High LP fuel pressure on VP 5.0 GXI

[saltymoff]

Hello, I have been having issues getting my 2008 chaparral 215 5.0 GXI-J past 4400rpm and 40mph.
The boat should go to around 4800-5000rpm and 48-50mph.
I have tried changing props, changing spark plugs, she has had a new fuel pump and all resulting in slight improvement but never breaking past the 4400rpm range.
I pressure tested the fuel system the other day, HP rail was 50-60psi which is correct but the LP was almost double at 17psi when it should be closer to 8psi..
Could this be my issue..any ideas what could be causing it...my thinking is that the injectors are still seeing 50-60 then this shouldn't be my issue...never the less I must have an issue here..
I have also remove the screen on the FPR as per VPs bulliten...
Any advice would be gratefully received as I'm beginning to think this may be all the engine has to offer...
Thanks

 

[alldodge]

Not a VP expert but I believe the low pressure pump should be around 16 to 17 psi on the GXI model. This came up on another thread. Have been trying to look it up at boatinfo but don't know which manual to look in (NC, MD, WC, etc)

Has the boat always run this way?
What pitch prop do you have on it?

 

[Maclin]

Sounds like the screen issue, the one that gets clogged up from the paint on the inside of the fuel bowl housing that eventually succumbs to the harsh environment and removes itself in clumps. No expert here, I have only read about it in the VP forum.

Need to get this moved to the VP forum for sure.

 

[Maclin]

"Need to get this moved to the VP forum for sure."

That was fast!

 

[Thalasso]

Your fuel pressure is where it should be.
It comes down to trimming the boat were it needs to be to achieve this. Your not trying to do this with a boat load of people are you? The engine is only putting out 270 hp. It's a heavy boat for that engine. Any added weight is going to effect performance

 

[evantful]

Do you have a SX (single prop) or Duo Prop outdrive?

That does seem low as long as you aren't loaded down with people.

I have a 1999 Cobalt 206, weight is just about 4000 pounds with fuel and gear and I can easily hit 50-55mph at 4800rpm with a Volvo Penta 5.0GI (250hp) and DP-SM outdrive with F6 props.

 

[Thalasso]

First thing i would check is the cables to see if there adjust correctly for full travel.
Engine overheating?
Restricted exhaust outlets?

 

[saltymoff]

Hi thanks for all the replies...
It's a single prop, currently an 18p 4 blade but tried a 20p 4 blade same results.
The boat has never went past 40mph since I have had it, I have checked linkage travel it's ok, boat will rev up to 5000rpm no probs in idle.
Yesterday there was just two of us, it was a windy day and the canopying was up but again 40mph was all it would see at 4400rpm....that boat should fly past 40mph no.? Have tried it on calm days in the past with no canopy and same results..
Every other owner of this boat says she will easily hit the 48 mark
The engine runs fine, planes in 5-6 secs, not overheating and always starts first time.

I was sure the LP pressure should be 8psi +- 4 psi

 

[saltymoff]

May I add.....When I bought the boat 2 years ago with 20 hrs on the clock, it had sat down in Poole bay for 2 years without use, the local boat yard serviced it and I was delivered to me up in Scotland, when I ran it the fuel that was in the tank looked like it had been there for two years....the marina that serviced it in Poole bay , had changed fuel filters they said and even put a new LP pump on it....well that's what they charged for.

Anyway....So since then I have had the tank flushed out, brand new fuel pump, injectors out and cleaned....filters changed regularly....boat runs fine apart from never breaking the 40mph mark....
The hull is unmarked and I get it washed a few times a season rather than use anti-fouling..

 

[saltymoff]

Oh yes and that is with trimming it ....I only ever really notice a couple of mph difference trimming....really though a 270hp 5.0 V8 should be breaking thru the 40 mph.... The boat is only 21.5 ft , I think around 1800kg dry

 

[saltymoff]

Regarding clogged screens....Usually you will hear the pump struggle / cavitate when there is a restriction...I had this issue prior to removing the screen on the FPR, when the engine was just ticking over the pump would squeal as the FPR screen was causing a restriction....the fuel pump shows no sign of noise or overheating

 

[saltymoff]

And thank you moving my thread into the correct section x

 

[Fun Times]

Pretty sure you low PSI pump should be in the 8+/- 4PSI range like mentioned in the last link below. If your low pump pressure is around 17 psi then there's a good chance that the area/passage way for the fuel pressure regulator is clogged up causing high fuel pressure on the low side and in-turn causing poor engine performance on the top end.
A good cleaning of the fuel pressure regulator inside and out plus cleaning the fuel rail system should get you back up to speed. Below are many stories of just about the same symptoms you seem to be experiencing at the moment.

http://forum.chaparralboats.com/ind...ressure-regulator-service-bulletin-confusion/
http://www.thehulltruth.com/boating...rviceable-volvo-penta-fuel-cell-serviced.html
http://www.justanswer.com/boat/2knex-2001-volvo-penta-gxi-fuel-pump-dual-hi-pressure-right-hand.html

Also item number 22 in the photo below, while it says fuel regulator, it is actually a fuel pulse damper to basically soften the fuel pulses to the injector/rail system. While the damper is an very expensive part to buy OEM, Marine engines don't use it as a regulator like found/used in a GM truck. iboats recently had a member that was able to carefully remove the fuel damper, clean it and cleaned the inner fuel rail system easier while it was off then reinstalled it and all was good there after. You may want to consider doing the same. In the links above, you'll notice some said they cleaned the fuel rail too which has been a common thing needed to be done if any debris (paint chips) gets pass the regulator and up to the rail system.
Let us know what you find, good luck.

 

[saltymoff]

Thanks for that fun times....I have had the fuel rail off in the past and cleaned it thru with carb cleaner and it seemed spotless but I will do this again particularly due to the increase in LP pressure....I will also have a look at that damper/fuel valve..

Ah the joys of boating....

 

[saltymoff]

This is the same FPR that I removed the screen from last year and replaced it with the e-clip as per VP bulliten.... This screen was clogged with fine specs of dirt, this also caused the FP to cavitate at idle...
Will pop it off this afternoon for a look....cheers

 

[alldodge]

A 4 blade prop gives you more lift but also increases the power it takes to turn it. Going from an 18x4 to a 20x4 will reduce your rpms as you probably noticed. I would suggest a 19x3 blade

 

[BRICH1260]

I agree with the three blade for top end speed. A four is generally for power.

 

[saltymoff]

Thanks guys...I went from 20p to 18 p with no difference in rpm change, WOT rev range on both props 4400rpm....regardless of blades and top end speeds...4400rpm is too low...that engine should be 4800-500rpm....even with a 4 blade 40mph is too low I feel...I'm sure this boat is under-powered, that engine should burst thru the 40moh range no...?
Anyone with a 21.5ft boat and this engine agree or dis-agree

 

[alldodge]

You went from a 20x4 to a 18x3 and had no change in rpm?

 

[saltymoff]

20p 4 to 18p 4 ...Yes I can get the engine past 4400rpm when under load....I did have a 19p 4 with the boat but it is damaged....with all 3 props max rpm is 4400rpm and around 40 mph..