Another crazy APV

Here's the situation
94 Lumina APV,3.1,auto
Last July this engine siezed two rod bearings.I finally got the engine out and rebuilt in february.The engine is now back in and runing ,but it's not right.When the engine is cold it will start fine,when warm it will only start (most of the time) if you hold the throttle down.It is very sluggish and has no power. I have had it in a shop getting the computer checked It shows no codes,but a backpressure check showed 6 lbs of backpressure,so he said The converter was stopped up.Ok replaced exhaust from header pipe to tailpipe.It helped some but not much .Still no power.It runns like the cam is a tooth out so I pulled timing cover to make sure I had not made a stupid mistake.everything was right on the marks.I am now at a loss I don't know what to look at next.So i'm hoping someone might be able to point me in the right ,or at least the next direction
Thanks for your help

You seem to have taken care of serious things, but since you did not mention it, what about loosening the distributor hold down nut and rotate it a little and see if you can get something from the timing adjustment...?

I haven't changed the timing away from stock(5 deg),but I will try.Right now I still have the timing cover off,so while it is off I am going to dig out the old cam and turn the engine so that number 4 intake valve is completely open and compare the position of the cam dowel pin to see if maybe the holes were drilled wrong at the factory. I have already compared the timing set. Thank you for your reply and if you think of anything no matter how simple please post and mention it.I know I checking the major stuff but it could be something simple that I am missing.Thank you all for your help

Ok I am a lot closer to getting this APV straightened out but I'm looking for more help.here are the vitals 94 Lumina APV 3.1 fresh overhaul 100 miles on it.This thing was running like the cam was a tooth out so I finally broke it back down to find that it was right on the money. (by the way it was not throwing any codes prior to this).I pulled a plug to do a compression check and found that my brand new delcos were blacker than coal and smelled like raw gas at arms length,so I put in a new set of plugs new o2 sensor test drive time again.While the engine was warming up it ran great as soon as it went into closed loop it became a dog again and backfired through the intake. checked the codes when I got back and had a 13(o2 sensor),and a 34 (map sensor voltage low).Also the egr was stuck open halfway so i cleaned it and made sure it was sealing before this test drive.Now I am at a loss as to where to go next .Any idea's or thoughts are appreciated
I have replied in the original thread to help others who might enter here to start with the whole story.
Backfiring is generally a fact of lean mixture - when other causes like burnt exhaust valves are excluded, which is the case here, I assume.
code 13 says O2 circuit open, ....an open can be associated to low voltage, and is indicative of lean mixture, then the computer would enrich the mixture, explaining the black smelly spark plugs ..but this code 13 conditon is said to inhibit closed loop operation....So not sure here what to think. Anyway, check for proper wiring condition to O2 sensor.
34 is low Manifold Pressure signal , meaning high vacuum...that would correspond to a very small throttle opening, prone to induce lean mixture if actual throttle opening is wider....that is almost contradictory...
www.avigex.ca/xport/dtc13_31.jpg
www.avigex.ca/xport/dtc13_31b.jpg
www.avigex.ca/xport/dtc34_31.jpg
www.avigex.ca/xport/dtc34_31b.jpg

With what you say about the EGR valve, I would have expectd a DTC32....If in doubt about EGR operation, I would, also as suggested by GM, plug the EGR holes to see how it runs just to be sure about it...or maybe, to begin with, just ensure EGR is closed then disconnect the vacuum line from it.

BY the way, did you "flash" the codes yourself this time?

Thanks for the help and here is the lastest.I cleared the codes.(I can't swear if I did or not before last test drive).This time it ran the same but no codes were tripped.I decided to look elsewhere so I pulled the fuel line(after it was cool)I dont have a way to check pressure so I decided to at least check flow.It flowed solid for a second then slowed downbut didn't quit. I added gas to the tank to make sure it wasn't empty(been keeping it low in case I have to pull it)with the added gas it flowed more steady but not really consistent.I know it is only suppose to have 14ish lbs of pressure but I could hold my finger over the line and stop it without a lot of effort.Could a failing,but not stopped, fuel pump that is causing my problems

Yeah the pressure is supposed "not to fall below 9 psi" so the typical 14 psi you mention would be a normal expectation. However, on a 3/8 " pipe, 14 psi translates in something rather easy to block with the finger...so it is somewhat subjective. INstalling a meter would clear the subject one way or the other..but fuel supply (including pump, filter, strainer, regulator ) could be your problem, indeed.

May have found another clue.the fuel pressure at the fuel line is 13 lbs ( checking directly from the pump only ,it has a new regulator diaghram) so i talked to a couple other people and they said to have the ignition module checked.I had noticed when I set the timing(short the diagnostic terminals on this model) that the timing was erratic even with the aldl shorted it was jumping maybe 4-5 degrees either way then you could rev the engine just a little and it would settle down Should it be erratic with the terminals shorted? anyway I decided to take it off and get it tested. First thing I noticed was that it had been replaced before then I noticed it was not tight (you could move it around under the screws when I took it off there was no dialectric grease on the bottom it and the distributor were drywuth nothing but dirt between them .I am on my way to get the old one tested ,but even ifit shows good could the fact that it was loose and no gel be my problems i.e. bad ground ,module overheating etc

New update its still not right Since last post I have replaced fuel pump drained all fuel from tank to ensure it was not contaminated. I am still having problems now it will start fine but runs rough for about the first 60 secs or so When ou drive it it runs great for short distance (a mile or so)When ou get on the hway after a couple of miles it feels like it is running out of gas i downloaded winaldl and hooked it up i don't really know what i'm watching for but i did notice that the 02 sensor data was jumping like crazy at stead throttle it will go from .04 to upwards of .900 the battery voltage will show correctl at times and sometimes it shows no voltage in the battery voltage line but the fp/ps switch line shows the correct voltage.before running the winaldl when i was just checking the codes by flashing I would get an occasional knock sensor circuit or a high map voltage or rich exhaust but never with an consistency it is almost like it just wants to through a code so it just picks one out. Does this sound like a bad computer or is there something i am missing by the way the 02 sensor is a new bosch and the new pump is a delco not advance junk could it be bad injectors(they came from a car that had been totaled,bad front end impact) I appreciate your help I'm about ready to give this thing a dynamite enema