Hi all, I'm trying to get rid of my last DTC, I hope.
1984, F-150, 351W, EEC-IV, TFI Ignition, Ford Sonic EGR W/ Black EVP.
I did all the Volt and Resistance checks both on and off truck and concluded that my EVP shaft/wiper needed to be shimmed (ie. searched the forums and found it to be a common problem w/ EVP's, I used JB Weld to extend the EVP shaft) to bring the Sig Ret to EVP Sig voltage to what I hope is the .8-.9v spec. for the black EVP w/ pre-load and no vacuum. I used a nickle to get me close and then more than enough JB hoping to just sand down the excess. Here is what my issue is in order of testing procedure...

1. Put EGR/EVP shimmed back on engine for starting point.
2. Sig Ret to EVP Sig 2.3v ...too much shim...I would think!
3. Ran KOEO got Code 31, only code...Below Min Voltage???
4. Went to run test again...Key Off, connect DVOM to Sig Ret and EVP Sig, 0.0v, good so far, Key still off, start connections for Self-Test, jumper STI to Sig Ret, Test light probe to STO, and final connection was test light clip to POS Battery.
5. Key still off. Test light comes on which it has in the past and I would think is normal 'cause I've got a + to ground.
6. Here is where I think I've got a problem...w/ key still off the DVOM gives me a reading of .7 or .07 from the EVP's Sig Ret to Sig (I forget now, but I've got voltage!!!).

Is this ok or do I have a short somewhere or losing my signal? Also, what are the pinouts for the EEC-IV V-Ref, Sig Ret, and EVP?
Thanks in advance, Dave

 

Unhook the battery to clear the codes, then run a jumper from the supply pin in the plug to the sig pin. This should put voltage on the pin, and you should get the egr too high code. If this works, then you know your wiring is good.

 

Thanks for replying Dave, I was hoping you would be the one of the replies!!! Will try in the AM. By supply pin you mean VREF? So, jumper VREF to EVP Sig and run code check. And that would give EVP Sig ~5.0v and I should get a code 34 or 35 above closed limit? BTW, the EVP connector wires are a PITA to get to at the back of engine @ firewall, that's why I wanted the pinout for EEC connector which is really easy to access under dash. I would also rather puncture the wires under dash where they are more protected from moisture and less likely to accidentally short to ground on something. Thanks again Dave F, Dave S.

 

Thought about this overnight. I guess I have to jumper the wires up at the sensor in order to test the whole length of the wiring circuit, duh. Guess I just needed some sleep to think about that one. Also, I had already cleared codes, right now this is only a KOEO code till I put it back together and take it for a drive and warm it up, no continuous codes. And I just want to confirm your test procedure... Is this w/ the plug connected to the EVP and then take say a sewing pin and pierce both the reference and signal wires to jumper them(this is my guess 'cause I still need to keep the Sig Ret circuit in play)? Or is this with the plug disconnected from the EVP and jumper the plug terminals w/ aligator clips and some wire? Thanks again Dave F,
Dave S.
P.S. Guess I may not get it done today, right now we've got about 2" of snow and it's still snowing and I'm doing this in a parking lot .

 

You don't have to keep it plugged in. You can just jump the plug. Jumping it to the vref should give you the too high code, and jumping to the sig ret should give you a too low code.

It would check the wiring and make sure the computer input is working correctly too.

 

Finally got back to it. Here's results:

Had DVOM connected at EEC harness to Sig Ret and EVP Sig to test dc volts

1. Jumped reference to signal on EVP plug(Franklin2's Test)...read 4.96v, but still got KOEO Code 31, no other codes

2. With no jumper and EVP plunger extended, read .25v, only get Code 31

3. With no jumper and EVP plunger taped fully in, read 4.95v, still only get Code 31
Once again, volt readings were take just before EEC harness. Reference voltage reads ~4.96v everywhere I test and I am testing it to the Sig Ret wire(blk/wh) not other ground.
I did voltage tests at the TPS just to see if I could find anything screwy there, they all pass.

Code 31 no matter what I do, This is the only code the truck gives KOEO.....wiring, computer???
Going to put EGR back on and take it for a drive and see what continuous codes I can get 'cause right now they have all been errased.

 

I got my book out and this is what it says;

Code 31 is generated when the voltage to pin 27 is less than .2 volts during the KOEO self-test.

The first thing he says to do is jump the vref terminal to the signal terminal in the sensor connector. This must be were I got this idea from. He said when you do this, you should get a code 35.

If you do not get a code 35, he says take the connector off the ECA, and probe the connector pins. He says probe between pin 27, and 40, 46, and 60. You should read infinity, and that means the wires are not shorted.

If the wiring checks out good, he says replace the computer.