Hello all,

i bought Powerquest 257 legend with Mercury 496 mag HO engine on a test run we saw that the engine didnt have full power with a maximum speed of 45 mph after a little bit of a research compression on 4 cylinders (cca 125psi) was low so we decided to check the engine.

Problem was on a head gasket and head itself, we had mounted stainless steal exhaust system and we had checked the engine with computer.

On computer it shows 100% power availability but there is alway but.!

Problem:

- Today we tested the boat first time in the water and the boat could push up to the same around the same speed cca 47 mph so the problem is still there even the compression is now fixed,
- what are your recommendations.

I am already thanking you all for really good content here.
Best regards from Slovenia,
Vid Vidic

need to know what rpm it is showing at the 47 mph. may not be the engine.

It shows 4500 rpms but there is lack of power through whole rpms… propeller is 21 pitch 3 blade inox and for bravo x which has probably gear ratio 1.50 that should be like a rocket from the start already… today when I was driving around there was also a strong smell of fuel when I was driving slow. And there is another thing I can hear when you press the gas in neutral you can hear weird squeezing noise from the engine but on computer it doesnt show any errors as some would say it could be IAC regulator… hmmm

the noise is probably the IAC but you need to find the gas smell. is it coming out of the exhaust or is the smell in the bilge? that needs fixed first. as for the speed it works out to around 20% slip which is not terrible but not great. lots of things can raise the slip but on a boat like that you may never see better than 15% slip depending on the weight and prop condition, etc. find the gas smell first for safety and then work on whether it will make any more power.

You may have the dreaded paint flakes contaminating your fuel rail. regulator, and injectors from the cool fuel module.

When it happen to me, the boat ran fine, no codes, but in reality was dumping gas in just to keep running. And yes, it had a STRONG smell of gas that wasn't traced to any leak. Are you using more fuel than normal?

Time to get a fuel pressure test ASAP.

496HO Down on power - Offshoreonly.com

have a 496 HO with that issue. Best way to check is remove your fuel filter and see if there is any black paint on the inside of the case. If so that was a recall years ago. There is certain years only.

The gas smell is coming from the exhaust and not from the bilge…

Vidic,

You are either running too rich or not burning all the fuel the engine is being given. These are not necessarily the same thing.

I may be biased from my experience, but I’d get those injectors out and have them inspected, cleaned and flowed. I don’t know if you have anybody in your area to do them, but Smitty (ArcticFrirends here on OSO) does a fantastic job. He posted often in that thread I posted above. Look him up.

It also wouldn’t be a bad thing to pick up a Rinda Techmate Pro. It will allow you to diagnose about any ECM-adjacent issue you may have, including a fuel-related or ignition-related misfire.

Thanks. Brad.

Yesterday I made fuel pressure test and the results were around 41 to 45 psi on the lower, mid and high rpms. I am going to do the test driving on 1500 rpms and pluging one by one cylinder coils out so I can see if all cylinders are working or not. I bought the boat last season and I am not fully aware of what are the maximum performance with this boat but I am sure that there is no real power. I know that the boat top speed was around 60 mph and now I can do 45 mph. What happened to your performance of the engine was the top speed also lowered?