4.3L MPI V6 Vapor Lock (again)!

Start swapping stuff until the problem stays with the swapped part (well, I don't have any better suggestions other than sell the boat and get a different one).
 
ZZ13 said:
Start swapping stuff until the problem stays with the swapped part (well, I don't have any better suggestions other than sell the boat and get a different one).
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I would start with the blowers......there cheap and it seemed to work for me
 
ZZ13 said:
(well, I don't have any better suggestions other than sell the boat and get a different one).
Click to expand...

Oh that very thing has crossed my mind more than once! Especially when it first happens. Thankfully my head has cooled a bit. Plus, I have a lot invested in this boat now and if I were to do what you say, I'm sure it would have it's own set of issues to deal with...

kkalsch said:
I would start with the blowers......there cheap and it seemed to work for me
Click to expand...

I think I am going to replace the existing blowers. They could very well just be worn out and not moving as much air as they used to.

I also read in the Mercruiser vapor lock tech bulletin (I'm going to attach it to the first post in this thread), that 90deg. bends in the fuel line should be minimized and there should be no more than 2. Well, there are (I think) 5 in my line! So I may re-route with smoother bends.

Thanks!

Tom
 
How could you possibly have vapor lock at 130 deg. ? That vapor would have long condensed back to fuel way before that temp.

Why aren't both engines affected by this vapor lock theory.

Me thinks you have a different issue.
 
I have looked thru all the wiring diagrams i have and have yet to see where the safety valves are powered from. I put a test light on both of mine while the engines were running and expected voltage, but didn't. Anyone ever check theirs?
 
I too had this problem, I changed the fuel filer 90 degree fittings to straight, changed the thermostats from 160's to 140's and haven't had the issue since.
 
must be vapor locking in the fuel pump on the stringer. That is if this really is a vapor locking issue. Is there a return line? If so were is it?
Pressure raises the boiling point. Also injectors opening and should release any air (vapor gas) in the system rather quickly if there is no return line in the tank. If there is a retrun line to the tank. The vapored gas will go there if fuel pressure is high enough to go pasted the regulator like it should. If not, vapor lock in fuel pump or just bad pump.
You really need a pressure gauge on the fuel rail when this happens to see what your pressure is. If your pressure is dropping off when this happens, chances are is vapor locking in the fuel pump. If pressure is stay at factor spec. Chances are it's not vapor locking at all.
 
susanandlance said:
I too had this problem, I changed the fuel filer 90 degree fittings to straight, changed the thermostats from 160's to 140's and haven't had the issue since.
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Glad to hear that. I'm thinking of removing some of the 90 fittings too. Do you have a part # on the 140deg. thermostat? I found one that looks like it would fit but it doesn't list my engine.

If I don't have vapor lock, I'd sure be open to other suggestions!? But all signs point to it. And both engines are affected, pretty much equally. Difference this time was that I had trolled with one engine for several hours, causing the possible imbalance.

The fuel pump is mounted on a bracket (and inside a plastic box) that is bolted to the engine mount directly beneath the engine. There is a fuel return line back to the fuel filter. Only a single line from tank to filter. Fuel pump on starboard side is brand new 2012.

I'm going to run it this weekend and bring it back home. Hopefully get them to vapor lock. Then I'll hook up the fuel pressure gauge and see what's going on.
 
The fuel pump is mounted on a bracket (and inside a plastic box) that is bolted to the engine mount directly beneath the engine. There is a fuel return line back to the fuel filter. Only a single line from tank to filter. Fuel pump on starboard side is brand new 2012


Don't like the part about the return line going back to the filter. If the gas starts to boil, The air or boiled gas is going right back to the filter and into the fuel pump. This return line should go to the tank and there would not be this problem.
 
Gunn, I don't have part#, I just told the mercruiser parta guy to gibe me 140's and then I installed them, I replaced only the 90 degree fittings that enter the fuel/water sep filter with straight ones I got at ACE hardware. I read about this fix in a Bryant boat website on the 4.3 engine and thought I'd. Give it a try. Both of my engines were vapor locking, not anymore
 
Lance it only worked because you stepped up tot the plate and got that big ole Chevy diesel!
 
bigblockcutlass said:
Don't like the part about the return line going back to the filter. If the gas starts to boil, The air or boiled gas is going right back to the filter and into the fuel pump. This return line should go to the tank and there would not be this problem.
Click to expand...

Good point; so another design flaw...go figure.

Bucit said:
Lance it only worked because you stepped up tot the plate and got that big ole Chevy diesel!
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Hey, I have one of those too, but it isn't helping me any! :smt001
 
Gunn said:
Good point; so another design flaw...go figure.



Hey, I have one of those too, but it isn't helping me any! :smt001
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Me too! Maybe that's why I've been good so far. (knock on wood)
 
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