1996 4.3 Wiring Diagram?

[Stamey]

I'm looking for a wiring diagram for the engine on a 1996 4.3., SN: 0F821477.
My fuel pump suddenly doesn't work. I am in the process of doing a compression leakage test and I pulled the valve covers. To do this I had to pull the shift bracket and disconnect shift interrupter switch, as well as the remote stern drive lube tank, and sensor. Additionally I pulled number one spark plug and the distributor cap. I need to warm it up to operating temp before I begin the leak-down test so I'm trying to start it to do so. I put the dist cap back on and plug wire number one back. When I attempted to start it is wasn't getting fuel. I can get it to run with carb cleaner sprayed into the carb.
I cannot hear the electric fuel pump running, therefore I'm looking for diagrams so I can figure out what to look for in this system. I imagine the ignition control module controls the fuel pump, and I may have a blown fuse or something, but that's why I need the diagram. I didn't see anything useful in manual 18.

Thanks,
Chris

 

[Struc]

Re: 1996 4.3 Wiring Diagram?

If it doesn't run at all, it's probably a problem with the oil pressure switch that is in line with the pump. It's designed to turn off the pump when there is no oil pressure.

Here is a generic diagram:

 

[dingdongs]

Re: 1996 4.3 Wiring Diagram?

oil pressure switch is faulty and this is linked to the fuel pump.it is the one with the 2 wires near oil filter and if you put a jumper wire in the terminals your feul pump will more than likely have you running again.change switch as soon as possible if this is the cause as its a safety feature if oil pump has failed too.
As the above drawing shows another quick check is that you will also lose supply to the choke(mauve wire) when the switch fails too, when your ignition is switched on.a cheap multimeter is a godsend to keep in the boat toolkit.

 

[ENSIGN]

Re: 1996 4.3 Wiring Diagram?

Just a thought,Is the lanyard switch turned on???

 

[Stamey]

Re: 1996 4.3 Wiring Diagram?

Yeah, I thought about that, and did notice that once when it fired, for the few seconds it did, that the oil pressure was zero on the gauge, but I figured that was because it had not run long enough.
As soon as this hurricane has passed I plan to get back on it.

Thanks,
Chris

 

[Don S]

Re: 1996 4.3 Wiring Diagram?

The fuel pump should be running as long as you are cranking the engine, oil pressure or no oil pressure. If you crank for 4 or 5 seconds, the carb would be full of fuel and the engine should run for 15 to 20 seconds until the carb runs out.
Look at the purple yellow wire in the wiring diagram. It comes from the starter solenoid and powers the pump. Get your meter and start doing some voltage tests. Since you have been taking things apart, did you remove some ground wires for the distributor or the fuel pump?

 

[Struc]

Re: 1996 4.3 Wiring Diagram?

Yeah, I thought about that, and did notice that once when it fired, for the few seconds it did, that the oil pressure was zero on the gauge, but I figured that was because it had not run long enough.

I'm not 100% sure about your boat, but in most, the oil pressure gauge sender is different and totally seperate from the fuel pump oil pressure switch. Have you checked your oil level? Like Don says, though, if it was working properly, it should be powered from the starter while cranking, regardless of oil pressure. It's possible the switch failed in such a way that it never sends power through to the fuel pump, however.

 

[Don S]

Re: 1996 4.3 Wiring Diagram?

The voltage from the starter solenoid in the Purple/yellow does not go through the oil pressure switch in any way, before it gets to the fuel pump. Look at the wiring diagram.

 

[Stamey]

Re: 1996 4.3 Wiring Diagram?

That is a curious thing about this boat. There is one wire down by the starter that was not connected to the starter, on the terminal that is hot while starting, that had silicone sealant squeezed into it, presumably to insulate it. I noticed it when I bought the boat in May, but never touched it because the boat ran fine and I did not know the history as to why it was disconnected. It is kind of dark down there so I have not really been able to make out the color, but it does have a little insulator "cup" around the terminal which is where the silicone was squeezed in. I will certainly have to check that closer when I get back to it.
The engine ran fine the day before, as I was working on power steering issues and was running the engine for that. My guess is that I disconnected something inadvertently while removing the valve covers. I was being very careful as I did it, and labeling what I disconnected, as there are at least 2 wires over the manifold that aren't connected to anything, and I wanted to be sure I didn't mix those up with what I disconnected.
Looking over the oil filter I see two oil pressure switches, but I have not been anywhere near the wiring going to either of them. I will be looking much closer at everything when I get back to it, now that I have a diagram and know what *should* be going on.

Thanks,
Chris

 

[Struc]

Re: 1996 4.3 Wiring Diagram?

The voltage from the starter solenoid in the Purple/yellow does not go through the oil pressure switch in any way, before it gets to the fuel pump. Look at the wiring diagram.
View attachment 173650

I guess it depends on the setup. My oil pressure switch has a normally closed position, which is where the starter feed goes. The normally open is the power feed purple wire from ignition switch wiring. Mine is of course aftermarket. I'm not 100% sure how Mercruiser does it from the factory. The diagram doesn't exactly show functionally how it's connected - just that it is.

 

[Stamey]

Re: 1996 4.3 Wiring Diagram?

I checked the loose wire by the starter. It DOES power the fuel pump and was disconnected for unknown reasons. I did find that my wire is brown with a yellow stripe, rather than purple. It does, however, kind of match the system since one wire on the oil pressure switch is brown with yellow stripe and the other is purple. I found the proper nut in the junk drawer and that brown wire is now connected to the "slave" terminal on the solenoid.
I now have fuel to the carb but it still will not start. I have spark but the engine isn't turning over very fast. I need to do some cleaning on the battery terminals and I have the batteries charging overnight, since I have been discharging them while trying to start it.
A couple of questions would be nice to have the answer to.
1. Is the shift interrupter switch NO or NC?
2. If I have the remote gear lube tank sensor disconnected, will it affect whether the engine runs or not?

Thanks,
Chris

 

[Don S]

Re: 1996 4.3 Wiring Diagram?

I did find that my wire is brown with a yellow stripe, rather than purple.

They fade like that. Fumes, heat etc. It started out purple/yellow.

I have spark but the engine isn't turning over very fast.

They won't start cranking slow like that, those Thunderbolt V ignitions like rpms to fire right.

1. Is the shift interrupter switch NO or NC?

normally open, but if it was your problem, you wouldn't have spark.

2. If I have the remote gear lube tank sensor disconnected, will it affect whether the engine runs or not?

Nope, it only activates the alarm buzzer.

 

[Stamey]

Re: 1996 4.3 Wiring Diagram?

Excellent. Wanted to make sure that I should be OK disconnecting the wiring and moving the shift bracket out of the way.
Thanks for the info. After a charge and terminal cleaning, I'll give it another go.

Thanks,
Chris

 

[Stamey]

Re: 1996 4.3 Wiring Diagram?

Battery charged overnight and it fired right up. Smoked black for a little while, but cleared up and runs nice again.

Thanks,
Chris