Hotboatwannabe

I am new to this forum but an experienced boater and with good knowledge of the 5.7. I have a 2001 Stingray 22’ bowrider (220LX) stock 260HP 5.7 EFI TBI. New plugs, wires, distributor cap, fuel/water separator, new battery, fresh marine synthetic outdrive oil, timing set exactly at factory spec 8 deg BTDC and procedure as per factory manual, fuel injectors work perfectly and have been cleaned, fresh fuel in tank. Fuel pressure also tested between the high pressure pump and the TBI = 38 PSI. Compression. Is good at 162 +/- 2 psi on all 8 cylinders. The return line is clear and does not have an anti-siphon valve (factory)

However, I cannot get max rpm unless I am running wide open throttle for at least 2 minutes straight 4150 rpm and then it literally jumps to 4450 rpm, like it just let go and I achieve 61 mph versus 55 mph GPS! This is a 23” Ss prop. I have the same symptoms when I use the 21” prop. ( it jumps 300 rpm after WOT for at least 2 minutes) and also I tested a 19” prop. Same symptoms. It’s also slow and bogs out of the hole. I am in Las Vegas, elevation 1100ft at Lake Mead

I don’t know if it is a fuel pressure issue, or an electrical problem that kind of cures itself at sustained high rpm. Or would a gimbal bearing cause these problems?

Also, just this last weekend I had a no start issue at the end of the day (105 degrees). I checked and had spark but the fuel injectors did not spray like they normally do during start. So I removed the fuel supply line on the back of the TBI, cranked it over and hardly any fuel was coming out and then it blasted a bunch of fuel. Connected the fuel line back up, and it fired up right away. It was a Vapor Lock. Strange. I’ve been out on the lake for the temperature was 115° and no issues with starting. I wonder if this has something to do with my problem? Thanks for all your help.

AllDodge

Fuel pressure should be 30 psi. Have you run with pressure gauge attached, and if so are there any changes during the WOT?

There should not be a antisiphon valve on the fuel return line, the valve should be on the supply line coming from the tank

Check the antisiphon valve and pump

Hotboatwannabe

Ok I just double checked the fuel lines and I misspoke. There is NO anti siphon valve in the fuel line pickup from the tank to the fuel / water separator at all. (Factory Mercruiser)

Also there is the large fill line into the fuel tank from the gas fill cap, and also there is a vent line into the tank as well from the gas cap.
I also checked the check valve for venting in the gas cap took it apart, blew it out with compressed air and reinstalled it.

If my fuel tank was not getting vented because of the check valve stuck closed in the fuel cap, it would have produced a vacuum in the fuel tank, not allowing fuel into the lines? Maybe this would cause the non start vapor lock issue until I removed the fuel line from the back of the TBI allowing the pressure to equalize? Maybe this is causing all of my issues?

as far as fuel pressure, a very good shop in Boulder City, All Seasons Marine, did the timing and the fuel pressure check, they are an authorized MERC REPAIR SHOP, and they said 38 PSI is factory psi. And I thank you for your advice!

AllDodge

I wish you well and hope you can figure it out

Hope someone else has some advice to help

BillK

But did they do it on the water at WOT ?

Trash

It is likely the fuel pressure regulator. I know you said fuel pressure was normal but it was not tested at all loads and rpm’s. I worked with a guys boat that had very similar symptoms. He thought it was the tune, but when I looked tune was normal. It ended up being bad fuel pressure regulator.

TomZ

There most certainly should be an anti-siphon valve there per USCG requirements. It's part of the tank fitting and could very well be overlooked.

As stated by the other very knowledgeable guys that have commented - the problem is most likely a fuel pressure regulator issue when under load. You cannot put a gauge on it and call it good without water testing.

You're new here so I'll just put this out there... Not sure I would have added the "they are an authorized MERC REPAIR SHOP, and they said 38 PSI is factory psi. And I thank you for your advice!" comment.

The knowledge many of the guys on here have goes well beyond that of the average "authorized MERC REPAIR SHOP" mechanic, I promise you. A comment like that is going to turn away the guys that were willing to give you some help.

Hotboatwannabe

I have not run the fuel pressure test under load, but I will. I actually did my own fuel pressure test at my home and the shop said the same thing. I won’t mention this anymore and I appreciate the advice. I also ordered an anti siphon valve. I generally do every repair on all my equipment myself, but this own has me scratching my head. I will lake test this in 2 weekends and post what I find. I think I will order the fuel pressure regulator anyway. Thanks again!

And one more question I forgot to ask regarding timing. The factory base timing is 8 degrees BTDC and total timing of 30 degrees is in at 2200 rpm. But the 5.7 Magnum and 5.7 L total timing is 2 degrees more at 32 degrees total. Can I increase timing 2 degrees on my 5.7 EFI (increase base timing from 8 to 10 degrees) to achieve 32 degrees without any detonation?

TomZ

Really, the only way to know is to run it. On the BBC MPI engines, some guys have gotten away with it. I doubt you would see any real difference in performance honestly.

Tartilla

If the 2001 5.7 marine has Vortec heads, 30° all in timing would be all you would need.