3.0L Mercruiser Fuel Pump Installation

[Ballingbob]

I have a 1989 Mercruiser 3.0L engine that I took the mechanical fuel pump off and when I installed it again it isn't pumping. There's a shaft coming out of the pump with a wear mark on the top of the shaft which I think runs on a cam to push it down for the pumping action. When I put it on the engine it doesn't do any pumping. If I push it down by hand when I have it off I hear air coming out near the fuel line to the carb so I think the pump is working.

Is there a slot or anything that the shaft should fit into when I install it or does it just go in and bolt down. When I just bolted it down nothing happened as far as pumping.

Any help would be appreciated.

 

[mpdive]

Re: 3.0L Mercruiser Fuel Pump Installation

The shaft your talking about is the cam lever. The top of the shaft rides under the push rod. If you are installing it by pushing it straight in you are probably not contacting the pushrod. You may have to push it up with your finger. Hold the pump at an angle till you feel the resistance on the lever and then push up to seat the pump. All should be well.

 

[Ballingbob]

Re: 3.0L Mercruiser Fuel Pump Installation

The shaft your talking about is the cam lever. The top of the shaft rides under the cam lobe. If you are installing it by pushing it straight in you are probably over the cam lobe and not under it. Hold the pump at an angle till you feel the resistance on the lever and then push up to seat the pump. All should be well.

Thanks for your feedback. I tried what you said but still no suction. I took the pump apart and cleaned it real good and put the pump on the engine without the bottom of the pump attached so I could feel if the diaphram was going up and down but couldn't feel any movement. I pushed up on the diaphram as if it was screwed together. I took it off again and operated the pump by hand and again I could feel air coming out but I pushed the cam lever quite a ways which was probbably more then the cam would do in the engine. While the pump was off I put my finger into the slot so I could feel if the cam was turning and it was. I then coated the cam shaft on the pump with grease at the wear point where the cam touches and cranked it and the grease was moved.

As long as the screws are lined up and go in easy the pump should be installed correctly, right?

Could it be that the pump needs to be rebuilt with a new diaphram even though it felt like it was pumping when I did it by hand?

Thanks again

 

[mpdive]

Re: 3.0L Mercruiser Fuel Pump Installation

Not rebuilt but replaced. You answered my question already when you said there was movement of the push rod against the cam lobe. Worst case scenario would have been a worn cam lobe which would not have been good. Why was the pump removed to begin with? Was the boat running before you took the pump off?

 

[Ballingbob]

Re: 3.0L Mercruiser Fuel Pump Installation

Not rebuilt but replaced. You answered my question already when you said there was movement of the push rod against the cam lobe. Worst case scenario would have been a worn cam lobe which would not have been good. Why was the pump removed to begin with? Was the boat running before you took the pump off?

I had to replace the head because it had cracked and to be honest I don't remember why I took the fuel pump off. The boat was running but it got water in the oil so I found the head had a crack. I just got it put back together and tried to start it but it wasn't getting the gas. That's when I started messing with the fuel pump trying to figure out if it was getting fuel.

Thanks a lot for all your help. Do you know if a marine repair shop would have a way to test it before I buy a new one?

 

[mpdive]

Re: 3.0L Mercruiser Fuel Pump Installation

This is what I would do if it were mine. Push the pushrod up and put a dab of grease at the tip to hold it. Reinstall the pump and the inlet line. Disconnect and isolate the coil wire(very important). Grab a gas can and run the outlet line into it and crank it over for about 10 seconds and see if its pumping. If not, wait five minutes and retry(give the pump time to reprime). If you still have no fuel, disconnect the inlet line and connect a barb and hose to the pump and pull fuel from a good source such as another fuel can. Crank it again. If you still have no fuel, your looking at a bad pump, bent puchrod, or a worn cam lobe. It is possible the cam lever on the pump may have become slightly bent or distorted. Poor maintenance via oil changes or overheat conditions are about the only things to wipe out a lobe and I would hope that's not the case with yours. Following these steps will help isolate the trouble area. I once had a GM vehicle with the same problem. I had someone tap the starter as i held the pushrod against the cam lobe and it barely pulsed. Cam was wiped. These usually dont go bad overnight though especially since the boat was running. Keep me posted.

 

[Ballingbob]

Re: 3.0L Mercruiser Fuel Pump Installation

These are great ideas. I will try them. When you say pushrod, what pushrod are you talking about?

 

[mpdive]

Re: 3.0L Mercruiser Fuel Pump Installation

Your cam lever is either pushrod activated or is direct contact with the cam lobe. I am almost sure yours is pushrod actuated

 

[FreeBeeTony]

Re: 3.0L Mercruiser Fuel Pump Installation

I am pretty certain the inline engine's fuel pump lever is actuated by direct contact with the cam. Make sure the lever is UNDER the cam when you install it.

Do you have a manual?

 

[mpdive]

Re: 3.0L Mercruiser Fuel Pump Installation

I am pretty certain the inline engine's fuel pump lever is actuated by direct contact with the cam. Make sure the lever is UNDER the cam when you install it.

Do you have a manual?

Thanks for the additional help on this Tony. I looked at my exploded view of the 3.0 and it shows a pushrod. I was thinking the same as you that it was direct cam lobe operated and edited my original post showing that. I thought it was on the 3.0 too but my exploded view shows a pushrod.
If your reading this post Ballingbob, look inside the hole where the pump was and see if you can actually see the cam lobe, or a pushrod. If it is lobe operated be sure to get the arm under the lobe by installing at an angle. You will feel the pressure on the arm when you have it right. Thanks again Tony for trying to help. Any Merc mechanics feel free to advise.

 

[fishrdan]

Re: 3.0L Mercruiser Fuel Pump Installation

The fuel pump on a 3.0L is driven direct off the cam, no push rod. You can look into the hole (flashlight) to inspect the cam lobe while turning over the engine slowly. Though, I think it would be weird for the lobe to be wiped out since the fuel pump doesn't exert near the pressure the lifters do.

While installing the pump, it should be cockeyed a bit and then tighten flush to the block as the bolts are secured. The pump arm hits the cam and puts a bit of pre-load on the arm, causing the pump not to sit flush against the block if you try to just hold it into position. If you can hold the pump flush against the block in it's bolted position, something is whacked.

Are you bolting the pump onto the block in the proper orientation, the correct end up? This might be a dumb question as the fuel lines probably wouldn't line up and I'm not even sure i the pump would fit without hitting the cam wrong, but just a thought. Old 3.0's (181 CI, 3.0L displacement, 140HP) have the filter on top of the pump and new 3.0's have the filter on the bottom. The pumps are different, but someone, at some point, could have change it over.

Do you have any pics?

 

[mpdive]

Re: 3.0L Mercruiser Fuel Pump Installation

The fuel pump on a 3.0L is driven direct off the cam, no push rod. You can look into the hole (flashlight) to inspect the cam lobe while turning over the engine slowly. Though, I think it would be weird for the lobe to be wiped out since the fuel pump doesn't exert near the pressure the lifters do.

While installing the pump, it should be cockeyed a bit and then tighten flush to the block as the bolts are secured. The pump arm hits the cam and puts a bit of pre-load on the arm, causing the pump not to sit flush against the block if you try to just hold it into position. If you can hold the pump flush against the block in it's bolted position, something is whacked.

Are you bolting the pump onto the block in the proper orientation, the correct end up? This might be a dumb question as the fuel lines probably wouldn't line up and I'm not even sure i the pump would fit without hitting the cam wrong, but just a thought. Old 3.0's (181 CI, 3.0L displacement, 140HP) have the filter on top of the pump and new 3.0's have the filter on the bottom. The pumps are different, but someone, at some point, could have change it over.

Do you have any pics?

Thanks for helping out fishrdan.. It's been years since I put one on a 3.0 and I too remember them being lobe driven. Funny my Seloc manual shows the pushrod on the 3.0, and that's the only option they show. Should I throw away the Seloc? LOL Thanks again for the help and hopefully he can get it up and running. Have a great Labor Day.

 

[Ballingbob]

Re: 3.0L Mercruiser Fuel Pump Installation

I checked the cam inside the engine and it is direct contact with the cam and fuel pump lever. I checked the lobe on the cam and couldn't tell that it was worn at all.

Can someone tell me what the line coming from the fuel pump to the top of the carburator is for? It's the smaller line that has a flexible hose. The other line that I think is the main fuel line is metal and attached near the bottom of the pump.

I have the pump on the bench right now and if I put my finger over the small outlet on the upper half of the pump I can't push the cam lever down. If I take my finger off I can and then I can feel air coming out the small line. Nothing ever comes out of the main line. Does that sound normal?

I don't have any pictures of it because I'm at my cottage and didn't bring the camera and I can't send it with my cell phone. The filter is on the bottom and there is only one way that it will fit.

I know for sure that when I install the pump it is under the cam.

Thanks everybody for the help.

 

[mpdive]

Re: 3.0L Mercruiser Fuel Pump Installation

The hose is for if the pump diaphram fails, it dumps fuel back into the carb instead of in your bilge. Any fuel in the line indicates a bad pump. As far as the install goes, as fishrdan explained, when you install the pump the lever goes under the cam lobe. As you will see the pump will be angled to get it under the lobe. This is what you want because you are preloading the lever. Then you push upward and towards the block. Quickly start the bolts and hold the pump to the block as you tighten the bolts. The pressure you feel on the pump lets you know you installed it correctly. If you just push the pump straight in, you would be intalling it incorrectly. I would temporarily reinstall the pump and test it as I said before. Again, any fuel in the clear tubing indicates a bad pump. Let me know your progress. And thanks again to the other posters.

 

[NetDoc]

Re: 3.0L Mercruiser Fuel Pump Installation

Any help would be appreciated.

Thinking outside the box, why not take this opportunity and switch to an electric pump and put a cover over the hole? Most are virtually silent now and they are quite reliable.

 

[mpdive]

Re: 3.0L Mercruiser Fuel Pump Installation

Good point! Less moving parts can be a good thing unless your getting old like me and were talking about knees, back etc....

 

[Ballingbob]

Re: 3.0L Mercruiser Fuel Pump Installation

Hello everybody,

I took the fuel filter out of the fuel pump and pushed the cam lever down by hand on the bench and could feel air coming out of the main fuel line port going to the carburator. When I had it in I couldn't feel anything. Does that mean that the filter is clogged and the pump is good or is the filter so fine that I shouldn't feel air?

I was also able to push the cam lever farther down with the filter out than when it was in.

Thanks again

 

[mpdive]

Re: 3.0L Mercruiser Fuel Pump Installation

Pump lever travel is not the same as when it is moved by the lobe, nore is the frequency of lever travel able to be duplicated . Best thing is to put a filter in it and reconnect the pump. Run it off an external fuel source and see if it's pumping. It's the easiest way to diagnose it.

 

[NetDoc]

Re: 3.0L Mercruiser Fuel Pump Installation

Good point! Less moving parts can be a good thing unless your getting old like me and were talking about knees, back etc....

Moreover, you can put in a simple push button switch that will allow you to fill the carb BEFORE you crank the engine, ultimately saving your battery. Be sure to cap off the extra vents or send them back to the tank.