jlbdp2

I have a 2001 Baja Islander with a Merc 7.4 MPI engine and need some help figuring out what could be causing the problems i'm having. I've had the boat in the shop 3 times and about $900 later and still no resolution yet. Typically, we will be on the water running the boat for a good part of a day, pulling a tube or just running about the lake and all of the sudden when i give the boat throttle all of the sudden the motor will fall on it's face and start popping and banging. When you give it any throttle the motor does nothing but pop, bang and it will not go anywhere. Trying to pinpoint a common time it happens seems to be impossible. Sometimes you can run the boat for 5 hours until the problem occurs and sometimes it may only take a couple hours to start. After the popping and banging starts, a few times the motor has gone into protection mode where the rpm's rev really high and then really low (almost like it has a really big cam in it). This past weekend we took it out and and ran around a few coves and then decided to park on a beach for about an hour. I then took off and went about 60 yards and then it started the problem. It finally died and wouldn't start again. The motor would turn over but it wouldn't fire or anything. Something i did notice when it started acting up is the motor was sucking in air and it was very loud! After about an hour we got towed in and i pulled it out of the water. The first thing i did was try and start the boat and of course it started without any problems. I gave it throttle and it was clean and crisp. But, this seems to be typical of the problem. During my trips to the shop, they first said water in the fuel and changed the fuel filter/seperator and treated the fuel. The next time i took it out it did it again and i changed the filter again and it still did it. The 2nd trip they said it was the ignition module. They replaced the module and i drove it around for 4 or 5 hours without a problem and then it happened again. It's been really frustrating and expensive so far. Any help or tips would be greatly appreciated here.

I uploaded a video of the boat having the problem-

http://www.youtube.com/watch?feature...&v=FPSrolRk-SY

tunertech

lean sneeze.

You have a fuel delivery issue

jlbdp2

because i don't know, what would cause that? Bad fuel pump? Some have suggested a vapor lock issue.

Thanks so much for your help.

mr3dman

I had something similar happen to me a few years ago. The boat would run great till it fell on it's face like yours. Might be the same issue but might not. Get a fuel pressure guage on the rail to see if your fuel pump is going bad. My bad running was accompanied by a loud whining of the fuel pump/ normally can't hear it when the motor is running. I let it sit for a bit and it would run ok. Maybe? who knows but worth checking out

Knot 4 Me

Could be the ECU. Merc was reflashing/replacing them early on during the 1998 - 2001 run of the 7.4MPI. Your symptoms are identical to a new, 5.7L EFI I had in 1999. Ended up being a sensor in the distributor. They had two different ones. One had a green stripe on it and one had a grey. Can't remember which was the good or the bad one but once they replaced it I never had another problem.

Griff

Does this only happen right after being restarted when the engine is already warmed up????

honez

could be vapor lock mine does this if i shut down after a run. the hot water from the block drains down to the fuel cooler and boils the fuel in the pump. the result is a slug of air in the line and fuel filter. there is a kit to keep the water from flowing back. i leave the blower on pretty much all the time to keep the eng compartment cooler and that helps.

stevesxm

all of the above that talk about fuel delivery and lean are correct to some degree...

the first thing i would do is , as mentioned, is a fuel pressure gage and then i would crack the hatch about 4 inches and block it there with a couple of pieces of 2x4 and run it around that way. traditionally the vapor lock deal is starting related but if the underhatch temps are getting very very high then i have seen and experienced all manner of overheating components that were marginal to start with. my 502's did this in the beginning on very hot days right up until i got the engine compartment ventilation correct and got the temps down to ambient. that fixed everything. in your case it may just be a matter of the pump getting soft and the pressure down just a bit where, when the intake manifold et al get to be 150 degrees or so causes a lean condition...

gasoline has a high vapor pressure and can boil at temps as low as 100 deg F and go as high as 400f depending on its composition with that number being increased by pressure... typical fuels in use are about 160 f so what happens is that if you get the intake manifold and fuel log and all the rest very hot , again, depending on the composition of the fuel, you start vaporizing it in the log and the af ratio immediatly goes impossibly lean.

i know it all sounds impossibly theoretical but, in fact, it is a very very real and practical issue that you shouldn't ignore. you would find it hard to believe how much better your motors will run if you can keep the engine compartment 20 degrees cooler...

but... regardless, i think the people that are suggesting it is going lean are correct.