First post here - what a great forum and most of you follks apear to be military very cool. This one has me stumped. I have many years of automotive experience and am fairly new to the marine engines.
I purchased a 1998 Mariah Deck Boat that has no power to the point it will not plane out. I purchased it at a lower 2000 ft. elevation and brought it to Denver area at 5000 ft. Cannot find the outdrive ratio or engine S/N. It starts, idles, and runs perfect either on the garden hose or on the water. Idle is smooth and exhaust does not pulsate (like a dead cylinder will do). As soon as it goes under load it will not go above 2000-2500 rpm. Originally I had backfiring through the carb. but not so much now since the carb. has been rebuilt. It appears to rev. O.K. under no load as I can get it up to 4000 rpm in neutral.
I cannot find a engine S/N and have looked all over the motor. All I got is a casting number 10054724 which is a 5.7L. So I suspect the motor has been replaced and maybe the ignition has been cobbled together - see below under timing...
Here is a list of what I have done.
Rebuilt carb - Rockester Quadrajet 4 barrel. Idle screws will stall the engine if turned all the way in and I have them set at 2 turns. I can see fuel spraying through the primary venturies under load. The secondaries are opening about 1/4 and I can see and see fuel dumping into the secondaryies under load. If I push the secondaries open by hand under load on the lake it makes it worse as in the boat loses power.
Pulled spark plugs and found they are sooted up black. Not real bad but definitely running rich. Plug type appears to be correct for 5.7L non vortec head - don't recall the number as it is written down at home.
Replaced fuel filter water separator.
Replaced ignition coil - it is a inexpensive part and the old one looked old and it does not hurt to have a fresh one for reliability. I am getting 12.5 to 13V at the coil + terminal at all times. The new coil package said it was supposed to have an external resistor so I think I should see 9.5V. I think this will just shorten my coil life? Will address this later.
Inspected the exhaust flappers. They were free to move. The riser elbows were pretty rusty but I think this is just the water jacket. Internal cavity was free looking back into the manifolds. My temp gage stays rock steady at 175F.
Timing set at 12 deg. using the base timing method per the service manual. Looks like I have the Thunderbolt V ignition without the knock sensor. This is shown in the 1997 service manual for a V8 without the knock sensor. I do not think it is the TIV ignition as the wires going into the module do not match the service manual for a TIV but do for a TV without knock. However, I have a 861459-1 ICM module which does not make sense as this crosses over to a 5.0L and the sticker says 5.0L GEN+. I have a 5.7L block with the old style heads (no vortec). Isn't GEN + the vortec heads? I checked the advance under load on the lake and it appears to be correct as I am getting 10-15 deg advance over the base timing. I also adjusted the distributor on the lake under load and could feel the power slightly go up and down as it was turned back and forth but no huge improvement to where the boat would plane.
Prop. was originally a 19 pitch so I tried a 17 pitch with no change.
Vacuum gage reads 13-14 inches and very steady at idle which is O.K. for my altitude of 6300ft. Vacuum gradually increases when revved without load to about 18 inches and increases above 22 when throttle is closed.
I have checked the ground wire at the ICM module. I checked the shift interrupt switch and it is working O.K. but I think this would mostly cause a no start condition.
So what do you experts think. I am leaning toward ignition problem and possibly the module. They are $400 and don't want to waste $$. So how do I determine what is the correct module for a 5.7L.
And one more question - sorry about the long wind. I have two other GM motors I could swap distributors. A 1985 Chevy pickup with a 5.0L and a 1970 Olds 455 with a newer HEI (75 vintage). Will the 1985 distributor drop into the mecruiser engine casting 10054727?
Thanks In Advance
I purchased a 1998 Mariah Deck Boat that has no power to the point it will not plane out. I purchased it at a lower 2000 ft. elevation and brought it to Denver area at 5000 ft. Cannot find the outdrive ratio or engine S/N. It starts, idles, and runs perfect either on the garden hose or on the water. Idle is smooth and exhaust does not pulsate (like a dead cylinder will do). As soon as it goes under load it will not go above 2000-2500 rpm. Originally I had backfiring through the carb. but not so much now since the carb. has been rebuilt. It appears to rev. O.K. under no load as I can get it up to 4000 rpm in neutral.
I cannot find a engine S/N and have looked all over the motor. All I got is a casting number 10054724 which is a 5.7L. So I suspect the motor has been replaced and maybe the ignition has been cobbled together - see below under timing...
Here is a list of what I have done.
Rebuilt carb - Rockester Quadrajet 4 barrel. Idle screws will stall the engine if turned all the way in and I have them set at 2 turns. I can see fuel spraying through the primary venturies under load. The secondaries are opening about 1/4 and I can see and see fuel dumping into the secondaryies under load. If I push the secondaries open by hand under load on the lake it makes it worse as in the boat loses power.
Pulled spark plugs and found they are sooted up black. Not real bad but definitely running rich. Plug type appears to be correct for 5.7L non vortec head - don't recall the number as it is written down at home.
Replaced fuel filter water separator.
Replaced ignition coil - it is a inexpensive part and the old one looked old and it does not hurt to have a fresh one for reliability. I am getting 12.5 to 13V at the coil + terminal at all times. The new coil package said it was supposed to have an external resistor so I think I should see 9.5V. I think this will just shorten my coil life? Will address this later.
Inspected the exhaust flappers. They were free to move. The riser elbows were pretty rusty but I think this is just the water jacket. Internal cavity was free looking back into the manifolds. My temp gage stays rock steady at 175F.
Timing set at 12 deg. using the base timing method per the service manual. Looks like I have the Thunderbolt V ignition without the knock sensor. This is shown in the 1997 service manual for a V8 without the knock sensor. I do not think it is the TIV ignition as the wires going into the module do not match the service manual for a TIV but do for a TV without knock. However, I have a 861459-1 ICM module which does not make sense as this crosses over to a 5.0L and the sticker says 5.0L GEN+. I have a 5.7L block with the old style heads (no vortec). Isn't GEN + the vortec heads? I checked the advance under load on the lake and it appears to be correct as I am getting 10-15 deg advance over the base timing. I also adjusted the distributor on the lake under load and could feel the power slightly go up and down as it was turned back and forth but no huge improvement to where the boat would plane.
Prop. was originally a 19 pitch so I tried a 17 pitch with no change.
Vacuum gage reads 13-14 inches and very steady at idle which is O.K. for my altitude of 6300ft. Vacuum gradually increases when revved without load to about 18 inches and increases above 22 when throttle is closed.
I have checked the ground wire at the ICM module. I checked the shift interrupt switch and it is working O.K. but I think this would mostly cause a no start condition.
So what do you experts think. I am leaning toward ignition problem and possibly the module. They are $400 and don't want to waste $$. So how do I determine what is the correct module for a 5.7L.
And one more question - sorry about the long wind. I have two other GM motors I could swap distributors. A 1985 Chevy pickup with a 5.0L and a 1970 Olds 455 with a newer HEI (75 vintage). Will the 1985 distributor drop into the mecruiser engine casting 10054727?
Thanks In Advance
