Surging at WOT and loss of power Mercury 250xs

[Helo-md]

serial # 0t819362
2004 250xs
surging above 2100 rpms

Have taken it to two Merc mechanics and do not have any codes associated with motor. $1000 later with the plugs changed, fuel filter changed still surging.
This motor is using the same fuel line that was set up for the 2001 trition with a 225 Evirude. The boat was repowered and ran fine at first but when I re-proped it to a 26P fury I brought my rpms up and now it surges.
Looking at replacing the fuel line from tank to motor. Also was told by a merc mechanic that races a 250xs that the primer ball is not needed. Any help would be great!

[bulletrb]

Don and others will chime in later, but I run a 2003 250 xs and have always made sure primer is pumped tight before I start my engine and after long periods of fishing.You maybe hitting rev limiter, causing the surge.

[M4A1]

serial # 0t819362
2004 250xs
surging above 2100 rpms

Have taken it to two Merc mechanics and do not have any codes associated with motor. $1000 later with the plugs changed, fuel filter changed still surging.
This motor is using the same fuel line that was set up for the 2001 trition with a 225 Evirude. The boat was repowered and ran fine at first but when I re-proped it to a 26P fury I brought my rpms up and now it surges.
Looking at replacing the fuel line from tank to motor. Also was told by a merc mechanic that races a 250xs that the primer ball is not needed. Any help would be great!

Wow. Don will help you out. He usually logs on early in the morning. It seems you have unfortunately been given wrong advice.

[EuropeanAM]

Primer bulb is required! And... it should be pumped FIRM before every single engine start, too!

Read the following post for information on fuel lines. Ensure ALL (EVERY SINGLE) recommended item is addressed, all AT THE SAME TIME:

http://www.bbcboards.net/mercury-3-l...tem-first.html

Please verify the RPM range at which the engine is surging. Your original post indicates that it surges at ANY RPM above 2100 (that's an awfully big range). Also... questioning the 2100 RPM figure, as that's simply not an RPM we normally run a bass-application at (not planed, pushing lots of water in most cases).

[Savage]

Some props can also cause a boat to surge depending on the condition of the prop and if any work has been done to it. Fix the fuel portion, but try a different prop if the condition is still present.

[bitsy bug]

mine was surging. it was the lower fuel pump. i dont know if there the same. mines a 2009

[Helo-md]

2100 was the wrong number, I don't know why I posted that "Age I guess" above 5100 rpm is where the surge happens. It feels just like a bad fuel filter but mines new.

[EuropeanAM]

2100 was the wrong number, I don't know why I posted that "Age I guess" above 5100 rpm is where the surge happens. It feels just like a bad fuel filter but mines new.

No problem, Gary- and thanks for clarifying (that really helps).

A couple of items that need to be addressed/verified:

-Fuel Line/Primer Bulb/Pulse Fuel Pump. As referenced above (earlier), read through the following post, and upgrade ALL (every single) recommended item. Very, Very important! http://www.bbcboards.net/mercury-3-l...tem-first.html

-Tachometer: Unless you're using a Smartcraft Instrument for your RPM figures... I would strongly recommend that you have the engine connected to the Computer Diagnostic System, for PRINTOUTS of:

1. Run History
2. Freeze Frame (Fault) History
3. Fault Seconds Counters

Additionally, while on the CDS, it would be a very good idea to check the Tachometer. This can be done via the Active Tests (there's a test there that will generate a 3000 RPM signal, so the tach can be verified accurate at 3000 RPM's).

There is a possibility that the tach may be inaccurate- and you're actually in GUARDIAN (which could be perceived as surging).

I'm always happy to review printouts (as recommended above) by email, if necessary.

[Helo-md]

Had the engine ran through the ringer with a total diagnostic. No codes or freeze frames detected! Thats why I believe its fuel related. I looked at my fuel line and its the grey with red lettering. I cant get to the line from the tank to the bulb because of the the location but I will replace from the bulb to the motor. I will post the outcome after the line is replaced. Do you recommend taking the small fuel pump apart to ensure no obstructions are present?

[canadabullet]

Had the engine ran through the ringer with a total diagnostic. No codes or freeze frames detected! Thats why I believe its fuel related. I looked at my fuel line and its the grey with red lettering. I cant get to the line from the tank to the bulb because of the the location but I will replace from the bulb to the motor. I will post the outcome after the line is replaced. Do you recommend taking the small fuel pump apart to ensure no obstructions are present?

Change your fuel lines and VST filter as soon as possible and also install a new primer bulb.. The old grey line with the red writing will deteriorate with ethanol exposure and starve your motor for fuel .. You can use the new 3/8 mercury line with blue writing or 3/8 black fuel injection line from any auto supply store… Your filter in the VST tank is probably plugged with bits of deteriorated inner liner of your existing fuel lines also.. You will absolutely need to replace ALL the old fuel line right from the motor to the tank , because it will all have inner liner deterioration , due to the ethanol now found in most gasoline...

[EuropeanAM]

Read the referenced fuel line post (above), and replace lines (EXACTLY as described- A1-15 EPA Approved Low Permeation line from tank to bulb, MERCURY 5/16 B1-15 Gray w/blue print EPA Approved Low Permeation line from bulb TO FUEL PUMP INSIDE COWLING).

ALSO replace fuel filter, AND CLEAN CHAMBER AS IT MAY BE CONTAMINATED.

REBUILD FUEL PUMP (pulse fuel pump) AT THE SAME TIME.

Don't skip any one of the above... or you may find yourself back-tracking and chasing debris around the system.

[Helo-md]

Ok, all things have been replaced and cleaned although I had no debris in the filter or chamber and fuel lines were intact. Was leary of taking the pulse pump apart but the directions were straightforward and easy to follow. Used a timing light to check for spark on all cylinders and had a good strobe. Pulled all plugs and all looked good. Just don't understand why this motor is doing this and not showing any codes. Changed props from a 26 to a 25 and no different, MPH is 62 on the GPS and the tach shows 5100-5200 when it starts to surge. I know this motor should be able to run at 5800 RPM. Any other ideas would be great.

[evanmcleod88]

i had this same problem and after several hundred dollars later. it was the bushing on the big roller for the throttle.it looked fine but had side play when touched. just something to look at. it' the big roller above the fuel filter.

[Triton19x2]

I had an intermittent FUEL injector a few years back. It did not act up long enough at any single time to throw a code. This surge was only about 100 RPMs but before this I had a 1000 RPM surge that was the low pressure fuel pump and motor would only get to 3500 RPMs. Not sure this is what you are experiencing.....

[Helo-md]

Ok, pulled out all the stops and pulled everything out that can be replaced. while checking the plugs I noticed that the mech didn't gap them, they were all set to .025! My merc book states they should be at .038. Replaced everything with new parts and will run on Wed for the practice for the Lucas Oil at Lake Mead. I hope this is it, if not i'm afraid it could be injectors or the reeds up front.

[EuropeanAM]

Reeds and/or injectors are a possibility- but I personally suspect there's a LOW PRESSURE fuel delivery problem (low pressure pump has debris in it's screen, low pressure pump failing, or possibly the DEFLECTOR for the fuel return line is MISSING/DAMAGED).

Good idea to try and verify LOW PRESSURE fuel pump pressure when the surge is occurring... also Air/Fuel Pressures at the rails. Results there may help to narrow down the field of "possibilities".

[bitsy bug]

sounds like the same as mine....it was the lower fuel pump..

[Helo-md]

Just rebuilt the fuel pump, as questioned before, would the plug gap cause this problem?

[Savage]

Just rebuilt the fuel pump, as questioned before, would the plug gap cause this problem?

It doesn't help.....What are the CURRENT maximum RPM's that the motor can produce at wide open throttle?

[Helo-md]

5100-5200 and then starts to surge