Merc 250 EFI High Fuel Consumption

[srq_fl]

This is a follow up to an earlier post about my 1996 250 EFI. <br /><br />My 254 Chriscraft with the above engine is burning about 25 GPH while cruising @4000 RPM. Accoring to my understanding about HP to GPH conversion, the engine should be burning 25 GPH at WOT. (My WOT RPM is 5500)<br /><br />Reading the trouble shooting section of Clymer Mercury manual, it suggests checking for:<br />1. Blocked air bleeds<br />2. Incorrect Metering Jets<br />3. High fuel pressure<br /><br />I know the fuel pressure on this engine is regulated by a pressure regulator (I will need to get a special gage to chech for this fuel pressure)<br /><br />Does any one know what/where are the "Air Bleeds" and the "Metering Jets" and how to check for them?

 

[rodbolt]

Re: Merc 250 EFI High Fuel Consumption

hello<br /> your motor has neither air bleeds nor metering jets. best I remember the high pressure fuel should be something about 35 psi. <br /> what is the consumption at 5500 rpm?<br /> but 25GPH at or near wide open throttle is about right. you could have a leaking low pressure pump or a leaking needle on the vst or a leaking pressure regulator all will result in over rich conditions do you see excessive fuel on the water at idle ?<br />and the conversion is not an absolute. the computer will allow more or less fuel tobe sprayed by the injectors based on throttle angle and engine load. I can tell you a pair of 250 yams on a 33 grady marlin will burn 59.8 GPH all day long at 5000 RPM. thats why they hold 310 gallons

 

[Kiekhaeferscurse]

Re: Merc 250 EFI High Fuel Consumption

rodbolt is right the conversion is not perfect but a good guide.<br />I will never forget the first 3 liter I bolted onto a boat, it was the carbed version, as usual we took the boat down to the chuck for a quick run on a 5 gal day tank, I couldnt believe it when that thing sucked the tank dry in about 15 minutes, when I got back to the shop I phoned the Merc dudes, after passing there secret tests I was allowed to chat with an engineer at the famous Lake X.....if you promise no to tell anyone, heres what he told me, Quote" Yeah it makes lots of power but when tied to the post, it will suck down 45 gph" end quote, this was back in 92 I think, but that engine still has not changed much.<br /> Dont let it get you down though, it still does better than a 200 hp Johny,<br />If you get the chance swap for a 200 Merc. Till then borrow a flow meter, figure out your best rpm/speed/ time/gph, mark it on your tach and stick with it.

 

[srq_fl]

Re: Merc 250 EFI High Fuel Consumption

rodbolt, I have not run the 250 @5500 RPM long enough to tell the consumption at that level. I tipycally cruise at 4000 RPM. <br /><br />I have only recently had this boat and am trying to figure few things about it. My older carbed YAMAHA 200 burned about half the fuel. I was under the impression that the EFI would have been more economical.<br /><br />The 250 EFI engine does seem to be running rich (I do see traces of oil or fuel in the water at idle. I have checked the sensors (throtle position, tempreture, ... using Quicksilver DDT) and every thing checked out fine.<br /><br />Does merc have different computer/firmware settings for the fuel management system? Maybe there is a new version of firmware that makes the engine not run so rich!<br /><br />I will check the low pressure pump, high pressure regulator. What is the needle on the VST???<br /><br />Question: When the low pressure pump leaks, does it leak into the engine block or ouside? I do not see any evidence of fuel leaking externally.<br /><br />Also thinking of getting the Navman F3100 Fuel Flow meter to find optimum running settings. Does anybody know anything good or bad about Navman?<br /><br />Kiekhaeferscurse, you suggested swap for merc 200. How is the 200 different except for 50 less HP? Since I do not run the 250 WOT, I figure I am using 200 HP or even less at cruising speed!<br /><br />Thanks...

 

[gss036]

Re: Merc 250 EFI High Fuel Consumption

Everything I have read about the 250 Merc has always been complaints about high fuel consumption. My 200 hp burns about 1/2 that amount. I am thinking that may be case. A fuel flow meter would definately answer your concerns.

 

[BW23]

Re: Merc 250 EFI High Fuel Consumption

I bet your not running on all 6 cyl's. <br /><br />I noticed this while troubleshooting a CDM (missing) problem on my 97 225 EFI.

 

[Kiekhaeferscurse]

Re: Merc 250 EFI High Fuel Consumption

Sorry srq_fl didnt relize you had asked me a question, I'm of course referring to the older 2.4litre 200, in my experience's with both motors the 200 was just a far better performer, fair fuel flow rates, not quite as much torque as the 3 litre, but it weighs a lot less and to me it only gave up 2 to 3 mph on the same givin applications.<br />Hope this helps, but of course cover all your bases first, Chipped or broken reeds will also cause fuel loss among the other suggestions here. Good luck