2007 Merc 4.3L - Freeze damage or other issue?

Somehow on the last winterization only 3 of the blue drain plugs were removed and the 2 furthest to the back were left in place. I know, I know, not good. Anyway, it popped the front 2 casting plugs. Those were replaced and everything seemed to be fine. There are no external water leaks or water in the oil. For the most part she runs great, but is having an intermittent bogging issue which is new this year, and seems to be getting more frequent. The accelerator pump is squirting fuel as it should. The bogging issue has always occured after we have been running then shut the motor off, then get under way again. The motor starts back up just fine. I hit the throttle and about the time she starts plaing out it will just die (still running but barely). I don't think it is going lean because if I pump it, it just continues to barely run. Sometimes if I just take it back to neutral, then back in gear, it will accelerate fine after that. Some other times, I have had to slowly bring the rpm's up while in neutral and once she clears out, everything is fine after that until after we shut it down again. Although it does not usually happen every time it has been shut down, this last trip it was very frequent as opposed to the first time out this year where it only happened once.

It acts like it is flooding out some how, but if it was happeing while the engine was off, it would not start and run fine until under a load. I am starting to worry now about if water could be working its way through a crack somewhere.

Does anyone know how high the water level in the block is with those 2 back drain plugs in? This is the only year we have not ran antifreeze through it and of course also happens to be the only year any drain plugs have been missed!

Any other ideas? I am generally pretty good at troubleshooting engine issues but the timing of when the bogging occurs, has me baffled. I have not removed the spark plugs yet to see if they offer any clues.

Thanks.

Re: 2007 Merc 4.3L - Freeze damage or other issue?

I hit the throttle and about the time she starts plaing out it will just die (still running but barely). I don't think it is going lean because if I pump it, it just continues to barely run. Sometimes if I just take it back to neutral, then back in gear, it will accelerate fine after that.

Click to expand...

Howdy,


Welcome aboard. Well, it sounds like you dodged a bullet on the freezing. Usually, if a core plug pops out, there'll be a crack in the block either internally or eternally.

The bogging issue is most likely related to fuel starvation if everything else is "ok"..

Ensure that you have check/replaced plugs, filters, and maybe dist cap and rotor etc (normal "tune-up" stuff)

You might also consider checking the fuel pump and fuel pickup/screen.


Regards,



Rick

Re: 2007 Merc 4.3L - Freeze damage or other issue?

With blue plugs, am I right that it is a MPI 4.3?

Re: 2007 Merc 4.3L - Freeze damage or other issue?

jkust said:

With blue plugs, am I right that it is a MPI 4.3?

Click to expand...

No, it is a 2bbl carb.

Re: 2007 Merc 4.3L - Freeze damage or other issue?

HT32BSX115 said:

Howdy,


Welcome aboard. Well, it sounds like you dodged a bullet on the freezing. Usually, if a core plug pops out, there'll be a crack in the block either internally or eternally.

The bogging issue is most likely related to fuel starvation if everything else is "ok"..

Ensure that you have check/replaced plugs, filters, and maybe dist cap and rotor etc (normal "tune-up" stuff)

You might also consider checking the fuel pump and fuel pickup/screen.


Regards,



Rick

Click to expand...

Yeah I am keeping my fingers crossed. I check the dipstick regularly to watch for any signs of water. Thanks for the welcome, I am a regular reader and thank you guys for the wealth of information. I also want to apologize to Don S. because he has such a good write-up on winterizing, which will be followed TO THE T from now on!

Last night I was thinking about my statement that I did not think it was going lean because pumping the throttle did not help, and I realized I missed a critical point, that if the carb was running dry, pumping would have no effect. So you may very well be correct that it could be starving. It still boggles me that it would only happen following a shutdown though. I have not really read anywhere that these later year engines are prone to vapor-locking, but is that maybe a problem with these? That would explain why it is happening after a shutdown when things are nice and toasty, and possibly why it seems to be happening more that earlier in the year. Why this has not happened in previous years, is still a good question if it were vapor-locking, unless the 10% ethanol they are now using is causing it.

The fuel filter/separator is new this year and I checked it a few weeks ago for water and there was none.

Re: 2007 Merc 4.3L - Freeze damage or other issue?

could you be getting a vacuum in your fuel tank from a plugged vent line. Thus it starves after running a bit. Take your fill cap off so you can't get a vacuum and see if you get the same problem. If not, then your not venting your fuel tank. Or even run it off a separate portable fuel tank to isolate any issues from there back to the fuel tank.

Re: 2007 Merc 4.3L - Freeze damage or other issue?

Pull out a plug and see how it looks before grasping at straws.

V

Re: 2007 Merc 4.3L - Freeze damage or other issue?

FishHog said:

could you be getting a vacuum in your fuel tank from a plugged vent line. Thus it starves after running a bit. Take your fill cap off so you can't get a vacuum and see if you get the same problem. If not, then your not venting your fuel tank. Or even run it off a separate portable fuel tank to isolate any issues from there back to the fuel tank.

Click to expand...

Hmmm, I was taking the gas cap off to check the vent. I go to looking to see how the cap gets vented and it has 4 little notches beind the O ring. Nothing was blocked, but then a bell went off. Lately I have been putting the cap on quite tight with the little tool, and I wonder if that was deforming the o-ring enough to seal those little notches. I just lightly tightened the cap this time, and last trip out, the problem did not occur. Not sure if it might just be that the weather was cooler or if I really was getting a vacuum in the tank. The vacuum theory would correlate with why it only happens after running for a while. I guess only time will tell.

Thanks for all the ideas.

Re: 2007 Merc 4.3L - Freeze damage or other issue?

mudsnowh2o said:

Hmmm, I was taking the gas cap off to check the vent. I go to looking to see how the cap gets vented and it has 4 little notches beind the O ring. Nothing was blocked, but then a bell went off. Lately I have been putting the cap on quite tight with the little tool, and I wonder if that was deforming the o-ring enough to seal those little notches. I just lightly tightened the cap this time, and last trip out, the problem did not occur. Not sure if it might just be that the weather was cooler or if I really was getting a vacuum in the tank. The vacuum theory would correlate with why it only happens after running for a while. I guess only time will tell.

Thanks for all the ideas.

Click to expand...

Ayuh,... The Vent is a 5/8ths" hose on top of the tank,...
Check it from the Tank end....

Re: 2007 Merc 4.3L - Freeze damage or other issue?

If it starts doing it again, run your blowers constantly while underway and for at least 10 minutes when shutdown and see if it goes away. Manufacturers are sealing the doghouses pretty good and it could very well be vaporlock. If it helps, you'll know what to look for.

Re: 2007 Merc 4.3L - Freeze damage or other issue?

Bond-o said:

Ayuh,... The Vent is a 5/8ths" hose on top of the tank,...
Check it from the Tank end....

Click to expand...

I do still need to check the tank end as well, but that 5/8 hose runs out to a vent which is behind the filler cap. The only way this vents when the cap is on, is through 4 small notches in the cap by the O-ring. I am pretty sure by looking at it, that it would be possible to deform the o-ring enough to block those vents if the cap is tightened too much. The neck and cap I have is the Perko 540.


Is it possible that if it were to create a vacuum in the tank while underway, that the vacuum could draw some of the fuel out of the line/filter/float bowl (that scenario would certainly match my symptoms), or are there check valves that would prevent that? It seems to me that the anti-siphon valve would prevent any flow in that direction.