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Mercruiser 454 7.4 bravo 3 Issues once warm

C

courtrusu

New member
Hello all, Im hoping someone can help me out...fingerscrossed. I just inherited a 97 crownline with a mercruiser 454 bravo (4454110jt). It runs great when I first fire it up, nice responsive throttle with smooth acceleration through the RPMs. After a minute or two onece she warms up it starts to sputter and doesnt like revving over 2500-3000 then starts to spit backfire then stall. It will restart but stay in the poor running state until I come out the next day and try again and it repeats the process.

So far, I have isolated the fuel tank by running a remote tank with known good fuel. Checked the voltage at the coil ( 12.6 with key on and jumping between 12-14 while running). New Plugs and wires, new digitals in the distributor, rebuilt carb.

Ive been trying to find a wiring diagram with no luck...unless i pay 90 for a service manual.

Any input?

Thanks,
excited but anxious boat dude
 
I’m assuming it’s got a Tbolt V ignition. Go through this thunderbolt ignition trouble shooting Logic tree after it starts acting up.

are the ignition components in good condition? Might check the coil connections for corrosion if you didn’t when putting the coil in, and connections at ignition module for corrosion and looseness. Is the sensor in the distributor have two wires coming off it or three? I think they later added a third wire to the sensor As a ground cause they had problems , yours may be older design. Only other idea is disconnect tach wire off negative side of coil to rule it out .
 
Dieter said:
I’m assuming it’s got a Tbolt V ignition. Go through this thunderbolt ignition trouble shooting Logic tree after it starts acting up.

are the ignition components in good condition? Might check the coil connections for corrosion if you didn’t when putting the coil in, and connections at ignition module for corrosion and looseness. Is the sensor in the distributor have two wires coming off it or three? I think they later added a third wire to the sensor As a ground cause they had problems , yours may be older design. Only other idea is disconnect tach wire off negative side of coil to rule it out .
Click to expand...


It is a tboltV...Everything looks good (checked connectors in the plugs, good connection to the coil). It has the three wire set up, Ill disconnect the tach on the next test run. Logic Tree?
 
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