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1998 Merc 5.7 efi tbi sputter/hesitation under load

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Old 10-03-2017, 09:56 AM
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Default 1998 Merc 5.7 efi tbi sputter/hesitation under load

Got twin 1998 Merc 5.7 efi tbi, starboard runs flawlessly but port engine when under load sputters, wants to die between 1800 to 2800 rpm, at 3000 rpm runs great. No water in fuel tank, filter, cleaned cap and rotor, checked for loose connections and issue still present.
Any ideas? Thank you all.
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Old 10-03-2017, 10:27 AM
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Check the MAP sensor and TPS sensor for that motor by swapping one at a time to the other motor. If the problem follows the part you've solve the issue. You can also do a voltage sweep test of the TPS to check it.
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Old 10-03-2017, 10:42 AM
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If 1800-2800 is getting on plane and 3000 is on plane, check everything in ignition system especially cap/rotor/wires and plugs.
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Old 10-09-2017, 08:01 AM
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Trash and SB, i did a voltage test of TPS readings are good and also compared to starboard engine, minimal difference.
I took spark plugs out, cylinder 7 plug had a thin crack, replaced hoping issue was solved but problem persists, today i will check cap, rotor and wires. Anything else i should look for??
Thank you for your advice
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Old 10-09-2017, 08:15 AM
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The wires, if merc, will have part # printed on them. The last two #'s are the date they where made. So, if last two #'s are 98, they where made in 1998.

Did you just replace one plug ? If so, when where all replaced ? Cap/rotors only good for approx 4 yrs on average. What plug/plugs part # did you install ?

Are these engines closed cooled ? By your location I assume good guess engine's used in salt water ?
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Old 10-10-2017, 08:27 PM
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Wires were replace 2 years ago the same with cap and rotor. New spark plugs. I disconnected wire going to fuel pump and check for voltage, initially nothing after wiggling voltmeter wires got about 15 volts and immediately going down to zero. Fuel pump fuse was melted, replaced. But still don't have consistent rpms when getting out of the hole, I think the problem is somewhere in this area... any thoughts?
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