1991 B-250 318 running lean, hesitating and stalling.

My 91 B-250 w/ 318 with 68,000 miles on it is having a little hesitation just off of idle. It is intermitently stalling. I have hooked the van up to a friends diagnostic computer and it shows it's running lean. I ran the van on the fuel injection cleaning solution, The fuel pressure reads good (a little above specs before the regulator, reg. is on the throttle body). I cleaned the O2 sensor (seems to read normal according to diagnostics) I have gone through this thing left and right, up and down and cannot figure out a thing. Everything checks out normal, and no error codes. I'm thinking the problem has to do with the lean condition, what would make it run lean?

Thanks in advance,
Jim

Anybody? Any clues as to what would make it run lean? Fuel pressure regulator? I don't know, I'm about ready to give up on the van.

If it was the O2 sensor, maybe resetting the computer (by disconnecting the two battery cables and holding them together for 30 secs) might reset all the values to their original settings. Worth a try. I'd also have checked the air filter to start.

I don't believe it's the O2. The spark plugs read lean and the diagnostic computer says lean (which I would assume it gets it's reading from the 02). I have added a ground to the ECM main ground lead, I have replaced the engine block ground, I have replaced the Throttle position sensor, I have run the van on fuel injection cleaner, I have replaced a broken vacuum line, I have tested the fuel pressure (the regulator is on the throttle body so I tested before the regulator and got about 16 psi, the specs say the van runs on 14.5 psi after regulator) Is 16 good before regulator?, or should it be a little higher? If by chance the regulator is bad would that cause a lean condition? The fuel pump makes a consant humming noise (heard from the rear of van) even during the hesitation, so I don't think that's bad. The problems still exist whether air cleaner is on or off and air cleaner is fairly new. It seems like a fuel problem, but is stumping the hell out of me. I'm half tempted to just replace the fuel pump and the regulator, but I really don't have the money to throw away if that doesn't solve the problem. I'm thinking of trying to find a used ECM at a junk yard to see if it runs any different.

Oh yeah, and I have reset the computer numerous times with no change.

I asked earlier, but does the van have a clean air filter and fuel filter?

Yes, both are new.

I have to admit I'm stumped. It could be the computer, or a sensor somewhere that's giving off the wrong signal; I don't know.

However now that I'm thinking a bit more, there are some posts in another forum where either the crankshaft position sensor or camshaft position sensor went bad and caused similar problems, so those may be the cause.

Well, I replaced the ECM today and I think it may have solved the problem. I'm keeping my fingers crossed.

Well, the new computer made it run great for about 4 days, and now it's back to the same problems! I am 100% stumped, any ideas?

hesitation problems linked to egr valve opening to soon, try unplugging the vacum leading to the egr and plug the hose and see if it runs smoother.

That was a very good idea, but I just checked the EGR and functions. Its all good, works fine and is clean. I think I'm going to replace the fuel pump, I'm thinking that might be worn. It is whining a little loud, and it takes more turning over after the van sits over night to get it started as if the pumps not holding pressure in the line. Thanks for the ideas though.

JimmyV