tomtc

I have a 99 SeaRay with twin 7.4MPI inboards. The port engine just developed a strange problem that I need some help with.

At all RPMs below 4,000, it occasionally starts running VERY rich and power and rpm drops way off. It will do this sometime for just a few seconds and other times for minutes. I have a Floscan and when the problem occurs, the fuel flow will jump way up. For example, at idle it will jump from about 1.2 gph to 5 gph or so. At 2,200 rpm (about the fastest it will run when the problem occurs), it jumps to something like 19gph. When the problem occurs, you can smell the strong odor of the unburned fuel. It does this both when the engine is basically cold and when it is fully warmed up.

If above about 4,000 rpm it runs just fine and the problem does not reoccur until I slow back down and the rpm drops.

This weekend, the problem took on a different nature. Now, the opposite is happening. The fuel flow is very low (lean) for the engine speed and load, and the engine is running VERY rough. For example, it is only showing about 5.5gph at 2,500 rpm, about the fastest it will now run under any circumstances. The problem is now also no longer intermittent and is occurring constantly.

Water temp is normal, oil pressure is normal and battery voltage is about 13.8. It did this once before about two years ago (the rich running part) and the Mercruiser tech put a scan tool on it and saw no codes. It mysteriously went away until reoccurring again now.

Any idea on what could cause this and what I might look for?

Thanks!
Tom

Boat Tech

The map sensor plays a big part in how much fuel the engine needs. If It has A short in it I could see it doing this to you'r engine and It might not in some cases do It long enough to have A code.

Pismo10

It's the damn EFI, have fun for the next month/year chasing it down.

Pesky Varmint

Yep, it's a pretty sure bet all the engine manufacturers will be going
back to carbs in the next few years. Too much trouble with EFI. And no
one can fix them.

obnoxus

ZING !!!!!!!

outlawinil

How old is your battery or batteries?

Pismo10

Boat EFI IMO is more trouble than it is worth. Car EFI they seem to have figured out but not marine. A two minute problem for a standard setup becomes lots of fooling around with EFI. What is the benefit? Easy starting, are people rally that lazy? I never had any problem starting a carb setup. A few more hp? It is just not worth it yet. I have had both and know which way I will go next time I need a rebuild unless the technology improves markedly. Many fewer problems, much, much easier to repair. If a carb setup doesn't start, it is a two minute diagnosis, spark or fuel, if an EFI doesn't start it could be two dozen things.

The technology is cool and the maps are much tighter but who cares when you dead in the water, or under the hatch for days diagnosing, or sitting at a marina for even longer while they guess along replacing every sensor, charging you for each of course. Carbs setups are so much simpler for now and much cheaper to fix.

I will be out boating while you are zinging...

obnoxus

Seems to be speaking more of the repair shops you choose rather then the technology.

I highly doubt Merc now makes all there big HP motors EFI just to leave you strandedin the water one day.

Oh,,,, and try to get that carb motor through emissions ( you know its coming )

txriverrat2001

I would test the injectors if no codes are present ....One sticking and or not closing all the way will do what you're describing. With an injector tested you can build fuel pressure - then "pop" the injector for a set time - 500ms, 50ms, etc... and compare the pressure drop on each one. You may find during the pop test another injector fire as well meaning you have one shorted out. There is an "A" trigger and a "B" trigger for the injectors - obviously if the fuel pressure doesn't hold after cycling the key - you have one leaking pretty bad.

outlawinil

I agree boat EFI is a pain in the azz but with all the emissions laws it's here to stay. I think more of the EFI's bad rap is mechanics trying to diagnose and fix a customer's problem without the right tools or even a scan tool. I know in my town there is a place that wrenches on boats and he does alot of business and he doesn't even have a scan tool. For the cost of a spare prop you can buy a scan tool from Rinda and eliminate all the guess work on these EFI's. I bought one for my laptop and it tells you alot of info.