I got codes today using the procedure from fordfuelinjection.com and cam up with this KOEO Code 34: "PFE or EVP circuit above the closed limit of 0.67 volts"

How can I fix this problem? What causes this?

Also, when pulling codes, i got a code 41, but in fordfuelinjection theres no KOEO code for 41.

Oh, and truck is a '93 F-150 with 302 engine.

Thanks

 

Take a look at this link:

MODERATOR NOTE: Expired link removed

 

The EVP sensor is on top of the EGR valve. I think that's at the front passenger side corner of the upper intake manifold on your motor. The EVP screws to the top of the EGR valve with 3 screws. Apply vacuum to the EGR valve nipple with a hand vacuum pump while reading the EVP resistance and see if it falls within spec. Weird it's an overvoltage, I wonder if it's a wiring problem.

41 is system lean. It's a little misleading and there are a lot of possibilities unfortunately. The system is running lean and the computer has enriched past a point that it considers normal to keep it running rich enough. Now, it knows how lean or rich the engine is running from the O2 sensor. When the O2 sensor gets old it can read leaner than it should, making the engine enrich too much. This is one possibility. The other is a vacuum leak or low fuel pressure. If the exhaust smells rich and your mileage is really bad it might be the O2 sensor. If its smells normal look for a vacuum leak first.

 

O2 sensor codes are tricky. Often they do not mean that your sensor is bad, they mean that something else is throwing your mixture outside of the normal range.

EGR codes are also tricky. There are many threads here on EGR codes and some people have bad luck with them. If you buy an EGR valve and sensor, get them from the same place. There have been problems with incompatible parts that were not bought together.

Generally start with the lower number codes and work your way up. Clear your codes after you change something.

Let us know what you find.

Start by checking for vacuum leaks or blocks.

 

Well, I am a newbie to this, but I'm willing to learn. How can I check for vaccum leaks? Also, my exhaust does smell odd and I have horrible mpg. Other problems include hesitation, rough idle, and on rare occasions, stalling.

 

I bought a Mityvac vacuum pump at AutoZone for $24 several years ago. I also have a vacuum guage.

A simple leak test would be to unplug the vacuum line going from the coffee can looking vacuum reservoir to your EGR solenoid. Hook that line to the gauge. Start the truck and see if it pulls a vacuum. Stop the engine and see if it holds the vacuum.

You can use the pump the same way. Plug one end of a line with a golf tee, etc, pull a vacuum with the vacuum pump from the other end and see if it holds a vacuum.

 

I,m going to jump in here and come up with a lead, first you have a code 34, evp above limits, I believe the true value is to be .35 or .45vdc, I'm not at my books and it is late here, so EVP is high or the EGR valve is stuck open, EVP is just sending information to the computer that it sees, if the EGR valve is stuck open and it is actually letting the EVP send a correct signal of above .65 vdc, then what is the code that could follow, how about a code 41 lean O2 sensor, possible the EGR is froze open sucking air or a vacuum leak, then a rough engine condition could occur. Hope this helps, Broken Wire

 

How can i check if EGR valve is stuck open?

Thanks for helping out a n00b

 

Get a propane torch and open the valve without lighting it. With the motor running, move the tip around in different areas in the engine compartment. If there is a vacuum leak it will suck up the unburned propane and you will see a very noticeable increase in idle speed.

Hesitation, rough idle and stalling can very well be EGR problems. I think there is troubleshooting in the Haynes about EGR.

Think about testing the O2 sensor as well. There is a way to take it out, put it in a vise (gently), hook up a digital voltmeter (digital is important for impedance reasons) to the black and gray wires, and play a lit propane torch over the tip. Once it heats you should see close to a full volt out of the sensor. It actually generates voltage when it's hot enough and there is no oxygen at the tip (like in the middle of a propane flame).

Edit: I just read more, Broken Wire is exactly right (listen to him, he knows his stuff!!). To see the condition of the EGR valve itself, get a hand vacuum pump, attach it to the nipple at the top edge of the EGR valve, and pump vacuum while watching the diaphragm if you can (you may have to take it off to see). It should smoothly move up and down by putting vacuum on and then removing it. You can see the pintle valve at the bottom if you remove the valve, it's visible from the fitting where the EGR tubing attaches. It should seat cleanly and then pull off of its seat a decent distance with vacuum applied. This is probably bad on a truck this old..

 

With the truck idling you hook up the vacuum pump to the EGR and pull a vacuum to open the EGR. The truck should stumble and maybe die. When you release the vacuum the truck should run smooth again.

You really need to get a book, there is a series of tests to run to pinpoint the problem. Haynes and Chilton may not be good enough, try to find a factory manual or a Mitchell or Motors manual. You will probably waste time and money by trying to fix this with advice off of the internet. Run some searches and read some old threads, many have asked these same questions before.

 

I agree with the book thing. I know that the test you wrote for the EGR is basically what the book says, but how will that tell him it's stuck open a certain amount? I will tell if it's stuck completely but if there's crap on the pintle valve surface that's holding it open the truck will run like crap to begin with and only run worse as it opens further. I've had better luck by actually inspecting what it's doing personally.

 

testing of the EGR valve, without tools, except a wrench, take off the EGR pipe under the EGR, start up the engine, place finger under EGR and feel for vacuum at EGR port not the pipe, if vacuum is pulling on your finger, EGR is leaking for sure, with a spec. of .65 vdc the EGR should be open quite aways, with the EGR unhooked at an idle nothing great is going to go wrong, don't be afraid to unpipe the EGR and start up the engine, hope this helps, Broken Wire

 

Truck won't run smooth if it is open. And you are right, we can't cover all of the possibilities here, use the book.

You can block off the EGR port for testing, if the truck runs smoother suspect that the valve leaks.

There are a lot of threads here on this topic, we are reinventing the wheel at best.

If you do some studying and some testing I would like to hear what you find.

 

Code 34 is one of the simpler EGR problems. The computer is telling you: I want (or wanted) the EGR valve to be shut. The position sensor says it is (or was) open. For this code, it does not matter if the diaphragm is shot, the vaccuum lines are off, or the EVR refuses to send vaccuum to the EGR valve.

If this is a KOEO code, it is a static, continuous problem and should be easy to track down. The only components implicated are the EGR pintle, the spring that is supposed to return the pintle to the closed position, the EVP position sensor, and the wiring between the EVP and the computer.

If you have a voltmeter, you can probe the EVP sense voltage with the key on and engine not running, and see what value it is. Normally it should be 0.41 volts or less, but the computer is complaining that it is not.

The most likely explanation is that the EGR valve is sticking due to carbon in the seat area. You can probably pull it off and clean it up.

 

I've got a related question for you. I'm used to seeing specs for sensors in resistances. Very easy to measure, just disconnect the sensor from the harness and measure. EEC seems to like to give you specs in voltages output against the reference voltage, meaning it obviously has to be plugged in. How do you all probe something that is plugged in?