No Power, Running Rich, and backfiring through the intake. Tige 2100v

[Astonishmints]

Hey everyone, I just finished a rebuild of a 2100v with a 350 mag MPI. Had the block machined, new rings, new bearings, heads gone through, and new gaskets.... a completely new motor. After I finished rebuilding it, I took it on the water. It would plane out, lacked power, and would foul plugs very quickly. I took it to a local marina, and had them set the timing with their computer, and now I do not have enough power to get onto plane, and as soon as I give the boat any throttle, it backfires through the intake.

I replaced the plugs, rotor, distributor cap, fuel pressure regulator, wires, ignition module in the distributor. I am getting 35 (not sure the units of measure) when I hook up a vacuum gauge at idle, the Mercruiser service manual says it should be around 15. I am getting 62 psi fuel pressure at the schrader valve at idle, and today I checked it while running, and it was up around 80 at one point. I changed the fuel pressure regulator with a genuine part yesterday, and it did not solve my high fuel pressure. Lastly I have traced the plug wires 3 times to ensure I had the firing order correct.

I am at a complete loss here, ready to throw on a carburetor.... Any insight anyone can give me would be greatly appreciated!!!!!

[chpthril]

My first ????, why did the engine need rebuilt? Is the cam the same, either the actual OEM cam or new OEM? Either the original issue is still there or the cam timing is off.

[Astonishmints]

My first ????, why did the engine need rebuilt? Is the cam the same, either the actual OEM cam or new OEM? Either the original issue is still there or the cam timing is off.

the boat was not winterized and had a cracked block. It is the cam that came out of the marine engine.

[freeheel4life]

Fuel pressure should be closer to 30 psi. 26 ish at idle on fake a lake. If there really is increased vacuum that would possibly make sense. Increased vacuum on the vacuum line that connects to regulator will return less fuel and cause pressure to go up(I think).

High engine vacuum is possibly an intake valve seat(s) letting air by when they shouldn't or too long of pushrods?? Somethings letting air get sucked in when it shouldn't from the sounds of it.
Maybe even an intake valve hanging open enough that it's causing the backfire in the intake??

[Astonishmints]

Ok, so I went back to basics, and started with solving the fuel pressure, thinking this could lead to other problems. Treat the cause and not the symptom. I found a blockage in my fuel cooler that was spiking the pressure. With that solved I am getting 30 psi when the pump primes, 30 at WOT, and 22 when at idle. This resulted in a massive improvement in how rich the engine ran, almost completely eliminated the backfiring through the intake, and the boat isn't fowling plugs right away.

It starts up, idles great, but it sounds like I am missing on a cylinder. I put new plugs in, ran it for a while, but still missing. I can get up to top speed, but it takes a while, and the Hole shot is terrible.
I am going to put a new fuel pump in, as the one I have is 20 + years old.

Today I am going to pull the new plugs and see If one looks off. Maybe I have an injector that isn't opening?

Any thoughts to this misfire? I have done plugs, rotor, cap, wires, cleaned the gas tank, fuel pressure regulator, and installed the ignition module with the three wire.
At least I have the backfiring and fuel blockage solved.

Thanks!

[chpthril]

Unplug one injector at a time and look for a cylinder that does not change how the engine idles. Thats the "dead hole" so to speak. Now focus on that cylinder. Spark, compression, fuel, vacuum leak.