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Jason
Jason, Marine Mechanic
Category: Marine Electronics
Satisfied Customers: 549
Experience:  Degree in Marine Technology, Also Certified with Mercury Marine, MCM, MIE, VP, Yamaha, Honda, Suzuki
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Mercruiser 1999 5.7 surges only at 3600 rpm any answers

Customer Question

mercruiser 1999 5.7 surges only at 3600 rpm any answers
Submitted: 1 year ago.
Category: Marine Electronics
Expert:  Tan replied 1 year ago.

Hello Harold. My name is Tan.

Surging is fuel starvation. Does the engine run good up to 3600 rpms?

Will the engine run over 3600 rpms?

Could I get the engine serial number please?

Customer: replied 1 year ago.
runs real good above and below 3600rpm the 5.7 is a new rebuild
Expert:  Tan replied 1 year ago.

So it runs good at 3500 and 3700? Finding an issue of surging at one specific rpm between high and low is going to be hard.

Is the tach fluctuating?

Customer: replied 1 year ago.
I think it an electrical problem more then fuel
Expert:  Tan replied 1 year ago.

What your going to have to do is get a timing light and check the timing when engine is running at specific rpms. Check where it doesn't surge and check where it does surge. The timing should be steady at all rpms.

Does it feel like the engine is surging or do you just notice it in the tach.

Customer: replied 1 year ago.
feel the motor surging in the boat
Customer: replied 1 year ago.
does it under load when the boat is moving
Expert:  Tan replied 1 year ago.

Ok all you can do is check the timing for fluctuation. If the timing is steady at 3500 rpms then we have a fuel issue.

What you have to do on this is connect a vacuum gauge on the suction side of the fuel pump and watch the gauge. If the vacuum gauge needle moves up and down when engine is surging you have a bad anti siphon valve. The check ball in the anti siphon valve can start to chatter at certain rpms when they start to go bad.

Does this make sense?

Customer: replied 1 year ago.
this could be it I will have to try it when we take the boat out when my friend gets back in a week
Expert:  Tan replied 1 year ago.

Ok let me know what you find.

Customer: replied 1 year ago.
will do
Expert:  Tan replied 1 year ago.

Thanks.