Sorry all wasnt sure if this was best here or in the tech/general so I tried both,

Car-89 2.8 firebird
Symptom- idles @ about 1100, revs fine with steady throttle up to 2800+/- then completely drops off, spits out copious amounts of white smoke then mellows back out when the throttles closed again.

Checked-Timing, 10* though most of the time it retards slightly upon opening the throttle before advancing?, Fuel press & compression both well within specs, no oil/water loss no overheating or fluids from the tailpipe, recently changed intake gaskets, o2 sens, plugs & wires. cap looks good buttons clean, fresh ect, icm, pickup coil and pass. donut (drivers side is shot could this cause any issues aside from heat) fuel pump, tps, iac, oil press sender are all within about 2 yrs old. only guage test ive found bad is my vac hold a steady around 5in timed at 10* and a steady 10in timed closer to 12*

Any help you all could give me or ideas to throw out would be much obliged, I've drove this thing with plenty of power daily for 3 yrs (although i bought the vac guage in feb and it always held slightly low but was always steady and built back up when opening the throttle pretty quick now it doesnt build back up at all) shut it down at a gas station was runnin great, went to start it back up and she wouldnt.

 

Check the torque settings on EVERY part you removed when you changed the upper end gaskets. I know that in the past, I've had trouble getting the valve covers to seal, which causes a MASSIVE vacuum leak due to PCV system pulling in air through the leaking gaskets. Also check the end of EVERY vacuum line/hose to make sure it's not damaged/cracked/etc.

Unless you bought a bum gauge that is wildly inaccurate, the engine vacuum should be around 15" Hg and increase as the throttle is opened, but drop to almost nothing with the throttle plate opened wide momentarily ("goosed").

 

Preciate the ideas, ima walk out and double check those bolts, used the torque on the manifolds but not the valve covers so its definately worth me goin to look. I had this problem last year around this time it would start, idle fine but wouldn't rev, wound up being that horrid pump assembly coming apart in the tank, anyone have a thought on this can that rubber hose in the tank crack or slip off enough to give it pressure at an idle or with key on/engine off but not enough to rev it?

 

It's possible that low fuel pressure could be the problem, but you will need to either rent or buy a $50 fuel pressure gauge to check. Pressure should be between 37 and 47 PSI and hold for 20 minutes without losing 1 PSI fuel pressure. my posts for further fuel pressure testing if the fuel pressure fails to reach specifications.

When was the last time you replaced the fuel filter by the left rear wheel?

 

Check the pressure yesterday, i get 45 at the rail and it drops off pretty quickly (should i leave the key on for this "bleed down"?) at the rail it loses all 45 in under 20 min, at the pump its self (before the filter) it hits 50 and seemed to bleed very slowly (took over two hours for it to bleed down to 20) but im pretty sure my old gauge has a slow leak in it so imma try renting one today n give it a good test, i dont get gas when i suck on the fpr but i get the smell of it through the vacuum like (ive heard these things should be under alot of pressure but when i took the final screw outta mine and lifted my fingers off it she only moved about a 1/8 in) but it doesnt look like its seen extreme wear & i can still compress the spring in it about a 1/4 to a 1/2in by hand.
other things i noted doing the pressure test, the needle bounces back n forth slightly between the 44-46 marks, it has a slight drop when it starts like it should, then it rises back up to about 45 (aside from the bouncing i mentioned) if i unhook the vac line from it itl rise up to about 47-48 & drop again when i hook it back up, if i suck on the vacuum line with my smoky lungs i can make it drop to about 39-40 psi at an idle and with the vacuum line hooked up when i open the throttle my pressure goes up to about 50 and holds (but i can only give it around half throttle before it quits revving and just bogs down)

 

Post up when you get the results with a known good gauge...

Again, when was the last time the fuel filter was changed?

If the fuel pressure stays high, I hope you have an air compressor as you will want to start by blowing out the return lines starting at the pressure regulator (remove the FPR, put the blow gun with rubber tip in the brass fitting in the middle of the FPR space, and blow it out).

 

Def will bring an update soon, holidays got me slowed to a stop