Merc (4.3L) Fuel & Electrical Problems

[2052rider]

Hello all,
I have a 1992 MercuryCruiser 4.3L that isnt getting power to the exterior electric fuel pump,
I put a voltage meter on the main plug going to the pump itself(it is a plug with one black and one purple wire)
I have checked the fuse box all looks to be good.

I am curious if anyone can throw me some trouble shooting ideas as i have checked most of the typical problems.

thank you

2052rider

 

[jayrodoh]

Re: Merc (GM 350 4.3L) Fuel & Electrical Problems

Re: Merc (GM 350 4.3L) Fuel & Electrical Problems

Did you have power at the black/purple wire plug for the pump?

Also, do you ahve a 350 or a 4.3l? Those are both totally different engines.

 

[Silvertip]

Re: Merc (GM 350 4.3L) Fuel & Electrical Problems

Re: Merc (GM 350 4.3L) Fuel & Electrical Problems

Just to clarify, you have either a GM 350 (5.7 liter V8) or you have a 4.3 liter 262 cubic inch V6) -- can't have it both ways. Count the spark plugs to determine which you have. When you checked voltage, which side of the plug did you check. The one going to the pump or the other side. And did you separate the plug to make the check. May sound like a rediculous question but lots of folks disconnect a plug and then expect to find voltage on the load side of the plug. If you don't have power on the source side of the plug the problem is up stream. You said you checked the fuse box! But did you actually check the fuse? They often look good but show open with an ohm meter. Or simply try a different fuse. Does the engine crank when you turn the key to START? Does everything else on the boat operate properly.

 

[wca_tim]

Re: Merc (GM 350 4.3L) Fuel & Electrical Problems

Re: Merc (GM 350 4.3L) Fuel & Electrical Problems

without knowing what you have, I might suggest checking the oil pressure switch pressure switch that is often located right above where the oil filter screws in on both 4.3 and 5.7 (350). Trace the wires from the fuel pump. Check to see if you have current before the switch. It's there so that the pump doesn't keep pumping fuel if the engine isn't running and there's a leak...

Also check for fuses if that's not it...

If you post more detailed specific information on which engine set-up you've got, one of the real experts on here could probably pinpoint the most common problem specific to your set-up...

 

[2052rider]

Re: Merc (GM 350 4.3L) Fuel & Electrical Problems

Re: Merc (GM 350 4.3L) Fuel & Electrical Problems

Did you have power at the black/purple wire plug for the pump?

Also, do you ahve a 350 or a 4.3l? Those are both totally different engines.

No i did not have power at the plug to the fuel pump

and to correct my own ignorance it is a 4.3 V6

thank you

 

[2052rider]

Re: Merc (GM 350 4.3L) Fuel & Electrical Problems

Re: Merc (GM 350 4.3L) Fuel & Electrical Problems

sorry it is a 4.3

i checked the end that plugs into the pump itself, and yes i did separate the plug to make the check,
I just visually checked the fuses did not check Ohm's.

and yes the engine turns over, and will actually start if i cheat and put a little gas in the carb, so i in-turn cracked the fuel lines and they were bone dry which tells me fuel pump so i checked the voltage at the plug to the pump and no power.

and yes everything else on the boat works as it should

thank you

 

[2052rider]

Re: Merc (GM 350 4.3L) Fuel & Electrical Problems

Re: Merc (GM 350 4.3L) Fuel & Electrical Problems

I have not checked the oil pressure switch as therer are no wires that go from the fuel pump to the oil pressure switch.

From the fuel pump perspective there are only the two wires encased in a plug that run directly back to the operators station, i think the purple one goes to the "dead mans switch"

thank you

 

[Don S]

Re: Merc (GM 350 4.3L) Fuel & Electrical Problems

Re: Merc (GM 350 4.3L) Fuel & Electrical Problems

Here is how your pump SHOULD be wired in. 92 was also the first year that used an electric fuel pump, or, a previous owner may have plumbed in an aftermarket pump.
Can you post a picture of your fuel pump?

 

[2052rider]

Re: Merc (GM 350 4.3L) Fuel & Electrical Problems

Re: Merc (GM 350 4.3L) Fuel & Electrical Problems

Here is how your pump SHOULD be wired in. 92 was also the first year that used an electric fuel pump, or, a previous owner may have plumbed in an aftermarket pump.
Can you post a picture of your fuel pump?

I can post some pictures either tonight or tomarrow, thank you for the schematic and will check it out further due to your information after work, thank you for the advice also. will update the findings tomarrow or later tonight.

2052rider

 

[Maclin]

Re: Merc (4.3L) Fuel & Electrical Problems

Simply put, you will not see 12v on the pump with just the key on. There should be 12v at the pump when the key is in the START position. The oil pressure switch will not allow voltage to the pump if there is low or no oil pressure. There is a bypass during cranking (key in START position). Once the engine is running the idea is that the oil pressure switch lets voltage thru. This is a safety feature to keep the fuel pump from dumping fuel into a non running engine if something really bad happens and the key stays on.

I would try jumpering the oil pressure switch wires together then turn the key to ON (don't start) and see if the pump gets 12v. Be sure of what you are looking at, the oil pressure safety switch is NOT the same as the oil pressure sender used for the oil guage.

It is all in the schematic, good luck, you will figure it out.

 

[2052rider]

Re: Merc (4.3L) Fuel & Electrical Problems

Ok i jumped the wires to the oil pressure switch as advised, the fuel pump did turn on and create flow within the fuel lines.

Does this mean i need a new oil pressure switch???? Or a Oil sending unit??????

And second question,
When the fuel pump was running while the jumperwire was in place it did not build pressure and shut off, Should it have???
it is carburated so i would think not because there is nothing closed to keep pressure is there????

Im one step closer but still kinda far away,, thank you for all the help

2052rider

 

[twag4]

Re: Merc (4.3L) Fuel & Electrical Problems

You need mercruiser part number864252A01, they now call it an oil sensor kit. It is $28.03 merc retail price. Very easy to change. I just replaced mine after a long spell of problems. I took the two ends off of the original and connected them together and bypassed it and pump worked fine. Just don't leave the ignition on with the engine not running. You can change pressure switch with an adjustable wrench, it will slobber oil out so use a rag or a soda cup to catch it when you change the part.

 

[2052rider]

Re: Merc (4.3L) Fuel & Electrical Problems

Thank you too all that was helping with the trouble shooting, and after further investigation it was actually a really stupid problem to have.

The float was stuck in the carb, I ran a jumper wire from both wires thet lead to the oil pressure switch, which in-turn hard wired the Fuel pump then i turned the key to the "ON" position and just tapped the carb intake with a plastic screwdriver and could actually hear the pressure build and then wired the Oil pressure switch back to normal. and turned the key and it fired right up to hesitation at all,

THANK YOU TO ALL FOR THE HELP!!!!!!!!! Very much Appreciated

2052rider

 

[scooterwilson81]

Re: Merc (4.3L) Fuel & Electrical Problems

I actually have a similar issue, except mine is on a 2003 4.3L.

I've just changed the fuel pump this morning, man it's expensive. I also changed the distributor cap and rotor yesterday. I tried jumping the pump and it runs, except no fuel comes thru. I even tried running the pump w/o having the fuel line attached to the carb to see if anything was going to come out and nothing.

Any suggestions further down the line? Would the water separator do anything to prevent fuel from flowing?

Oh yeah, this is also the first start of the season, so the carb is dry and the lines are probably empty. And yes, the fuel gauge says 1/2 tank....

I'm at my wits end... hope you can help.

Scott

 

[2052rider]

Re: Merc (4.3L) Fuel & Electrical Problems

I actually have a similar issue, except mine is on a 2003 4.3L.

I've just changed the fuel pump this morning, man it's expensive. I also changed the distributor cap and rotor yesterday. I tried jumping the pump and it runs, except no fuel comes thru. I even tried running the pump w/o having the fuel line attached to the carb to see if anything was going to come out and nothing.

Any suggestions further down the line? Would the water separator do anything to prevent fuel from flowing?

Oh yeah, this is also the first start of the season, so the carb is dry and the lines are probably empty. And yes, the fuel gauge says 1/2 tank....

I'm at my wits end... hope you can help.

Scott

My first assumtion would be since you hard wired the pump and nothing still came out, you would think the problem is before the fuel pump, the only things before the pump is the In-line Fuel filter and i think the sending unit from the tank?????

Have you checked to see if the fuel Gel'ed up on you? thats a possibility

how long has it been since it ran last?????

If you put a Very small amount 1/8 cup or so in the carb does it fire???? if it does then it could only be the few things i would assume. Im not an expert by no means i was on here to figure out my problem also.

If you post a new Thread your more likely to get the other guys to respond Vs. just me

thanks

2052rider

 

[J JACKSON]

Re: Merc (4.3L) Fuel & Electrical Problems

I actually have a similar issue, except mine is on a 2003 4.3L.

I've just changed the fuel pump this morning, man it's expensive. I also changed the distributor cap and rotor yesterday. I tried jumping the pump and it runs, except no fuel comes thru. I even tried running the pump w/o having the fuel line attached to the carb to see if anything was going to come out and nothing.

Any suggestions further down the line? Would the water separator do anything to prevent fuel from flowing?

Oh yeah, this is also the first start of the season, so the carb is dry and the lines are probably empty. And yes, the fuel gauge says 1/2 tank....

I'm at my wits end... hope you can help.

Scott

is there fuel in the filter? i changed mine and the pump wouldn't pick the fuel up so i filled the filter and then is started pumping