Volvo Penta VST problems

[Bill4452]

I have a 1998 Four Winns 25 foot Vista Cruiser. It has the Volvo Penta 5.7 GSI motor (57FCPBY). Up until this year it has been a very dependable motor. When you start the motor, the engine idles just fine. When you take it up to 1,100 or 1,200 rpm, the motor starts starving for gas. The dealer has run thru diagnostics and believes the VST is bad. (The TSP and Low and High-pressure pumps have been replaced. The fuel pressure is within specs as well) Of course, Volvo doesn't make that part anymore. I need help in finding the whole VST or at least these part numbers (3850374, 3853575 and 3853575). The dealer would rebuild it with those parts. Does anyone have any ideas? Thank you for looking.

 

[alldodge]

The fuel pressure is within specs as well

Why does the VST need to be rebuilt if fuel pressure is within spec of 30 psi from idle thru WOT?

Part numbers listed is vst seal kit and float. One of the numbers is listed twice

 

[Bill4452]

Sorry, 3853576. Tech is saying the float is not telling the low pressure pump to fill up as the high pressure calls for more fuel. I was told the fuel pressure spec was between 9-13 psi. It was showing 10 psi.

 

[alldodge]

Maybe it's a choice of words but the float doesn't tell the low pressure pump, it simply opens and lets more fuel in.

Depending on which GSI you have the LP pump can be as low as 2 psi to as high as 12 psi and still work. The pump being 9-13 is great pressure.



The VST is like a carb float bowl, so long as there is fuel in the tank the HP pump will push it to the throttle body. So if the tank needs more fuel then adjust the float slightly higher.

It the Throttle body pressure stays at 30 psi thru WOT then your good. If pressure starts falling off the check things like antisiphone valve, clogged fuel line, fuel tank pickup tube, fuel filter

 

[Bill4452]

The fuel tank pickup tube was replaced along with the anti-siphon value. The fuel line between the tank and fuel filter was replaced. The Fuel filter and TSP were also replaced.

 

[alldodge]

ok, so is the pressure staying at 30 psi?

 

[Bill4452]

Tech said the pressure was 10psi and within his spec.

 

[alldodge]

Tech said the pressure was 10psi and within his spec.

If the 10 psi they are talking about is for LP pump then that is good, and no issues.
If that is the HP pump side at the TB, then you need to find a new Tech

For your motor to run correctly the TB must have 28 to 32 psi. A Tee fitting must be installed between TB and fuel line, or remove the other test port and measure there

VP TB Tee fitting

 

[Bill4452]

How can I tell which motor I have? All I see is it's a 5.7 GSI with Duoprop (model shows as 57FCPBY) I'll call the Marina and make sure I understood them correctly about the psi and where they measured it from. Thanks for your input.

 

[alldodge]

Exactly which model would be good to know but it's not critical. All 5.7 GSI's are TB injected and all should have 30+/-2 psi at the TB. The only part that can be different is the LP pump for the LK-WT models which can have a low pressure LP pump. Your LP pump has been replaced so it should have the higher pressure low side pump

 

[Bill4452]

The low pressure pump is right by the fuel/water separator in the front of the motor. The high pressure pump is by the back of the motor, above the VST.

 

[alldodge]

correct

 

[Bill4452]

(model shows as 57FCPBY) but that doesn't match anything from the above chart.

 

[alldodge]

Guess we're at a impasse, you belive you only need 10 psi and I say you need 30.

 

[Bill4452]

I have a call in to check with the marina tech to see how he got that psi. I appreciate your insight.

 

[dypcdiver]

Hi Bill
My problem with The VST was that,
a) The salt water chamber was clogged up with a corrosion deposit that would not allow water flow ie no cooling.
b) The base of the fuel float chamber had rotted through from the salt water chamber allowing salt water to contaminate the fuel!
I am attaching my copies of the purchase, but I have no idea if they are still available now, best of luck.

 

[Lou C]

Hope you can still get one of those, the only other option (more expensive but better long term solution) is to convert to a 4 bbl marine carb. You can always get parts for Holley or Edelbrock carbs and they will run off an inexpensive Carter marine electric pump with the safety cut off harness. It’s not that I’m against marine TBI or EFI but with parts that are NLA, that’s a good solution.

 

[Bill4452]

Thanks, I'll try reaching out to them. The Carb swap was one of my last options.