No power under load

[AllDodge]

Don't see any issue with the way your fuel pump is running. The ECM (which is a MEFI-1) turns the VST high pressure pump on for a couple seconds when key is first turned ON. It does this buy appling a ground to the fuel pump relay. Once the engine starts cranking or starts the ECM turns the pump ON again and keeps it going until the key is turned OFF.

Does appear your issue is in the high fuel pressure area. Fuel pressure should be at 37 psi while running. With you being able to turn the key OFF and the pressure stays up, tells me your injectors are not leaking, nor is the regulator. The lower then normal pressure can be caused by the fuel pump or fuel regulator.

I would start with removing and cleaning the regulator (item 18, p/n 805227A1).
http://www.mercruiserparts.com/bam/subassembly/31810/2336/10
http://www.mercruiserparts.com/805227a1-regulator-kit

It can be checked by applying regulated air pressure to the inlet, and see when the Reg opens

 

[larry1954]

Many thanks for this. The fuel regulator was one of the items replaced in a service on the boat by the marine shop not long after I purchased the boat. It ran once with no problems after that service. We then did not use the boat for about a year and when we next took it out we had this problem that it would not rev over about 3000 rpm.

So I am thinking that maybe the problem is more likely with the fuel pump itself than the regulator? Though there is also an item on the invoice 'remove disassemble and clean fuel USU', and I wonder if that refers to the high pressure fuel pump?

Here is a picture of the invoice and all the work that was done by the local marine shop:

 

[AllDodge]

Dang they went hog wild, sure hope they did do all that is listed form the cost of it all. Don't know why they replaced the intake manifold gasket because there was no reason to remove it. I do see the plenum gasket, which would be necessary.

What your probably running into is a weak pump, but the only way to find out for sure is to test. The pump should be able to output 60 psi when restricted. You remove both lines going into the fuel rail, leave the one coming from the mechanical fuel pump. The fitting coming out of the upper one on the VST is the output, the other is the return. The far left top in link below
http://www.mercruiserparts.com/bam/subassembly/31810/2336/10

Install the fuel pressure gauge on the fitting or end of the line and test.

 

[AllDodge]

BTW, you can change from VST to cool fuel with only minor changes. I removed my VST a couple years ago during repower, not because I had to (it was still working) but because if it goes bad you can get another for under 200 US.

 

[larry1954]

Yes, it was not cheap. But you have to remember that in Australia parts and labour are probably a good deal more expensive than in the US.

So have I understood this correctly? I can see marked on the top of the unit: fuel in (RHS), vent (LHS), return (LHS) and then an unmarked uppermost pipe coming out (LHS) (just near where the electrical wires connect) which I assume is the output line. Do I remove that line and attach the gauge where the line was connected to the pump and then start the engine and see what pressure the gauge reads?

 

[larry1954]

I would be interested in doing that modification, VST to cool fuel, after I get to the bottom of this problem.

 

[AllDodge]

I wasn't the cost, it was how many items were on the list.

Either way the one I'm pointing to is the output, were the gauge would go. You can connect to it, or leave the hose on the pump and disconnect the other end and attach. Note: you need to bleed out the air to get an accurate reading.

 

[larry1954]

Ok. Thanks for that. But I was thinking that of course once I disconnect that line I cannot start the engine because that is the output line that supplies fuel to the fuel rail. So I guess I must just turn the ignition to ON and see what pressure I get.

I am not sure how I will bleed air out of the line, but maybe there is some fitting in that fuel pressure tester kit which I bought that would allow me to do that. That makes we wonder whether the problem could not actually be air in the fuel rail or elsewhere in the fuel system and that that is what is causing the fuel pressure to be lower than expected? But then, for the times we have run the boat would not the air have got out through the injectors? Or maybe not, since the injectors will maybe only inject fuel, not air, so that the air would still be there?

 

[larry1954]

On the other hand, how would air have ever got into the system? It ran fine, then the next time we took it out without doing anything in between it would not rev over about 3000 rpm.

 

[AllDodge]

Air bleeds out of the fuel rail system on its own, but if disconnected, its best to use the key to build pressure and depress the shrader valve (rag over the end) to bleed air. To bleed air from the tester, you could loosen the fitting slightly (use rag over end) to bleed. I would suspect maybe the low pressure pump if the pressure was up to specs (37 or so psi).

With the pressure being 30 an below it really looks like the pump. Increasing rpm's in neutral doesn't use much more fuel then at idle. If there was air in the fuel rail the boat would have a heck of a time even starting.

First law of hydraulics: Pressure exerted on a confined area transmits with equal force on all areas. If there was air, pressure would have a hard time even building until its gone

 

[larry1954]

Thanks again for that. The marine shop did replace the low pressure 'manual' pump as I think you can see on the invoice.

Do you think that I should order a new high pressure pump? It will have to come from the US since it would be about twice the price if I buy it here (even with a relatively unfavourable exchange rate), but it will take a week or two to come. It does not look like the marine shop ever replaced the high pressure pump as far as I can see from the invoice. Or if I go the route of changing over from VST to cool fuel do I use a different high pressure pump? If I have to replace the pump maybe this is the time to also do the VST to cool fuel modification?

 

[AllDodge]

The bill just reminds me that they were using a shot gun to fix a problem, don't know if it was by request or otherwise.

The pump kit is 808505T01 and cost around $800, plus you will also need the O-ring kit which is another $100. While your in there might need to also replace the float valve seat and needle.

Here is the pump for 725
http://www.cpperformance.com/p-65374-pump-kit-fuel-mercruiser-808505t01.aspx

To shift over to cool fuel you would need to get the complete assembly. Easiest way would be to get it from a donner boat then replace the fuel pump if needed. If you have folks that are building high performance motors, they probably have some lying around they took off a customers boat during repower (how I got mine). Otherwise you have to buy each piece.

To change it over, it takes some lines and fuel module gets mounted on the port side behind the motor mount.

Never shipped anything over seas, but I'll sell you the one I removed for 250. It worked when I took it off, but that was two years ago.

 

[larry1954]

AllDodge, I am very appreciative of that information. I assume the cool fuel system is a considerably better system than the VST? So, if that cool fuel system of yours is reasonably straightforward to connect up in my engine compartment, I think that I would be interested in buying it from you for the $250 if you are happy to ship it to me overseas. I can pay you by Paypal if you have an email address connected to Paypal and I would pay you the extra for the fees Paypal charges you and of course for the shipping.

In some defense of the marine shop, the boat was in a pretty sick state when I bought it with more than one thing wrong. That may be because the boat does have a rather sad history. The original owner was from Cumberland, RI. It was bought in the US by the man from whom I thereafter bought the boat - he may have been for a time working in the US. Anyway, he bought it from Shep Brown's Boat Basin, Meredith, New Hampshire, and had it shipped to Australia. He evidently used it here as you can see from this Youtube video: www.youtube.com/watch?v=m4DRF1U08gc. Tragically, he lost his wife in a motor vehicle accident, perhaps not long after that video (you can see her in the video). He never really got over that, I think, and the boat just sat for years until I bought it in about 2014.

But we were new to power boating (though I did a lot of sailing when I was young) and my wife was just frightened of the Formula at first - that's why we also bought the 1988 Malibu Skier a little later on, just to get used to boating with a smaller boat. The Malibu has been very good for that and I have managed to be able to work out how to do most things on it, so the Malibu has never been taken to the marine shop. It runs beautifully and never any trouble - just a 350 Chev motor with carburetor .

But I really want to progress to the Formula - partly because I find the Malibu a little uncomfortable after awhile - get leg cramps sitting too long so close to the floor. I am trying to persuade my wife that the Formula will be a more satisfying boat in the long term and that we can just leave the Malibu to the children (4 daughters) for wakeboard riding and things like that. Three of them have boat licences and manage the Malibu without much trouble. I think that I am gradually succeeding with my wife. Even though we have had this trouble with the boat for quite awhile and it has been a struggle to solve the problem, I think she can see the potential of the boat. You have to understand too, that these sorts of boats are not at all common in Australia. People here often stare when they see it. It is just a beautiful boat, in my opinion, and goes beautifully when it does go, which sadly has not been very often for the time we have owned it. But I am hoping that may soon be coming to an end. I could have taken it back to the marine shop, but then I have to trailer it in there, leave it with them, then pick it up when they are finished and of course pay them, but I would not necessarily learn anything more about how the boat works or how to fix at least some things myself.

BTW, here are some pictures of our boat shed and the 2 boats and one also of where we live:

 

[AllDodge]

Very nice setup

I don't have another cool fuel, I have the VST which was removed (pic in post 67) from my boat during repower. Only reason to offer is IF it turns out the pump is the problem, and you don't want to switch things out, this would be an option. I also don't use pay pal, use to but stopped. If your still interested, I'll ship it and you can send back a check or similar something.

 

[larry1954]

Oh, I see that I misunderstood your post and thought you had a cool fuel set up. Sorry.

I don't know about sending a check. It would have to be in US funds and then it might go astray in the post and it would be from an Australian bank, so I do not know how that would work.

I guess I was thinking that it must be the pump. Is there anything else it could be? Would it still be worthwhile for me to go ahead and check the pressure at the outlet from the pump to see if it is below what it should be, i.e about 60 psi?

 

[AllDodge]

Oh, I see that I misunderstood your post and thought you had a cool fuel set up. Sorry.

I don't know about sending a check. It would have to be in US funds and then it might go astray in the post and it would be from an Australian bank, so I do not know how that would work.

I guess I was thinking that it must be the pump. Is there anything else it could be? Would it still be worthwhile for me to go ahead and check the pressure at the outlet from the pump to see if it is below what it should be, i.e about 60 psi?

It could be the regulator, and the receipt says it was replaced, but that is about the only two items it could be.

 

[larry1954]

So it would be worthwhile attaching the pressure gauge to the exit line of the fuel pump and if it gave a regular pressure, then it must be the regulator?

Or is there any way of directly checking if the regulator works?

 

[AllDodge]

So it would be worthwhile attaching the pressure gauge to the exit line of the fuel pump and if it gave a regular pressure, then it must be the regulator?

Or is there any way of directly checking if the regulator works?

If you put the pressure gauge on the shrader valve and install some kind of valve on the exit then you could check the regulator. The valve on the exit would need to allow for pressure to increase but make sure it does not exceed 50 psi, because the regulator can be damaged. Blocking off the exit allows the pressure to build, but once the regulator started to open, pressure would equalize. So if it opened at 37 psi, you might not know it unless your were letting fuel leak out as the pump was running. If it wasn't leaking fast enough, then the pressure would increase above the 37, but if it did increase above the 37 then your pump is pumping enough.

 

[larry1954]

Thanks for that. I have not yet tried what you suggest partly because I am not quite clear on it. I still have the pressure gauge connected to the Schrader valve and the gauge has a line going away from it with a release valve, presumably to release the fuel each time before you do another pressure reading, though I have not yet used it. This valve is normally closed but the pressure will not rise above what I said it was before,30psi at idle (because the regulator works?)

I was puzzled that when I checked the voltage at the fuel pump it was only 11.6V, so I connected the pump directly to a battery which had a voltage output of 12.6V and watched the pressure gauge. The fuel pressure went up to about 36psi, which given some inaccuracy in the gauge could be equivalent to the 37psi quoted for it. Also, putting your hand on the pump you can certainly feel it working, it is just very quiet. So, when the engine is running, and probably at least 12.6V is available from the battery, the pump is evidently capable of 36psi, though it idles at only 30psi.

Sometimes I wonder if there is nothing wrong with the fuel pump or regulator and there is a kinked breather pipe somewhere. We do get wasps here that build nests, even though the boat is in the shed. But I can never seem to see where that breather pipe is. There is very limited access to the tank area through the inspection hole in the compartment under the back seat. You can hardly even see anything beyond what's immediately in front of you, much less actually get to it.

On the other hand, I cleaned a fair bit of junk out of the fuel tank after this problem first arose, and maybe it was some of that junk in the fuel that got into the newly installed regulator and caused it to malfunction (?), so that the problem might in fact be the regulator.

I am tempted to take it back to the marine shop, but it would be great if I could solve the problem.

 

[AllDodge]

when I checked the voltage at the fuel pump it was only 11.6V, so I connected the pump directly to a battery which had a voltage output of 12.6V and watched the pressure gauge. The fuel pressure went up to about 36psi

I would say the regulator is working, the pump is just now putting out enough pressure normally. If a regulator is set at 36 and the pump can output 50, the regulator will keep it at 36. Same thing happens in a air compressor regulator. If the regulator was not there, the pressure would increase to what ever the pump could reach. So the first test I was talking about is to take the regulator out of the equation.

The electrical connection to the pump may be the problem. If the connections between the engine harness, thru fuse, relay and connections are corroded then the pump doesn't get sufficient voltage.

Junk in the tank should get stopped by the filter. Remove the filter and dump the contents into a clear bag or jar, you should see nothing but clean gas. The regulator has a screen on the inlet, and if it gets clogged then the pressure will go higher then spec. The button on the side of the gauge is to bleed off air as well was release pressure from it so the gauge can be removed without spraying gas when the fitting is removed.