Engine issues

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tedhrs

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i have a mercruiser 350 magnum and it is doing the popping thing when put under load when we first start off.

After it gets enough speed under her to get up on plane it stops and runs great, 40+ mph all day. I have also noticed that while it does this popping sound that it feels like it's missing on one or two cylinders.
But why would it do that and then right itself and sound wonderful at WOT?

It doesn't do it on the muffs and idle's and sounds perfect out of the water.
I checked the rotor and cap, cleaned any corrosion off. Its got a brand new ignition module. New gas, sea foam cleaner run through it, new water pump, water temp runs right below 160 all day long. Oil pressure stays above 40 all day long. My volt meter shows me running about 13.5 volts.
I'm puzzled. My next thing to try was a new fuel filter/water seperator thingy.
 
Bondo

Bondo

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Re: Engine issues

My next thing to try was a new fuel filter/water seperator thingy.
Click to expand...

Ayuh,... She's goin' Lean, under heavy load...

If the filter change don't fix it,...
Rebuild the Carb, 'n check the fuel pump output...
 
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tedhrs

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Re: Engine issues

Bond-o said:
Ayuh,... She's goin' Lean, under heavy load...

If the filter change don't fix it,...
Rebuild the Carb, 'n check the fuel pump output...
Click to expand...

i was thinking the Carb was next if the filter change don't help. I'll first off check the fuel pressure following the 'how to' article for fuel systems checking. I am going to assume that it is a mechanical fuel pump and if the pressure is low then i would need to check the pickup line for any obstructions and/or replace the fuel pump.

When i unscrew the cap where the fuel tank is, all i see directly under it is a cap with some wires going in and to the right of it what looks like my filler hose and vent hose.

How would one find the pickup line?
 
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tedhrs

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Re: Engine issues

oh, if looking at the pressure guage for the fuel, what pressure is acceptable?
 
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tedhrs

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Re: Engine issues

So, I went to take the fuel water filter off and it is stuck. I can only.get to turn a fraction....had to unbolted.the whole housing. Yes I was turning the right direction.
So, looks like I will be getting a whole new setup. Yippee! !
 
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tedhrs

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Re: Engine issues

put the new assembly in place tonight. Wow, i could tell a difference in the engine as soon as she fired off. The throttle is a little more responsive than before. Also, it used to be that before when i shut the engine off and went to restart it i would have to crank it for a few seconds or even give it some gas before it would fire off. Now, if i turn it off and turn the key to start it, it fires right away. The real test will be on the water. I hope that was my issue and that it is now fixed. I'll find out sunday.
 
bds85466

bds85466

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Jun 11, 2007
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Re: Engine issues

I initially didn't think this would make your throttle more responsive, but I kept thinking...

Your fuel pump is (basically) responsible for keeping a bowl (reservoir of readily available gas) in the carb full. If you starve the pump via a plugged filter, you starve the bowl. If your bowl keeps full (vs being partially full or running on empty), fuel might be less "hand to mouth" so to speak? Also why you might be popping off quicker than you had been.
 
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tedhrs

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Re: Engine issues

that ended up not being my problem. Still did it, but it seemed to get up on plane a little faster today. What should i be looking at next?
 
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Pete104

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Re: Engine issues

Double & triple check the firing order.
You could have a tuliped valve or a flattened cam. Pull the valve covers. Look at the valve stem length from the guides to the tip of the stem. With the V/C off & plugs out compare how much lift you have at all valves, by cranking the engine and watching the rockers. Flatten cam will hardly make a valve move.
It's alot of work. I hope someone comes in with something less time consuming for you. But, It is what it is!
 
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tedhrs

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Re: Engine issues

is there a diagram that shows which plug goes to which spot on the distributor cap? Like if i were to be looking at the engine from the front of it and i say i want to trace the front left wire to the cap, where on the cap is it going?

I'm thinking i'll call the guy that got the boat running for me and see what he thinks. He's a boat mechanic and should know what to do.
 
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Pete104

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Re: Engine issues

Front port cylinder is #1. The cap (dist) is marked. Also, the firing order is cast into the intake.
 
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tedhrs

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Re: Engine issues

okay, so i ordered new cap, rotor, spark plugs and wires. started taking out plugs one at a time and re hooked new wires one at a time to old wire location on cap. When taking the cap off, i swapped new wires to new cap to same location. Put new rotor in, noticed the top flap metal thingy was bent down, bent it up so it makes contact with top of cap.
I found my original problem, spark plug #3 was broken.

after replacing all spark plugs with AC Delco MR43t plugs and the wires and cap it won't fire off at all. I took the old cap put it on, same thing.
old rotor, same thing. I took the old coil wire and pulled the end off that goes to the cap and plugged in to the coil and then ground it to a intake stud, sparks a flying, orangish redish in color. Hooked up to the cap, no fire.
i took one of the old wires and stuck a screw in it and then grounded that to same stud, used cylinder #1 for this, no spark.

WTF is up.
It ran fine except for my issue before this. help please, was doing this tune up in hopes of running it around this weekend.
thanks in advance.
 
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tedhrs

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Re: Engine issues

i'd also like to add that the old plugs were champion spark plugs. Could my coil not be providing enough spark for newer plugs?
 
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Pete104

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Re: Engine issues

No, your coil is fine! You had a running engine with the old parts & now it don't run! Does the rotor/wheel assembly have 8 prong/spaces in it? Has somebody turned your kill switch off? Check the position of the shift interupter switch.
 
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tedhrs

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Re: Engine issues

Pete104 said:
No, your coil is fine! You had a running engine with the old parts & now it don't run! Does the rotor/wheel assembly have 8 prong/spaces in it? Has somebody turned your kill switch off? Check the position of the shift interupter switch.
Click to expand...

I have checked using my old rotor. That's what is in it now. Old rotor ands cap, new plugs ands new wires.
I just checked. Voltage across the coil and it read 11.27 volts. That so, I tried again with my test spark plug wire and I saw a small spark from the screw. I thought the spark would be brighter than and make a clicking noise. Ill check switchable tomorrow. I've also got a coil I can throw in it to test.
I've never seen a kill switch on my boat though.
 
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Pete104

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Re: Engine issues

That's our problem, all we know is that you have a thunder-4 ignition! You do have a shift interupter. Find & check it!
 
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tedhrs

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Messages
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Re: Engine issues

Pete104 said:
That's our problem, all we know is that you have a thunder-4 ignition! You do have a shift interupter. Find & check it!
Click to expand...

You are correct, I do have the thunderbolt IV system and a new icm
Why would the shift interrupt switch just all of a sudden start causing a problem?
 
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