2001 Mercruiser 5.7 EFI poor power

[tjwieseler]

I have a 30' cruiser with twin 5.7L EFI Mercruisers, new long blocks with approx 150 Hrs on them. One engine performs just fine, the other when trying to get up on plane, it is only getting 2800 RPM until the other engine gets it up on plane enough at 4800 RPM then it will get 3200 or so. Both engines have new caps and rotors, and wires. I went check the timing on the engine, and it has an intermittent spark.
Could this be the ignition coil, or do I replace the sensor in the distributor? I always figured when a coil goes bad it just fails.

 

[alldodge]

What is one of the motors serial number?

Most coils never fail, folks replace them often but very, very rare if they actually are bad

Could pull some plugs to see if they look the same or if a few are fowling out

 

[tjwieseler]

They are manufactured long blacks, so no real s/n.
Fouled plugs wouldn’t make the inductive timing light skip firing thoug, would it?

 

[Bondo]

They are manufactured long blacks, so no real s/n.
Fouled plugs wouldn’t make the inductive timing light skip firing thoug, would it?

Ayuh,..... Welcome Aboard,..... There should still be a serial number on it, to tell how it was dressed, with which components,....

 

[alldodge]

The number of the old motor
If not available lets see some pics of the motor or tell us what is the make up?

Ignition, TBI or MPI, closed/open cooling, what ECM

 

[tjwieseler]

The number of the old motor
If not available lets see some pics of the motor or tell us what is the make up?

Ignition, TBI or MPI, closed/open cooling, what ECM

It is 5.7 TBI open cooling

5.7L EFI GM 350 V-8 1999-2001 - 0L325977 THRU 0M299999​

Parts breakdown shows the ECM is a 861925T3

 

[tjwieseler]

The number of the old motor
If not available lets see some pics of the motor or tell us what is the make up?

Ignition, TBI or MPI, closed/open cooling, what ECM

I did find the actual S/N 0M081724

 

[alldodge]

I did find the actual S/N 0M081724

Thanks
TBI, MEFI-3, TBV ignition, cool fuel, could be open or closed cool

Fouled plugs wouldn’t make the inductive timing light skip firing thoug, would it?

Not normally
With skipping I would think the distributor module or a bad connection. You should have the 3 wire Distributor module and check to see if the black wire has a good ground

Here is the TBV troubleshooting chart. With it being intermittent the chart may not show a problem. The Green/White wire gets tapped real fast

 

[tjwieseler]

Thanks
TBI, MEFI-3, TBV ignition, cool fuel, could be open or closed cool


Not normally
With skipping I would think the distributor module or a bad connection. You should have the 3 wire Distributor module and check to see if the black wire has a good ground

Here is the TBV troubleshooting chart. With it being intermittent the chart may not show a problem. The Green/White wire gets tapped real fast

Thanks,
I went ahead and ordered a new coil, sensor, and cap and rotor. Figured as long as I am back there, I should have everything available to replace.

 

[stresspoint]

check the leads are on the correct cylinders , ,they could have got mixed up when working on the motor.
TPS out of range or broken.

plug up to soft ware and check perimeters of everything before you ruin the engine running it like it is.

 

[Chillythe1]

Well you can hook them up to a Mercruiser ddt if you want but that never showed a damn thing, no real ecm to hook up to with Mercury's g3 program, you might possibly be able to use an aftermarket scan tool but even then with the age and technology of the engine there's not a whole lot to display. That being said main go to for me is first look if the newer 3 wire ignition module has been installed, if so I'd still look under the distributor cap and make sure the one that's installed isn't full of rust, vents in distributor get plugged and module rusts easy.