1994 mercury mercruiser engine not starting

[Cap'n bubba]

good morning all,
First post here. I am looking for some ideas to look into as to why my boat wont start. So I have just completed a top end rebuild. replaced cylinder head and put all fresh gaskets from the head gasket and up. I have a manual for all torque specs and all wiring seems to be back in place according to pictures I had taken during the tear down process. I freshly charged the battery. Engine will crank but not fire. Starter fluid sprayed into carb once and small flame seen and engine back fired. I am figuring it is bad gas and will be syphoning the gas out and putting fresh gas. Other concern I have is whether this sounds like it could be a fuel pump issue as well. Any help or advice on this would be helpful. Thank you.

 

[Chris1956]

Mercruisers have a shift assist switch that kills spark. So, do you have spark?

 

[Cap'n bubba]

This might be a dumb question but as I am still learning how to do these repairs wouldn't having a flame in the spark arrestor with starter fluid mean it has spark?

 

[Chris1956]

Possibly, but ether explodes under compression as well as any kind of spark. Keep a fire extinguisher handy when using ether.

Testing the spark to all cylinders, especially with a timing light is the best way. Remember, on your 4 cycle motor, spark needs to occur on the compression stroke, not the exhaust stroke. Timing marks do not distinguish between compression and exhaust strokes.

When repairing my 4.3LX ignition system, i found that the distributor did fit into the block 180* out of time. This provided spark on the exhaust stroke, and motor would not run.

 

[Cap'n bubba]

Possibly, but ether explodes under compression as well as any kind of spark. Keep a fire extinguisher handy when using ether.

Testing the spark to all cylinders, especially with a timing light is the best way. Remember, on your 4 cycle motor, spark needs to occur on the compression stroke, not the exhaust stroke. Timing marks do not distinguish between compression and exhaust strokes.

When repairing my 4.3LX ignition system, i found that the distributor did fit into the block 180* out of time. This provided spark on the exhaust stroke, and motor would not run.

So update on post. Replaced fuel pump since I had already ordered it. Breather tube from carb into the fuel pump was clogged. Once replaced and attempted to fire it up there was a significant amount of fuel that had leaked on the carb. Possibly from where fuel line goes in. Unsure where is was leaking from. Thinks gaskets in carb have dry rotted and gone bad. Rebuild kit was cheap. Going to do that. Any other thoughts on this?

 

[ryan 98]

So update on post. Replaced fuel pump since I had already ordered it. Breather tube from carb into the fuel pump was clogged. Once replaced and attempted to fire it up there was a significant amount of fuel that had leaked on the carb. Possibly from where fuel line goes in. Unsure where is was leaking from. Thinks gaskets in carb have dry rotted and gone bad. Rebuild kit was cheap. Going to do that. Any other thoughts on this?

Kinda sounds ignition related still. Especially the backfire you mentioned earlier. Should run for a second regardless of any thing to do with the fuel system If you put some gas down it's throat. Cyl 1 on TDC compression stroke. Is the rotor pointing towards cyl 1 in the cap? I'm assuming a distributor on your setup, but I'm not too familiar with what you have. The other question is did you mess with the timing chain at any point during your rebuild? Not sure if it's an interference engine or not, but that could be way out too. Finaly and the absolute simplest thing is the firing order right? I've been doing motors a long time and I still mess up firing orders sometimes. Sit down and really check it out since you obviously already have all the documentation on your motor from your post before. Fuel leaking all over the carb is likely a stuck float letting it poor out the carb vent and in to the motor also. Make sure it's not hydrolocking on gas before cranking it. Bad things happen then

 

[Cap'n bubba]

It does have a distributor. First thing I thought of was the ignition order as well. I labeled the ignition coils prior to removal and placed them back per the manual I have. I have an est ignition system. I did not tear down far enough to get to the timing chain. I had to remove the intake manifold and the valve cover to get to the cylinder head. Did not have to pull the front cover off the engine. I was thinking maybe something with the carb or the gaskets. I think it’s been having carb issues and just never got a chance to rebuild it. I still have to get a chance to check the spark which I will be doing next week when I have the free time. I looked over the wiring 2 days ago and it appeared that all had been replaced properly but the firing order had been something I considered as well. I’m not sure if it is because of the new head but it doesn’t seem to try to turn over quite as hard anymore. It’s not as loud and seems a bit smoother but I assumed it was from having new parts.

 

[CaptnKingfisher]

When diagnosing issues I start with the ignition circuit because it's easy to test the entire ignition system with an adjustable spark tester and a multimeter. And the results are black and white. If your spark jumps 7/16" and you've got good compression then you move on to fuel. So my suggestion is to measure the strength of your spark at each cylinder, let us know what you find

 

[Cap'n bubba]

When diagnosing issues I start with the ignition circuit because it's easy to test the entire ignition system with an adjustable spark tester and a multimeter. And the results are black and white. If your spark jumps 7/16" and you've got good compression then you move on to fuel. So my suggestion is to measure the strength of your spark at each cylinder, let us know what you find

I’m hoping my manual has all the specs on what the electrical read outs should be because electrical is not my strong suit. I still do need to check the spark on each plug.

 

[CaptnKingfisher]

I’m hoping my manual has all the specs on what the electrical read outs should be because electrical is not my strong suit. I still do need to check the spark on each plug.

The manual has it all. The manufacturers service manual is way better than the aftermarket companies (seloc, clymer, etc) so if you don't have the real manual you may want to get it. Testing the ignition circuit is easy to learn. I always start with spark though, because that tests the entire ignition system. If you've got strong spark you're good and you can move on, unless your problem is intermittent or after the engines warmed up, that complicates the matter. But you need to have an adjustable spark tester so you can tell the difference between strong spark and weak spark. If you've got weak spark or no spark you start backtracking through the circuit. First test your spark plugs leads for resistance. Set the multimeter to ohms and connect a lead to each end of the spark plugs wire. Resistance should be close to zero. If you have a lot of resistance that means the wire is damaged and your losing electricity through the wire. If your spark plugs wires are good you move on to the coil. Your manual will tell you the specs to test for but the coil has two circuits, one between the positive and negative terminal which will have a specific amount of resistance, something like 2 ohms, check your manual, and then there's a secondary circuit that you test going from positive to high tension lead (where spark plugs wire connects) and negative to high tension lead. This will have a lot of resistance. If your coil(s) is(are) good then you got back and check things like point gap, dwell and timing. Tons of videos on YouTube of how to test different parts of the ignition system. That's how I learn

 

[ryan 98]

I’m hoping my manual has all the specs on what the electrical read outs should be because electrical is not my strong suit. I still do need to check the spark on each plug.

It's all super simple and there's 1000 videos on line that explain the process better than I can here. But from what you described the obvious starting point is 1, does it have strong spark? 2, is the spark happening at the right time? Regardless of the carb condition it should bark off for a few seconds and die with a bit of gas pored down the carb, and I mean a bit, don't go crazy. One thing to keep in mind is if timings out it will very likely backfire out the carb. Make sure there isint a bunch of gas or anything flammable sitting up there when your messing with it. If it keeps burning for more than a few seconds just smother out the flames with an old blanket or something. Obviously don't go hitting it with water or you will be sorry. Gas floats on water....

 

[Cap'n bubba]

So I believe the shift assist switch was not in the correct position. Spark is good from what I can tell in all cylinders. Already have the rebuild kit for the carb so I’m rebuilding that and am replacing the choke as well because I think I’ve been having issues with it for awhile with the way it struggled to start for the last few years. Carb should be rebuilt and back on tomorrow. Will then try to start it again and see what happens.

 

[CaptnKingfisher]

So I believe the shift assist switch was not in the correct position. Spark is good from what I can tell in all cylinders. Already have the rebuild kit for the carb so I’m rebuilding that and am replacing the choke as well because I think I’ve been having issues with it for awhile with the way it struggled to start for the last few years. Carb should be rebuilt and back on tomorrow. Will then try to start it again and see what happens.

If it has good spark on all cylinders then the shift assist switch is not your problem as that switch will interrupt spark. How are you testing spark? "Spark is good from what I can tell" get yourself an adjustable spark tester. One of the more important tools in my diagnostic bag which gives you black and white data on how strong or weak your spark is

 

[Cap'n bubba]

If it has good spark on all cylinders then the shift assist switch is not your problem as that switch will interrupt spark. How are you testing spark? "Spark is good from what I can tell" get yourself an adjustable spark tester. One of the more important tools in my diagnostic bag which gives you black and white data on how strong or weak your spark is

I bought an inline spark tester which lights up when it gets spark

 

[CaptnKingfisher]

I bought an inline spark tester which lights up when it gets spark

I think you're right to be rebuilding the carb then. Recommend picking up an adjustable tester at some point. If you've got access to a timing light and a dwell meter then id verify timing and dwell were set correctly after your rebuild.

 

[Cap'n bubba]

So carb is rebuilt. Everything is back the way it should be. But still won’t start. Had a slight backfire but nothing else. Only other thing I can think of is bad gas so I’m draining the tank tomorrow and putting new gas in it. Any other ideas?

 

[Chris1956]

You are sure she is firing on the compression stroke?

 

[Cap'n bubba]

Might sound like a dumb question but how do you know if it is firing at the right time? I’m still learning all of this

 

[Chris1956]

Remove spark plugs and distributor cap. Turn engine over with wrench and put finger on #1 spark plug hole. Feel for compression, and observe distributor rotor turning. As piston nears top of cylinder and compression increases, distributor rotor should be pointing at #1 spark plug "post" on distributor cap.

Alternatively, remove valve cover and set #1 piston to top dead center, with both valves closed. Distributor rotor should be pointing to #1 post on dist. cap.

 

[ryan 98]

Remove spark plugs and distributor cap. Turn engine over with wrench and put finger on #1 spark plug hole. Feel for compression, and observe distributor rotor turning. As piston nears top of cylinder and compression increases, distributor rotor should be pointing at #1 spark plug "post" on distributor cap.

Alternatively, remove valve cover and set #1 piston to top dead center, with both valves closed. Distributor rotor should be pointing to #1 post on dist. cap.

This is your answer. From everything you have told us it's sounding out of time or firing order. Follow these steps and you will find out quick.