Vortec 5.7 L engine problem

[Mozart]

My boats main engine when cold would run fine. But when it's warm up it'll rave slow fast slow fast.

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Anyone know what might've caused this problem?

Thank you.

 

[noluck]

sounds like the iac hunting

 

[Fishing?]

Check the vent on your gas tank. Maybe a fuel pump going south. FI or Carb?
I had a vent plugged and it was collapsing the gas line.

Pretty cheap and easy fix. Can do it yourself, no special tools or parts.

 

[ship happens]

Yeah I'm with Dave on this one. I'd look at the iac first

 

[Capt_Ed]

sounds like the iac hunting

I agree I had the same issue with my 5.0. Thankfully those days are being me.

 

[Mozart]

Changed a new IAC it's now reving at higher RPM but still surging. Could this be a bad IAC? (Got it off Amazon).

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[salmonkiller01]

lots of power still? Almost seems like a fuel supply issue.
Fuel tank vents clear?
Fuel pressure check? Pump might be cavitation. Changing pressure.
All fuel Filters new?

Does seem like an IAC issue but if it is new it should be fine.

 

[Mozart]

Pump pressure checked okay. New filter and new high pressure fuel pump. I think vent is clear. I took the boat to fuel up and can smell gas fume coming out of the vent.

 

[ship happens]

Possible the crank sensor wire running on a pully?

 

[salmonkiller01]

Would be good to get someone to put a laptop on it to check sensor values, might help Pinpoint
Have you gone thru and checked all your wire connections? Ground is good?
Alternator putting out a steady 13.5-14.5?

The older iac could be reset they had a plunger you pushed to reset and then fire up and let idle and they would almost re-learn. That was early 90 tbi.

Odds of having purchased a new iac and the old one both failing I would say is very low.
You cleaned any carbon in the port for iac out using carb cleaner?