Mercruiser 5.7 won’t make power

[itsathepete]

Advance timing light $32 at horror fraught

 

[jimmbo]

A SB 350 isn't going to need 600CFM until it is long past 6000rpm

 

[Oldpos]

Thanks everyone for the things to check , keep the ideas coming. I am going back to the boat tomorrow with a new distributor, new timing light, and I bought a piston stop.

Let me know if y’all have anymore ideas.

 

[Scott06]

Thanks everyone for the things to check , keep the ideas coming. I am going back to the boat tomorrow with a new distributor, new timing light, and I bought a piston stop.

Let me know if y’all have anymore ideas.

Id start with the timing verify it is going into base mode set the initial timing, take it out of base make sure you are getting 30-32 at 3 k rpm or so.

Based on comments here I think you didn't have it in base mode and likely are missing some advance. If you cant get it in base mode rev it to 3 k or so and set the total to 32 BTDC which should get you in the ball park. If the timing is actually ok then would look into the TDC verification.

Are you still runnning the delco ? or did you revert back to the Thunderbolt

 

[Oldpos]

Id start with the timing verify it is going into base mode set the initial timing, take it out of base make sure you are getting 30-32 at 3 k rpm or so.

Based on comments here I think you didn't have it in base mode and likely are missing some advance. If you cant get it in base mode rev it to 3 k or so and set the total to 32 BTDC which should get you in the ball park. If the timing is actually ok then would look into the TDC verification.

Are you still runnning the delco ? or did you revert back to the Thunderbolt

I am sticking with the delco, the thunderbolt was a 1996 or 1997, everything was almost 25 years old, and very expensive.

Not to be a dumb a$$ but can someone answer when you go into base mode will the Rpm’s change? On my 3.0 it jumped a couple hundred rpm, when I try it on the 5.7 there nothing at all

 

[Scott06]

I am sticking with the delco, the thunderbolt was a 1996 or 1997, everything was almost 25 years old, and very expensive.

Not to be a dumb a$$ but can someone answer when you go into base mode will the Rpm’s change? On my 3.0 it jumped a couple hundred rpm, when I try it on the 5.7 there nothing at all

I would think rpm should drop, but you should also see the timing be fixed on the timing light. Otherwise i think it would be moving around some.
you do see a fair number of posts on having trouble getting into base mode, which is why i suggested just set the total advance at 30-32 at 3 k or so. Wonder if you may be stuck in base mode ?

 

[Oldpos]

I would think rpm should drop, but you should also see the timing be fixed on the timing light. Otherwise i think it would be moving around some.
you do see a fair number of posts on having trouble getting into base mode, which is why i suggested just set the total advance at 30-32 at 3 k or so. Wonder if you may be stuck in base mode ?

I installed the new distributor and it did finally go into base timing, but no help . I am doing the vacuum check now, any idea of range I’m looking for?

 

[Oldpos]

This is the vacuum reading, it bounces a few degrees either way also

 

[Oldpos]

Current vacuum at idle, 3000 rpm not change

 

[Scott06]

Current vacuum at idle, 3000 rpm not change
View attachment 364387

That is on the low side. Might be taking Danforth's advice and see if you have a flat cam lobe by checking lift at the rockers. Also would look for intake and carb gasket leaks. If you had a intake leak I would think your plugs would be way lean and you would have top adjust your idle mix screws way rich to compensate

 

[Scott06]

I installed the new distributor and it did finally go into base timing, but no help . I am doing the vacuum check now, any idea of range I’m looking for?

What was the total advance coming in at now that initial timing is properly set and was tdc verified , or am I asking questions faster than you can wrench....

 

[Oldpos]

What was the total advance coming in at now that initial timing is properly set and was tdc verified , or am I asking questions faster than you can wrench....

24 degrees roughly, 8 degrees base. Both still occasionally jump around

 

[jimmbo]

Just curious, what altitude do you do your boating? Myself the lakes I go to are between 1950 and 2400 feet above Sea Level, and it reflects in the power the engine produces, and also in the Readings on things like Vacuum Gauges

 

[Scott Danforth]

Put a dial indicator on the rockers, make sure all the intakes move the same, and all the exhaust move the same. You will need to crank to have oil pressure to keep the lifters pumped

This you can check without pulling the intake

 

[Oldpos]

Just curious, what altitude do you do your boating? Myself the lakes I go to are between 1950 and 2400 feet above Sea Level, and it reflects in the power the engine produces, and also in the Readings on things like Vacuum Gauges

800 ft eastern Alabama, lake Wedowee

 

[jimmbo]

Hmm, the Vaccum at Idle does look a bit low, but that might be because of the Grind of the Cam, retardation of Cam and/or Spark timing.
Did you Degree the Cam when you built the Engine? Also did the Timing Chain Sprockets have more than one Keyway?

 

[Oldpos]

Put a dial indicator on the rockers, make sure all the intakes move the same, and all the exhaust move the same. You will need to crank to have oil pressure to keep the lifters pumped

This you can check without pulling the intake

 

[Oldpos]

Too late on the intake not being removed

 

[jimmbo]

With the intake off, you can easily remove a Lifter or 2 and check for Dishing and other indicators of Camshaft Wear.

 

[Scott Danforth]

Too late on the intake not being removed

use a dial indicator on the cam lobes, a degree wheel on the crank and the cam card to see if your cam is installed at 0 degrees now that you have the intake off.

if you have a wiped out cam lobe, it will look like someone went at it with a grinder