New Engine, Won't run for more than 5-8 seconds

[baylinerbill]

:redface: First thanks for all info found in these forums!

1997 Bayliner Capri 1850
1997 merc 4.3 LX Gen +
2 BBL Carb, I believe Thunderbolt IV
Alpha one gen 2 outdrive

OK, I will try to run through the time line first to give all the info:

Bought the boat about a month ago with a cracked 4.3l engine. (from poor winterization)

I ordered a brand new 4.3l vortec engine from 1800runsnew.

reused- carb,manifolds, wiring, alternator, fuel pump, distributor, Harmonic balancer.

new- water pump, coil, cap , wires,rotor,plugs,starter.

I put the engine in and am now trying to start it. I followed the distributer install instructions. Felt the spark plug hole in #1 and got TDC on compression stroke and set it to TDC on Harmonic balancer.

The engine will not start with it at TDC. If i move it about 1 inch clock wise it will start right up and run for about 5-8 secs and stall. it idles up to about 600rpm. it sounds like i am close but the adjustments seem to make it not start.


There were a couple things that i was wondering about.
2 wires on the harness up near the front left not connected to anything. a black wire and a purple and white. both were just left unhooked hanging there when i bought it. Also a Purple and yellow wire was not hooked up by the starter solenoid. that one looks like its hooked up to the right stud of the solenoid.

Does anyone know what I am doing wrong or need to look at?
Your input is greatly appreciated!

Thanks,
Bill

 

[Don S]

Re: New Engine, Won't run for more than 5-8 seconds

Also a Purple and yellow wire was not hooked up by the starter solenoid. that one looks like its hooked up to the right stud of the solenoid.

And which stud might that be? A-B-C-D

 

[baylinerbill]

Re: New Engine, Won't run for more than 5-8 seconds

the purple/yellow wire is on D

The yellow/red is on B

2 reds/orange on A

 

[baylinerbill]

Re: New Engine, Won't run for more than 5-8 seconds

i cahnged the fuel water seperator and fuel filter in the carb. it almost acts like its gets gas and then starves out. throttle adjustments will do nothing when its runs for that breif time.

 

[mtnrat]

Re: New Engine, Won't run for more than 5-8 seconds

Similar thing happened to me. Ended up the wires to the starter were not hooked up properly. The wire to stud D or B (in DonS pic) was the culprit, cannot quite remember. It is getting spark when you turn over the engine, enough to start, but when you release the key it is losing it. Only runs for a few seconds. DonS as usual has it narrowed down in short order. That is where I would concentrate my time.

 

[MikDee]

Re: New Engine, Won't run for more than 5-8 seconds

On a point here, on the starter, there is a small terminal for (start), a full 12volts, that is only powered when you push the key to start. Then the other small terminal usually has a resistor (or resistor wire) less then 12volts, on it for normal running (ignition) key on. If you mix them up, then it will only run when you hold the key on start.

 

[Don S]

Re: New Engine, Won't run for more than 5-8 seconds

Are you giving it any throttle when it does start up, or are you just leaving it at idle?

 

[Maclin]

Re: New Engine, Won't run for more than 5-8 seconds

Please disregard this post if that engine has a mechanical fuel pump....If that year has an electric fuel pump then it sounds like the classic oil pressure switch problem or wiring for that circuit, and a wiring problem in that area was certainly mentioned. If the pump gets power during cranking thru the bypass circuit then it pumps into the carb fuel bowl for a bit. Then when no longer cranking and the normal circuit is supposed to power it thru the oil pressure switch it does not get power and the engine just runs on whatever got pumped into the carb fuel bowl during cranking. That amount of fuel seems to give just a few seconds of run time.

 

[baylinerbill]

Re: New Engine, Won't run for more than 5-8 seconds

I hooked the starter wires exactly as shown in the thunderbolt 4 wiring diagrams shown in the mercruiser service book 18. Not being that well versed in i/o , Does one fuel pump only run during starting?

Don - I can throttle all i want and it really wouldn't affect the engine. it just dies out. I did start it at about 1/4 throttle, not at idle.

 

[baylinerbill]

Re: New Engine, Won't run for more than 5-8 seconds

Maclin - Yes it is all electric fuel pumps. That sound like what is happening. I am not familiar with the "classic oil pressure switch problem". I will have to do a search on that now. It was reused from the old engine so like everything else used on it, I don't trust it. Can you bypass the oil pressure switch for testing purposes?

 

[baylinerbill]

Re: New Engine, Won't run for more than 5-8 seconds

Bubba1235 - Yes fuel goes to the carb during starting, but i never got around to check if it continued after starting. it got to dark out lastnight.

 

[baylinerbill]

Re: New Engine, Won't run for more than 5-8 seconds

By the wiring diagram it looks like i can jump the oil pressure cut-off switch wires to test if it is bad.

 

[Maclin]

Re: New Engine, Won't run for more than 5-8 seconds

Yes, you can bypass the oil pressure switch for testing. Be sure you know what it is, the oil pressure switch will have two connections while the oil pressure sending unit will only have one. Before bypassing anything first check the voltage at the pump with the key just in the ON position, it should be zero. (Turn the key back to OFF) Then jumper and bypass the oil pressure switch and measure again with the key ON, it should be 12v or close. If not then there is a wiring problem somewhere, remove the jumper and check voltage at the oil pressure switch terminals with the key ON to see if it is before or after that piece. However if there is good voltage at the pump when jumpered then see if it will run that way long enough to make sure it is past the failing point, and that it can rev some. (Turn the engine off) Then remove the jumpers hook the oil switch back into the circuit and see if the problem returns.

 

[baylinerbill]

Re: New Engine, Won't run for more than 5-8 seconds

Great advice, i will test it later and get back to everyone with the results.

 

[newport dave]

Re: New Engine, Won't run for more than 5-8 seconds

Try tapping on the carb a little, sometimes a stuck needle valve will cause similar sypmtoms.

 

[baylinerbill]

Re: New Engine, Won't run for more than 5-8 seconds

Newport dave,

Bingo on the carb, only it was completely crapped up and needed a rebuild. just got off the water and couldn't be happier with the way it runs. only 8 more hours of breakin left !!