Running really rough after long runs

[J hickman]

New member, longtime lurker. I've been battling my mercruiser for the last year and I'm running out of options..

I've got a 2588 seamaster with a 2000 mercruiser 5.7 EFI, TBI serial # 0m034934. Engine has 450 hours.

So for the last year I have been experiencing all kinds of issues after a relatively long run I would say after 30 to 50 minutes of 3/4 throttle or cruising speed around 25mph. Usually I will hear a pop or backfire then shortly after I will have really rough runability. The best way I can describe it rough idle, surging, hissing or sucking sound from the TBI. Occasionally the boat will not re- start immediately but after a long cooldown it will fire right back up and good for another run. Once it did a full instant shutdown at cruising speed.

I have also found when it will not restart I have pulled the fuel filter off and found the canister to be 1/2 empty. I have topped the filter back off and been back to the races.

So the boat had bees at the shop 5 times and they come up with something to fix but never complelty solved the issue. I've had 2 coils, plugs, wires, cap, rotor, 3 fuel filters, redone the fuel filter housing, the tps, had the floor taken out of the boat for inspection and adding another vent line. Checked and cleaned the pickup, fuel pressure regulator, new manifolds and risers. Compression test done all within the last year.

I was told the fuel pressure was good,spec is 30psi from what I gathered. but I got my own guage set up to verify and I was reading 43psi all day??

I also noticed today that my engine temp never got much more than 140. I was messing with the engine and I noticed that even when warm the throtttle body would never open up when I opened the throttle. That doesn't seem right to me?? With the engine off the throttle body would open up with the throttle lever.

I did a slow motion video of the spray pattern and it looked very uniform and cone shaped

Hopefully one of you guys can help me out and give me a direction!

 

[J hickman]

I took a couple videos that I think would help but I cant seem to upload them, do I need to talk to an administrator?

 

[J hickman]

Bump

 

[Rick Stephens]

I think you have to have 4 posts before you can upload a pic or vid. Probably easier to just post a link to your video if it is on utube.

By your description, when this problem occurs you are still maintaining over 30 PSI on your fuel pressure gauge? That would have been my first guess. Then blocked vents on the tank, which was doubled up to be sure, but not the issue anyway if you are maintaining fuel pressure. Coil is a good guess since it can be reactive to heating. Shop replaced it. I don't know enough about the MPI to go wherever next is. Sorry. Some realy good techs hanging here, one of them will nail it down for you.

 

[J hickman]

I think you have to have 4 posts before you can upload a pic or vid. Probably easier to just post a link to your video if it is on utube.


By your description, when this problem occurs you are still maintaining over 30 PSI on your fuel pressure gauge? That would have been my first guess. Then blocked vents on the tank, which was doubled up to be sure, but not the issue anyway if you are maintaining fuel pressure. Coil is a good guess since it can be reactive to heating. Shop replaced it. I don't know enough about the MPI to go wherever next is. Sorry. Some realy good techs hanging here, one of them will nail it down for you.

Yea fuel pressure never dropped below 40 psi

I went as far as running around without a fuel cap to ensure no venting issues, now I have 2 vent lines and a new fuel cap.

 

[J hickman]

https://youtu.be/MA8DVgikx-w

https://youtu.be/nyL75yaqkOg

https://youtu.be/9b83NMnBw5c

 

[Rick Stephens]

If the pattern looks good, that is as much diagnosis you can do from just looking at injector spray. Seems to me about the only thing you have left to consider is a possible ECM problem, and I don't know how to evaluate or test that, never tested a Chevy TBI system.

 

[J hickman]

Bump. My next move is to try and check vacuum pressure and then I am thinking ignition module?

 

[Silverbullet555]

Get tech to go out with you and data log when you make the problem happen.

 

[CamaroMan]

could either be heat building up slowly, an erratic thermostat or possibly - not a pro tech just trying to help out. long runs could be heat soak into a coil or something? have you checked for vapor lock in fuel tank? building up pressure over time and eventually too hard for pump?

just throwing out ideas here - ecus not my thing tho

 

[J hickman]

could either be heat building up slowly, an erratic thermostat or possibly - not a pro tech just trying to help out. long runs could be heat soak into a coil or something? have you checked for vapor lock in fuel tank? building up pressure over time and eventually too hard for pump?

just throwing out ideas here - ecus not my thing tho

Yea I was thinking heat soak so I moved the blower hose up to pull hot air out and I added some vents to make sure I had plenty of circulation, has not made a difference.

My engine runs at 140 and from what I understand that is low. I have the 160 thermostat in the garage waiting to get installed. So I think you may be onto something with the t-stat.

I also put another coil in just to be sure .

As far as vapor lock In the the fuel tank goes, I have been through that. Pulled the floor, inspected and checked all hoses and fittings. Added another vent line just to be sure. Even ran without a gas cap. Replaced the old gas cap with a new one.

 

[Rick Stephens]

Heat is typically not something to worry about. If your cooling system is working correctly you have nearly unlimited cooling. Things just don't get hot in the engine compartment, not like they do in a car or truck. I would not be worried about the 140 reading either. That is a common boat motor temp range. A little more efficient at 180-190 but unnecessary.

 

[J hickman]

Thanks Rick

 

[CamaroMan]

dont put in a 160 - salt/raw engines crystalize at 160 - bad move, use a 140.

I mentioned heat soak cos a failing elec issue will be prone to heat soak, even if your engine is running at the right temps. Whats your timing curve look like?

 

[J hickman]

dont put in a 160 - salt/raw engines crystalize at 160 - bad move, use a 140.

I mentioned heat soak cos a failing elec issue will be prone to heat soak, even if your engine is running at the right temps. Whats your timing curve look like?

I was considering putting a BBQ temp guage in the engine bay to see if that had a correlation. What temp do you think I should be looking for?

 

[CamaroMan]

well if it stays under 180 i think ur good - from there you would have to try figure out the original issue. I was just mentioning using a 160 for raw/salt water is bad.

 

[J hickman]

Do you guys think this could be a sensor that is failing?

Anyone have a list of sensors or components that could be causing the issues seen in the videos I took?

I am thinking I should replace every sensor that is on that motor.

 

[alldodge]

5.7 EFI, TBI serial # 0m034934. .

after a relatively long run I would say after 30 to 50 minutes of 3/4 throttle .................. hear a pop or backfire then shortly after I will have really rough runability.
................. Occasionally the boat will not re- start immediately but after a long cooldown it will fire right back up and good for another run.

Once it did a full instant shutdown at cruising speed.

I have also found when it will not restart I have pulled the fuel filter off and found the canister to be 1/2 empty. I have topped the filter back off and been back to the races.

.... boat had bees at the shop 5 times and they come up with something to fix but never complelty solved the issue.

What are bees at the shop?

I've had 2 coils, plugs, wires, cap, rotor, 3 fuel filters, redone the fuel filter housing, the tps, had the floor taken out of the boat for inspection and adding another vent line. Checked and cleaned the pickup, fuel pressure regulator, new manifolds and risers. Compression test done all within the last year.

You need to stop taking your boat to the current shop, they are just throwing parts at the problem and have no clue how to fix it

I was told the fuel pressure was good,spec is 30psi from what I gathered. but I got my own guage set up to verify and I was reading 43psi all day??

I also noticed today that my engine temp never got much more than 140. I was messing with the engine and I noticed that even when warm the throtttle body would never open up when I opened the throttle.

The throttle plate opens all the way with the motor OFF, but does not open all the way when the motor is running?

Fuel filter 1/2 empty, says your pump is not able to keep fuel flow requirements. This could be pump, anti-siphon valve, restriction in tank pick up, lines or fittings.

Looking at your vid I'm seeing the injectors firing at different times and not sequential. This is not to say that what I'm seeing is not an optical illusion. Thing about vids is they do not show enough frames per second so for example, seeing a prop spinning can look like the prop is rocking back n forth

 

[J hickman]

What are bees at the shop?

Boat has BEEN at the shop 5 times.

You need to stop taking your boat to the current shop, they are just throwing parts at the problem and have no clue how to fix it

I agree with you 100%

The throttle plate opens all the way with the motor OFF, but does not open all the way when the motor is running?

I think that was a bad observation on my part. After looking at the throttle body again I dont see how it would be possible for that plate NOT to open up with the throttle cable. My bad.


Fuel filter 1/2 empty, says your pump is not able to keep fuel flow requirements. This could be pump, anti-siphon valve, restriction in tank pick up, lines or fittings.

what is the best way to check this? This situation occurs rarely, when the engine will not restart. Out of the last 15 times I have had the boat out, usually the engine will continue to run, just runs like crap. I normally start the kicker and run on that for 30 mins. The kicker will start right up and it is plumbed into the same fuel filter as the main engine. I removed the kicker from the same main fuel filter thinking that possibly I was pulling air through the kicker and hooked it to a separate fuel source. I had the same result so I plumbed it back into the main filter. Yes the kicker has a inline shutoff valve, and the results have been the same with the valve open or closed.

I was reading somewhere about putting a piece clear hose in the fuel line to check for air bubbles. do you think this would help eliminate any possible issues.


Looking at your vid I'm seeing the injectors firing at different times and not sequential. This is not to say that what I'm seeing is not an optical illusion. Thing about vids is they do not show enough frames per second so for example, seeing a prop spinning can look like the prop is rocking back n forth


What if I took a video and slowed it waaaaay down with video soft ware, could we confirm one way or another?




Thanks for your help

 

[alldodge]

If I took a vid and slowed it waaaaay down could we know for sure if it's injecting correctly? I could compare when engine is cold vs. hot?

Thanks for help

The vid may not work, but you looking at it would be better.

My thought is your running out of gas mainly because your filter was half full. So tis is a restriction, vacuum, etc as mentioned above