Ok, tried searching, didn't see anything. My problem is, if the truck is above ~1/2 tank of gas, the thing runs terrible, and smells very rich. And by terrible, I mean it's dangerous to drive, lol. No power at all, more than just cracking the throttle will cause it to stall. Once the fuel level drops low enough, it's fine.

In the last three months or so, it's gotten a new Delphi fuel pump, filter, and a new spider injector. I leaked checked the crap outta the fuel lines, when the first spider I bought wouldn't hold pressure. Not a drop. Returned it, and the replacement doesn't hold pressure with the key off, either. The pump does, so I know it's the injector. Seemed to run fine, and I didn't wanna **** Advance Auto off any more, so I kept it.

I'm inclined to believe there is a problem with the evap system, since the problem seems tied to fuel level. Just not familiar enough to figure out what.

Only code I've gotten is a cyl #5 misfire twice when it was in the running bad phase, and I was going up a hill, or with heavier throttle.

 

Just spit-balling here but is it possible there is a problem with the fuel return line? Can two of the three lines to the tank get swapped?

 

I've only got two lines to the tank, not counting vents. If I swapped the pressure and return at the pump, would it even run?

 

The pictures I've seen and the ones in my manual showed what looked like three similar looking lines going to the top of pump/sender unit. Whenever I reassemble something and it doesn't work, I always suspect something like that. (Lesson learned the hard way!)

 

You are probably correct that your problem lies with the EVAP system. Since you just replaced the pump your FTP sensor is probably good. So with no codes I would suspect either the vapor canister or the purge valve. The fact you are smelling fuel makes me lean more towards the vapor canister. The purge valve could be not closing all the way when there is no demand for it to be opened. You can remove that from the engine and use a 9 volt battery to see if it is opening and then closing all the way. If you have a scanner you can see if your O2 sensors are pegged high while idling indicating possibly that your purge valve is not closing all the way. The best thing is to have the EVAP system smoked and checked with a bi-directional scanner to insure the vent solenoid and purge solenoid are sealing the system, though you should be getting a code if they're not. But I'm really leaning towards your vapor canister. If you top off your tank by going past the first automatic shutoff, it is possible to get fuel in the canister and ruin the charcoal. Before all this OBD stuff it didn't really matter if you squeezed every last drop into your tank you could. Now it does and shops are instructing their customers with similar problems not to go past the first auto shutoff at the pump. Not necessarily assuming you are.

 

I don't usually go past the first shutoff, but with 335K miles, I'm sure it's happened a time or two lol.

On my '95, it appears that the evap solenoid mounts to the driver side of the intake manifold. What would the effect be if I were to disconnect the hose running from that to the intake? And block off the port on the intake, of course. For diagnosing purposes, only, I know that you're not supposed to defeat emissions systems like that.

If that's the only point where the evap system connects to the engine, it seems as if that would alleviate the problem. Or am I over simplifying?

 

Aww, I failed to catch it was a '95. Forget what I said about the 9v battery check. Yours works off vacuum I believe (I think). But to your point, sealing it off to see if the truck runs better should rule it in or out as stuck open or not.

 

Tomorrow, if you haven't found the problem yet, I'll fire up my tools and give you some diagnostics to try. If I remember correctly, they used different purge solenoids on those and I think I need to know the number of wires your solenoid has at the connector.

 

Alright, man, I appreciate it. I'll get it capped off tonight, fill it up in the morning, and report back after that.

Edit: Ok, went ahead and took a picture of the evap setup, to aid in diagnosing. This located on the driver side, and is mounted using two of the intake plenum bolts. (Sorry for the grainy pic, it was pretty much dark outside)

Also, went ahead and taped off the hose going to the manifold. We'll see how she does in the morning.

Edit #2: Had a quick errand to run, so I put about 9-10 gallons in. Epic fail. Ran like crap, could barely get out of it's own way. This was with the evap line to manifold blocked off. Did give me a P0441 code, lol

 

One of those solenoids should have a GRN-WHT wire going to it (don't have a diagram so I'm not sure the other wire color). The solenoid with the the GRN-WHT wire is the purge solenoid. I think it might be the one on the left? The PCM controls that solenoid by providing the ground through that GRN-WHT wire. The other wire should show IGN(+). It is a pulse width modulated solenoid and the PCM uses engine temp, operating time and other factors to determine the duty cycle on-time. It's kind of limited the tests you can do without a scope, but I can pass along the resistance test for the purge solenoid, though I realize that can be of limited help. Key off, disconnect solenoid from harness, using an ohm meter across the solenoid terminals, resistance should be 25-30ohms.

There is a DC voltage test for the vacuum switch, but I honestly have to jump off right now. Oh, and this is nice...your truck came with three different wiring possibilities for the vent solenoid. Also, I'm using vin "W" for your truck, is this correct?