500EFI fuel pump test
 

I'm testing my fuel pump with a gauge on the fuel rail,when I turn the key the pump comes on for a couple of seconds then shuts off.While the pump is running the guage reads 44 psi the second it shuts off it drops to 39 psi.I hav e the shop manual and it says I should see 34 to 38 lbs and should hold presure for 15-20 seconds.It holds presure without a problem except for in initial 5lbs drop when the pump shuts off.Is there any other test to perform to check the pump.Im have popping in the pipes under load,hard starting,once started idles good until you try to get on plain then falls flat on her face.spark plugs show lean condition ,checked timing numerous times .Just feels like a pump problem and been warned about the alcohol tearing up the the pumps since they increased it a couple of years ago..any ideas?
Thanks, Guy

Pump is good at that pressure. Plugs show lean at idle? ISorry it stock?

The motor is a fresh bottom to top rebuild,all stock.end of last season put it in the water for the first time would stall out when going in and out of gear but once in gear got right up on plain ran good up to 4000rpm but I didn't go any further do to fresh motor wanted to take it easy.Checked timing when I got home and was off so reset base timing back to the bay and this time little hard to start but went in and out of gear no problem,thought all was good until I tried to get on plain,started popping ,missing and fell on its face.Went home, new plugs, checked timing again looked good still a little hard starting(for 13 years this engine would fire right up instantly)just not starting like she use to,back to the bay,hard start went into gear no problem idled out ,went to get on plain same deal as before,back home ,pulled plugs ,5 plugs look clean but 2 of them look like they just came out of the box the other 3 are black sooty but dry.Trouble shooting with the Mercury Service manual leans towards a lean condition with the popping under load all suggesting fuel pump issue.the boat sat for 3 years before I had the motor done(building house)so I thought the alcohol in the gas might have killed the pump from spitting.Haven't done a fuel check with engine running or under load but don't see why the pump would fail under those condition when the presure is fine with the ignition on.

If 2 of them have no color at all there is probably the issue of no spark, no fuel or no compression to those 2. Possible injector issue?