I am troubleshooting my 1996 4.9 straight six 300 engine. Unfortunately, I hate to say this, but since I’ve returned it from a mechanic shop, this situation has been occurring. Never had an issue with this truck for over eight months when I bought it. There seems to be an issue when it warms up 4045 minutes I get a PO10701. Which is bank one lien. I’m trying to diagnose this situation. The first suggestion is vacuum leak. That’s where I’m having a problem. Identifying the engine parts. It seems like when I look for let’s say the PV sea valve, I get one group saying it’s underneath the EGR, I got another group saying as on the backside of the valve cover, I got another group saying it’s underneath the manifold. I’m going to try to attach several photos of the engine bay and several parts of the engine that I would hope someone can identify these parts. I can’t troubleshoot this vehicle if I don’t know what I’m looking at. Thank you for any help each picture numbered so I can identify what the part is. Thank you. Rich oops, there seems too be 2 #1. Note: I have replaced all o2 sensors, cleaned egr, check fuel pump pressure.

 

Welcome to FTE
I dont know the EFI motors that well and more so when not seeing it in person but you may want to post this same question over here in your year truck area https://www.ford-trucks.com/forums/forum28/

Dave ----

 

The first 1: EGR valve
The second 1: The vacuum reservoir/tank
2&3. These are the air valves controlled by the TAB and TAD relays; used by the computer to inject air during some tests. These aren't made anymore and should be hoarded when found at junkyards. The TAD, TAB, and EGR control relays are in picture #6 right below the EGR valve.
4. That's an exhaust check valve that allows pumped air to flow one way but stops back flow
5. Idle Air Control - it's the Computer's private gas peddle.
6. Yep, EGR valve, again
7. That's the vapor canister purge valve
8. That's the DPEF-something or other - Dual Pressure Exhaust Flow (don't quote me on that) - when the EGR valve is open a pressure difference is generated across a restriction in the exhaust gas tube and this detects that pressure difference. That exhaust-to-EGR tube isn't made anymore (unique to 1996 4.9s, and maybe some 1995 California 4.9s) and geniuses at the junkyards around here usually run a sawzall through it so that they can get to the lower intake a few minutes quicker than otherwise, so it's another salvage and hoard item.
9. I'd have to see where the hoses go to tell what this is; it's maybe a manifold or splicer that has something to do with the vacuum reservoir?. That it looks like it's missing a hose or two is a bad sign
11. I think that's the fuel pressure reg?

You've still got the original plastic vacuum lines, which are now 30 years old and have breaks in them, old and new, some that you'll never find and will cause endless little problems. I recommend replacing them all with silicon vacuum lines.