Please help with OBD code 556 I pulled the code manually and this is the only one I got, if I did it right.

556

I've replaced the fuel pump relay and it still didn't work. It says primary circuit failure on some code charts and I am not sure what that means. Before doing this several other parts had been replaced and I was hoping this would take care of it.

I have a Ford 1991 F150 4.9L and the symptoms are stalling when giving gas. It started as a rough idle that turned into rough running that finally stalled and left me stranded. Changing the tps at least got it to run again, but it won't stay cranked when I give gas.

Any ideas would be appreciated to get my truck back on the road at this point. Driving the wife's minivan isn't fun for any of us, lol!
Thanks!!

 

No one has any ideas on what I can do next to get back on the road?

 

Sounds like a fuel delivery problem for sure. Change your fuel filter if you haven't done so recently.
Check to make sure you've got good voltage at both sides of the relay
Check to make sure you've got good voltage going to the pump(s)
Check your ground connections for broken/corroded wires

If none of these pan out, use a fuel pressure gauge to see what kind of pressure you're getting at your injector rail (there's a fitting near the firewall).

Let us know what happens next.

 

Now checking the code today I get a 33,

33 EGR did not open/ respond during test or if memory code, did not open intermittently - EVP EVR PFE

Any ideas on what to do to fix one of those or do I just replace it and I'm good to go?

 

33 is your EGR valve. If it's stuck open that might explain your bad running condition, but that's sort of unlikely. Check the vacuum line running into it to make sure it's not leaking. With the vacuum line off and the engine running, apply a vacuum to the EGR. If it holds the vacuum and changes the idle of the truck it's probably OK.

The EVP sensor could also be out of whack too, which is an easy fix. You can test whether or not the EVP is functioning properly with an ohmmeter.

 

I can't find an EVP on mine and autozone doesn't have one for it.

So I tried to do a diagnostic with it running using the jumper wire and it ran better than it has in a while and when I pulled the wire, it died. Could that mean I need to replace the EEC relay to fix the problem or is that what is supposed to happen?

 

Whatever caused it to behave earlier isn't working anymore.