5.0 efi running rich

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 twin 5.0 efi in a 1998 290 sundancer. Did alot of work to it this year and ran great all summer. One of my last trips out running at about 1800 rpms in a no wake zone it just died. Was able to get it started again but when i reved it it bogged acouple times then ran fine and died a bit later. Got it started again and was fine and got to dock. Changed fuel seperator and was free of water and only had a minor amount of crap. Ran it again and ran strong but now smokes a bit and smells like it is running rich. Not very good with fuel injectors. Any clue why it could be running rich
 
A faulty coolant temperature sensor or thermostat stuck open are 2 things that come to mind.
 
There is one sensor for the gauge and another for the ecm input.
A computer scan should show the coolant temperate that the ecm is “seeing”
 
New thermostat this year. Both motors run at 170 deg. Where is sensor located. It is raw water cooled
 
There are 2 sensors on the thermostat housing, right near each other.

The 1 wire sensor is for the dash gauge. Unplug it and watch the temp needle drop.

The 2 wire sensor is for the ECM. I suggest you do not unplug that while the engine is running.
If you don't have a diagnostic scan tool for the motor, You could compare the ohm readings between the 2 wire sensors on each motor at various coolant temperatures and look for any inconsistencies.

ctsmatchartpp3.jpg
 
Could also be faulty injectors

Or faulty fuel pressure regulator

Or (if it has one) faulty o2 sensor
 
Replaced all injectors this year aswell as o2 sensors. Fuel pressure reg is at the cool fuel? When i look at injector spray it is strong.
 
what about a faulty ECT (engine coolant temperature) sensor?.....if this sensor does not tell the ECM the engine has reached normal operating temp the fuel/air mix will be kept rich as if the engine was running cold all the time....

cliff
 
Replaced all injectors this year aswell as o2 sensors. Fuel pressure reg is at the cool fuel? When i look at injector spray it is strong.

You have oxygen sensors on a 1998?

Are they replacement motors with catalysts?
 
Yes, (at least on some versions) the fuel pressure regulator is part of the cool fuel module...

On the cool fuel III, there is a known paint flaking/corrosion issue that clogs the screen on the fuel pressure regulator, causing gross over pressure. Should be somewhere about 40 psi ish (don’t recall the exact number) but if out of range mercury say to change out the whole module- when one of mine failed it was stupid high, like 90 or something. Left a fuel sheen on the water, ran rough as guts, damaged some injectors. The paint/corrosion particles also contaminate the fuel rails and injectors.... big $ job to rectify properly if that’s your problem.... can you get a mechanical fuel pressure reading at the rail?
 
I don’t think a 1998 would have cool fuel 3 but still a good idea to check fuel pressure.

Summarizing the posts above, the external things to check are:
Coolant temp sensor
Map sensor
Fuel pressure
Check wire harness for damage
Possible misfire (these motors are pretty good at compensating for one)

Does the engine reach proper WOT rpm? If not, you may have a misfiring condition.

How does it run at higher rpm?
A leaky fuel injector will cause havoc at lower rpm, but most likely won’t affect operation at higher rpm.
 
Boat is new to me this year. Had several problems early in the season and decided to replace anything i could think of. Ended up being a timing issue and a half witted mechanic installing wires to wrong plugs.

This year. New map sensor, knock sensor, fuel injectors. Plugs and wires, cap and rotor. Coils and fuel seperators. Had new props installed 15x15 4 blade. WOT only hits 4300 rpm. But gonna go back to ss 17x14.5. Runs strong at WOT but bogs at the go and then comes up.

Pressure test on both were good and issue only happened my last trip out
 
Has anybody bought this? Is it worth getting? Had a hard time trying to get my motors scanned and when i finally found a guy he wanted $175 to do. I have a 1998 290 with twin 5.0 efi's
Screenshot_20181028-165129_Chrome.jpg
 
I thought same thing. But if you look up description its gives the tool spec. Will call and get answear
 

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