5.0 efi swap out to carbs

Jeff Delbuono

Jeff Delbuono

Well-Known Member
Jun 11, 2018
1,126
Edison New Jersey
Boat Info
1998 Sea Ray 290 Sundancer
Engines
5.0 efi w/ alpha 1 gen 2 drives
I have a 1998 290 sundancer with twin 5.0 efi on alpha 1 gen 2 drives. Having prob with 1 motor not being able to get it over 3000 rpm. Trued everything and mechanic is stumped. Said i should just go old school carb and junk the efi. Told its just manifold, distribitor, carbs and a msd box. All in $3000 parts and labor. Any thoughts pros or cons. Please help
 
I'd fix it. Very simple system, assuming you have a EFI and not MPI. You could spend the coin and it may still only go to 3000 rpm. Original 20 year old motors ? How's the compression ?
 
Compression was 130 across the board on both motors. Left has 345 hrs right has 415 hrs. Its the left i am having problems with. I just got it
 
How about a complete list of what you have done. With 2 engines it would cost very little to swap parts from 1 motor to the other. When it stops at 3k is it still smooth or not ?
 
Fuel injectors, cap, rotor, wires, plugs, fuel filter, Map senser, knock senser, coil, oil change, balancers (to make sure timing is on) , had props re-pitched frpm 19 to 17, compression check 130 lbs across the board. Vacume test 16 lbs and at WOT goes to 0.

Motors fun awesome and revs to 5000 when in N. Only under a load it bogs
 
Are the motors raw water cooled and run in salt water? If so after 20 years they are on borrowed time. Has the mechanic gone thru the exhaust system to eliminate possible restrictions?
 
Have you checked for spark to the plugs on all 8. Revving in neutral tells nothing, it could hit 5k on 4 cylinders.
How about the TPS ? What's your fuel pressure when it hits the wall ? Could have an exhaust shutter stuck in the y-pipe.
 
All plugs were changed when compression check was done. Flappers checked and in place. Heading down now to the boat. Gonna check fuel pressure under a load. Dont have a scanner to check computer. As far as the motors health. Dont run hot (170 ) and oil pressure is good. Volts at 14. Only thing i see not working is trim tab guage on left motor. Should not effect motor rpm ot does it
 
Couple more questions
Did the performance of this motor happen suddenly or over a long period.
How is the power and smoothness up to the 3k?
There is a filter by the fuel pump and fpr.
 
I just got the boat in march. Last owner said he never had any problems with it. Was unable to sea test at time but guy is pretty honest and i believe him. Pulled out of water winterized and Sat 7 years on land. Runs great till u hit about 2800 to 3000 then just boggs. The motor i am having problems with i did change the fuel pump cause it was not getting gas to injectors. Has the cool fuel and are u talking about the dime sized filter above the pump? Checked it on other motor and was clean but did not check that one yet. Mechanic was sitting in motor compartment under a load and said its getting plenty of fuel
 
Mechanic: "I tried everything, and can't figure it out, so I think you should spend $3000 to retrofit a carb system."

Me: "your services will no longer be required"

You might try swapping the fuel connection as it enters your throttle bodies, between the two engines (using the appropriate temporary plumbing). This will eliminate (or implicate) the fuel system on the affected engine, and half the battle will have been won.
 
Will a fuel pressure guage show me a drop in pressure if it is my issue. What should the pressure be at At idle and WOT
 
Jeff Delbuono said:
Will a fuel pressure guage show me a drop in pressure if it is my issue. What should the pressure be at At idle and WOT
Click to expand...

That should give you a good data point. Dunno what the correct pressure should be, but again, twins are your friend. Check it on the good side, and compare those readings to what you get on the problem side.
 
Jeff Delbuono said:
Pulled out of water winterized and Sat 7 years on land. Runs great till u hit about 2800 to 3000 then just boggs.
Click to expand...

Even if properly winterized, there is going to be some issue with the fuel system if it sat unused for 7 years.

You may want to look into having the fuel Injectors cleaned and flow tested.

They may be clogged with debris and not reaching maximum flow, thereby limiting your rpm.
 
New injectors was the first thing i did to both motors. Fuel pump was bad on 1 motor so i changed it out. Did not change fuel regulator or cool fuel. Just changed fuel pump.

Now thinking i might start at the gas tank and trace entire fuel line and change. Such a bitch because its right up against the generator.
 
Jeff, I think it's time you seek the opinion of another Merc Service Rep. No disrespect to the first guy....he did his best. Now it's time to get another opinion. If your arm stopped working and the doc you went to said "Hmmm, I tried everything and I just don't know what is wrong." you would go to another doctor for a second opinion. It's time to find that other opinion.

This forum is really great for getting advice and sometimes a good point in a right direction but, after reading this entire thread you are now just throwing the poop against the wall and hoping something sticks. Find another Tech now before you lose the entire summer. And on your next boat get a pre-purchase survey. And if you can't....don't buy until you can.

Best of luck. I hope you get it solved soon.
Shawn
 
Good plan, access the fuel tank through the sender on top. Chances are you clogged the injectors again with the old fuel.
 
if I missed this I apologize but I did not read where the 'mechanic' was using a scanner to try and diagnose the problem....if he did not use a scanner find a mechanic that has one and get him to dig into this....my bet is a scanner will reveal what is going on....

cliff
 
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