Twin 5.0 efi loss of power

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 with under 400. Hrs on both. I have taken it for its first trip out this year and it ran great but WOT could only get 4200 rpm and port motor seems to be lagging. When i go WOT the left motor goes to 3200 rpm and the right motor goes to 2800 rpm. It takes about 10 seconds for them both to start to climb and then the boat will plane off. Today i took it out and the same thing with the rpms but would not go over 3400 to plane off. What can i check. Props were just redone and bottom is clean paint. Seems like a loss of top end power that is needed to drop nose to plane
 
Old fuel? Last time they were tuned up?
 
How old are the caps, rotor and plugs? My 2003 had original caps and rotors. The plugs had only been changed once in the prior 15 years. I must say it passed survey with all the old stuff but the old girl has some bounce in her step now. BTW I also had all the fuel filters changed as well.
 
Boat was boaught last year. Sat on land for 8 years. Was a mess. Nd had motor loss of power alo. Ended up being a timing issue.

Complete tune up last year. Cap, rotors. Wires. Map sencor. Knock sensor. Coils. Fuel filters Fuel injectors. Ignition
module. Props.

This year. Plugs. Fuel filters riseres and manifolds. Engine temp control module. Boat at WOT first trip ran great but only got 4200 rpm. Next trip was sluggish and would not climb over 3200. Thinking a timing issue again but how weird can it be that i lost timing 2 years in a row. Seems loss is only at top end and thing timing is not advancing
 
Update. Today took it out and ran like a beast. Got up and planed off and both motors were getting 4600 rpms. Ran for 30 minutes and stopped for a well deserved drink. Started to head back and boom. Problem there again. Port motor would not get over 2800 rpm and just boggs. Now thinking a fuel problem. I do not know how to do a fuel pressure test. I did change the starboard fuel pump last year cause it stopped working. Could this just be a fuel pump problem? I have the older style cool fuel and is tucked under the motor. Runs great at 2000 rpm and at dock hits rev limit. Any clues?
 
Also very weird. Boat runs at normal temp of 170. On way in port was running 130 while starboard was 170. I just did the manifold and risers just a month ago
 
You can borrow the fuel pressure tool at Autozone, it screws onto the shrader valve on the fuel rail.

Probably got a chunk of rust stuck in the t-stat. Drive it like you stole it usually opens it enough to clear it. If not , pull it out and replace it.
 
Do you know the location of the shrader valve? It should be on top correct by i did not see it.
 
Go to mercruiserpartslookup. put in your engine number and look at the diagram for your fuel system. It's there somewhere, it has a cap on it like a car tire valve stem
 
Single line with a TBI setup/electric carb ? It's on that line somewhere. Look from one end to the other.

Mpi with 8 injectors on a fuel rail ? It's on that fuel rail somewhere.
 
scoflaw said:
Single line with a TBI setup/electric carb ? It's on that line somewhere. Look from one end to the other..
Click to expand...

I’m not familiar with the marine engines with the TBI but I remember the automotive (GM) engines with TBI needed a special fitting to be inserted Into the fuel line to T off for the fuel pressure testing gauge. It was about a 5” Long hexagonal pipe with a threaded or barbed fitting T’eed in for the pressure gauge.
 
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