Mercruiser 5.7 won’t make power

[Oldpos]

The electronics under the cap is the ignition sensor. Did you ever verify that your timing is advancing?

Honestly I can’t tell, either my light is messed up or something is wrong, I was hoping I did something wrong and that’s why I asked if the idle changes when you put in the jumper. At idle about every fifth pulse the light is way off, and the light is very erratic , I checked spark between cap and wire and spark is very consistent. So I can’t see if it’s advancing, I’m on my third ignition module, could it be the actual dizzy? Is there something there that mechanically advances?

 

[jimmbo]

By "way off", what do you mean?

 

[nola mike]

. At idle about every fifth pulse the light is way off, and the light is very erratic ,

Misfire...

I checked spark between cap and wire and spark is very consistent.

What wire?

So I can’t see if it’s advancing,

Why not? Use an advance light, rev to 2k and see where you're at

Is there something there that mechanically advances?

No

 

[jimmbo]

I have never used an Advance Light, just a regular Inductive Timing Light aimed at the Harmonic Balancer
I too suspect that the Erratic Flashes are the result of a miss, but it couldn't be every 5th, as that would mean every cylinder is misfiring at some point.

 

[jimmbo]

Have you inspected the inside/underside of the Distributor Cap and the Rotor for Carbon Tracks, and or Cracks? Are all the Plug Wires Good?

 

[Oldpos]

By "way off", what do you mean?

I can’t see the line on the balancer for awhile, then all of a sudden I can and it moves up about an inch then back to where I set it

 

[Oldpos]

Have you inspected the inside/underside of the Distributor Cap and the Rotor for Carbon Tracks, and or Cracks? Are all the Plug Wires Good?

Cap and rotor and wires have been replaced, when I replaced the distributor, also three ignition modules

 

[Oldpos]

Misfire...

It has new plug wires , rotor cap, rotor button, I’m on my third ignition module. Plugs are new from when I rebuilt it and maybe 8 hours on them. They are the Ngk iridium and when I did the compression check they were not fouled.

What wire?

Between rotor cap and plug wire has consistent spark

Why not? Use an advance light, rev to 2k and see where you're

I’m going to have to try another light I don’t trust this one

Could the actual dizzy be bad?

 

[jimmbo]

I can’t see the line on the balancer for awhile, then all of a sudden I can and it moves up about an inch then back to where I set it

It just suddenly moves several degrees, then returns to where it was? and you are not revving the engine when it is doing that?

 

[itsathepete]

Based on your gear ratio and prop you have a potential top speed of 50mph at about 4600rpm. If you only got 23mph with the 140hp 3.0 I would expect 35-40 assuming you are making about 300hp now. I think you are still overpropped

 

[Oldpos]

It just suddenly moves several degrees, then returns to where it was? and you are not revving the engine when it is doing that?

No

 

[jimmbo]

Based on your gear ratio and prop you have a potential top speed of 50mph at about 4600rpm. If you only got 23mph with the 140hp 3.0 I would expect 35-40 assuming you are making about 300hp now. I think you are still overpropped

If the cam change moved the Powerband up higher in the rpm range, the engine is certainly producing less Torque at lower rpms, exactly where the boat needs all the Torque it can get to get it up on plane, the drop in Torque might be part of what is keeping it from getting past 2000 rpm
I wonder if the prop is Drilled, and if not, doing so might unload the engine enough to get get the Revs up a bit to where the Cam can make some Torque

 

[Oldpos]

The distributor has a two wire connector that comes out of the center of the distributor, I assume for the pick up, does it sound like it’s bad to you? Is this distributor known for failing?

 

[Scott06]

The distributor has a two wire connector that comes out of the center of the distributor, I assume for the pick up, does it sound like it’s bad to you? Is this distributor known for failing?

So you originally had the Merc Thunderbolt V on this , didn't get the performance you were expecting and swapped in a Delco EST ( normally both are very good systems). On the Delco EST you are on your third ignition module? I have seen postings here that the aftermarket modules cause issues like not going into base mode.

If you set the timing not in base mode (timing will be locked from electronically advancing) , you r total timing will be retarded and not have enough advance. In base the timing should hold steady when you pull the 12 v off the timing should advance to like 15 degrees or so.

Yes could be a bad pick up or bad cap and rotor would try a spark gap tester to see if you are loosing spark from coil to distributor to plugs

Bottom line erratic and inconsistent you either had a bad timing light or a ignition issue. Most auto parts stores will rent you timing lights and yes you can use and advance light to see if you have around 30 degrees total advance at 2800-3000 ish

 

[dubs283]

I thought the electronics self timed, it does have a large mechanical head under the rotor button but I’m not sure what it’s for

Sounds like a Delco hei/est distributor. And no, the electronics don't self time. The operator sets initial timing following proper protocol, the module advances the timing with rpm increase

The distributor has a two wire connector that comes out of the center of the distributor, I assume for the pick up, does it sound like it’s bad to you? Is this distributor known for failing?

Sounds like a thunderbolt distributor with old style, two wire ignition sensor

Post a picture of the distributor you currently have installed and a picture of the one you replaced

 

[nola mike]

It just suddenly moves several degrees, then returns to where it was? and you are not revving the engine when it is doing that?

Sounds like it isn't in base timing mode

 

[nola mike]

The distributor has a two wire connector that comes out of the center of the distributor, I assume for the pick up, does it sound like it’s bad to you? Is this distributor known for failing?

The 2 wire version is. Newer ones are 3 wires.

 

[nola mike]

I have never used an Advance Light, just a regular Inductive Timing Light aimed at the Harmonic Balancer
I too suspect that the Erratic Flashes are the result of a miss, but it couldn't be every 5th, as that would mean every cylinder is misfiring at some point.

Which is certainly possible if you have a problem with the ignition sensor.

 

[Scott Danforth]

That cam pulls more torque from 1500 RPM to 5200 than stock cam. It's not the cam unless you washed out the lobes

Carb is a bit small, however should get you to 4400 rom under load

You do need to verify fuel pressure under load

You do need to verify TDC with a piston stop tool

You do need to verify ignition advance

 

[Oldpos]

So you originally had the Merc Thunderbolt V on this , didn't get the performance you were expecting and swapped in a Delco EST ( normally both are very good systems). On the Delco EST you are on your third ignition module? I have seen postings here that the aftermarket modules cause issues like not going into base mode.

If you set the timing not in base mode (timing will be locked from electronically advancing) , you r total timing will be retarded and not have enough advance. In base the timing should hold steady when you pull the 12 v off the timing should advance to like 15 degrees or so.

Yes could be a bad pick up or bad cap and rotor would try a spark gap tester to see if you are loosing spark from coil to distributor to plugs

Bottom line erratic and inconsistent you either had a bad timing light or a ignition issue. Most auto parts stores will rent you timing lights and yes you can use and advance light to see if you have around 30 degrees total advance at 2800-3000 ish

Yes I’m in my thi

That cam pulls more torque from 1500 RPM to 5200 than stock cam. It's not the cam unless you washed out the lobes

Carb is a bit small, however should get you to 4400 rom under load

You do need to verify fuel pressure

under load under load 4 psi

You do need to verify TDC with a piston stop tool,

came home today, new distributor arrives tomorrow, I will do the piston stop deal Thursday morning

You do need to verify ignition advance buying another light also tomorrow