Ok Gentlemen, For starters, I'm a shade-tree mechanic. By no means am I, a long-time skilled mechanic, but I do have a basic understanding of automotive functions. Here is my issue...
I have a 91' F150 long bed / dual tank / 302 EFI / regular cab, auto. I assume 4 speed. I have recently been going through all the stuff I should have fixed when I bought the thing 6 years ago. Stating this, I knew a 30+ year-old truck was going to have issues. Recently, this has turned into an everyday driver for which it was NEVER intended. So I'm trying to fix stuff. I have questions about fuel injection on these, and how it works.
Basic stuff here... Upon a cold start-up ( before patching vacuum lines ), she would fire at a high idle pretty much immediately, warm up and decrease idle as it should.
( Post vacuum line patching ) Cold start-ups are still pretty good, almost the same as before with one small difference. When I patched up the vacuum leaks, as best I could, verifying the EGR was working again, not to mention the Vac lines coming off the throttle body to the charcoal canister. Suddenly, I'm getting really hard starts after warm up, mind you I have not replaced the fuel filter as of yet. It's just strange to me how so much has changed from simply repairing vac lines. By the way, in MHO putting that vac cluster directly the intake plenum was an idiot move. I had a hissing ( air-sucking noise from the rear fuel tank every time i would shut down as well as fueling issues i.e having to slow fill the rear tank.

So I repaired the lines, replaced the Char can. and this bitch is being more difficult now. Still starts with throttle help but is pissing me off. The fuel up issues seem to be fixed somewhat, occasionally tho i'll hear that god damned whistling noise. My understanding is there are 3 fuel pumps, one in each tank and one on the frame under the bed I assume.
Long winded question I know, but trying to give a picture on what the hell is going on.

Just saying that when i spent time and money fixing stuff, why is it getting worse?
Any thoughts on this would be appreciated.

 

You have several different problems... which wouldn't be surprising with one of these old trucks.
But first.. that vintage truck has the simplified fuel delivery system with just a high pressure pump inside each tank, nothing on the frame but a filter.
The whistling sound from the tank is a concern, that means it it building a vacuum when in use or is building pressure when not in use, and neither should happen if the tank vent and vapor collection are working correctly. It could also indicate the truck has the common fuel transfer problem between tanks.. depends if it's building vacuum or pressure.
You don't have the EGR valve connected directly to mani vacuum do you? If so that is incorrect it should connect to the EVR solenoid just below the ignition coil on the same bracket.
Hard warm starts could be a number of things, could be an ignition issue(distributor mounted TFI modules are known to overheat), could be a fuel delivery problem... not uncommon for old pumps to weaken as they warm up, or if the pump is working against an ever increasing vacuum in the tank it will get to a point where it can't overcome it. Fuel pressure at the engine should be upwards of 40psi all the time, min of 32-35psi with engine running and full vacuum applied to the regulator. It could also indicate a corroded main ground wire, corroded battery terminals, starter connections, or a failng starter.

 

Thanks for your input on this. I do have the egr connected to the solenoid correctly. Sounds to me I need to start at each tank and check all lines and trace them out.

 

I just had a quick thought, sir. So this fuel transfer system thing you mentioned is what exactly? I get that there are 2 tanks and the delivery can be switched between the 2. My switch works without fail. however, fuel mileage is complete garbage on the rear tank. I can watch the fuel gauge move as if it's dumping fuel on the ground, while the front tank afFORDs me the great 10 MPG I love so much lol.

 

There are probably dozens of threads on the topic. It usually has something to do with one of the tanks is overflowing. The fuel delivery module (FDM) has check valves that are supposed to prevent fuel returning from the engine into the tank that is not in use.


Picture stolen from another thread.

 

This should help me. Thank you.