454 MPi running rich

[maxton]

Hi I’ve got a 2001 mercruiser 454 gen 6 . It’s running very rich, it takes it longer to warm up also then the starboard engine. The fuel pressure is correct, no codes, where should I start?

 

[Fun Times]

Hi there maxton , Welcome to iboats... You'll want to start with replacing the engine's "Thermostat" as they do tend to get stuck open do to debris inside holding them open and in-turn the engine typically would take a longer time to warm up and not surpassing the cold fuel enrichment run mode temperature (typically 154+ degrees) giving the ECM false signals to continue adding more fuel during the cold run status mode under 154* with these engine models.

Post your engine serial number and we'd be able to help you find the correct parts if needed.

There are other scenarios that could also make the engine run rich as well but since you mentioned engine temperature taking longer than normal, it's a place you have to start even if it's not the main issue.

Replace your spark plugs as well with the correct plugs too.

 

[Scott Danforth]

first, welcome aboard

start with the basics...... what is the temperature its running at? not with a gauge, with an actual IR thermometer taken at the intake manifold water log. since you state its taking longer to warm up, I would focus on the cooling system and find what is broken there. my guess the thermostat was removed or its broken

cold motors run rich.

 

[scoflaw]

coolant temp. sensor on the t-stat housing, if it's broke the ecm won't come out of open loop and think the engine is running cold

 

[tpenfield]

Beyond some of the basics mentioned above, at some point (probably soon) you will want to get some diagnostic info from the engine's control module (ECM / MEFI). For that you will need the computer software or to have it done at a shop.

All to often, problems with MPI/EFI engines are not accompanied by fault codes. However, if your engine is running rich it may be doing so because the engine 'thinks' that what it is supposed to be doing. So, something is not right and you will need the computer data to figure out what it is.

As mentioned, temperature would be a good thing to check, because the computer in the engine makes it run rich to varying amounts while the engine is warming up to its specified running temperature. If the ECT sensor is telling the computer that it is cold, then the computer will adjust the fuel mixture accordingly (rich).

Also, the readings from the RPM or load sensors could be telling the computer to run rich.

Do the easy stuff first, but don't go replacing a bunch of parts until you can get some data from the engine.

 

[wingless]

Welcome to the forum.

All good info...

Don't forget to clean the flame arrestor (air cleaner). On mine, I also remove, clean, replace my intake plenum and throttle body (and associated parts) on an annual schedule.

 

[QBhoy]

Great advice above. All I would add is to check the TPS too.
Also worth checking you Diz cap is good.
The thermostat would be the obvious first port of call though. Make sure plugs are good too. Leads etc etc.