Mercruiser 5.7 Surging

[kyles609]

I've spent two weeks trying to research forums and troubleshoot with my Seloc manual but I'm still having an issue. I bought a 96 Bayliner 2250 SS this summer and it ran great when I picked it up. After trailering around and a tank of gas later I'm getting a pretty consistent but slight surging at just about any rpm once my speed is steady in cruise. I also get one solid hiccup when I go from idle RPM in gear to full throttle. I'm able to pull skiers but sometimes it creates slack in the rope due to the surging at cruise. The boat starts and idles perfect and doesn't run rough, the only time I crank a little extra is when I shut down for a bit when its hot and start back up.

From reading my manual and other forums I felt I should start with troubleshooting the fuel over the ignition since my surge seems so slight and I could test pretty quickly. I rented a fuel pressure tester and got it hooked up after some fitting issues and it shows 5-6 Psi at all different Rpm's with no load on it. I'm going to go out in the morning and see it under a load.

Some other things I've checked with fuel - Pulled the brand new fuel/water separator and drained it and found zero water and zero sediment so I reinstalled. I pulled the pickup tube to check the screen and it was 100% clear of debris. I took of the anti siphon valve and played with it and sprayed a lot of carb cleaner in there but everything seemed to move freely. I don't have an external tank to test on but aside from bypassing the anti siphon valve I feel I don't need to try the external tank.

I've also taking off all the plug wires and dist cap wires one at a time and put back on to make sure they were all secure.

I'm going to check fuel pressure under a load at different RPM's tomorrow if it isn't raining and will try it with the fuel cap open to make sure the vent isn't blocked.

Can anyone give me some more items to check with the fuel when I go out or some areas with the ignition to begin with this? Has anyone had this issue that I'm describing with a concrete answer?

Thanks for any help with this issue, any help would be great.

 

[alldodge]

Howdy

I see it being the carb, and probably needs cleaned out.
What carb do you have?

 

[Bondo]

I see it being the carb, and probably needs cleaned out.
What carb do you have?

Ayuh,.... Welcome Aboard,..... The carb is 'bout the only thing ya don't mention,.....

 

[kyles609]

Yeah, maybe I'll have the carb done at the end of the season. Not sure which 2 barrel carb I have. Anything I can clean or spray in there now to try and clean it out? I had run a can of sea foam in it for a few hours but didn't see any change. I dumped it into a half tank of gas.

 

[alldodge]

Would need your serial number to verify, but with it being a 2 barrel its probably the Merc carb
http://www.mercruiserparts.com/bam/subassembly/31835/1014/180

 

[drexton311]

I am currently fighting through a similar issue. Do you have any trouble putting gas in the boat? If so, check your tank vent hose.

 

[NHGuy]

You can check for a clogged fuel vent by loosening the fuel fill cap to see if it runs better.

Sometimes you can solve little carb leaks by snugging the carb hold down bolts where they attach to the intake. If you have a torque wrench it's better. the spec is 132 inch lb which I believe is 11 foot lbs. Or without a torque wrench, snug but don't go all gorilla on it.
Look straight down at the carb from above, Check that the assembly bolts which hold the carb together are snug. Including looking through the choke flap.
Intake to head leaks can act badly. The intake manifold bolts are either 18 or 35 foot lbs. The engines after 97 use the lower value.
Your choke isn't disconnected and floating around freely is it? That would affect running.
If it's none of that come back and let us know what your engine serial # is. Perhaps we can walk you through a carburetor float height check.

 

[kyles609]

I am currently fighting through a similar issue. Do you have any trouble putting gas in the boat? If so, check your tank vent hose.

No problems putting fuel in but I am going to check it with the fuel cap cracked once it stops raining here in Ma. Thanks


Thank you Everyone else with input and for posting. I called the previous owner and he got me in touch with the mechanic who did work on it 2 months ago before he sold it to me. They did pretty much all of the ignition - Cap, Rotor, Plugs, Ignition Coil, Ignition Module and they also rebuild the Carb - All done end of June this year so not long at all.

They are leaning to fuel pump but advised to bypass anti-siphon valve for testing purposes and to rule it out.

I found I have a 2 Barrel MerCarb part number 807312 Date stamp is 5402 so I guess it was made in 1995 but recently rebuilt
My engine Serial number is 0F605391 Which tells me I posted the wrong engine size and it's a 5.7 and Not a 5.0

I'll report back once I check fuel pressure on the water today.

 

[NHGuy]

Well, you could put a pressure gauge on the fuel line to see if it gets behind underway. Surging is normally from lack of fuel. Yours could also be from that. Most of the things I recommended are easy to check. You can also spray some carb cleaner in those spots to see if the engine speed changes. Very quick check.

 

[kyles609]

Okay, I just got back from the lake and watched everything while someone else drove. To backtrack, yesterday running it in the driveway I saw about 2-3 psi revving it up to about 1500-1800 RPM's. Today I dropped in the water and was looking for the same fuel pressure and assumed it would drop under a load but I never saw fuel pressure at idle, under a load, or revving in neutral. One time I saw the gauge come off of the lower pin by just a hair but other than that I could not measure pressure. Could I get my boat up to 43 Mph and topped out at 4,00-4100 RPM with no pressure?

When I test rode the boat we had two adults and got the boat to indicate 48 Mph and today I topped out at 43 Mph and 4,000 with two adults again. It still hiccuped once to start off and I actually watched the electric choke partially close while it did that but then it never closed again. I could see plenty of fuel spitting into the chambers the entire time too. It ran smooth at 43 Mph with no surging but anything slower than 40 seems to surge and I swear it doesn't have the same power off the line that it did a few weeks ago.

Could the fuel pump still be bad under these conditions? Any idea why I indicated fuel pressure under no load yesterday but not today? Thanks

 

[Bondo]

Anything I can clean or spray in there now to try and clean it out?
Could the fuel pump still be bad under these conditions? Any idea why I indicated fuel pressure under no load yesterday but not today?

Ayuh,.... Welcome Aboard,.... Carbs need to be completely disassembled to be cleaned, commonly called rebuildin' 'em,....
A rebuilt carb can become Bad again, if poor quality gas is run through 'em again,... even same day,....

I'd guess either the fuel pump is starvin' for gas or dyin',... or yer gauge is beat,......
Checkin' the contents of the fuel filter for anything other than fresh clean gasoline is a good 1st step,....

 

[alldodge]

To start in post one with 5-6 psi and today to see next to 0 psi on fuel pump pressure, there is a gauge, gauges or something else being an issue.

You need to get the pressure up, and with a carb, the only thing to fix this IMO is the pump
http://www.mercruiserparts.com/bam/subassembly/31863/1939/60

Are you seeing in fuel in the clear tube going to the carb, or seeing your oil in the crankcase.

 

[kyles609]

To start in post one with 5-6 psi and today to see next to 0 psi on fuel pump pressure, there is a gauge, gauges or something else being an issue.

Are you seeing in fuel in the clear tube going to the carb, or seeing your oil in the crankcase.

Just a quick update. I have a fuel pump coming today but I really wanted to see a reading and then watch it drop under a load first before swapping. I took the fuel tester off this morning, ran it and then connected the fuel tester and it reads 6psi from idle to 2,000 rpm so now I need to get in the water and try again.

I don't see any fuel in the clear tube coming off the top rear of the carb. It looks like it travels down near the fuel pump. Should I see any?

Also, what do I check for oil in the crank, just proper levels?

Thanks

 

[alldodge]

Should I see any?

No, there should be none seen, if you do your pump is leaking.

The pressure is good, but reving the motor on the trailer is not a good test, hope the water test goes well.

 

[fairshopperguy27]

Just a thought. Check your plugs for any hairline cracks in the white ceramic part. could be shorting out your coil. I had this happen to me once and surging was the symptom. The cracked spark plug actually fried the coil in my case. I learned my lesson on carelessly installing plugs without a rubber lined socket.

 

[NHGuy]

To further explain checking the spark plugs. You can remove one wire at a time and try to wiggle the exposed spark plug ends with your fingers. If cracked they can move a little and feel crunchy, even though the metal base is snug in the head.

 

[kyles609]

Just a thought. Check your plugs for any hairline cracks in the white ceramic part. could be shorting out your coil. I had this happen to me once and surging was the symptom. The cracked spark plug actually fried the coil in my case. I learned my lesson on carelessly installing plugs without a rubber lined socket.

Thanks for the heads up. I pulled all of the plug wires and felt them but none felt crunchy or cracked. I have 8 new spark plugs on the way to replace for the heck of it this week.

I'm trying to get out today to check pressure before I swap the pump but I need some help using the fuel tester since I may be doing something wrong. I put the t-valve on and left the tester off of the shrader valve and started the boat (I've tried it with it already on too but no pressure indicated). I then screw on the fuel pressure pressure tester and I see pressure (6 or 7psi). Then I try to relieve a little pressure with the relief button and the pressure goes to zero and never comes up again under any rpm. If I unscrew the tester and reattach it reads pressure but does the same thing over and over again. I don't feel I'm getting an accurate reading. What am I doing wrong?

To add, while I ran the boat today I started getting the audible alarm on the boat after it warmed up during my test. I had the muffs on with water and engine temp and oil pressure all looked good. I've never hear the alarm except when the engine is not running and the ignition is turned on. I'm guessing I have a big problem.. any thoughts?

 

[kyles609]

My gauge was bad and not showing fuel pressure once attached. I just got one from another auto parts store and hooked it up and it showed about 9psi as soon as I started it. Like I said before, I'll report back after the water test.

 

[alldodge]

The 9 psi is high, would guess the current gauge may have issues.

 

[kyles609]

The 9 psi is high, would guess the current gauge may have issues.

Thanks for the info. I went out to check pressure this morning before a test in the lake (Again!) and I showed 0 Psi. I tried a different tee fitting and got the same. I'm really confused how I got two fuel pressure testers to indicate 0 PSI but my boat goes 40 mph and pulls skiers, although it still surges and hiccups here and there. Also, I showed pressure build perfect yesterday and I was able to relieve pressure and watch it build right back up while the engine was running.

Can the fuel pump really be failed and go 40 mph? I'd really appreciate some help with testing the fuel pressure specifically before I swap the pump and am unable to return it.

Thanks