Mercruiser 3.0 won't run

[Thalamas]

I recently bought my first inboard, a1991 Sea Ray 170 with a 3.0 Mercruiser engine. The previous owner(who seems reliable) stated that last year he put the boat and it ran for about five minutes then stopped. he loaded it back up and brought it home. He states that he "worked on it" but couldn't get it started. It sit up over the winter (mild winter down here) in an enclosed shed. I've replaced the starter, coil, plugs, battery, points, condenser, circuit breaker, changed all the fluids including gas. I've gotten a spark as far as the spark plug--it backfires, but there is a purple yellow wire that was connected to the + post of the coil that I can't seem to find out where the other end goes. one schematic shows it connected to the slave starter, and another schematic doesn't show a purple yellow wire at all. I read in this forum that this wire supplies extra voltage when starting, but I don't know for sure. Can anyone help. Would be greatly appreciated. I've enclosed a pic of the slave if that will help.

 

[achris]

Re: Mercruiser 3.0 won't run

Hello and welcome to iBoats.

In order to better help you we need the engine serial number. That helps us identify the correct service procedures to follow. You also need to let us know if there has been any modifications done. Don't know how many times I've been giving advice only to later find out that as the engine has xyz mod, all the time I've spent has been wasted...

Have you done a compression test? If not, start there...

Also, which service manual are you referring to? There are good ones and bad ones (and some down-right shockers)....

Chris........

 

[Chef Shawn]

Re: Mercruiser 3.0 won't run

You have a purple/yellow from starter to coil (+). Under all the electrical tape it is spliced into the purple from your choke and purple resistance wire from the alternator.

If you have spark, and on Earth, your have air. So do you have fuel? AT THE CARB? The Carter pumps don't prime easily. Verify you have fuel in the carb. Slave solenoid failure, I doubt it. Don S. will correct me shortly...

1. Make sure you have fuel to the carb. (it WILL backfire if you dump gas or starting fluid down the carb without having proper pressure in the gas line)
2. Check the fuel filters. And by check, I mean GET NEW ONES.
3. Prime the fuel filter/lines. Use a manual pump, suck gas up the line to the first filter. Attach lines. Use manual pump to suck thru first filter to the carb (line off of course). Once you have gas there, connect line and try the engine.

 

[1960 Starflite]

Re: Mercruiser 3.0 won't run

When I am getting my 3.0 engine ready after a winter layup I remove the intake arrester/filter and prime the carb so I don't have to crank the engine so long to pull/push fuel to the carb. If you look at the carb air horn you will see a small hole just below where the filter mounts. I use a plastic bottle with a tapered cap/tip and fill the carb float chamber. The hole is to vent the float chamber. Put the arrester/filter back on so if you get a backfire it wont lite up the carb. Now push the throttle lever back and forth a couple of times so the accelerator pump puts fuel in the airhorn, like pumping the gas pedal on you old car. Should fire right up if it is a fuel problem.

PS Don't forget the muffs, even cranking the engine will trash your impeller.

 

[Rockinsince85]

Re: Mercruiser 3.0 won't run

You said you serviced the distributor yes? Check for shaft play? Timing? If its back firing then the engine is firing. I agree with shawn, verify that the carb accellerator pump is functioning. You should see 2 streams of fuel when you pump it.

The purple yellow wire gives the coil 12v when cranking. I would disconnect the + of the coil and jump a wire from the battery to that post. That will eliminate the possibility of not getting the correct voltage during cranking. Dont leave it connected for that long or you can burn out your coil. But this will determine if its a wiring issue.

If it has sat for a extended period of time with no attention you could have corrosion in the carb..

Fuel+Spark+Compression = GO TIME

 

[Don S]

Re: Mercruiser 3.0 won't run

Below is the wiring diagram you should be using for your engine.

View attachment 3.0Wire.pdf

The purple yellow wire goes from the coil + to the starter solenoid D terminal.

 

[Thalamas]

Re: Mercruiser 3.0 won't run

First, thank all of you. The engine serial number is D504162. The schematics came from an online service manual from Mercruiser ( at least that's what it says), and the second schematic came from iboats forum. I'm unaware of any modifications made to the engine--the previous owner bought it in 2011. as far as compression, I used an old trick I learned years ago--removed a spark plug, put my thumb over the hole, turned it over and it blew my thumb off the hole.
I had to order a fuel filter--not many boating supply houses here. But I was wondering about the impeller---should
I replace it and where the devil is it at? If y'all can get me through this, then you all are truly lifesavers.

 

[achris]

Re: Mercruiser 3.0 won't run

As far as I'm aware Merc don't have 'on-line' manuals. So it's not the real deal.
Here's a proper manual for you to download and save...

ENGINE MANUAL

For the drive manual I'll need the serial number from that. It's too close to be able to determine Alpha One or Alpha One Gen II without it.

The water pump impeller is inside the drive. Between the 2 halves.

The 'trick' of putting your thumb on the a spark plug hole only tells you that cylinder has compression. It can't tell you what the compression is, or more importantly, how the cylinders compare.

Chris.......

 

[Chef Shawn]

Re: Mercruiser 3.0 won't run

The impeller is a little rubber 'propeller' inside the drive unit which sucks in water from lake/river and pushes it into the engine cooling system, via the small ducts on the lower half of the drive unit. It's hard rubber on harder rubber, if you fail to provide water to the ducts on land, (i.e. muffs) at any time that the engine is being cranked and or ran, it will self-destruct in a matter of seconds.

If you are running muffs and not seeing much water coming out the center of the propeller or the two small holes in the stern you probably have a problem.

I'll be the first to admit, last year working on my boat, had the muffs hooked up and was checking things over, fired up the motor for 10 seconds and then realized I didn't have the water hose turned on. Shut it down thinking everything was OK. Five minutes into my first lake trip, engine temp alarm, overheating. Just a heads up.

 

[2005bay]

Re: Mercruiser 3.0 won't run

Sounds like a fuel problem to me I would bet you need to rebuild the carb.

1. Do you have spark?
2. If so, shoot a tiny bit of carb cleaner down the throat of yout carb and turn the key. My guess is that it I'll run for a couple seconds and die.
3. When you cycle the throttle does the accelerator pump squirt fuel?

 

[Thalamas]

Re: Mercruiser 3.0 won't run

Alright, sorry I haven't kept you all up to date. Vacations, baseball practices, and the sort. But I got the engine up and running like a top. my next problem started soon after. won't shift into forward or reverse. The shift cable at the transom end was corroded and unmovable. Ordered a shift cable kit that doesn't include a " Shift Shaft Slide Stabilizer Tool". Do I need it ? And if so, does it remain inside after reassembly ? Also I'm replacing the exhaust, shift cable, and u-joint bellows. Do I need to look for anything else while I have this puppy open?

 

[joysticks]

Re: Mercruiser 3.0 won't run

be careful if u pull the gear lube hose off-it is on a plastic nipple that many have broken

 

[Don S]

Re: Mercruiser 3.0 won't run

Hard to say what all you need at this point, you never answered achris's question up in post #8

For the drive manual I'll need the serial number from that. It's too close to be able to determine Alpha One or Alpha One Gen II without it.

 

[stonyloam]

Re: Mercruiser 3.0 won't run

doesn't include a " Shift Shaft Slide Stabilizer Tool". Do I need it ? And if so, does it remain inside after reassembly ?

You do not not and it does not. Just make sure the control is in forward, the gearcase is in forward (prop locks when turned counterclockwise) and the roller on the underside of the upper shift shaft lever is between the two arms of the shift slide when you slide the outdrive on.