1997 4.3 Mercruiser engine barely cranks over.

[60hpmercguy]

My 1997 Stingray with a 4.3 Mercruiser will barely crank over now. Was running and cranking fine and all of a sudden the engine will barely turn over. This occured after a 30 minute wide open throttle ride. The engine all of a sudden started slowing down and finally stopped. It will barely crank over one revolution and then stop with a known good battery and even a 200 crank assist battery charger even with the sparks plugs REMOVED. Removed the starter and it bench tests good (ie. it will spin freely when connected to a battery, i spun it over 10 times or so at least). The teeth on the starter and flywheel look fine and the bendix gear snaps back and forth fine. There is no clicking sound coming from the solenoid like a dead battery would indicate. Does anyone know what size the crankshaft pulley nut is? I need to turn the engine over by hand.

 

[NHGuy]

Yah, don't try to turn it with the crank bolt. If it's as stuck as you say you;ll just shear off the bolt. You can get a good grip on it with a crank tool though. They attach to the 3 9/16 (I think) pulley bolts.
You will probably need to remove the drive, then check to see if the engine spins. The engine and drive are connected solidly.. So If you get the drive off you eliminate one or the other.

 

[60hpmercguy]

Hey NHGuy. Thanks for the reply. I am not sure what you mean be a "crank tool". I have removed the serpitine belt which drives the alternator, power steering pump etc.. Of course, I can put the belt back on and try turning one of the pulley bolts to see if the engine turns over. Is that what you are suggesting? I was planning on using a long handle ratchet with socket on the crank bolt. Thanks again

 

[QBhoy]

Hi.

Without doubt...what you need to do first is pull the plugs out it and see if it turns over...and look for signs of water ingress on the plugs. I have a feeling you may have a rotten manifold or riser perhaps.

 

[Bondo]

I was planning on using a long handle ratchet with socket on the crank bolt.

Ayuh,..... Again, Don't do that, the bolt will break,......

Pull the drive 1st, then the spark plugs,....

This occured after a 30 minute wide open throttle ride. The engine all of a sudden started slowing down and finally stopped.

My guess is,.... The motor was detonating, you didn't hear it, 'n the motor burnt up,......

Look for melted aluminum on the spark plugs,.....

 

[60hpmercguy]

Thanks for the comments. Again,as stated in the original post, with all the spark plugs REMOVED, the engine will barely crank over for just a couple of revolutions. The plugs look good, are not wet or oily with NO melted metal on them. I have to get the engine cranking over before assessing the other issues with the engine. I am unsure about the reason for two starter solenoids, since the bench test seems good, if the external solenoid is defective, would that cause the poor cranking? Thanks

 

[achris]

A few things you can try. But first off, you need to eliminate the starter motor (and it's supply) as a source of the problem....

You need to do 3 tests with a multimeter... Do these exactly as, and in the order I lay out...

1. Volt drop test on the negative.
Set the multimeter to the 20 VDC scale. Connect the red multimeter lead to the starter motor case (not the engine block, the starter itself, there's a reason for that).. Push the end of the black multimeter lead into the battery negative post (not the terminal or the lead coming from the terminal, that piece of lead that sticks up when the terminal is removed). Now crank the engine (I'd use a remote starter switch so you can hold the lead and read the meter all at the same time). It doesn't matter if the engine doesn't actually turn, as long as the starter engages. You should get a VERY low reading, like less than 0.2 volts. Turn the meter to a lower scale, like 2VDC and do it again. Write down the voltage you read for the 'Negative volt drop test'...

2. Volt drop test on the positive.
Set the multimeter to the 20 VDC scale. Connect the black multimeter lead to the starter motor post itself (again, not the end of the cable, the stud).. Push the end of the red multimeter lead into the battery positive post (same like you did on the negative). Now crank the engine. Again, it doesn't matter if the engine doesn't actually turn, as long as the starter engages. You should get another VERY low reading, like less than 0.5 volts. Turn the meter to a lower scale, like 2VDC and do it again. Write down the voltage you read for the 'Positive volt drop test'...

3. Actual cranking volts.
Set the meter back to 20VDC and put the red lead on the starter terminal stud and the black lead on the engine block (or some other convenient 'ground') and crank the engine. Write down the voltage as 'Cranking voltage'...

These tests will determine if and where there is an electrical system problem....

If these all look good, then we move on to removing the drive and trying again...

These sorts of faults need to be troubleshot using a controlled, logical, elimination process. Just shooting in the dark will get you absolutely nowhere.

And as everybody has said, do not, do not try to turn the engine using the crank pulley bolt. All you'll do, if the engine is that tight, is break it off. Then you'll have 2 problems to fix....

Chris.............

 

[achris]

.. This occurred after a 30 minute wide open throttle ride. The engine all of a sudden started slowing down and finally stopped. ....

OK, what revs where you pulling at wide open?

What you describe is what I hear from people who's engines have 'grenaded'... The revs are too low at wide open, the pistons overheat (and expand more than designed) due to the higher cylinder pressures and temperatures and start seizing up... That's why the engine is too tight to turn now....

But let's get the electrical system tests done, then pull the drive (which isn't as big a job as people convince themselves it is ) and go from there. If the engine has locked up, then the drive will need to come off anyway.

... I am unsure about the reason for two starter solenoids, since the bench test seems good, if the external solenoid is defective, would that cause the poor cranking? Thanks

The reason for 2 solenoids is to reduce the current passing through the keyswitch. The starter solenoid draws about 4-5 amps, and over a long cable run (up to the dash and back) the harness will get hot and the voltage will be lower. Adding the slave solenoid means the keyswitch is only passing about 1 amp...

Chris............

 

[60hpmercguy]

Hey achris. Thanks for the test procedure. What test results am I looking for after completion of the tests in your #7 post? Thanks

 

[achris]

Hey achris. Thanks for the test procedure. What test results am I looking for after completion of the tests in your #7 post? Thanks

What test results do you have?

 

[Bt Doctur]

Do yourself a favor and do it the correct way, remove the drive. shift into fwd, remove the rams and 6 nuts and pull straight back. Not try to spin the motor Y,N
Running wide open and having it go lean will severely damage it internally

."a 30 minute wide open throttle ride. The engine all of a sudden started slowing down and finally stopped. It will barely crank over one revolution and then stop with a known good battery and even a 200 crank assist battery charger even with the sparks plugs REMOVED.

A sign that either the drive is seized or the motors pistons are damaged and binding in the bores.
At the very least get an old outdrive input shaft, weld it to a T handel and try to turn the motor by hand. A good motor will turn easily by hand , a damaged motor will not. Your 30 minute ride cooked the motor

 

[Bt Doctur]

If you must , use the harmonic balancer with the pully removed and the 3 bolts inserted into the balancer and pry on 2 bolts to try and turn the seized motor

 

[Bt Doctur]

just to undate this, hes on the other site also and is pretty sure he has an internal engine problem , ya think

 

[60hpmercguy]

Hey bt doctur. Yep, on the other site too just trying to find a solution. BTW, your post #13 above is exactly what I was talking about on the other site. Just another meaningless post.

 

[Rick Stephens]

Fun part of this, if the drive was just a little low on oil, and he ran WOT for 1/2 hour straight, the upper gear case got really hot unless he has a drive shower installed. Add a little low on oil and easy to seize up the input bearings.