like a system concern than a simple tailpipe outlier.
• At this point, EGR was already on the suspect list.

Smog Check #2 — 2/28/2023

• Everything passed, including emissions, ignition timing, and fuel evap controls.
• This is important because it shows the truck can cleanly pass when the system is behaving properly.
• The later failures are therefore not random; something changed or degraded afterward.

When it was time for the next test, it failed badly.
Smog Check #3 — 7/8/2025

• This was a much worse result: visual inspection failed for tamper, functional check failed, emissions failed, ignition timing failed, and fuel evap controls were listed as disconnected.
• The diagnosis again came back as EGR not functioning properly.
• I also got a list of things to inspect: TPS, catalytic converter, coolant temperature sensor, and oxygen sensor.

What I Fixed

• I adjusted the TPS to the proper voltage range of 0.96V to 4.3V.
• I repaired electrical faults and grounds.
• I fixed the O2 sensor connector.
• I changed the oil and gapped the plugs properly.
• After those repairs, the surging issue was largely gone.

Went to go get it resmogged, still failed, but less so.
Smog Check #4 — 10/17/2025

• Visual inspection passed again, functional check passed, ignition timing passed, and fuel evap controls passed, but emissions still failed.
• The diagnosis shifted slightly to: vacuum checked within spec, but EGR may not be functioning properly.
• The vacuum supply looked okay, but the EGR still was not doing its job.

So from this point, I knew I had to go through the EGR System.

(Vacuum routing for vehicle)

1. EGR Valve 2.EGR Vacuum Regulator (EVR) Solenoid 3. EVP Sensor

• I identified the EVR porting: bottom port = vacuum source from the EGR tube/manifold vacuum side, and top port = EGR valve side.
• I measured about 20 mmHg at the tube feeding the bottom port of the EVR while the engine was running, which supports that the vacuum source is present.
• The EVR coil resistance checked around 50 ohms, which suggests the electrical coil is not open.
• I measured that the EVP sensor is getting 5V, ground is solid, and the sensor wire is giving off ~3.18V
• When I compared it with a new EVP, it gave the same reading.
• When I use a vacuum pump on the EGR, I can hear it move
• The Vacuum Reservoir holds a vacuum.

Where It Stands Now

• The truck has shown it can pass smog when the system is right.
• I have already ruled out or improved: TPS, grounds, O2 connector, plugs, timing, and vacuum supply.
• The remaining focus is on the EGR control path, especially whether the EVR is actually sending vacuum to the EGR valve when it should.

Code 84 is persisting regardless.:”84(O.R) Solenoid/ circuit fault for Electronic Vacuum (or Voltage)Regulator (EVR) Exhaust Gas Recirculation (EGR) cutoff solenoid or Exhaust Gas Recirculation (EGR) solenoids, whichever is present”

Code 32 (memory) (Test): “Pressure Feedback EGR or (EVP) lower than normal”

Code 33 (memory) (Current): “EGR Valve Position (EVP) was out of range”

TLDR: The engine has the vacuum source, but the computer is sensing that the EGR still isn’t opening correctly during the test.

 

[sgtsandman]

Usually, when there is an EGR problem, the valve is clogged or stuck. You could try cleaning out the EGR valve. Sometimes that works. It just depends on how fouled up it is inside. If it's stuck, you might be able to get it to break free with some penetrating oil but It might just be easier to just replace the valve. It's been a good while since I changed one on one of my vehicles but I seem to remember them not being all that expensive.

 

[Nelson and Hudson]

Usually, when there is an EGR problem, the valve is clogged or stuck. You could try cleaning out the EGR valve. Sometimes that works. It just depends on how fouled up it is inside. If it's stuck, you might be able to get it to break free with some penetrating oil but It might just be easier to just replace the valve. It's been a good while since I changed one on one of my vehicles but I seem to remember them not being all that expensive.

EGR valve moves freely; it's a new EGR.

 

[sgtsandman]

EGR valve moves freely; it's a new EGR.

Does it actuate as it should under vacuum? With the crap shoot that new parts are these days, it is entirely possible you did everything right but a bad new part is keeping you down. A good number of us have been stung by bad new parts.

 

[rusty ol ranger]

Check the port behind the EGR where it bolts to the plenium. Its a pretty small passage and it very well could be plugged.

Did you also replace the pulse sensor? (Little black box clipped in right above EGR with a tube running to it)? If thats shot or the wiring is bad the ECM wont know whats going on.

Last but not least it could be the ECM itself.

 

[Nelson and Hudson]

@rusty ol ranger @sgtsandman
I believe the "Black Box" you're referring to is the EVP Sensor.

I took measurements from all 3 wires

Orange is 5V
Black/White is Ground
Brown is the Signal; From this, I'm getting 3.18v on Key On Engine Off

The Code 84 makes me think it's the EVR (Solenoid).
From my understanding, the EVR gets 12v, the computer pulses the ground connection, which in turn causes the vacuum to pulse. When I connected an LED to the back of the ground connection and to the chassis, the LED did not pulse, which leads me to believe either the EVR is still bad (3rd one) or the computer is not able to create the pulses.

I know the vacuum is solid because I've had to reroute the tubes with new lines. I also pressure tested them with a pump, and they hold pressure.

 

[rusty ol ranger]

That brown signal wire looks suspect, i know the broken insulation isnt much...but being so low voltage it wouldnt take much corrosion to throw the signal to the ECM off.

That is how the vacuum solenoid works. When i tested mine i just stuck a black wire in the ground side, and turned the key on and touched the black wire i inserted to the negative battery terminal. Youll hear it click if its good.

Also, the top pops off the solenoid, theres a little filter in there, its rare but the filter can become plugged.

If the solenoid clicka when you ground it its likely the wire between it and the ECM or the ECM itself.

Are you in a smog testing area? If you arent you can get a 88-92 ECM and swap out with yours, itll eliminate the EGR as only 86\87 had them. Along with the knock sensor. Ive done this with both my 86 and 87