Engine/transmission problems

Looks like I'll be taking my boat to the mechanic, but since it'll be a day or two, I'm looking for some armchair diagnosis of the following problem:

- prop is fine and spins relatively freely in neutral
- engine starts with no problems and revs with no hesitation or problems with boat out of gear
- when in gear, boat won't go much faster than idle. Any more throttle and it hesitates and/or surges, but still without any real power.
- problem orginated last week while wakesurfing and I thought some water might have gotten in the gas vent line. I used a bottle of Heet and filled the tank.
- all fluids have been changed within the last 50 hours

Any quick thoughts on where the problem might be?

do you have perfect pass? Sometimes our old boat acted like that after surfing alot.
We would shut it down, turn the knob on top of the servo clockwise until it stopped, the back half a turn. When you power back up it will reset.
I'm pretty sure it was clockwise

(Message edited by tlb on August 01, 2007)

(Message edited by tlb on August 01, 2007)

No perfect pass.

check your water pump

Wouldn't the engine temp get elevated if it was the water pump? Engine temp is normal.

carb or efi? not sure on the 97 p star mc's? did it shift ok into gear? no bangs, clunks, grinds? loss of power and hesitation with periods of surge sounds more like carb or injector problems. tranny = lots of moeny, hopfully its just the above or mabey a fuel line problem. have you changed the fuel filter recently. try that. it worked for me once. my boat wouldnt go past idle then it would die. turned out to be a bunch of gunk in the filter. is it dieing on you? good luck

I agree with Bryan. Sounds like a fuel delivery issue. Fuel filters are cheap. Go ahead and change it to see if that fixes things. It might also be a carb that needs to be rebuilt or injectors that are clogged.

Did you change your fluids before or after the problem started? How did they look then? How do they look now?

EFI...no noises when going into gear.

I haven't changed the fuel filter, but wouldn't that affect it in neutral as well as in gear?

"I haven't changed the fuel filter, but wouldn't that affect it in neutral as well as in gear?"

Not likely. Generally when a fuel filter fails, it still works under light load but chokes under heavy.

Might be a throttle cable problem

any luck with the fuel filter yet D. i keep thinking about it and it just sounds more and more like a fuel issue. try that filter then have the injectors look at.

It takes very little gas to rev the engine with no load and lots of gas to rev loaded (in gear) could easily be a filter or fuel pump. Another potential is spark from the ignition system. Check the distributor cap and plugs. I had a distributor cap with corrosion cause very similar symptoms.

Lack of fuel(lean) will cause backfireing in the intake should sound like it is comming from the engine compartment.

a problem with the ignition will likely cause a rich condition and backfire through the exhaust.


there should be a valve on the fuel rail to test fuel pressure should be 35- 40 psi running.This will confirm/rule out a fuel system concern. I think fuel pressure gauges rent for like 5$ at the parts store.

Is the dealer the only place to get a fuel filter or can I get one at the auto parts place since it's basically an automotive engine?

There are potentially 2 fuel filters, for sure there is a water seperating filter (looks like an oil filter) you can buy it at Wal-mart or any marine store. There may also be an inline fuel filter. Trace the lines from the fuel tank to the engine. If there is an inline filter they are hard to find aftermarket. From my experience marine applications use different fittings and the auto stores do not carry. My mercruiser has a Parker (Racor) inline filter have never found a cross reference.

george did you just say the "W" word. dude im out of here, good luck.

http://www.wakeworld.com/MB/Discus/messages/4387/479928.html?1185553552

I don't buy much at "W" and I hate going in there but they have Quicksilver (Mercruiser Aftermarket) filters, and oil for about 2/3 the dealer price and Boaters World. I'm not going to pay the dealer $6.00 a quart for oil and $13.00 for a filter that I can buy for $4.00 and $7.00.

im just kidding g, we dont have a you know in santa cruz.hell where im from we had a year long riott for "books without borders", when they tried to put one down town. i love borders there the only place that has all the cool mags. im lucky my friend is my mechanic and he gets whole sell pricing for my stuff. but i to would get my supplies there if i had to t save money. mortgage and boat payment = coupon clipping for me.

(Message edited by westsiderippa on August 03, 2007)

I picked up a new inline filter at AutoZone and have it installed. It was just a standard Chevy filter. I'm grabbing a quick bite to eat as I post this and then I'll drag the boat to the lake to see if that resolved the issue. The filter was only $7 and is a maintenance item anyway. Now I know the last time it was changed (I bought the boat in May).

I'll post results in a few hours. Thanks for all the input.

No joy on the fuel filter. It ran a bit better, but still had issues.

It seems like the problem gets even worse after the engine has warmed up a bit.

if you water pump is half shot and the boat is not getting enough water then the computer will put the boat in limp mode because it is getting hotter than it should. It just takes a minute to look at the water pump

I haven't looked at the pump, but the temp is normal and there's plenty of water coming out the back when I've got the fake a lake hooked up.

d, i want to figure this one out for you. help us out again with the specific details of todays outing. time ran? amount of idle time? lack of power? does the boat plane? what noises? give us a full run down again of today and lets start from the top.

Thanks, Bryan. Here goes:

I backed down the ramp but left the boat on the trailer. Started it up and let it idle for a couple of minutes with a few revs to 3000-4000 RPM. Then I put it in gear and brought the throttle up a bit. Obviously I couldn't go to far, but there were no problems and it made me confident that I could at least get the boat back on to the trailer, so I backed it off.

Throttle up to about 1200-1500 RPM was okay with no noises or anything else out of the ordinary. Any higher on the throttle and the power would immediately drop to nearly non-existent. The boat wouldn't even come close to planing. I only had it out on the water for 3-4 minutes before getting it back on the trailer. Temp never got above normal.

I was going to try and do a fuel pressure check, but the damn thing has no port to hook up to. The fuel pressure is an interesting point, by the way. Both the 1996 and 1998 MC Prostar manuals say the operating pressure is 30 psi (they don't have a 1997 manual online). However, the pump has "25 psi max" stamped right on the side of it. Another oddity, the 1994-1997 Maristar 200 and 205 manual and the 1995 Prostar 205 manual both say the operating pressure is 10-12 psi for what sure seems to be the same engine.

I was going to at least try a flow test (manual says 1 pint in 20 seconds). I'm pretty mechanical, but a bit ignorant, so I'm not sure how to make the fuel pump stay on for that long.

I pulled the top of the throttle body last night and checked out the fuel pressure regulator. I'll admit I'm not much of a mechanic, but I'm pretty sure it's not supposed to look like this!

I'm not a mechanic either, but that looks like "varnish" -- gasoline that has broken down after sitting for a long time; possibly a couple of seasons. If so, you could have more of that stuff sitting in the gas tank.

Somebody on here should be able to outline a step-by-step process for cleaning the entire fuel system.

that looks like a diaphram from a fuel pressure regulator off a gm tbi. there is a spring inside the regulator housing that puts pressure on that diaphram. the gm spec on that tbi system is 9-13psi. it probably doesnt have a port. if you buy a tester from the parts store, it will have a shrader valve that you screw in between your fuel line and the tbi. yhe gauge will then screw on the schrader valve. this is how it is an an automotive application, but its probably the same for marine.

Thanks Dewayne. Everything you said is spot on. It definitley is the regulator off a GM TBI and Actron makes a GM TBI adapter to T into the line and connect the pressure tester.

I didn't bother doing the pressure test once I saw that, though. It was pretty clear that the diaphragm was the culprit, not the fuel pump. That's a good thing, since the pump is $300-400. I just got the TBI maintenance kit from AutoZone (for $41) and replaced the diaphragm (along with all the o-rings and gaskets since the kit had them). Problem solved.

The issue wasn't likely caused by bad gas, since the boat hasn't sat for more than a couple of weeks without going in the water. It was almost certainly caused by water entering the vent hose fitting on the transom when wakesurfing. I'm trying to decide how to address that in the future: maybe a check valve on that vent hose, I don't know.