Engine doesn't start

[sebas54]

Hi, I have a 1987 GM 4.3l I/O Merc.


I am getting it ready for the summer and went to start it today. It wont start. I sprayed starter fluid into the carb and it starts for a couple of seconds. After it dies the fuel pump starts vibrating more than it ever did. So it does start but dies after a couple of seconds and it only start when I spray starter fluid. The gas looks and smells good and I added 5 more gallons today with startron.

What could be wrong, the fuel pump?? I think it is an electrical pump. I posted a pic of it some time ago and people told me it was from a Jeep.


Please help, I only have a limited number of days to work on the boat. Is there a fuel filter other than the water separator?




Thank you.

 

[havasuboatman]

Re: Engine doesn't start

Make sure your water separater/fuel filter is full of gas if your fuel pump is between the carb and the filter.
To check your fuel pump, disconnect the fuel line after the pump and place it in to a can then crank the engine. Fuel should come out. But make sure that filter is full of fuel.
If you are pumping fuel out of the pump, your float valve is probably stuck in it's seat.

 

[sebas54]

Re: Engine doesn't start

Thanks fro the quick reply.

The water separator was full of fuel. I removed the water separator and cranked the engine. I heard the pump vibrate but no gas came out. I did it again and gas dripped out.


So, it is the fuel pump??? Should I replace it???

Is it a simple replacement of part?

 

[Maclin]

Re: Engine doesn't start

Does the carb have fuel in it? Easy to check: Can you see fuel spray into the carb throat when the throttle is moved? You should have to hold the choke plate open to see this. If the choke plate is not closed (on a cold engine) then the choke may not working.

 

[littlebookworm]

Re: Engine doesn't start

Before replacing anything, first check the fuel pick-up in the tank. There's a screen at the end of the pick-up tube. That may have become clogged. There is also, on most tanks, a one-way valve at the tank hose fitting which allows fuel to flow out but not back. This may have become blocked or stuck closed. This has become more of a problem lately with the e-fuel now available. In other words, before replacing, check that you have a clear, flowing line from the fuel in the tank to the fuel pump itself. By the way, if, as you say, the fuel pump is from a Jeep, that's where it belongs, not in a boat. You should only be using a marine certified fuel pump in a boat. Replacing an electric fuel pump is fairly simple: disconnect and plug the hoses, disconnect the wires, unbolt and remove. Do the reverse to connect the new one. Good luck, and let us know what you find. Hy

 

[sebas54]

Re: Engine doesn't start

I do not see an fuel being sprayed into the carb.

I removed the water separator and no gas comes out. There was also a fuel filter before the pump so I removed it and it had debris in it. I left it off and still no change. I also had the pump running while I put my finger against the intake of the fuel pump and there was no suction.

Should I go and buy a fuel pump?


Thank you all very much.

 

[sebas54]

Re: Engine doesn't start

Could I just blow on the hose going to the gas tank to see/feel if it clogged. I am really leaning towards the pump because as I said before it was running and there was no suction on my finger from the inlet.

Thank you all.


I can find the serial number on the engine or there isn't one. this engine was built by the previous owner and I don't know what he did. How can I get the part without the serial number.


So far it most defiantly sounds like the pump?? Right????

 

[sebas54]

Re: Engine doesn't start

Ok I blew into the hose before the pump going into the tank and it is not clogged. I also sucked and it doesn't not seem clogged. I removed the gas cap for this. I also put the hose after the pump into a can and let the pump run and no gas(maybe a drip). The pump makes noise and vibrates but that is about it.



So, do you think that it is advisable to go and buy a new pump??



Thank you all sooo much again.

 

[Maclin]

Re: Engine doesn't start

Sounds like the pump to me now too.

If I recall, your boat's fuel delivery system is from an OMC due to a previous refit (good or bad, not the point now). You may be able to guess a year and engine size and start from there when looking for a direct replacement. Otherwise you may have to find a good universal marine 12v fuel pump and fit and plumb it in yourself to the bracketing that is there on the boat.

As I recall you have persevered tougher things than this with your boat, good luck!

 

[sebas54]

Re: Engine doesn't start

Surprised you remember Maclin, thanks for the encouragement, I needed it.

Which pump does my engine need High pressure or Low pressure? I found a universal electrical pump for $90 but need to know High or Low pressure.

 

[sebas54]

Re: Engine doesn't start

OR how many gallons per hour. 30 gallons per hour????

I found this pump and it looks identical to the one thats there know

 

[sebas54]

Re: Engine doesn't start

Not sure. Carb 2 barrel.

 

[sebas54]

Re: Engine doesn't start

And what PSI 2.5 to 4 psi or 5 to 9 PSI

LOW pressure or High pressure


Thank you

 

[Maclin]

Re: Engine doesn't start

Definitely low pressure for your carbed engine. Carbs can take only up to 7-8psi before the needle and seat is overrun and the carb overflows. Most specs are from 3-7 psi.

 

[Maclin]

Re: Engine doesn't start

Just now saw your post, the 2.5-4 psi sounds perfect.

 

[sebas54]

Re: Engine doesn't start

Does the pump have to be marine? Is it just the casing that makes it marine?


Thank you so much!!

 

[sebas54]

Re: Engine doesn't start

Dose the PSI of a fuel pump affect performance?? The lower the PSI the less fuel will be delivered and the slower the boat will go??? Should I get a pump that is 4-6 psi? Will that make any difference vs. a pump with 2.5-4 psi???

 

[Maclin]

Re: Engine doesn't start

You do not want to put too much psi to the carb's needle and seat or the carb will overflow. Most carbs like 3-4psi and can keep up with the engine at that rate. GPH can be a factor, but the pump you are looking at in the 2.5-4psi range should work fine.

 

[sebas54]

Re: Engine doesn't start

The reason I ask is because this pump that has 2.5-4 psi is listed for a 4 cylinder.

Thank you, I will go and order it.

 

[Maclin]

Re: Engine doesn't start

I am not going to comment on the Marine vs. Auto except to say that if the replacement you have found matches what you have now then it will be at least as safe as what you have been using.

Here are some specs I found and use when needed. It shows how much fuel flow is needed to feed a particular level of horsepower.

Flow in GPH = HP * BSFC *(1 / fuel weight)
For BSFC(brake specific fuel consumption) rated in lbs per horsepower-hour, use:
0.45 to 0.5 for naturally aspirated engines
0.55 to 0.60 for supercharged engines
0.60 to 0.65 for turbocharged engines
For fuel weight, use
6.216lb/gal for regular unleaded
6.350lb/gal for premium unleaded
For example, here is the calculation for a naturally aspirated 250HP engine on regular unleaded gasoline.

250 * 0.45 * (1/6.216) = 18 GPH

With recommended 30% safety factor a 24 gph fuel flow is recommended.


Your HP is lower than 250 so a 24gph flow is sufficient. Carb inlet pressure should be at least 3psi at wide open throttle, regarding psi 7-8 is at the high end of what the needle and seat can handle.