Fuel Pump/Pressure Problem Or Something Else? TIGE Mercruiser Magnum 454 EFI

alldodge

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I would just replace the pump. It has been leaking and this is build up from gas, rubber and other things. Search for Airtex 60932. Airtex makes the pumps for Merc and are a lot cheaper.

The sea pump area has a cam (item 14) and ring (item 15) which rides against the pump arm. It doesn't take a lot of movement to pump the fuel. Here is the break down of the pump. It is fairly cheap to rebuild the pump if its ever needed.

http://www.mercruiserparts.com/bam/subassembly/31416/2355/16

The anti siphone valve is a one way check valve and I would NOT pressure test the tank. If it was tested 5 psi is a LOT of pressure. Unscrew the valve off the tank and check to see how it looks inside

Looking up your serial number at Merc comes back weird and not even clear (which is strange). In any case I would say that this is your current make up of the motor

http://www.mercruiserparts.com/454-mag-mpi-ski-gen-vi-gm-454-v-8-19-1
 

Mike B3

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I would just replace the pump. It has been leaking and this is build up from gas, rubber and other things. Search for Airtex 60932. Airtex makes the pumps for Merc and are a lot cheaper.

The sea pump area has a cam (item 14) and ring (item 15) which rides against the pump arm. It doesn't take a lot of movement to pump the fuel. Here is the break down of the pump. It is fairly cheap to rebuild the pump if its ever needed.

http://www.mercruiserparts.com/bam/subassembly/31416/2355/16

The anti siphone valve is a one way check valve and I would NOT pressure test the tank. If it was tested 5 psi is a LOT of pressure. Unscrew the valve off the tank and check to see how it looks inside

Looking up your serial number at Merc comes back weird and not even clear (which is strange). In any case I would say that this is your current make up of the motor

http://www.mercruiserparts.com/454-mag-mpi-ski-gen-vi-gm-454-v-8-19-1

Okay looking sound on the airtex pump and will get that ordered and new filter. Would anything else besides the pump and maybe seal around the filter cause the boat to not pull gas into the filter? I have put a vaccumm on the intake line from the tank and it pulls it right up so from the tank to that line is good from what I can tell. This is the "in line" to the filter I am talking about.
 

alldodge

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Would anything else besides the pump and maybe seal around the filter cause the boat to not pull gas into the filter?

Only ting between those is the tank filter screen inside the tank and the bottom of the dip tube, and the anti siphon valve
 

Mike B3

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Well new fuel pump, new filter. When crank over the gauge goes to about 7psi and holds it for a bit. Sits around that pressure so figure no leaks. However boat still does not start up. I am wondering if something pat the gauge could be clogged. That VTS system or injectors maybe? What would be a good route to go next. If I pop that cover off the VTS will that be first or some tests to run before that? Should I bypass the tank and put fuel in a gas can and run that to the pump?
 

alldodge

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Having 7 psi on the low side then your good. Need to find out if the VST pump is powering up when key is turned to ON/RUN. If pump is running then check fuel pressure at the high pressure shrader valve under the plenum.

You can pop the top off the VST to see if there is any gunk in there
 

Mike B3

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Having 7 psi on the low side then your good. Need to find out if the VST pump is powering up when key is turned to ON/RUN. If pump is running then check fuel pressure at the high pressure shrader valve under the plenum.


You can pop the top off the VST to see if there is any gunk in there

Well cap I had about 7psi before replacing the pump haha. Oh well needed a clean filter and atleast it was cheap.

Okay I wanted to make sure popping the top off wouldn't cause anything to need to be replaced. I assume it is an O-ring on the top?

Also what will the VST system sound like. When I turn the key on there is a bit of a sound and a few seconds after I turn the key off there is the same sound. It doesn't sound like an electric fuel pump. It sounds like a click, and then the sound if you had a straw or small hose with a little liquid in it dribbling out.

I watched a quick video of cleaning a VST system but for a different motor. I assume they will all be very closely related. From the looks of the video I still am optimistic that something simple is filled eith debris and that is why the boat won't run.
 

alldodge

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There is an O-ring but if it is not damaged when removing it can be replaced. There is minimal pressure in the tank so slight chance of a leak. That said if it does leak afterwards it needs to be replaced.

You should hear the hum of a pump running for a few seconds/ If you put your hand on top the VST you should feel it hum.

Don't know what your hearing after the key is off.

Need a pressure gauge on the high side valve
 

Mike B3

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There is an O-ring but if it is not damaged when removing it can be replaced. There is minimal pressure in the tank so slight chance of a leak. That said if it does leak afterwards it needs to be replaced.

You should hear the hum of a pump running for a few seconds/ If you put your hand on top the VST you should feel it hum.

Don't know what your hearing after the key is off.

Need a pressure gauge on the high side valve

Okay so removing high side hose and install gauge correct? Will I be testing pressure when turning the key to "on" or when cranking the motor?
 

alldodge

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No, you test high pressure on the fuel rail at the shrader valve which is under the intake plenum. Removing the top lets you see if there is any crud building up. The high pressure pump can be lifted out to have a look

plenum.jpg
 

Mike B3

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Okay and to test pressure on this do I just turn the key to "on" when te VST begins to hum or does the motor need to be cranking like the low pressure line?
 

alldodge

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Okay and to test pressure on this do I just turn the key to "on" when te VST begins to hum or does the motor need to be cranking like the low pressure line?

When the key is turned ON, the pump should run for about 3 seconds and pressure should build. So if you turn the key and hear nothing, check the fuses on top the motor. One fuse is the main power and other is fuel pump. The fuses also are in line with 2 relays, main power and fuel pump. Both the relays are square and either gray or black and can be swapped with each other.

If no sound is heard and the fuses are good, leave the key ON and check for 12V at the fuses and relays. See if you can hear a click or place hand on relays and when key is turned ON they both should click
 

Mike B3

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Well took apart the VST, wasn't terribly dirty inside. Cleaned out the screens and junk at the bottom of the unit. I was trying to figure why there wasn't much fuel inside and I saw a float that controlled a needle and seat. Usually on the skis I work on these either are stuck closed and you won't get fuel or they have a large piece of debris on the tip of the needle. Well, it was either of those. But there is a 90? where the fuel comes in and was a large amount of sediment stuck in that corner and built up to the point no fuel was coming past. Cleaned that out and the boat took alot of cranking and cycling the key. Finally it got to the point of coughing but still wasn't firing. Figured I would let it sit a few minutes and cycle the key a few more times. Not sure what exactly cycling the key does but I was figuring sends a bit of fuel to the motor to help it start up. Either way, boat fired up and ran without dying. Going to replace sea pump impeller and run it on the hose tomorrow or even out to the lake for a quick run possibly.

Thankyou greatly for your help. Now to test transmission and possibly replace clutch plates if the impeller keeps spinning.
 

alldodge

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Good to hear you got it running.

Cycling the pump doesn't do anything if the VST bowl is empty. The mechanical pump needs to get the fuel in there before the high pressure pump can push it on. Also since the VST was about empty there was probably some air in the fuel rail. You tried enough times to get the air bleed out and she fired up. If you run into this again, push the shrader valve and bleed the air out
 

Mike B3

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Good to hear you got it running.

Cycling the pump doesn't do anything if the VST bowl is empty. The mechanical pump needs to get the fuel in there before the high pressure pump can push it on. Also since the VST was about empty there was probably some air in the fuel rail. You tried enough times to get the air bleed out and she fired up. If you run into this again, push the shrader valve and bleed the air out

Would it be wise to still do this or is all the air gone now you think? I noticed the VST did not have a Schrader valve to test pressure on the high pressure end
 

alldodge

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Would it be wise to still do this or is all the air gone now you think? I noticed the VST did not have a Schrader valve to test pressure on the high pressure end

The air should be out with it running.

The VST does not have a shrader valve, it is only on the end of the fuel rail
 
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