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40HP EFI four stroke fuel restriction?

J

JRmedphys

New member
Hi everyone...my first post so please bear with...

I have a 2007 EFI four stroke 40HP Merc SN 1C052108 that I have been battling with for several months. Initially I thought it was a fuel delivery problem. Runs great and then at the end of the day (couple of hours of fishing) will lose power and can barely limp in.

Here's what I have done so far:
new fuel tank (had a kinked pick-up)
new fuel line (the existing one was breaking down inside due to ethanol in fuel)
new fuel filter and housing (it was clean and free of any debris from the fuel line)
new lift pump (plastic reed valves were damaged)
new plugs and wires
new ignition coils

The problem persisted. So I went deeper...
removed and cleaned the VST (was pretty clean...including all screens...didn't find any problems...to my eyes)
changed high pressure fuel pump in the VST (at one point during this process the fuel pressure to the injectors was dropping below 42PSI when it would stall out so I though it might be this fuel pump failing...but now I am thinking it is a fuel starvation problem at the VST...see below)
blew out all the fuel lines from the tank to the VST...didn't find anything in terms of blockage/debris.

Still the problem persists. Today, before fishing, I put a vacuum gauge on the input side of the lift pump and confirmed it was to spec according to Merc manual. I did not test the pressure side. I removed the vacuum gauge and put everything back together and then after fishing for a couple of hours and making only short runs, engine ran fine and then it died on the way back to the ramp on a longer run at WOT. This time it would not restart. Primer ball was firm. I changed to a second tank with fresh gas. Squeezed the ball again until firm. Still would not start. Removed the hose at the VST from the lift pump and there was fuel pressure there (fuel sprayed out). I could pump fuel through to this point with the primer ball freely. I put the hose back on the VST and then was able to force fuel into the VST with the primer ball. Once it was firm again, the engine started and I was able to limp back to the ramp.

Throughout all this, has never gone into Guardian. No beeps or tones at all.

Now, today's issues has me thinking there is a problem getting fuel into the VST for some reason but almost like a blockage at the VST. The longer run takes the fuel down in the VST causing it to starve out. I have taken it apart and cleaned it many times and have never found anything blocking anything or gummed up. In fact it looks mint. I can do it again but feel like I am chasing my tail.

When it gets to this state its almost like I can't even force fuel into the VST. I'm thinking VST Float? Needle Valve? What could be causing the VST to prevent it from permitting fuel...even by primer ball.

Thanks for any help.
 
Docksidemarineservices said:
Make sure the fuel cooler on the vst is clear and water is flowing through it.
Click to expand...

Thanks for the response Chris.

Yes the VST fuel cooler is running clean. Put some compressed air through it and everything else is completely unblocked. it stays cool tot he touch when runnings do I am assuming with our low water temps right now that water is flowing and the fuel is being cooled sufficiently. Water is always flowing through the tell tale which (I believe) is being fed from the VST cooler exit.
 
On today's test run, we took a good long run (15 minutes) at WOT and had no issues at all. Engine purred and worked perfectly. We stopped and fished for a while. On our third trip back up to where we started fishing the problem came back.

I first checked the primer ball to see if I could squeeze some fuel into the VST and it was rock hard.

So, I took Paul's advice (post #2 above) and I opened up the VST drain valve. There was fuel but my guess was 1 maybe 2 oz of fuel maximum. Tried using the primer ball again but it was still rock hard. Removed the fuel line to the VST and could then pump fuel freely into a container with the primer ball. Reconnected the fuel line to the VST and maybe got 1-2 pumps until it was pressurized again. Engine would turn over but not start. Waited a few minutes and then the engine started but only had maybe 25% throttle before it would cut out. No alarms. The fuel pressure was all over the place between 28 and 42lbs. Was only able to limp in.

When I got to shore I opened up the VST drain again and there was more fuel this time but not as much as I would expect if the VST was full.

My only conclusion right now is that it has to be the float needle or the seat itself causing a restriction right at the VST. I have looked at the needle and seat many times throughout this process and to my eye it looks fine. I have cleaned it and the seat with carb cleaner a couple of times and blown out the fitting with compressed air to ensure it is clear. There may be something subtle about the needle that I can't see but have it on order anyways. Not an expensive part and I am already several hundreds of dollars into this problem.

Also, while I had the boat in the garage, to rule out any electrical issues, I have checked the stator and the voltage regulator/rectifier and they both test out fine according to Mercury procedures.

It must be a fuel restriction at the VST at this point but I am shocked how good the needle looks (to my eye) to cause this catastrophic and persistent intermittent problem...
 
I cannot imagine that the vlotter needle is that stuk.
Is the first pump (lift pump) working correct?
Is the high-pressure pump leaking pressure into the VST?
When you drained the VST did the fuel flow out by ggravity or was there extra pressure?

You changed/maintained the lift pump, is it mounted correctly?
Valves, fuel lines etc.

It strange that you have a hard primer ball but ONLY 2 oz of fuel in the VST.
Mine has ca. 10-15 oz of volume (40pk EFI 2002)

Hope you can find the issue soon.
 
Hi Paul:

I can't either but that is certainly how it is appearing to behave.

Lift pump is brand new. I have tested the vacuum side and pressure side and it is to Mercury spec. Although lift pump is brand new, I guess it is possible it is defective? I have taken a look inside and it all looks good. I'm not making oil at all so no hole in the diaphragm. Also had clear hose on the VST inlet to confirm no air is getting there.

When I drained the VST, it was gravity only. I have blown out the vent hose and I know for sure it is not blocked and the VST itself is at atmospheric pressure only.

I believe it is mounted correctly. I took a picture before of the orientation and then matched it up. I mean...its pretty hard to screw that one up. Fuel goes in one line and out the other and then the water passes through two connections to the tell-tale.

Believe me...I know how strange this is. Like I said Ive been battling it for over 5 months now and have changed just about every part in the fuel circuit save the needle and the high pressure fuel regulator. When the VST is full I agree there is probably the same volume of fuel present.

I just had a thought...even thought the fuel line from the tank is brand new is it possible that the issue is at the primer ball? I have it mounted vertically as I have heard stories of problems when it is horizontal. I had a vacuum gauge on vacuum side of the lift pump during one of my test runs and everything tested fine to Mercury spec. So I took it off and then later that run the problem came back. But I never set it back up to see if the vacuum had spiked. Maybe I didn't give it enough time to show up? When I was stuck that time, I pulled the fuel line off the VST and was able to pump fuel all the way through. That might have opened the one check valve in the primer ball that was causing the problem? Although that didn't work for me today...I might have to get a second fuel line and start from scratch and go step by step through every fuel connection until I get to the VST. Unfortunately, for my set-up the primer ball is the only thing I can't isolate because I have a quick connect on my tank.

I have heard about nothing but issues with anti-siphon valves and primer balls which makes me suspicious of the damn things. That float needle looks ok to me. Its a little spongy but I think that it is in the normal range.
 
If you disconnect the fuel line that goes into the VST and crank the motor it should pump fuel out
Now you can check from tank to VST inlet.
 
Hi Paul:

Thanks for sticking with me on this one...

So, I just tried to crank the engine and put the fuel line to the VST into a container and I can confirm it is definitely pumping fuel to the VST both manually from the primer ball and now by the lift pump...although this in my garage and not when it is in the starvation state but that is something I can try again on my next test run if it happens again. Although...I am struggling to understand why the lift pump might stop working since it is just mechanical? Either way there is no restriction from the tank to the VST and the fuel pump is pumping fuel there.

I should mention that I did test the vacuum and pressure sides of the lift pump according to Mercury procedure on previous test runs and it was operating to spec. Although both tests were when the engine was running good, not in the starvation state.

Thanks for the help...learning a lot...
 
Well I'm out off smart ideas now.
Got one stupid idea left...is the vent open on the fuel tank when you go out?

I'm exited to hear what was the problem....

Good luck with solving this issue!!!
Paul
 
Well, think I figured it out today.

I put the vacuum gauge on the fuel tank side of the lift pump with a piece of clear tubing. At the same time, I put a piece of clear tubing on the VST inlet fuel line. I just wanted to make sure I wasn't sucking air into the VST causing the starvation.

When the starvation started, there were no bubbles in the fuel line so I knew it wasn't air getting into the VST. Primer ball was firm. Vacuum gauge was over 4in Hg. Pulled the quick connect off the tank and then plugged it back in. I could squeeze the ball again, filled the VST and it ran great again. Restriction must have been right at the quick connect. I don't know why I didn't check that before...probably because the fuel line was brand new so why suspect it?

At any rate, I think this one is put to bed.

One last question...should I replace the quick connect or just go with a hard fitting into the tank? I bet it is a matter of preference but just wondering what other people have done. I can see there are pros and cons and the fuel tank compartment on my boat isn't the most convenient from a refuelling perspective which is why I prefer the quick connect so I can pull the empty tank out and replace with a full spare. But I don't know if it's worth all this aggravation if the next one fails too. This was a brand new Mercury quicksilver line.
 
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