Mercruiser 3.0L Bogs down around 1800RPMs

[jbsengineer]

Engine runs fantastic out of gear throughout the RPM range. However when in gear and coming on plane it bogs down around 1800 RPM's or so only for a few seconds then it comes out of it and runs fine.

Also when shutting the engine off sometimes it still tries to run. Every once and awhile it will stall if I don't baby the throttle back down from higher RPM's. I have to slow it down gently.

I recently put a new distrib cap, rotor, plugs, and wires. Gapped the plugs to .35.

SN=0f120406

Any help is appreciated. Everyone here is always alot of help!

 

[newboater2day]

Re: Mercruiser 3.0L Bogs down around 1800RPMs

have you check the fuel filters and the timing ?

 

[jbsengineer]

Re: Mercruiser 3.0L Bogs down around 1800RPMs

have you check the fuel filters and the timing ?

Fuel filter was my next replacement part. Is there more than one?

I have not checked the timing.

 

[jbsengineer]

Re: Mercruiser 3.0L Bogs down around 1800RPMs

I should also note that this was occurring before the plugs, cap, wires, rotor.

 

[newboater2day]

Re: Mercruiser 3.0L Bogs down around 1800RPMs

i have a 89 mercruiser 3.0 and i have a fuel filter in the fuel line where it goes into the carb.. and on my fuel pump which is a carter style has a filter inside the pump .. if you'r pump looks like it has a bowl on top there probley a filter inside it.. there around $5 to replace just loosen the screw on top and slide the bracket off and the cover will come off.

 

[jbsengineer]

Re: Mercruiser 3.0L Bogs down around 1800RPMs

Do these symptoms scream fuel filter or should I be looking at other culprits?

 

[Bondo]

Re: Mercruiser 3.0L Bogs down around 1800RPMs

I should also note that this was occurring before the plugs, cap, wires, rotor.

Ayuh,.... That helps point out it's Probably a Fuel Delivery Issue.......

as noted by New Boater,...
You should have a little Filter at the Carbs Inlet, behind the Big Nut,... Use 2 wrenches so you don't Twist off the fuel line....
The Other Filter is hiding Inside the Fuelpump,... Under the Bell shaped part of it....

If I were running a set up like that,...
I'd add a Cannister type fuel filter, just Before the Fuelpump....
They're Soo much eaiser to change,+ will hold Alot more Junk before causing Issues.....

Good Luck....

 

[1999 Searay 180BR]

Re: Mercruiser 3.0L Bogs down around 1800RPMs

same engine and mine will do the same thing if I use 87 Octane fuel...I have to run the 93 Octane.

 

[jbsengineer]

Re: Mercruiser 3.0L Bogs down around 1800RPMs

same engine and mine will do the same thing if I use 87 Octane fuel...I have to run the 93 Octane.

Really? I am running 87. Did you have diesling after you shut the engine off as well?

 

[1999 Searay 180BR]

Re: Mercruiser 3.0L Bogs down around 1800RPMs

yeppers, sometimes have to turn key off and on 6 or 7 times before it would finally die. I believe the root cause is a timing issue. I've been told manufactures advance timing to the very upper limit to milk out top speed and WOT performance and the lower octane fuel plus the hi advance sometimes don't work so well together. I haven't had a problem since I 've been running 93 octane

 

[chiefalen]

Re: Mercruiser 3.0L Bogs down around 1800RPMs

Isn't there a screen on the bottom of the fuel pickup tube in the tank? The anti-syphon valve might be sticking. Thats on top of the tank. Your vent clear? Might be partially blocked with spiders or something.

 

[jbsengineer]

Re: Mercruiser 3.0L Bogs down around 1800RPMs

isn't there a screen on the bottom of the fuel pickup tube in the tank?the anti-syphon valve might be sticking.thats on top of the tank.your vent clear, might be partially blocked with spiders or something.

I will keep the AS valve in mind. What vent are you referring too?

 

[jbsengineer]

Re: Mercruiser 3.0L Bogs down around 1800RPMs

I just ordered the fuel pump fuel filter and the carb fuel filter. Should be here Wednesday. When I replace these filters is there anything else I should be looking for around the carb or fuel pump?

 

[jbsengineer]

Re: Mercruiser 3.0L Bogs down around 1800RPMs

Also do these symptons sound like an accelerator pump problem?

 

[MaxOD]

Re: Mercruiser 3.0L Bogs down around 1800RPMs

I would doubt its an accelerator pump but could be carb trouble. Maybe a power valve, if its got the holley carb, the powervalve sits low in the float bowl and could get dirt, corrosion etc. If you are having a run on problem its usually because the idle is too high, idle is too rich or there is a fuel leak inside the carb from a well plug or high float level. When its idling look down the throat of the carb with a flashlight and there should be no fuel dripping from the main nozzle and if you turn in the mixture screws the engine should run rough and stall. If one or the other mixture screws can be turned in with no real change in how the engine runs you have an internal fuel leak.

 

[jbsengineer]

Re: Mercruiser 3.0L Bogs down around 1800RPMs

Looking at the fuel pump I'm not sure how to replace it's filter. I don't have to take the entire pump off the block correct? I'd need a gasket for that.

It looks like I might be able to unscrew the bottom part of the fuel pump. I'm assuming this would be how I would put the new filter in. Tips?

Thanks everyone for contributing. Everyone is a huge help!

 

[jbsengineer]

Re: Mercruiser 3.0L Bogs down around 1800RPMs

Here is what i did:

Replaced carb inlet fuel filter
Replaced fuel pump fuel filter
Cleaned the flame arrestor
Once fired up sprayed some carb cleaner down the carb

First impression....wow does it run well now! Haven't put it in the water yet and only ran it on the muffs but it runs like a champ now. No hesitations, cylinder skipping, or run-on. We'll see when I get the engine much warmer on the lake how it performs.

The fuel pump filter was obviously never replaced. I first replaced that. There were alot of rust particles from what looked like the bottom of the bowl. I cleaned it out very well and it went back on tight. Next i replaced the carb inlet filter. I could tell this was where the problem was. The filter was packed with little particles (rust particles from the filter bowl on the pump I assume).

Going out first thing in the morning tomorrow for a little fishing. Hopefully everything is smooth!

Thanks for all your help guys!!!!!!!!

 

[cyril420]

Re: Mercruiser 3.0L Bogs down around 1800RPMs

If your engine is dieseling after you shut it off you definitely have a timing issue. It's a delco est ignition?

 

[chiefalen]

Re: Mercruiser 3.0L Bogs down around 1800RPMs

If after going on the water you still have the problem than there is a gas tank vent. It allows air into the gas tank as fuel is removed by the fuel pump ie no vacume. Check that it's clear.

The anti-syphon valve is on top of the tank it's the fitting that the fuel hose connects to. Take it off see if it's clogged and working

There is a screen on the fuel pickup tube most forget, or don't know it's there. You will have to take off the access to the tank under the anti-syphon valve.

One last thing could be water in the gas. You have a water separator? Dump it in a clean clear container. What do you see? Water is heavier than fuel.

When you go to shut the motor off after running it hard; do you let it idle for a minute or two? You should. When you idle it after running it hard it will let you start easier also.

 

[jpg1130]

Re: Mercruiser 3.0L Bogs down around 1800RPMs

Looking at the fuel pump I'm not sure how to replace it's filter. I don't have to take the entire pump off the block correct? I'd need a gasket for that.

It looks like I might be able to unscrew the bottom part of the fuel pump. I'm assuming this would be how I would put the new filter in. Tips?

Thanks everyone for contributing. Everyone is a huge help!

What was the verdict on this? I'm now having the same issue. I ran the boat to the lowest fuel level I've ever had (4 gallons left), and it started to stall. I filled the tank full and it still wants to stall (sometimes). I want to replace the fuel filter in the pump but am a little confused on how to get to the filter.
Same engine as yours (mercruiser 3.0L). A little help with the filter removal would be greatly appreciated!!