Hard starting 7.4 mpi - any suggestions please?

[George K]

Hello,
It’s in a 2000 2800 Maxum Bravo 3 with a single 7.4 (454) mpi
De-winterized start was difficult. Seemed to run okay in the fall - but had to crank more than I thought was necessary.
After a long crank, it would start, shudder and die. The alarm would beep. After a few times and by throttling it, it started and ran okay.
Took it out for a run. Got on plane okay. Ran to redline no problem. Came back to slip idling perfectly.
Next day, same thing happened with a cold start.
I ordered a IAC valve - will try that when it comes in.
New plugs, cap, rotor, gas was topped up all winter.
Any suggestions please and thanks,
GeorgeK

[mmwjr]

I’d start with the IAC or it’s filter. Maybe clean the throttle body but don’t spray carburetor cleaner onto the MAP sensor.

[George K]

I’ll get back to let you know if there were improvements with the new IAC
Thanks
GeorgeK

[George K]

Replaced the IAC - that definitely needed replacing - the old one seemed stuck in the outward position. When it started, it raved higher - the way its suppose to.
However,
This did not solve the hard starting problem. It would crank - a little too long for my taste, start, run momentarily, then die. Sometime the alarm would sound when it was about to die. When I throttled the level, it would start but would not run smoothly till warm. so...
Fuel???
I spun-off the filter/separator and did not see any sign of water intrusion - so.. wasn't a water problem.
Only thing electrically, I didn't change are the ignition wires. I took the multimeter and they were all within tolerance - so... that's not the problem.
I'll be having a visit from the mechanic next I guess. I wish he had the electronic diagnostic tool for it thought.

[mmwjr]

Have you looked at the troubleshooting guide in the Mercruiser manual for your engine?

[George K]

I’m now down to the MAP sensor and or TPS.
It’s almost worth investing in electronic diagnostic tools - that my marina mechanic does not have either.
GeorgeK

[mmwjr]

I’d be surprised if it was the TPS as it doesn’t know if the engine is cold or warmed up.

[AACoPD05]

I dont know if the 7.4 has it but my 5.0 had a little filter/muffler for the IAC that was dirty and caused it to hunt around for idle on a cold start. The little $2.00 filter/muffler was changed and all the problems resolved.

[mmwjr]

Originally Posted by AACoPD05

I dont know if the 7.4 has it but my 5.0 had a little filter/muffler for the IAC that was dirty and caused it to hunt around for idle on a cold start. The little $2.00 filter/muffler was changed and all the problems resolved.

I mentioned this in post #2. Since he replaced the IAC wouldn’t that have come with a new filter?

[George K]

Thanks for the suggestion but put a new IAC sensor - and it appears that it needed one (old one was stuck open).
Taking a closer look at the ignition wires, the ohms of resistance are a little high - so I ordered a new set of MagForce wires - waiting for them to arrive - will post results.
Thanks,
GeorgeK