Mercruiser 3.0LX engine problem

[CPro]

Hey guys, the symptoms are now that the boat (a 1997 Sea Pro with a Mercruiser 3.0 LX) idles beautifully and acts OK below 2000 rpm. If I try to accelerate slowly from 2000 I get coughing and backfiring. If I accelerate quickly, the boat skips through this problem area but won't accelerate past about 2700 RPM. It just kind of bottoms out...additionally, I think I can hear a bit of a muffled "slap" coming from the engine. Not sure if I'm paranoid or if it is truly something out of place.

Here's what I've done in the past 2 weeks:
*drained the gas tank 2 times. There was bad gas initially, but it is clean now.
*carburetor fuel filter replaced 2 times.
*replaced fuel pump
*new plugs
*new wires
*new distributor cap & rotor
*new ignition coil
*new ignition control module
*cleaned & rebuilt carburetor
*cleaned all the fuel lines
*ran the boat off a separate gas tank (still acted the same)
*adjusted the timing

All of these things helped some (adjusting the time helped the most). Are these symptoms indicative of burned valves or something? I am not as familiar with the inner workings of the engine as I now am with the "outer" workings (everything up to the carb).

 

[CPro]

Re: Mercruiser 3.0LX engine problem

Also - I pured some water around the intake manifold gasket and it did not appear to suck it in or anything.

- Thanks also for any advice you may be able to offer!

Trev

 

[Don S]

Re: Mercruiser 3.0LX engine problem

Assuming you have the EST distributor, did you have it in base timing when you set the timing? Does the timing advance work?
Have you done Compression Test?
Have you done an engine vacuum test with a gauge?

 

[CPro]

Re: Mercruiser 3.0LX engine problem

Hey Don, I followed the manual as to how to set timing:
1) use a jumper cable across the two white leads coming out of the 3 pin connector on the distributor.
2) disconnect the shift interrupt switch and then wire those leads togethor to bypass the switch
->I believe these 2 steps are to set it in "base timing" mode?
3) adjust timing

This is one thing I forgot to mention - the manual says that after adjusting timing as above, wire the interrupt switch back up and then disconnect the jumper on the distributor leads. It says that the timing should advance after doing this (without accelerating) - but this does not happen! When I accelerate, the timing does advance.

From what I have read I believe the ECM sends a signal to the ignition control module - could this be a problem with the ECM?

Thanks - Trev

 

[Don S]

Re: Mercruiser 3.0LX engine problem

When you put the engine into base timing mode and took it out of base timing, did you have the engine running? Are you sure you bypassed the shift interrupt switch properly. Hooking the engine side of the wires together?
If the answer to both of these questions is yes, then you need a new ignition module.

 

[CPro]

Re: Mercruiser 3.0LX engine problem

Hey Don,

I definitely kept the engine running while switching everything over. One time I unhooked the distributor jumper cable first and the engine shut down (which I believe is the correct response). Due to this, I believe that I had correctly followed the steps to get the engine into base timing.

The timing did not change from base timing mode to regular running mode (with the jumper in place and the interrupt switch bypassed per the manual & what you mentioned). In switching from base to regular, I kept the timing light hooked up, but everything else was disconnected in the reverse order that I put it on.

The ignition module is brand new but the engine does not change noticeably (either under the timing light or via it's behavior) going from base to regular mode...this is why I was curious as to whether or not something further up the line is bad?

Thanks,
Trev

 

[Don S]

Re: Mercruiser 3.0LX engine problem

I've had bad modules right out of the box, so don't just assume since it's new it works.
Here is something you can try.
Remove the connector that the attaches the jumpers to the distributor.
Then bypass the shift interrupt switch and jumper the white wires.
Start the engine and then plug in the connector. The engine should change rpm. IF not, then it's not going into base timing. Replace the module.

 

[CPro]

Re: Mercruiser 3.0LX engine problem

Don, you may be on to something...

Here's what I did before starting the engine:
*bypassed shift interrupt switch
*jumpered the 2 white wires on the 4 pin connector on the distributor
*unplugged the 4 pin connector from the dist. (the 4 pin connector only has the 2 white wires and a black wire on it)

Then I started the engine and let it idle at about 750 rpm.

I plugged in the jumpered connector...and no change in RPM.

Then I connected the shift interrupt & disconnected the jumper wire. Then I pulled the 4 pin connector from the distributor...and there is absolutely no change in the way the engine runs when that thing is plugged in or not. It backfires the same way, etc..

You must be right about that not being a good ignition control module..!

I'll mess with it more tomorrow...and if I can get the part, I will plug that in sometime soon. If this fixes it, I will be sending you my first born son....

 

[CPro]

Re: Mercruiser 3.0LX engine problem

OK - here's the fix!

My initial problems were due to poor timing (caused by a loose belt perhaps?) and bad gas (winterize correctly!).

Early on in the 2 week repair process, I replaced what I thought may be a bad ignition module. At Don S's suggestion, I tested this unit and found out that the NEW module was bad!

Here's the link in which Don explained how to test this part.
http://forums.iboats.com/showthread.php?t=194904

Here's a link to some other threads describing the boats ailments:
http://forums.iboats.com/showthread.php?t=194637
http://forums.iboats.com/showthread.php?t=194285
http://forums.iboats.com/showthread.php?t=194104

Thanks,
Trev