Fuel Pumps M400

[Bob Giaier]

I was out last weekend on a trip from Au Gres to Harrisville Michigan (about a 3 1/2 hour trip) in our 73 tri cabin. While cruising I always go below and check things out. We noticed a slight gas smell from the port engine and low and behold the port fuel pump was beginning to fail. It was dripping fuel.

My point in this posting is that the engines are very original and the fuel pumps are not vented to the carbs! They look like automotive style. Did the older Chrylser marine engines use a more standard automotive style fuel pump?

I coincidentally had an electric fuel pump that we converted on the spot. Right now I think I will convert the other engine to electric.

Just thought this posting can help others with similar engines.

[prowlersfish]

Bob make sure you wire the fuel pump to a oil pressure switch for safety

[larryeddington]

my 78 318s fuel pumps have a hose barb with only a rubber seal over it. Trojan/chrysler did not vent it to the carb. They are not vented. So at the end of the day who knows what they used for sure on any given installation.

[Stripermann2]

my 78 318s fuel pumps have a hose barb with only a rubber seal over it. Trojan/chrysler did not vent it to the carb. They are not vented. So at the end of the day who knows what they used for sure on any given installation.

Some builders used a dual diaphram pump, if the primary diaphram ruptured, it would leak gas into a sight glass (bowl) attached to the pump for a visual notification of failure...

[Big D]

Some builders used a dual diaphram pump, if the primary diaphram ruptured, it would leak gas into a sight glass (bowl) attached to the pump for a visual notification of failure...

+1
Newer pumps with the tubes are now available for Chrysler marine apps and should be swapped out for safety. Glass sight bowls on gasoline applications should not be on board anymore for obvious reasons. Amazing what used to be allowed

[Bob Giaier]

Thanks guys for the input. I Noticed the vent hose kits with new spark arrester on verious internet sights. Sierra sells replacement mechanical fuel pumps any recommendations for or against Sierra parts?

Also Prowlerfish, I temperarily wired the electric pump to get home using a manual switch to trun it on directly to the battery. That definitely won't stay since I'll keep forgetting to turn it off. We tried wiring it like you said over the oil pressure switch, but doesn't the engine need to build oil pressure for the pump to work? That means I'll have trouble starting the engine cold (no fuel is pumping). My thought is to add a relay connected to the 12 V side of the coil or ignition signal wire and let the relay power the pump.

[prowlersfish]

They make oil pressure switch that are just for this reason . Yes you won't have fuel from the pump until you get pressure ( about 5 psi ) . But you should have fuel in the carb bowl anyway . and it won't take long to get a few psi oil pressure


Using a oil pressure switch to control the pump is a must . If fact it is required by ABYC , I believe the coast guard also requires it also . surveyors will also check it,

Honestly I like a stock type pump better but electric will work if done right .

BTW you don't use the switch you have now you add one using a tee .

here is one switch
http://www.jegs.com/p/Holley/Holley-Fue ... 3/10002/-1

Or you can get a 3 wire swith to replace yours ( not replacing the sender to the gage )

[Big D]

For start up, the pump gets it's power from the "Start" circuit, usually an auxilury terminal on the starter solenoid. This powers up the pump prior to achieving oil pressure long enough to pressurize the fuel system/fill carb bowl. After the engine starts and the start circuit is disengaged, the oil pressure switch supplies power to the pump.

[prowlersfish]

It can be wired as Big D says but on a carb engine its not really needed IMO Although some OEMs do it. On EFI the PCM will let the pump run for a few seconds when the key is turned on

[Big D]

The OEMs that I'm familiar with do it this way (Merc, Volvo, Crusader, USM) unless earlier mods on the move away from mechanical pumps were different. The problem with not wiring it to the start circuit in a carb application is that you have no way of priming the system prior to achieving oil pressure if the boat has sat for some time and the fuel in the bowl has evaporated. It's a common oversight I've seen on retrofits where guys eventually end up installing a momentary switch at the helm. EFI of course is totally different.

[Bob Giaier]

You guys really know your @#$%. Thank you. I see what you mean about the ignition switch then the oil pressure switch.

Actually, I think the boat was trying to tell me I have a problem with my charging system when I temprarily wired the pump, since I found I can't run my blowers whille the fuel pump runs unless the RPMs are way up. I can see with the blowers running only the amp meter stays negative. With nothing running the amp meter is 0. I think my shore powered battery tender is what kept me charged all season. I plan to figure this out first. If I have issues I'll start a new posting on that one.

Thanks again guys.

[prowlersfish]

Big I have run into some that did not have a way to prime , but it was not a big deal as it won't take long to get 5 psi oil pressure , also on some that I have refitted the "I" terminal on the starter is used for the ignition system when cranking ( you could use a relay if needed ) and some starters do not have the extra terminal . I really don't see much difference in cranking to get fuel pressure of cranking to get oil pressure to turn on the pump . it takes about the same length of time I would think. Never took a stop watch to it as Its never been a issue . But again there is nothing wrong with getting the fuel faster .

Not a big fan of electric pumps to replace the Mechanical . but when replacing GM long blocks the new style may not be machined for a pump .

[Bob Giaier]

That makes logical sense. Anyways, after looking at my charging system and thinking about potential faulure modes between electric and mechanical, I'm beginning to lean toward replacing the mechanical pump with a marine version and using the electric as an onboard back up kit for either engine (just in case). I keep a box of "just in case items" they do come in handy.

Thank you everyone for your input.

[Bob Giaier]

I thought I should follow up with what eventually happened with these fuel pumps. I did get "Marine" style pumps from Marysville. I figured if anyone had a clean kit it would be the original manufacturer. The pumps had a hose fitting glued into the vent hole in the pump. The pumps that Marysville sells to replace the old style are very different from original equipment and are not easy to install. The fitting in the vent hole must be removed to install one of the pump mounting bolts and the fitting must be cut shorter to clear the engine casting not to mention it has to be re-glued in place. Additionally, the fuel outlet on the pump is positioned so close to the water pump (less than 3/4"), it's almost impossible to get any kind of fitting connected to it. If I had to do this over, I would consider rebuilding the old pumps and Glue with J B weld a piece of tube in the drilled out vent hole for the connection to the flame arrester. I would have saved allot of money and had a cleaner installation.

[larryeddington]

My 77 pumps have the barb, not I have a 78 and they do not, gonna put them on as I have used a bulkhead fitting to connect the vent hose to flame arrestor. I could not get a consensus as to where to put the vent line and IMO it needed to go directly into the carby air horn.