Failed Smog - No Vacuum signal to EGR- Code 334

[pad2383]

Hi,

I live in California and my old beat up but beloved 92 Ford Ranger was due for smog. I passed all the emissions testing no problem but I failed on the functional EGR test. The mechanic said the EGR valve was fine, there just wasn't any vacuum being sent to it when he would rev the engine. I checked for trouble codes and found "334 - EGR Closed Valve Voltage High". What parts of the electrical system regulates the vacuum pressure to the EGR? What is the likely culprit here and how would I go about investigating/fixing it? Any and all help is much appreciated. Thanks.

Pad

 

[cody93]

me thinking bad EGR vac line silinoid. trace the vac lines from the egr back to a little box thingy with 2 vac lines and wires.

 

[Bryan22]

i think the 92 has the vacuum regulator connected to the EGR valve, if not, just follow the vacuum line from the valve to the vacuum regulator. from there it goes straight to the manifold, so either a bad vacuum line or bad vacuum regulator for the valve, or bad wiring going to the regulator. good luck.

 

[tomw]

FoMoCo used to use a 'dithering valve' to regulate vacuum to the EGR. It has an 'apply' solenoid and a 'vent' solenoid. The vacuum from the intake would be applied to move the valve, which movement was reported back to the computer by a variable resistor embedded in the EGR valve linked to the valve mechanism. Once the computer thought it had enough, it would turn off the 'apply' solenoid, closing the vacuum, and leaving the EGR where it was. When the computer wanted EGR flow to stop, or to be decreased, it would energize the 'dump' valve to let 'out' some of the vacuum, allowing the spring in the EGR to close the valve further. This also is reported by the 'position sensor' part of the EGR valve.
If either solenoid(valve) goes bad, EGR won't work. If the variable resistor in the EGR goes bad, or the diaphragm leaks, the EGR will report it is in a position [ in its travel ] other than where the computer commanded. i.e., the valve reports being at 10%, given the resistance is XX ohms. The computer opens the apply valve, and the position changes to 40%, and the resistance is YY ohms. Later on, the position is reported as ZZ ohms, which is NOT what the computer wanted nor ordered. Trouble ensues, and the EGR is fired, to be replaced by a simple peasant from Idaho who sits under the hood, and moves the valve on command. oops, wrong story.
EGR closed valve voltage high would tell me that the voltage fed back to the computer when the valve is expected to be closed is higher than expected. Either the valve is jammed or the resistor/slider is giving the wrong resistance. You may be able to find a replacement 'electric' part at a boneyard. I think they can be disassembled, maybe even cleaned and lubricated with 'lock cylinder lubricant' {graphite powder} to improve resistance readings ... unless the resistor is worn away.
tom

 

[pad2383]

Thanks Tom. That's a thorough explanation and a bit over my head. Do you know if the dithering valve design applies to the '92 2.3L engine? I ordered a replacement EGR vacuum solenoid which I'll install Wednesday. Hopefully that does the trick. Otherwise, are you saying I have to replace the whole EGR in case the embedded resistor is shot? However things go Wednesday I'll be back to the forum to report.

 

[pad2383]

I just got back from the smog station and passed the test this time, no problem. Bryan22, Cody93, you guys were both right on. What O'Reilly Auto Parts calls the EGR Vacuum Solenoid and what the Haynes manual calls the Manifold Absolute Pressure (MAP Sensor) was the culprit. I swapped it out for a new one and vacuum pressure returned to the line at the EGR. $52.99 later and all is well. I wonder if my mpg will improve a bit? Thanks for the help.

Pad

 

[Bryan22]

glad you got it figured out!