Merc wont run

[Private Nemo]

Hi, I have a 1985 Mercruiser 260. When I start it , it starts right up, but dies. As if someone turns a switch off. It runs for maybe 10 seconds , give a take.. Motor sounds good, just wont stay running. Any thoughts are appreciated.

thanks

Drew

 

[dubs283]

Re: Merc wont run

have you inspected anything?? fuel/spark??

does it run longer if you increase throttle?? pump throttle??

does it fire right back up once it dies??

 

[Private Nemo]

Re: Merc wont run

Hi,

Yes , I inspected everything before I fire it up. It looks good. Does not run longer at higher rpms. Any speed , just cuts out. Yes, it starts right back up.

thanks

Drew

 

[dubs283]

Re: Merc wont run

i would start by checking the fuel supply, make sure the carb has fuel in it

one check is to see if the accelerator pump squirts fuel after it dies

when it does die, have a helper pump the throttle while you look down the carb, you should see two definite squirts of fuel, one down each barrel

are you pumping the throttle before starting the engine??

 

[Private Nemo]

Re: Merc wont run

Dont have a helper handy, but I discounnected the throttle linkage and check for squirt. Two perfect squirts. When the engine is running for example at 2000 rpms, I watch the tach just die, like power was killed.

 

[dubs283]

Re: Merc wont run

try running it with the tach disconnected, negative side of the coil

is this a t-bolt ignition??

 

[NHGuy]

Re: Merc wont run

That's a wiring or ignition fault, find the manual & troubleshoot it unless someone on here already knows the steps.

 

[achris]

Re: Merc wont run

If it has points, that sounds like the resistance wire is open circuit.

 

[Private Nemo]

Re: Merc wont run

Hi, Thanks for the replys. Yes this is a T Bolt ignition. I am not sure what eliminating the tach will show , but I will try it later today. I will give anything a try right now .

thanks

Drew

 

[Don S]

Re: Merc wont run

If the tach is shorted internally, it will short the ignition to ground.
Here is the troubleshooting chart for the Thunderbolt IV ignition.



You might want to check the purple wire on the coil while someone starts the engine for you. You may be loosing power due to a defective ignition switch or a bad connection, or the lanyard safety switch is either off or defective.

 

[Private Nemo]

Re: Merc wont run

I was able to put some time into troubleshooting this problem. What I did is disconnect the tach. The engine ran about 30 sec vrs. 10sec. But still cuts out abrutly . I even switch the module, from inside the distributor, from this engine to the other and vis a versa, made no difference. Either module , same results.

thanks

Drew

 

[Private Nemo]

Re: Merc wont run

OK, So I was able to put some time into this motor. So far , I have disconnected the tach , swap out the coil, swap out module inside dist, swap out dist computer. The little black box, that connects to coil and dist. Absolutely no difference. I would REALLY appreciate any advice.

thanks

Drew.

 

[Don S]

Re: Merc wont run

This engine hasn't been converted to an electric fuel pump has it?

 

[Private Nemo]

Re: Merc wont run

No it has not

Drew

 

[riptorn]

Re: Merc wont run

I am not sure about this type of motor but is there a primary pick up coil in the distributor? I think one end plugs into the module.

 

[Private Nemo]

Re: Merc wont run

Not sure what you mean, . There is a module inside dist, with two small studs for wires to go on , outside of the dist cap.

 

[achris]

Re: Merc wont run

You need to verify that you are in fact losing spark. Put a timing light on a spark lead and check that you lose spark as the engine spins down.

Chris..

 

[riptorn]

Re: Merc wont run

Do you have pictures of the dist cap and the module and cam (rotor sits on the cam).

 

[Pete104]

Re: Merc wont run

Disconnect the engine harness & try hot-wiring it! The original sensor could cause this, especially if it has bad ground.
Even at that, can you keep it running by nursing it?

 

[riptorn]

Re: Merc wont run

Good point

You need to verify that you are in fact losing spark. Put a timing light on a spark lead and check that you lose spark as the engine spins down.

Chris..