New engine, mechanical fuel pump inoperable

[Quack Addict]

I built a new engine for my Sea Ray last winter - all new internals. It is a Chevy 350 / Mercruiser setup.

Anyhow, the mechanical fuel pump works great on the bench (pulls and pushes out of the respective bosses on the pump), but it doesn't pull or push when put on the engine. I have gas to the pump but nothing is getting past the pump and lifted to the engine... not a drop.

Yes, I have the fuel rod installed that goes between the cam lobe and the actuator lever on the pump. I verified the rod is moving back & forth when the motor is spun up. The problem is like the push rod is either too short (it measures 5.290" long) or the fuel pump has a dead spot - I can't think of anything else. The push rod does not look to be worn short based upon the machining marks on the ends - I can still see the factory chamfers on the ends of the rod and the ends are square and not deformed any.

The fuel pump does have about a 1/4" of slack in the plunger that has to be taken up before the pump will operate but I think this is normal. Here is the style of fuel pump I have. It does have a plastic bowl on the side that says something like "replace pump if there's gas in here" and while there is no gas, it appears there may be a couple drops of oil... it's high viscosity fluid, definitely not gas.

Any ideas? The engine shows really good signs of life when a little gas is dumped into the carburetor but with no gas making it to the carb, it dies right out.

 

[JustJason]

Re: New engine, mechanical fuel pump inoperable

Sounds like you either have a restriction or an air leak in the fuel system. Run the test in this thread to find it -----> http://forums.iboats.com/showthread.php?t=283269

 

[Quack Addict]

Re: New engine, mechanical fuel pump inoperable

JustJason,

Thanks for the link but I don't think a restriction is my problem. I have plenty of fuel flow coming out of the fuel/water separator and have fuel at the pump inlet but no fuel comes out of the pump outlet.

When I remove the pump, chuck it in my vise and actuate it on the bench, I have good suction on the inlet side of the pump and good push on the outlet side of the pump. But there is about 1/4" of slack from the pump lever's free state until you feel the pump tension up internally to start deflecting the diaphragm. I think this is normal but don't have another fuel pump handy to compare to.

When I install the pump on the engine and crank the starter, there is no suction on the inlet or pressure on the outlet side of the pump - absolutely none. I verified this by putting a finger over both fuel pump ports while the engine was cranked. It is like the fuel pump push rod isn't even installed, but it's in there and the pump is properly installed. The only thing I can think of is the fuel pump rod is too short (somehow) or the pump itself has a dead spot in the stroke... the 1/4" of slack I mentioned...

 

[betayv]

Re: New engine, mechanical fuel pump inoperable

is your pump new? I will change it anyway I used to have the same pump on my boat and was really old.

 

[Don S]

Re: New engine, mechanical fuel pump inoperable

The problem is like the push rod is either too short (it measures 5.290" long)

That is too short. The push rod is supposed to be 5.76".

 

[John_S]

Re: New engine, mechanical fuel pump inoperable

The problem is like the push rod is either too short (it measures 5.290" long)

That sounds short. Do some further checking, but 5.75" is what is sticking in my head.


OK, looks like Don beat me. Sorry, walked away before posting.

 

[zbnutcase]

Re: New engine, mechanical fuel pump inoperable

Sounds to me like you have a 90deg V6 pump push rod.

 

[Quack Addict]

Re: New engine, mechanical fuel pump inoperable

Crap... there is a chance I got pushrods mixed up. I had several floating around my garage when I did the rebuild and I thought they were all the same length. Not sure where I would have got a V6 rod from as I pretty much only deal with SBC V8's.

 

[John_S]

Re: New engine, mechanical fuel pump inoperable

Besides length, you will need one to match the cam (cast or steel). Steel roller cams will require a different push rod, usually bronze tipped.

As far as using ones laying around the garage, not sure if that is the best way to go. While I have not ever heard about replacing the rod with the cam, like the flat based lifters, it would seem that it would apply. Maybe it is not an issue because of the smaller diameter rod area? Anyway, for less than $20 for a new one, might be worth the piece of mind.

 

[bomar76]

Re: New engine, mechanical fuel pump inoperable

You state you built a new engine.
Are you 100% certain the cam you used has a fuel pump lobe?
Not all do......and some of the cams for early fuel injected vehicles (late 80's) had fuel pump lobes that were never finish ground making them useless.

I have seen both of those problems.

 

[Quack Addict]

Re: New engine, mechanical fuel pump inoperable

You state you built a new engine.
Are you 100% certain the cam you used has a fuel pump lobe?

Yes, the cam has a mechanical fuel pump lobe on it. I spec'd the cam as such when I ordered it and when I crank the engine while pushing on the rod, the rod slowly moves back & forth (indicating there is an eccentric lobe on the cam).

I am picking up a new push rod after work today.

Thanks for the help guys!

 

[bomar76]

Re: New engine, mechanical fuel pump inoperable

Yes, the cam has a mechanical fuel pump lobe on it. I spec'd the cam as such when I ordered it and when I crank the engine while pushing on the rod, the rod slowly moves back & forth (indicating there is an eccentric lobe on the cam).

I am picking up a new push rod after work today.

Thanks for the help guys!

OK, just checking.....as I said, I have seen both of those situations firsthand.
One of those obvious things that sometimes can go totally unnoticed.

 

[Quack Addict]

Re: New engine, mechanical fuel pump inoperable

Don S nailed it. I got a new fuel pump push rod yesterday after work. It mic'd out at 5.76"

The old man at the parts shop said the 5.29" fuel rod probably came off a BBC, which makes a bit of sense because I parted out a 402 a couple years ago and may have got the fuel rod from that mixed in with my SBC parts inventory.

By the time I got things cleaned up and reassembled, it was too late to start & tune the engine but I did crank it over with the coil wire off and now have fuel to the carb. Rain today; plan is to put some life into the beast tomorrow.

Thanks guys!