Mercruiser won't crank/start after tune up

[Chunks77]

Performed a tune up on my 18' Crownline with a 4.3L thunderbolt V Mercruiser I/O. Replaced the distributor cap, rotor and spark plugs. Initially the motor would not turn over; it just cranked endlessly until I applied some throttle and it finally turned over but would not stay running and died after a second or two. After a few minutes of this, I'm worse off now as the motor is not cranking anymore and the starter is just spinning. I'm fairly certain I reinstalled the plugs correctly since I installed the new distributor without unplugging the old one and one by one plugged in the new cap. The rotor is seated as far down as it'll go and is identical to the old rotor. Also, I was thinking maybe the battery could be bad but I had it on the charger all night. This past weekend, before the tune up, the engine did crank to idle so I'm thinking it's not the battery. What mistake(s) could I have made to get in this situation and ultimately how do I go about diagnosing and fixing the problem?? Thanks in advance for the help.

 

[Bondo]

Ayuh,...... Welcome Aboard,.... Let's start with terminology,... When a starter engages the ring gear, the motor is, turnin' over, crankin' on the starter,.....

When the motor starts, it Lit, it's Runnin', it Started, it Fired up,.... or it can Fire, 'n not start,...

After a few minutes of this, I'm worse off now as the motor is not cranking anymore and the starter is just spinning.

So, in this quote, is the starter still engagin' the motor, 'n turnin' it over,..??
Or, is the starter just spinnin' all by itself, 'n nothin' else is movin',..??

until I applied some throttle and it finally turned over but would not stay running and died after a second or two.

This statement, best I can tell, says it ain't gettin' any Gas,....

For a cold, carbed motor, I pump the throttle to Wot, atleast twice, pull back to 3/4 throttle, 'n hit the key,.....

The 1st pump to Wot, sets the choke, 'n gives a shot of raw gas from the acc. pump, subsequent pumps, more raw gas from the acc. pump,....

Once the motor, Fires,.... I quickly yank back the throttle to idle or just above, allow the motor to warm, 'n the choke to pull off,.....

 

[Chunks77]

Best I can tell, the starter is "spinnin' all by itself, 'n nothin' else is movin'." If it helps, when I turn the key, there is a short click and then a "whirring" noise and nothing else. My best assumption is that's the starter.

Thanks for the tip on the throttle. I'll give that a try once we get back to being able to crank the motor.

 

[Bondo]

Best I can tell, the starter is "spinnin' all by itself, 'n nothin' else is movin'." If it helps, when I turn the key, there is a short click and then a "whirring" noise and nothing else. My best assumption is that's the starter.

Thanks for the tip on the throttle. I'll give that a try once we get back to being able to crank the motor.

Ayuh,.... Sounds like ya mighta smoked the starter,....

I'd put a charger on the battery, 'n pull the starter to inspect, 'n bench test it,....

It could be low voltage, or more likely the bendix drive in the starter is hangin' up/ failing,...

Ya might get it rebuilt locally, or might have to replace the whole starter,....

While yer doin' all this,... Clean to shiny metal clean, All the wirin' connections,... then grease 'em to keep 'em that way,...

 

[Chunks77]

Got it. We'll give it a shot.

Could the fuel issue be a clogged fuel filter? I mean, I know it *could* be but would that be a good place to start?

Appreciate the prompt replies!

 

[Triangleboater]

Sounds like you have two problems. First is fuel related, which everything you were doing was fine except it wouldn't keep running. In the meantime while trying to get her running you burnt out the starter which is what you have now. These sterndrive boats are new to me but, just my .02.

 

[Chunks77]

The gear inside the drive assembly ("Sun Gear") looks pretty well worn out. Difficult to tell if it's been a long term wearing down but there is plenty of gunk and pieces inside. Perhaps today was the day it finally gave out and would explain the whirring noise since it couldn't engage the drive. Found a replacement online and will be here in a few days. I'll update this post once I get it installed.

For anyone out there looking to remove a starter: it was actually pretty easy to do. Several videos on YouTube but the main thing to remember is to remove the two main bolts first, which are underneath on my engine, and it came out pretty easy. I ended up pulling the starter motor first before finding out it would've been easier just to pull the entire unit.

For the fuel issue, how should I approach troubleshooting this?? Let's say the new fuel filter doesn't immediately fix the issue. Where should I go from there?

Thanks.

 

[Bondo]

For the fuel issue, how should I approach troubleshooting this?? Let's say the new fuel filter doesn't immediately fix the issue. Where should I go from there?

Ayuh,..... 1st step is to inspect the Contents of the fuel filter,.... then replace the filter,.....

Pop the flame arrester off, 'n pump the throttle,.... does gas squirt into the carb from the acc. pump,..??

 

[Chunks77]

So the new starter is installed....works fine.

I do not believe gas is squirting into the carb. However, the engine does run for a very short amount of time. Longest being about 30 seconds. Usually from a cold start but afterwards ends up back in the cranking but not running situation. I've readjusted the choke, cleaned the carb with carb cleaner spray but can't keep her running. Fuel filter was replaced too. Perhaps the gas has gone sour but I added fuel stabilizer as part of winterizing the boat. Maybe water in the fuel?

I can't see this being a mechanical failure (but what I do know?) since the engine has always been solid and she does run briefly. Also, at least once, she started and ran like an engine should and I briefly thought we were past this. How's about the carb?

 

[NHGuy]

Stick a teaspoon of gas down the carb, if it runs briefly and quits you have a supply issue. If it primes good.
But if it quits, and I'd expect it will, try taking the fuel line off at the carb to check for debris in the inlet screen. Watch out that you don't round off the brass inlet hex, you should really use line wrenches on those critical and soft fittings. Sears/Craftsman has them, or cheap ones at Harbor Freight are fine for the few times a home user takes them out.
Also crank the motor a bit with a catch cup by the end of the fuel line to see how it pumps gas. The fuel should spurt pretty good with each compression stroke of the engine.

 

[achris]

As you stated you have Thunderbolt V, that means we're looking at a 1997 or later engine. So, electric fuel pump. You need to work out if the pump is getting power and working. On the port side of the engine, under the exhaust manifold, towards the back is the oil pressure sender. Tee'd off that is a switch with a pur/yell wire. and a purple wire. With the key on, you should see battery voltage at the purple wire. While you're cranking the engine (trying to start it) you should also see battery voltage on the pur/yell wire. If you see these, with the key ON, temporarily short the 2 wires together. You should hear the pump running.

Chris.......

 

[Chunks77]

Much appreciate all the assistance.

However, after I removed the fuel filter to check for water (there was none) and reinstalled, she cranked and runs normally now. I have no idea what the deal was. My best guess is the carb cleaner finally came through, some residual water in the fuel finally worked its way out or some other fuel supply issue finally resolved itself. Anyways, all's well that ends well I suppose.

iBoats forums are definitely a HUGE help to us novice mechanics!!

 

[achris]

Or the filer wasn't on properly and it was sucking air. Removing and replacing seated it properly...