Merc 4.3 in a 2006 Maxum SR3 1800. Will crank, won’t start. Seems to be fuel system related…

[danjoe34]

Hey all,

First time poster here, been lurking for the last week or so for an answer to my boat’s issues…here’s what I’ve got so far.

Boat ran fine to start the year, just got it last fall and had the water pump impeller replaced during winterizing. I’ve had it out a handful of times this season, ran with no issues but I did notice it took a few cranks to start the last couple times. Outside of this, no issues once the engine is running.

Last week I went to start it after it sat for about 2 weeks and it would crank but not start. I ended up pouring some gas down the carb a little later on and it would run until that gas burned up. I think based on these things I’ve narrowed it down to the fuel system. I can’t tell if it’s the pump or something else. From what I’ve gathered, it’s an electric pump run off the starter solenoid during the start process and once the oil pressure is high enough it provides power to the fuel pump during the on position. I’ve checked and during starting, the pump seems to be getting 12v. I held my hand to it while my partner turned the key and didn’t really feel anything(not sure if I was supposed to or not).

Anyways, I’m pretty new to all of this and would really appreciate any suggestions. I’m likely going to look into a mechanic if I can’t get it sorted out this week. But even if I have to, any help diagnosing it would be huge

 

[alldodge]

You got the right method and your down to the pump. You did say it was getting 12V, and if it is check the ground. If the ground is good, pull pump and bench test

 

[Scott Danforth]

tap the pump with the handle of a screw driver. could be something stuck. or the pump is bad. FYI, they are carter pumps that Mercruiser used.

 

[danjoe34]

Yeah, I just tried it again and tried bypassing the oil pressure switch. No difference and I definitely couldn’t hear the pump working at all, tried giving it a whack or two as well. I’m not sure if it might be a clogged line or something along the way but again, it doesn’t feel like the pump is working regardless. I guess my next step will be to remove it and replace it. I suppose I could try to put 12 volts to it on its own to see if I hear anything to eliminate for sure that it isn’t an electrical issue. Any thoughts on that?

 

[alldodge]

12V direct is of no issue, just connect +/- correctly and it should power up

 

[danjoe34]

Just bumping this for an update. I replaced the fuel pump and it fired right up, no problem. Just went to start it up after it sat for a week and a bit, same thing as before. Won’t fire up. Any thoughts what could be causing this? Maybe vapour lock?

 

[alldodge]

Not vapor lock
Need to tell us what you have and don't have. Is it spark or fuel issue?
If still fuel, what is the fuel pump doing or not doing?

What is the motor serial number?

 

[danjoe34]

Definitely fuel still, it’s a merc 4.3 TKS. After narrowing down the problem to fuel related, I pulled the fuel pump and replaced it about a week ago. It fired up no problem, took it out for a tour of the lake with no problems at all, came back and docked it for a week. Went to start it today and back to the same issues. The serial number for the engine is 0W612960, which I found on the flame arrester.

I’m going to head out and take another look at it this afternoon and make sure the pump is still working. It didn’t sound like it was whirring but I didn’t have a chance to actually troubleshoot and give it a good once over yet.

 

[alldodge]

Thanks, TBV Dizzy and TKS carb

If the pump runs for even a short time, the carb bowl gets filled and will run for a while until the bowl empties.

If pump is not running then look at the starter to fuel pump connection, purple/Yellow wire.

 

[danjoe34]

I went back over and checked it out again. It doesn’t sound like the fuel pump is working. Last week when I replaced it I could hear it whirring while the boat started and ran, and it isn’t doing that when I start it. I tried bypassing the oil pressure switch just to see if I wasn’t hearing it over the engine and still nothing. It’s driving me crazy trying to figure out why it would work well when I replaced it to now having it sit for a week and then get the same (or seemingly so) issue as before. I took a look at the wiring connections and everything looked to be clean as far as connections go.

For the hell of it, I just bench tested the pump I removed and there was a distinct click sound when I put power to it, but no whirring sound or anything. Not sure if that tells me the pump was in fact defective or not, but maybe someone else can interpret that better than me, lol.

I’m thinking I’ll probably talk to the local marina and see if they can take a look, but if there are any other thoughts based on those symptoms and what I’ve troubleshooted so far, please let me know. Again I appreciate all the info and help!

 

[alldodge]

Applying power direct to pump should make it spin. Kind of bad get a new pump and it goes bad after one use

The pump should get power from the pur/yel wire on the outboard terminal from the starter. Bypassing the pressure switch should also make it run if the fuse hasn't blown

 

[Rick Stephens]

If you have a helper, or if you have a remote starter button, unplug the plug going to the pump and test the purple/yellow wire when cranking for 12V power. Also turn on the ignition switch and test that the purple wire at the oil pressure switch has power and then test the other side of the oil pressure switch after cranking for 6 or 8 seconds, enough to get oil pressure started up. Those are the things you can pay a shop $150/hour to do for you or you can use a test light and a little help to do yourself.