350 Mag Merc Bogs Down

[Mike0686]

Hey, first time posting here but since buying my boat 2 months ago I have been reading left and right on ideas on fixing my boat.

I have a 1987 Cruiser Inc. Rogue 2100 with a 350 Magnum with Thunderbolt Ignition with a Alpha 1 outdrive.

We can cruise around at 3,000 RPMS fine and just cruise around, but when we trying to go WOT it will go for about 3 minutes than start bogging down losing RPM's. It will be from 4,000-4,600 RPMS sometimes hitting 5,000, but will slowly start to bog down to 3,000 backfiring here and their making a bogged down noises. If you cut the throttle back it will be fine and cruise normal, than you can go and proceed to stop the engine for 2 minutes not even enough to cool down and than have WOT for 3 minutes again before it starts. Runs great except at WOT.

Things we have tried...
New spark plugs, wires, distributor, timed it, replaced some fuel lines by the engine not from the tank. Emptied the gas tank....

Tried new altenator because we thought it wasn't getting enough voltage, gauge says its below 13 so we thought it was not getting enough volts. But new altenator did not work, wierd part is if you are driving and turn the blower or anything electrical on it will start to bog down alittle, which lead us to think its something electrical.

We are going to try maybe putting bigger gauge wires on the alternator and check the battery wires, but we are running out of ideas, we are going to check out the fuel pump today but I am tired of throwing money at it with no solution.

Any ideas will help! Thank you!

 

[Don S]

Re: 350 Mag Merc Bogs Down

Bogging and backfiring sounds like it running lean at high rpms. Sounds like it may be a fuel delivery problem to me. Try this test.

http://forums.iboats.com/showthread.php?t=167561

 

[jp89bayliner]

Re: 350 Mag Merc Bogs Down

Bogging and backfiring sounds like it running lean at high rpms. Sounds like it may be a fuel delivery problem to me. Try this test.

http://forums.iboats.com/showthread.php?t=167561

This has helped me twice to solve my problem. I love the search function never even had to ask a question.

 

[Mike0686]

Re: 350 Mag Merc Bogs Down

Ok... Believe my I have searched the forms plenty of times, anyways I did some fuel test I don't believe its this now since after it passed the test I now replaced the following...

Anti-siphon plug, line from antisiphon to fuel pump, and replaced the actual fuel pump.

Still having the same problem, I am not looking at the ignition module as the possible problem, seems like it only does it after engine gets hot. The ignition module it is mounted on one the exhaust chamber that is attached the the exhaust pipe going outside my boat.

You guys ever heard of these getting hot and acting up? We tried moving it but the wires are not that long so we couldnt put it anywhere to far or a cooler place, didn't bring any extra wires because we did this when we were out on the lake. Is there anyway to test these ignition modules?

 

[Bondo]

Re: 350 Mag Merc Bogs Down

Things we have tried...
New spark plugs, wires, distributor, timed it, replaced some fuel lines by the engine not from the tank. Emptied the gas tank....new altenator. Anti-siphon plug, line from antisiphon to fuel pump, and replaced the actual fuel pump.

Ayuh,..... And it Still sounds like a Fuel Delivery Issue to Me,......

Btw,.... I don't see Fuel Filters mentioned Anywhere there......

 

[Mike0686]

Re: 350 Mag Merc Bogs Down

Replace those, ran it looked inside looked fine.

At first I thought maybe it was only when I tried going WOT, but went tubing which went great for about an hour of stopping and going not really WOT at any point and it started bogging again after about an hour of doing this, so thats why we think its heat related. I am just running out of things to replace trying to find out what it is, last thing I can think of is ignition coil and ignition module/amplifier.

It could possibly be fuel still, the guy said he didn't really winterize it and left gas it in so it was sludgy, we siphoned the tank clean refilled burned that gas out than refilled. Next time I guess I am going to bring out an extra fuel tank and try to run it off that when it starts to bog down after awhile switch to that and see if it runs like a champ.

Thanks for the responses guys, much appreciated.

EDIT: Also did a compression test all went well

 

[Don S]

Re: 350 Mag Merc Bogs Down

Did you actually do the tests (with the gauge and clear hose), in the link I posted ?

 

[Mike0686]

Re: 350 Mag Merc Bogs Down

I will try the test and see what it results in, I will post back in a few days with the results. I am trying to learn as much as a I can about how everything works, if I check all the hoses and replaced them and the filter and fuel pump and anti-siphon what else would I do if the test fails? The only thing I can think of is the pickup inside of the tank, my friend and I co-own the boat so he is the one doing most of the work and he said he could not get to the pickup tube inside of the tank that is was basically welded on, I didn't really take a look myself. But I will perform the test and also try to run it on an exterior tank and see the results.

Thanks

 

[Mike0686]

Re: 350 Mag Merc Bogs Down

Just to close this thread and help people having the same problem...

RESOLVED:

Faulty ignition coil, coil did not have a brand on it at all, with most of the parts we found that the previous owner said he replaced, maybe not marine or possibly not the right one at all. Runs great, ran at or near WOT to Sterling State Park about 30 minutes south of me and back with some speed, just flying past boats.