1989 5.7L Mechanical fuel pump to Electric question

[will941s]

Wanting to convert my 1989 Mercruiser 5.7L with the Mechanical Fuel pump to a Electric fuel pump. Has a rochester Carb. Question is, what do I need to buy, what pump, relays, etc...? Also what and where should I direct the wiring and whats the max fuel PSI that I should run? Any help would be GREATLY appreciated!

 

[dan t.]

Re: 1989 5.7L Mechanical fuel pump to Electric question

First you need a marine rated pump that puts out no more than 6 psi, if it puts out more you will need a fuel pressure regulator.
Second you need a 2 terminal normaly open oil pressure switch that closes at 3-5 psi.
If you want a bypass circuit for priming and testing you will need a momentary switch or push button.
Normaly you wire the system to switched ignition, if the pump is more than 5 ft from the power supply I would recomend using a relay.
There probably is something I forgot to mention, if so ask and I will try to clarify things, good luck with your conversion.

 

[tazrig]

Re: 1989 5.7L Mechanical fuel pump to Electric question

Wanting to convert my 1989 Mercruiser 5.7L with the Mechanical Fuel pump to a Electric fuel pump. Has a rochester Carb. Question is, what do I need to buy, what pump, relays, etc...? Also what and where should I direct the wiring and whats the max fuel PSI that I should run? Any help would be GREATLY appreciated!

Just curious, why do you want to convert? That mechanical system is pretty bullet proof. I had 2 for 22 years and they were still working when I sold the motors.

 

[ENSIGN]

Re: 1989 5.7L Mechanical fuel pump to Electric question

There's more problems with the electric pump systems. Keep the mechanical pump

 

[Bondo]

Re: 1989 5.7L Mechanical fuel pump to Electric question

Just curious, why do you want to convert? That mechanical system is pretty bullet proof. I had 2 for 22 years and they were still working when I sold the motors.

Ayuh,... Ditto that,.... Replace what's there....

 

[Don S]

Re: 1989 5.7L Mechanical fuel pump to Electric question

Personally, I would rather have a mechanical than electric any day. But, if you really must convert to electric, here is how it's wired with an oil pressure switch. No need for a separate priming switch, as the starter supplies power to the pump during cranking.

 

[will941s]

Re: 1989 5.7L Mechanical fuel pump to Electric question

The reason why i'm considering this is mainly due to the issue of hard starting after sitting when the fuel evaporates in the bowls. Theres been times i've had to disconnect the fuel line and re prime it with the key to get it to start. Im sure the old pump is getting on it's last leg and it's pretty comparable to replace it with a elctronic system. After building it, it sure will make any trouble diagnosis easier. I often go to islands right by the ocean and when the tides begins to roll out, you need to be able to start and go...not have to crank and crank when it decides to lose fuel pressure from sitting. I think I may give this a shot and see what happens. Thanks for the info

 

[Don S]

Re: 1989 5.7L Mechanical fuel pump to Electric question

Maybe you should fix the cause of the fuel leaking out of the bowl. It doesn't evaporate in a few days, or weeks, or even over the winter.

 

[haulnazz15]

Re: 1989 5.7L Mechanical fuel pump to Electric question

I'd also recommend going with the one who brung ya, lol. No reason to go with an electric pump unless you want a lot of hassle for no improvement in performance over a mechanical unit. You are just asking for more headaches when you start adding electricity into the mix. Mechanical fuel pumps rarely fail, normally they last for decades.

 

[Augie56]

Re: 1989 5.7L Mechanical fuel pump to Electric question

The other weekend, I pulled my boat out of my garage for a pre-season run on the muffs. My 1979 Mercruiser 228 (GM305 / 4bbl) started after I set the choke and cranked it for maybe 5 seconds.....after not running and sitting for months with fuel in the bowls of the carb.

Point is, a properly tuned and in-good-working-order carb and fuel system won't lose prime or fuel in the carb due to evaporation after sitting. Adding an electric fuel pump may mask the true problem, and it may also result in the same symptom for your engine. One thing for sure is that it won't guarantee the symptom goes away, and it will add another point of failure to your boat engine.

 

[tazrig]

Re: 1989 5.7L Mechanical fuel pump to Electric question

Point is, a properly tuned and in-good-working-order carb and fuel system won't lose prime or fuel in the carb due to evaporation after sitting. Adding an electric fuel pump may mask the true problem, and it may also result in the same symptom for your engine. One thing for sure is that it won't guarantee the symptom goes away, and it will add another point of failure to your boat engine.

^^^+1

 

[will941s]

Re: 1989 5.7L Mechanical fuel pump to Electric question

To give you some background in it, the motor has 750 hours and its the original 350 that came in the boat. I began having the vapor lock problems with the carb over the summer last year, and about 2 weeks ago I installed a brand new, never ran, non remanufatured carb on the engine. The same exact carb that came off of it. The old carb had alot of issues, alot of wear and really wasnt worth rebuilding. I tuned the carb (which at the time the boat actually started easily and ran well) and got it set. Boat ran like a champ. Then out of the blue the vapor issue hit again. At least now it's not dumping fuel everywhere among a host of other problems. The only thing I can figure is the old Mechanical fuel pump is on the way out and somehow letting in air, probably from the crank case since theres no visible leaks or gas smell outside. Does this sound logical?

 

[tazrig]

Re: 1989 5.7L Mechanical fuel pump to Electric question

If by "dumping fuel everywhere" you mean out the top of the carb then you most likely have or had a stuck float in the old carb. The only time I ever heard of a mechanical fuel pump doing that was a couple of years back when they had a defective batch of mechanical pumps that somehow made it to market and were putting out more pressure than they should have but those have since been corrected. If you had a tear in the bellows you would have a consistent pumping problem not an intermittent one.