ridefast77

iTrader: (5)

i have a 1998-2000 7.4l mpi 454 330hp and it is doing some weard sh?? i have tryed just about very thing had a couple people try to work on it but still running like shhhh its kinda hard to type what it is doing so if there is any way some one could call me ill explaine what it is doing , NO disrespect to anyone but looking for someone like a mercruser tech. i have had a lot of joes say thay know but they don't know any thing so lets see if we have someone really smart on OSO that can fix my prob. 252-646-2751 thanks

tinman565

Try typing what its doing. I GUARANTEE someone on here has had/dealt with your problem. These are some smart and experienced guys.

firehawkcat

What did the joes say it was that way we can rule that out

ridefast77

iTrader: (5)

when you give it gas it has NO POWER and is poping throw the intake kinda like a back fire i guess, and when it is at idle it is sucking air REALLY load throw the intake so load it herts your ears some times, will not idle for more then a min. or two, one guy said it was triping a code for the map and temp sensor and thay run off the same grownd and if that didn't work it was the ecm so i replaced all of them and nothing, still messing up, then he said valve guides were leaking, thought it was a valve guides so pulled the head and had the valves reworked and new valve guides put in that did not work eather. and i don't know anyone around here that has a dynics computer for mercruiser that worth a crap. or thay even really works right. O yeah i had another guy say he thinks its timing but i have never mest with the timing ever, and it ran grate untill all of a sudden one day it started acting up.

mr3dman

Wow, I am no expert but have had alot of time in and around this motor. First the sucking sound through the intake is normal. It may have gotten louder recently if someone took out the small "muffler" covering the IAC intake. As for the backfiring, there are a number of things that can cause that, coil could be going bad, dist cap corroded, timing, you said the heads were rebuilt so valve is out, and a few more items. Second you are pulling codes for temp and MAP. the temp sender uses the block for its ground and the map sensor uses a closed loop and varies a voltage to tell the ecu what the map is. they are not on the same circut. It almost sounds like you have the cam timing off. Did you have the cam out before all this started? You have replaced the MAP sensor, temp sensor, ECM, and had the heads done. Who is working on your boat? That is alot of coin to spend with no results.

Boat1

It may have lost an exhaust lobe on the camshaft. Those symptoms lead me there. Hope I'm not right.

FIXX

iTrader: (2)

the banging and poping noise is caused from weak fuel pressure..

ridefast77

iTrader: (5)

i have 35+psi at the fuel rail i put a new cool fuel pump ang reg. on last year

ridefast77

iTrader: (5)

i have not have the cam out time thinking its timming im going to look at that today.

FIXX

iTrader: (2)

i guess it could be timing but you said that you already had the heads off and that should have been checked when it was put back together..

35 psi is ok but it calls for 37 psi..have you checked the mechanical pump as well? 3-7 psi @ 2000 rpm's..even tho you have 35 psi of fuel pressure you may not be getting enough fuel to the cool fuel pump..did you check pressure idleing or out on the water..

a bad injector will act like a fuel pressure problem also..