3.0L Merc Idle Problems

[jr1017]

Good day, I'm happy to have found this site and thanks in advance to any future advice with my problem...

1988 3.0L Mercruiser. Has always purred like a kitten since owned which has been a little over 3 years now. It was tuned right before I bought the boat (new plugs, wires, cap, rotor, condensor, points, etc) and I've just pretty much changed the oil and lower gear oil each year. The boat does not see alot of use each year, in fact I've used the boat maybe 6 to 8 times per year it has been in the water except for this year which to date I've only had in the water 2 times so far.

Problem: I brought the boat home and put the muffs on to fire up and run for a bit as I usually do before I leave for the lake. Ran like usually, purred at idle and everything seemed to be fine. Got to the lake to launch and I admit I was in a hurry and not thinking and launched without putting the drain plug in first. Once boat was in the water I got in and started it up. Idled for about a minute and then put into reverse to back off the trailer. When put into reverse and started backing, the motor died. I restarted the engine and as soon as I put into reverse it stalled again. Then it dawned on me what I had forgotten to do. Got the boat pulled back up the ramp some and allowed the water to drain out. It was still somewhat dark out and I have no idea how high the water got inside the engine compartment. (it didn't seem like the back of the boat was anywhere near sinking or that bad) It did take a few minutes for the water to drain back out of the boat. Me not knowing what I was doing, put the plug in after the water drained out and backed the boat back into the water and tried to start. It was a bit difficult, but it did fire up but I had to keep the rpms at 1800 or above. Anything less and it would stall out. Someone at the ramp told me that I needed to just let everything air out and dry before it would run properly again. (Something had gotten wet that is not supposed to) Brought the boat back home and parked. Someone told me to check the distributer for water or moisture, so after 3 weeks of sitting, I brought the boat home and checked the distrubitor. It was dry inside. I started and it fired up but same as before, I have to keep the rpms at 1800 or above to keep the engine running on its own. Anything less and the rpms gradually slow until the engine stops running. The oil looks clean and no signs of water in that.

I don't have a service manual for this yet (maybe I should buy one), but does anyone out there have any advice or some steps as to what the next thing or things I should start to check to figure this out? The gas tank had just been topped out and the gas is good, and the gas should still be good shouldn't it? Any advice is greatly appreciated and thanks in advance...

 

[JustJason]

Re: 3.0L Merc Idle Problems

even though you don't use the boat the much, you need to tune it up once a year.
Especially point's and plugs, those are mandatory, once a year always.
Fuel filters, once a year and sometimes more if you burn alot of fuel.
cap and rotor.... if i'm doing the work for someone then it's every year, if your a diy'er with low hours you can probably go every 2.
plug wires every 2 to 3 years depending on usage.
Setting the dwell, timing and adjusting the carb.... every year.

thats just the engine.... you should be changing your waterpump in the drive unit every other year.

these things aren't modern automobiles.... they need alot of maintence and tlc if you want trouble free boating.

 

[Don S]

Re: 3.0L Merc Idle Problems

Here are links to the OEM service manuals you can download to your computer.
Drive Manual #6
http://www-alt.mercurymarine.com/mnetdata/SERVICE/CRUISER/Servmanl/6/6covr3.pdf

Engine Manual #10
http://www-alt.mercurymarine.com/mnetdata/SERVICE/CRUISER/Servmanl/10/cover.pdf

 

[jr1017]

Re: 3.0L Merc Idle Problems

Thanks captJason and Don S for the helpful info...

I talked to a few mechanics today and I told them the whole story as well, and they seem to think that the water would have had to be extremly high in the engine compartment to cause any problems. (enough water to flood the engine compartment and into the boat) and the water was not that high. I didn't have any come into the boat itself. One had kept telling me it was just a coincedence that my problem started the same time I had forgot to put the plug in. They don't really have or want to give any further advice or offer any ideas of what it could be, other than to take it in to them and for $90 they can perform a diagnostic to find out what is wrong.

I've been trying to think of what would cause the engine to not want to idle below 1800 on it's own and what would be the most obvious to start at. I've read some good posts just now about fuel filters. Do you think that's a good place to start. If the fuel filters were bad would the engine still be able to run at 1800 or higher but not lower?

Any thoughts???

 

[jr1017]

Re: 3.0L Merc Idle Problems

Ok, just pulled off the fuel filters. Both except the screen that is at the fuel tank from what I have read on other posts. The filter at the carburetor which was more like a screen, seemed for the most part ok. A little debris but not very much. I sprayed out with carb cleaner and put back in. I took off the filter at the fuel pump, and I've attached a couple pics of what it looks like. Now my local boat shop says they do not have this filter in stock. What I am wondering is, can this be cleaned like the screen was. Can I just wipe away the funk and spray it down and use it again, or should I wait until I can find a new one.

Also, am wondering if this would have any effect on the engine performance such as running below 1800 rpms.

Thanks.

 

[Bondo]

Re: 3.0L Merc Idle Problems

Now my local boat shop says they do not have this filter in stock. What I am wondering is, can this be cleaned like the screen was.

Ayuh,....

You Could,.... But I Wouldn't....

The paper elements are a direct interchange for those ceramic 1s.....

am wondering if this would have any effect on the engine performance such as running below 1800 rpms.

Nope,... Probably Not..... High rpms maybe, but Not at idle.....

I'd sooner think that there's been some Water laying in the bottom of the Carb over the years,+ there's probably abit of corrosion that's Plugging the Carb's Idle Circuit......
A properly installed Carb Kit might bring it back from the Dead.....