454 gen v down on power
 

hey guys, looking for a bit of input from fellow techs on my current drivability issue. 1995 formula 252ss, 454 magnum efi w/ b3 drive. 760 hours. All basics are covered, cap/rotor, filters, plugs, so on and so forth. No misfire. Slight starting hesitation for first start of the day when cold, nothing alarming, fuel rail could be loosing prime a bit. The boat has been down on power the second half of last season and so far this season. It will get on plain, but without the urgency it should have. Midrange operation is ok 3-4000 rpm the boat runs good. Almost no problem detected. Punch the throttle at 4K and not much happens besides the engine sounding strained. No misfire, no pops or bangs. It struggles to hit 4100. I won't do it anymore. I have a few ideas as to what the problem could be, but they are still guesses at this point. Fuel pressure 43psi with regulator unplugged. 35-37 w/ vaccum applied. Drops to 20psi and holds when key is off. Any thoughts out there? Thank you guys.

I wanted to add...
 

engine serial...0F292367
fuel screen in vs tank cleaned
injector screens cleaned
dont have rinda tool, I have not gone that route yet
Haven't checked spark strength yet, waiting on tester from amazon
havent checked compression or leak down yet.
When I clamp the fuel return line into the vs tank, fuel pressure doesn't spike...I feel like it should.

Once again, any help or input is appreciated. Thank you.

Doug

I think this is key ^^^^ ............sounds to me like its running out of fuel or timing, or just tired @760 hrs

I understand how it can seem that way, but don't buy a worn out engine yet. I'm hesitant to sway anyone's thoughts by adding my own, but here it goes. I'm chasing inop/clogged injectors. 240$ to have them tested and cleaned locally. This thing ran so well and was ripping at 59mph on gps 50 hours ago. I will do compression check today after work. But it doesn't sound like a tired engine to me. Timing could also be an issue, but I've never had an engine change timing on its own.

Do you know what the fuel pressure is running at or near WOT?

If I remember correctly, it was in the 33-37psi range.
Thanks again guys for the help.

Doug.

With manifold vacuum connected.

The lack of fuel to the engine is a likely cause. Use a Tee and a vacuum gauge to test. Also place a section of clear line and look for air bubbles (air leak). This test is done under load at WOT. Anti siphon valve has debris or they may be a screen in the siphon tube that has debris.
Yes you will still have fuel pressure in the rail just not enough volume.

The 33 could be an issue, the 37 not so much. Would be nice to know what your AFR is running at.

Anti siphon has been inspected, and replaced due to the fact that it's 16$. The old one didn't look too bad. Good thought on checking vacuum. All the vac lines have been replaced with new, clear fuel hose. I can "t" into them tonight to check. Just seems to me vac doesn't play a part in a lean condition givin low vac = more fuel pressure. As far as bubbles, are you suggesting the low pressure fuel system is sucking air? Where would I install clear hose in that system? It's a stainless line from the low pressure pump to vst.