Fuel Vent Question

[jbourne210]

First the data:

2005 Mercruiser 4.3 MPI, 78 hours, 0W041707
2005 Stingray 195 RL
Turning Point Aluminum 4 blade Prop, 14 X 19, 21501930

Background:
Had trouble meeting the recommended 4400-4800 WOT rpm this last weekend. I never run her there, and rarely have an opportunity to open her up due to the choppy lake I take her to. I made no more than 3950 (based on boat tach), at about 43 mph (GPS based) Noticed a slight vibration in boat that, last year, I had attributed to a possible U-joint issue. But after the run, I noticed the vibration at anything over 1800 RPM. Other than that, the motor purrs, is easy to start, and has had zero backfires or anything of the sort. The boat had sat for a long time prior to me owning it, and after reading through the ADULTS ONLY sticky, I thought maybe I had a clogged vent line. After looking into it, I found the line may have been pinched a bit under the fuel filter. I may have fixed the problem, I'll know tomorrow when I take her out. I've also purchased a new set of plug wires (I'd changed the plugs last year), but haven't put them on yet. Testing one that at a time, and all that. I do have spark at all cylinders, and old school tested the plugs by pulling one at the distributor and listened for change in RPM, which was noted.

Question:
The vent hose feeds right back into the fuel fill hose. Where, exactly is the relief from fuel pump vacuum coming from, because, as far as I can tell, it's a sealed system. Unless my fuel cap has a vent in it, which I can't see. How does that work??

Thanks in advance y'all!
[h=1][/h]

 

[GA_Boater]

A fuel filler with the vent attached is venting the tank. A blocked vent will cause the motor to quit after a short running time because the fuel pump can't suck fuel. If you open the filler and hear a woosh sound caused by breaking the vacuum, you have a blocked vent.

You say the motor keeps running, so starting with simple things - How fresh is the gas and has the fuel filter been changed?

A truism - Most fuel problems are ignition related and most ignition problems are fuel related. A never ending circle, so issues like yours aren't always easy to solve.

I would start with this link from the Adults Only stickie - https://forums.iboats.com/forum/eng...6-list-of-possible-causes-of-low-wot?t=295070

 

[alldodge]

I noticed the vibration at anything over 1800 RPM.

Look at the prop real close and see if you have a blade a little off.
Check for play on the prop shaft with prop removed.

When was the last time the drive was removed?
Alignment checked?
Gimbal bearing?

 

[Bondo]

I thought maybe I had a clogged vent line.

Ayuh,.... What Vent,..??

The fuel tank vent,..?? Truly doubt it,.....

Have ya inspected the Contents of the fuel filter, for anything but clean fresh gasoline,..??

 

[QBhoy]

Yeah. Something way wrong there. That boat and the 4.3 mpi should be a quick machine and especially with a 19”. It should be on the limiter even.
As advised check the simple things. Really hard to tell not being on the boat myself, but after the obvious fuel delivery stuff is checked (as Bondo says check filter) and prop is inspected...then you need to look towards the more likely MPI related problems. We can go into that once the simple stuff is checked and ruled out.
My gut is it’s unlikley to be a vent problem. If anything fuel related it’s more likely to be water in the fuel or a clogged pick up.
Ad is correct in thinking towards the prop with the vibration you mention, but for the prop to see the rpm and speed drop you mention....god knows what it would be like. If anything the RPMs might even rise. You would know all about it anyway.
Good luck

 

[QBhoy]

Ok...I’ll say it....change the diz cap and rotor. Probably goosed...especially when you say it sat for a while. If nothing else, it’s one less mpi thing to go wrong for a while at least. Famous for gathering moisture and showing poor starting, poor mid range, intermittent wot and/or total failure ! Mine fails every 2 years on average and always shows its hand right after winter storage.

 

[Maclin]

QBhoy has a good piece of advice. I thought you had changed the electrical pieces in a recent tuneup, but reread and just saw that you have new sparkplug wires on deck, no recent tuneup.

My year-old-to-me (2002 4.3MPI) boat had an older cap and rotor in the box it's replacement came in that I found in the rear underseat storage. The box had "Not yet" handwritten on it. I decided to replace the cap and rotor, and in my estimation the one I replaced had reached the "Ok, Now" stage. This boat was kept covered on a lift in a slip with a roof, so a moist environment. I also found some weird green corrosion around the fuel filter base when I replaced the filter. Sanded all that off and hopefully it will not return, I store it in a pull-thru covered stall in a dry yard. The battery terminals were also corroded, looked like they had been recently cleaned though, mostly surface gack. I roughed those up again, will see how long they resist corroding this time.

 

[JoLin]

I'll chime in on the check/change the distributor cap advice. My 2014 Merc reman engine started to misfire at the beginning of its second season. Pulled the cap and the contacts were loaded with corrosion. Brought it to the machanic who installed the engine and he handed me a Sierra. Said the corrosion has become a common problem with newer Merc caps- they either stopped coating the contacts with brass, or made the coating thinner (can't remember which) and they corrode like crazy. Sierra still coats them. The Sierra cap has been on for 3 seasons with no issue.

Don't know where you're located, but 3-4 years ago, the main northeast Merc parts distributor got a run of faulty dizzy caps. Boats were breaking down all over the place. Most of them failed right away, tho.

My .02

 

[jbourne210]

Sorry for the long time in replying, but right about the time I was digging into this, work got in the way, and I'm just now getting back to figuring this out. And thanks for your replies!

So, per y'alls sound advice, I changed out the dizzy and rotor, and wires and plugs as well, and took her out for a spin this morning.

She ran perfectly! For about 20 minutes. Then I could feel a vibration again at any RPM over about 1200. And some loss of power as well. However, she starts within a second and just purrs at idle, with no backfires at any rpm. Put the young'uns in the water to swim about, while I messed with the motor.

With the engine compartment open, I turned the key on, just to make sure the fuel pump sounded okay. It didn't. The best way to describe it would be a small motor where the bushing/bearing was going bad. Very inconsistent sound, and not the way I've heard automotive fuel pumps pressure up.

SOOOO, I'm thinking that my pump may be on it's way out. And that maybe after a bit of running the pump gets too hot, and can't deliver the proper fuel pressure.

With that in mind, I'm going to try to locate a pressure guage, and monitor rail pressure. Additionally, I'm considering putting some clear fuel tubing in place prior to the pump in order to check for air bubbles. I'm still thinking that I need to change the fuel pump; it just sounds ugly. I'd rather be on the shore wishing I was out there, then out there, and wishing I was on the shore, you know?

What are y'alls thoughts on my plans?

And thanks again for all of your advice!

 

[Bondo]

Ayuh,.... Have ya checked the Contents of the fuel filter for anything but clean fresh gasoline yet,..??

 

[jbourne210]

And along those lines, is there an Airtex equivalent for the mercruiser pump, part number? [h=1]861156A1[/h]

 

[alldodge]

And along those lines, is there an Airtex equivalent for the mercruiser pump, part number? 861156A1

Yes its E11004 and your plan looks good.

 

[Scott Danforth]

No way can you plumb clear fuel line in an EFI system. Pressures way too high

You can read fuel pressure with a guage

 

[jbourne210]

Bondo, yes sir. I should have mentioned that. I pulled the filter, and poured the contents into a clear mason jar. Not a drop of water, nor was there any debris of any kind. I did notice that the filter was completely full though. The level was about 3/4" from the top of the filter. I guess I could have spilled some out, by I don't think so. Additionally, when I put the new one on, I added some Mercury Quickleen #2 (maybe 3 ounces?) to the filter before I topped off the filter with fresh fuel.

And Scott, I was thinking that I could tie in prior to the high pressure pump, maybe in between the filter and the pump, or at least between the tank and the filter. See if I could locate an air leak. Of course, I could CAUSE an air leak as well....

I'm off to grab some guages, and I'll also see if I can get a video added to accent the noise of the pump...

Thanks y'all!

 

[jbourne210]

Okay, so I added a short video showing the noise. To be honest, it sounds better than it did yesterday. In fact, on the second turn of the key, it was the first time I've heard it (recently) not make that shuttering noise. But to me at least, it doesn't sound right.

Additionally, when I uncovered her this morning, there was a pretty heavy fuel smell. My engine compartment always smells faintly of fuel, but this seemed a bit more than I'm used to. Thoughts?

 

[jbourne210]

Noticed a typo in a previous post. It should have read "I did notice that the filter was NOT completely full though."

Sorry about that!

 

[tank1949]

First the data:

2005 Mercruiser 4.3 MPI, 78 hours, 0W041707
2005 Stingray 195 RL
Turning Point Aluminum 4 blade Prop, 14 X 19, 21501930

Background:
Had trouble meeting the recommended 4400-4800 WOT rpm this last weekend. I never run her there, and rarely have an opportunity to open her up due to the choppy lake I take her to. I made no more than 3950 (based on boat tach), at about 43 mph (GPS based) Noticed a slight vibration in boat that, last year, I had attributed to a possible U-joint issue. But after the run, I noticed the vibration at anything over 1800 RPM. Other than that, the motor purrs, is easy to start, and has had zero backfires or anything of the sort. The boat had sat for a long time prior to me owning it, and after reading through the ADULTS ONLY sticky, I thought maybe I had a clogged vent line. After looking into it, I found the line may have been pinched a bit under the fuel filter. I may have fixed the problem, I'll know tomorrow when I take her out. I've also purchased a new set of plug wires (I'd changed the plugs last year), but haven't put them on yet. Testing one that at a time, and all that. I do have spark at all cylinders, and old school tested the plugs by pulling one at the distributor and listened for change in RPM, which was noted.

Question:
The vent hose feeds right back into the fuel fill hose. Where, exactly is the relief from fuel pump vacuum coming from, because, as far as I can tell, it's a sealed system. Unless my fuel cap has a vent in it, which I can't see. How does that work??

Thanks in advance y'all!
[h=1][/h]

Mud-dobbers!

 

[alldodge]

Its is a bit noisy but getting pressure should give some good info on pump status. The filter a bit low could be the pump is working hard, maybe from a restriction.

 

[jbourne210]

My thoughts as well. I may pull the vent tube off her, and double check for restrictions and/or debris. Additionally, I'm going to try the anti-siphon valve. Although, it seems to be pretty stuck. Not a lot of room to work with in there either. Oh, and it's raining. lol

If I do end up replacing the fuel pump (most likely), has anyone ever done it WITHOUT pulling the engine? It's pretty buried in there...

 

[alldodge]

If I do end up replacing the fuel pump (most likely), has anyone ever done it WITHOUT pulling the engine?

ts tight but there is no reason to remove the motor to do it. Did my own not long ago