Need help from the experts on the forum

Ive been reading the forums for a long while now but just finally joined. This is a great community of boaters and I thank you all for the stuff you post on here.

Here my problem maybe you can help.

1986 mcm 170 mr ( that's not the problem- I know there's plenty 170 haters out there)

Problem: after a solid 20+ minutes of anything over 2500 rpm or longer at lower rpm I suddenly lose all power and the engine stops like it's starved for fuel. I let it sit for 15 minutes or so and it cranks fine and goes again for a good stretch before a repeating the problem.
Oil pressure around 60 at higher rpms. Temp right at normal 160 or so never shows hot. No lurching, surging or anything like that. Idle around 600 rpm. She always cranks right up after a few prime pumps and runs great until the problem happens.

What I've done: not knowing much about boats I started with the easiest stuff. Replace the fuel filter- which wasnt dirty. Replaced plugs, wires, coil and cap. New fuel separator- very little water in the old when when I checked. I checked the fuel vent- no blockage.

I can't figure it out. Friends say it must be either temp or fuel related but I ruled out temp since the gauge always looks fine. Can't figure out how I can have a fuel problem at such specific times or circumstance. Shouldt fuel problems be consistent from crank?

I really appreciate any help I can get. My last resort is to haul it up to the shop and let them figure it out but Id love to save the cash.

Thanks again.

Re: Need help from the experts on the forum

when it happens again, see if the coil is really hot, like you can't touch it hot - normally it shuold be warm to the touch

also, have a helper pump the throttle and you look into carb and verify that fuel is indeed present, one full throttle pump should produce two nice fuel squirts into the throats (like a squirt gun squirt)

Re: Need help from the experts on the forum

You have to re-prime? Sounds like an air leak in the fuel lines.

Re: Need help from the experts on the forum

Shouldn't have to. There should be plenty fuel already in carb.

Re: Need help from the experts on the forum

Only have to prime when it's cold start. My choke doesn't work so that the only way I get her going. Once she's warmed up I don't have to prime anymore but I'll definitely check the fuel line from the tank all the way to the carbs.

Re: Need help from the experts on the forum

Here is a test procedure that will help you determine if you have a problem with an air leak or something in the fuel system being plugged up.
http://forums.iboats.com/showthread.php?t=283269

Re: Need help from the experts on the forum

I had a similar issue long ago, turns out it was a closed vent on my fuel tank cap.

Re: Need help from the experts on the forum

Took it out today ran great for hours then same problem. A friend suggested I open the gas cap when it happens to see if it needs air (depressurization) and I did it the first time it started to die out while pulling my kids around on a tube at around 2500 rpm or so. Seemed to work. But after going wot back toward the launch at the Ned of the day it died out completely. Waited ten minutes fired up and ran fine back to the doc.

So I felt the coil as suggested when it happened and it was very very hot. What can that mean? Its brand new. Acording to the diagram in the manual the coil gets it's juice from the slave solenoid - which seems really weird- and there's a resistance wire to the choke (the choke doesn't work).

Re: Need help from the experts on the forum

points ignition coil should have a resistance wire going to the (+) side of the coil

you need to get out your volt meter and check the voltage at the (+) side of the coil with the key on engine not running

it should be less than 12 volts, anywhere from 4 -6

when running, the voltage should be about 8-9 volts

if the voltage is 12 or more in either scenario, you need to inspect the wiring and determine where your resistance wire should be, then check the points, they could be fried

what are you using for a manual??

Re: Need help from the experts on the forum

Using SELOC manual #3200. Also have the original 170mr installation manual and they both have the same wiring diagram.

I'll check the voltage today and post the results.

Did the carb check and fuel was flowing nicely.

Re: Need help from the experts on the forum

throw that manual away - seriously, its garbage, do NOT read another word of it

click this link to download the OEM manual for your engine:

http://www.4shared.com/document/zTbCbkDD/Service_Manual_08.html

in it you will find the correct wiring diagram for your engine and what you should be looking for

Re: Need help from the experts on the forum

dubs - youre awesome! I searched forever for that manual and eventually ended up with the SELOC (which is now going away). Thanks again.

Re: Need help from the experts on the forum

Tidefanva said:

Acording to the diagram in the manual the coil gets it's juice from the slave solenoid - which seems really weird- and there's a resistance wire to the choke (the choke doesn't work).

Click to expand...

On the 470 (unlike other Mercruiser engines) you only get the voltage from the slave solenoid (purple/yellow wire to coil+) when the starter is cranking and you are bypassing the resistance wire. The resistance wire should be a purple wire from the choke to the coil +. The resistor wire should read between 1.8 and 2.0 ohms.

Re: Need help from the experts on the forum

Update: the voltage the the coil and resistance of the purple wire are normal. I haven't tried the fuel line pressure check yet. I have a gauge but not the right fittings. As an alternative I decided to check the fuel separator again. What came out was nasty brown and flaky. So I removed the sending unti from the 50 gal aluminum tank and took a look. Nasty in there. Flakes everywhere on the bottom, not completely covered but definitely a lot of varnish or whatever in there. I pumped out some fuels and it was all very dark with flakes.

Could this be the cause of my problems? I don't think the crude is making it to my carbs. Maybe it's just plugging the fuel pickup when it's on plane? Or maybe the gas is just crappy (brown).

I'm planning on cleaning out the tank and replacing the filler and vent hoses while I'm in there. I believe I can get the tank out of the boat, maybe, that seems like the easier way to clean it out. If not I'll have to work it out.

Re: Need help from the experts on the forum

If you had a vacume gauge on the fuel line it might spot low fuel pressure due to a supply line blockage. Certainly change the fuel filter / water seperator. I would shy away from removing the tank from the boat unless it looks like an easy job, but you might inquire to see if somebody provides a tank cleaning service (or perhaps "fuel polishing" which might be more for diesels but I think works for gas as well).

Re: Need help from the experts on the forum

Luckily the 50 gal tank came out easily. I pressure washed the outside today and inspected the aluminum tank all around - in great shape. The gas I took out was really dirty. Tomorrow I plan on getting something in the tank to let sit for a day to break up the particles then I'll empty it out and use the shop vac to air it out til dry. While Im there I'll clean out the 25 years worth of stinky sludge and oil residue in the bilge and replace all the old fuel line, fill line, and vent.
Maybe it wont solve my problem but I can say that it certainly needs the cleaning.

I've surfed around and found at least 25 different suggestions for cleaing a tank. With it out of the boat what are some of your suggestions?
I'm leaning towards some degreaser/solvent of some sort, slosh it around the tank, maybe throw a chain in there to help break it up, let it sit for a day then evacuate, dry and put it all back together.

Re: Need help from the experts on the forum

seems I have heard of gas fumes igniting from shop vac motors, please use care.

Re: Need help from the experts on the forum

Well, I think that may have solved the problem. Drained the tank with a hand pump (gas looked like sam Adams draft but darker), removed the tank, added some warm water and bilge cleaner, shook it really good for about 20minutes, drained it, did it again, added a long chain inside and shook it around, drained it again ( huge chunks of lord knows what came out), inverted and hook up a shop vac to blow through the fill hole and out the pick up hole, ran that for a good 20 minutes, let it air dry for a day, poured a little acetone in to get the last drops of water that wouldn't come out, replaced the fill cap assembly, fill hose, air vent and hose, and replaced the really old bronze fuel line with rubber line from tank to separator. Old bronze line had a significant pinch in it.
Anyway, I took it out yesterday and the motor gained about 4 mph at wot and I ran in there for a solid 30 minutes without hint of my shut down problem.
Not sure if it's completely cured until I take it out a few more times but I think it is. Also not sure which part of the fix cured it- gas exchange, tank clean, hose replacement, etc.
Oh well, I'll take it for now.

Re: Need help from the experts on the forum

Same problem.

I give up. Tking it to the shop.

Re: Need help from the experts on the forum

Never did the tests I gave you a link to did you.