454 MAG MPI issues. Won't rev under load.
 

My issue just popped up out of no where really. the boat idles fine, no miss and it will rev fine in neutral. when under load, she will run fine until you go to throttle up and then it hits 2500rpm and won't go any higher. I am thinking fuel. I changed out the filter to see if it might have been clogged up but didn't help. any help would be great. it's a 1996 454 MAG MPI.

454 MPI Magnum Losses Power Under Load
 

I am having the same symptoms:

'88 Regal Velocity
'96 454 Magnum MPI S/N 0F802570
Bravo Setup

Recently purchased boat, pulled motor to change rusted exhaust manifold bolts (had to drill heads off 90%).

Checked VST, cleaned filter, replaced gas, filters, checked prop, new outdrive oil, fluid levels OK

Boat shifts and idles perfectly.

RPM's drop to around 600 and bounce back, happens only under load.

Video Link:[YOUTUBE][/YOUTUBE]
http://youtu.be/xlx6_lw2rB4

check your dist cap for corrosion on the inside.. Also, how old is your gas? I had the same issue earlier in the year and found it to be my gas. I topped off with fresh fuel and issue was gone. I had maybe 20 gals left in the tank when it happened....

rreinke, your vid is set to private btw...

I filled up the boat jst before it happened the first time. I am wonderng if I got ****y gas.

Video settings have been switched to public. I did drain the fuel and replaced with new fresh gas, as well as new plugs. I will check the distributor next for corrosion.

I did notice that the outdrive reservoir oil level was low, but I don't think that this symptom would be caused by guardian mode.

It would be helpful if someone could comment on whether guardian mode would produce a momentary drop in revs or a constant drop.

The fact that the engine won't produce the power to get over about 2,700 RPMs, also makes the guardian mode scenario unlikely and a fuel or electrical issue more probable.

Thanks

Check/replace your plugs, wires, cap and rotor. Do you have a smell of raw gas in your exhaust when at idle or under acceleration? Any blackish smoke from your exhaust? Also you should check your timing advance to see if it is advancing as needed under acceleration..... This sounds ignition related to me....

rreinke, that definately sounds electrical to me as well. That isn't guardian mode kicking in. check connections, grounds, and ignition.. seems like something coming lose or partial contact..

Redhook98, Thanks for the input.

No raw gas smell and engine runs great with little smoke. When I was trying to plane and really worked the throttle, I did get one small backfire. Other than that, the engine runs smooth, just no power and hesitation.

I am waiting for decent weather to get into the distributor, raining every time I have free time.

Found the culprit, distributor cap contacts are completely corroded. Picked up a new cap - cross references to any '96 GM truck with the same engine BTW, exact match (engine is '96 Mag MPI), can even buy the upgraded cap with brass contacts instead of aluminum. I'll drop it in the water tomorrow evening and let everyone know if this was the fix.

Thanks to everyone who responded Redhook 98 & Mr3dman. Seansmp3, hope my posts get you pointed in the right direction. I'll confirm this was the issue once I water test.

If your cap was that bad, I would still throw a new rotor, plugs and wires in it. Just a precaution and it gives you a great baseline to start from.