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Mercruiser 3.7 wont fire

A

aaronp

New member
Hello All,
I have a 1989 ebko with a 3.7 mercruiser. I just purchased it and I know it ran when it was pulled from the water for winter storage. I seen this with my own eyes. Currently it wont start. It gets fuel through the carb. The plugs are wet. It has spark. I tested all the plugs. I checked all the wiring. Good compression on all cylinders. If I back the distributor off It almost fires. It wont start even with a shot of either. It seems the timing is off. Im a gear head, but new to marine engines. I know i didnt choose the best setup, but its what I have. My guess is somehow the timing is off. It was properly winterized also. The throttle doesnt allow me to give it gas . Theirs no push button or high idle control. Any help is appreciated.
 
Ayuh,...... Change the points,.....

The controller handle probably pulls out for throttle only,.....
 
Thing with boats is that you have to be far more attentive to the engine. Your life may depend on it! Every spring you should be doing a full tune up. New cap rotor points condensor wires plugs oil change and belts. Yup, seems excessive until your engine conks out somewhere miles from shore, and then you'll wish you'd spent the time and money...
Anyway, that and fuel. You really have to be a dick about what the boat eats. You must get your fuel from a trusted source, keep the filters clean (new spin-on every spring) and replace the rubber lines every few years.
Keep a full set of tune up parts in your onboard spares kit and the tools to install them.
Be the same way about all your lubricants in both the drive and the engine. Too-frequent oil changes are better than letting it go for years..
Finally, keep all your electrical connections clean and smear lots of grease all over the battery terminals to keep out the briny sea.
Do this and your only worries will be about bikinis.
 
RicardoMarine and kghost....

Stop with the personal tit for tat, the hen pecking and the childish antics. Get along, ignore each other or go away. If you can't do one of these things I'll be happy to help.
 
bondo said:
Ayuh,...... Change the points,.....

The controller handle probably pulls out for throttle only,.....
Click to expand...
well new poinrts, plugs and coil. Everythings gapped right. it still wont fire. As i mentioned I watched it get pulled from the water. Ive got spark and fuel. if i back the distributor off a little it almost starts, but carb floods quick
 
........................
aaronp said:
well new points, plugs and coil. Everything is gapped right. it still wont fire.
Setting or adjusting the contact point "gap" gives us an estimate ONLY of correct dwell angle.
You'll do much better if you were to use a dwell angle meter.
See your OEM specs for the correct dwell angle!

As i mentioned I watched it get pulled from the water. Ive got spark and fuel.
if i back the distributor off a little it almost starts,
(I posted to this topic earlier, but it has now been deleted)

You have a mechanically advancing ignition system with flyweights and flyweight return springs.
Once out of or above BASE advance, these components govern the advance per engine RPM.
At idle speed, they are inactive (i.e., no mechanical advance above BASE timing).
Look to see if these components are rusty, and if by chance the return springs have become rusted.
Rust compromised return springs loose their spring value, and may allow the advance to come on too early.... and sometimes at idle or cranking speeds due to the springs not being able to fully return the flyweights to BASE mode.
This may (key word "may") explain why you need to back off on the distributor in order to get it to "almost" start.

but carb floods quick
All that said above....... this could very well be the problem, or at least a major part of the problem.

Set the dwell angle per OEM specs.
If you can test the spark quality, you should be seeing a white or bluish-white spark.... not yellow!

Correct the carburetor flooding issue.

Check to see if the flyweight system is working correctly.
The flyweights should be free to move, and the return springs should be bringing the flyweights fully back into BASE mode.

Click to expand...



.
 
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Post what gap you set your point to.
Gap should be .022"
Dwell 28* to 34*

Base timing after released service bulletin is 6* BTDC for this engine.

Do you have a timing light? Do you have a dwell meter ?

Before you started replacing parts did you adjust the distributor and if so how much?
Did you change spark plug wire orientation/firing order?

FYI

Timing advance at this stage is irrelevant. All that is relevant at this juncture is BASE timing to allow engine to start and run.

Stick with the not starting issue first and once solved then if performance is lacking then confirm advance. With a point system the mechanical advance system will either work or not work but it has no relevance to engine starting at this point in time. Only ads confusion.
 
A 4 cylinder engine's distributor is given 360* of which to fire all 4 cylinders.
That equals 90* per cylinder.
In that 90*, the system will saturate and collapse the coil field once per cylinder.
Depending on what the OEM specifies, the dwell angle will typically be between 45* and 60* of that 90*.
The remaining 45* or 30* is open contact angle.

An 8 cylinder distributor is given only 45* in which to saturate and collapse the coil field per cylinder.
Of that 45*, the dwell angle will typically be around 28* to 32*.


With a point system the mechanical advance system will either work or not work but it has no relevance to engine starting at this point in time. Only ads confusion..
Click to expand...

I respectfully disagree.

If his flyweight system has not fully returned to BASE mode, the system may be giving more than what he may think is BASE or Initial advance, and it may be the reason why he felt the need to mess with the distributor clocking.



.
 
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Well yesterday a compression check was done. All cylinders were within 5 lbs of eachother. I checked the timing. At tdc and it was perfect at 4 degrees. All the replacement parts were done simply for preventive measure. All plug wires correct, firing order good, spark excellent. Ive determined the cause to be a stuck float on the carb. Its getting rebuilt today. Ill post with further updates. Hopefully this is the fix. At least I got to know the motor in the boat. I must say the 3.7 Merc is a very poor design from what I can see so far.
 
Yes it is and it was haunted with a huge amount of failures.
That engine was a Mercury design and was kept under warranty for many years after any warranty should have remained because of the chronic problems and failures.

You are very lucky to have one that still operates.
 
aaronp said:
.................. I must say the 3.7 Merc is a very poor design from what I can see so far.
Click to expand...

Yes, and that is sad because these were good torque producing engines.

If you'll notice, Merc used the Ford 460 cylinder head on this engine.
I believe that the bore/stroke is the same as the 460.

The camshaft drives the coolant circulating pump impeller.
There is a special seal between the oil side and coolant side causing this to be a problematic area.
The front covers are known to give issues as well.

The OEM crankshaft charging system is terrible.
There are kits that you can purchase that will allow you to eliminate the OEM system, and install a belt driven Delco 10si alternator.

Hopefully, you have a good one that will last you for years.



 
RicardoMarine said:
A 4 cylinder engine's distributor is given 360* of which to fire all 4 cylinders.
That equals 90* per cylinder.
In that 90*, the system will saturate and collapse the coil field once per cylinder.
Depending on what the OEM specifies, the dwell angle will typically be between 45* and 60* of that 90*.
The remaining 45* or 30* is open contact angle.

An 8 cylinder distributor is given only 45* in which to saturate and collapse the coil field per cylinder.
Of that 45*, the dwell angle will typically be around 28* to 32*.




I respectfully disagree.

If his flyweight system has not fully returned to BASE mode, the system may be giving more than what he may think is BASE or Initial advance, and it may be the reason why he felt the need to mess with the distributor clocking.



.
Click to expand...

What planet are you from?

If his flyweight system had not returned to is home position the boat would have ran horribly before he finished his last season........

In all of my experience I don't remember ever finding the mechanical advance stuck fully advanced. Found many rusted in the "home" position not allowing for any advance. Not one stuck fully advanced.............

This is not an issue of importance with regard to his not starting issues. Besides he responded with the correct information and his next steps.

Why would a post of this type be needed? To prove to someone that you can post the theory behind a point ignition system?

Whats your point? That I posted the incorrect dwell specification, Which I got from my Mercruiser service manual?

I didn't see any specifications in any of your posts..........Maybe that would be the correct thing to post instead of opinion and theory...
 
I must say the 3.7 Merc is a very poor design from what I can see so far.
Click to expand...

Ayuh,...... Mercruiser's redheaded bastard step-child they've been tryin' to forget since shortly after it was introduced,.......
 
RicardoMarine said:
Yes, and that is sad because these were good torque producing engines.

If you'll notice, Merc used the Ford 460 cylinder head on this engine.
I believe that the bore/stroke is the same as the 460.

The camshaft drives the coolant circulating pump impeller.
There is a special seal between the oil side and coolant side causing this to be a problematic area.
The front covers are known to give issues as well.

The OEM crankshaft charging system is terrible.
There are kits that you can purchase that will allow you to eliminate the OEM system, and install a belt driven Delco 10si alternator.

Hopefully, you have a good one that will last you for years.



Click to expand...

While I am at it,

What relevance does any of this have to do with his problem?

Am I the only one?

Just so you know, the engine circulating pump is driven by the crankshaft via the timing chain to the cam gear which the pump is attached.
And I have only had to replace a hand full of these seals. It is typically due to two reasons, 1. overheat, 2. high hours of use. Because it is a CLOSED system it does not see the affects of RAW water.....
 
RicardoMarine said:
A 4 cylinder engine's distributor is given 360* of which to fire all 4 cylinders.
That equals 90* per cylinder.
In that 90*, the system will saturate and collapse the coil field once per cylinder.
Depending on what the OEM specifies, the dwell angle will typically be between 45* and 60* of that 90*.
The remaining 45* or 30* is open contact angle.

An 8 cylinder distributor is given only 45* in which to saturate and collapse the coil field per cylinder.
Of that 45*, the dwell angle will typically be around 28* to 32*.




I respectfully disagree.

If his flyweight system has not fully returned to BASE mode, the system may be giving more than what he may think is BASE or Initial advance, and it may be the reason why he felt the need to mess with the distributor clocking.



.
Click to expand...

I would like to ad one additional comment,

""I respectfully disagree""


I am not sure why you would say this.

I have spent the last couple hours reviewing many of the threads here within the Mercruiser forum page.

So far 99.9% of the posts that I have read of yours have no relevant information to the specific issues with regards to the specific product or problem.

Lots of opinion, references to OEM but no specifications, many theories of operation or function and a lot of added information unrelated to the reported problem or product.

So how can you disagree, respectfully or not with anyone else's posts especially when their posts contain product/problem specific information?

Just my initial observation.
 
Well after pulling the carb and cleaning it, and replacing the float needle, the carb is now working properly. However it still wont start, and now i no oil pressure. hopefully the gauge or wires loose. After the starter, batteries, carb rebuild kit, and seven hours labor , im throwing in tbe towel.
 
@aaronp are you working from a service manual at all? Seems that you are chasing rabbits while the fat hog is sitting right in front of you. Don't take this as an insult, I'm simply saying it seems that you're not following standard troubleshooting steps to establish spark fuel and timing. We don't want you to be frustrated. we want you to succeed and enjoy the boat!
Let's try again with fuel. Get a can of starting fluid. You're NOT going to try to start the engine with this, merely see if the engine will sputter or even run a little after you shoot a 3 second burst into the open carb throat. If no, then the next thing to check is spark. Don't continue to try to start on fluid.
After this test report back and we'll try the next step.
 
I finally figured it out. Throttle cable was jammed up. After i fixed the carb and found that it fired right up. first test run tomorrow. I ordered the service manual. I havent recieved it.
 
I am glad that your advance flyweights and springs stuck OPEN (FULL ADVANCE) were not the cause.

Holy Moly Bat Man....!!
 
Test run while safely tied to the dock. Take it out after you are sure it runs well or you may end up paying for a tow. Be sure it is secure and that you're pointed at open water if it comes loose. Get it up to operating temp. You don't need wide open throttle. Ten minutes of this should be plenty then take it out. Be sure that there's someone on shore who knows you are doing this, how long you expect to be and generally where you are heading. Wear the PFD dammit. Don't just have it in the boat. OK mommy mode off.
 
o2batsea said:
Test run while safely tied to the dock. Take it out after you are sure it runs well or you may end up paying for a tow. Be sure it is secure and that you're pointed at open water if it comes loose. Get it up to operating temp. You don't need wide open throttle. Ten minutes of this should be plenty then take it out. Be sure that there's someone on shore who knows you are doing this, how long you expect to be and generally where you are heading. Wear the PFD dammit. Don't just have it in the boat. OK mommy mode off.
Click to expand...

Dont forget the cooler and beverages!!
 
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