'89 Merc 3.0 problems

[comet traveler]

I recently bought an '89 Maxum with a Merc 3.0. It reportedly ran well a year or two ago. The first time I had it in the water it idled great but when I gave it throttle it had no power, ran really really rough, and made 'pinging' noises (like a car engine working hard). Being that I have no history with the boat I took it to the shop and had them "fix" it. They did mostly simple tune up stuff... points, plugs, fuel filter, checked timing, adjusted shift cables (wasn't working right), checked fuel, compression test, and then the main part, rebuilt the carb. <br /><br />So I took it out and it ran absolutely wonderful... for awhile. About 20 minutes or so, and then I started noticing a slight miss which got worse and worse till the point I could only go maybe 20 mph if I was lucky and it was rough. If I gave it any more throttle it wouldnt speed up and would jsut get more rough. So it'd go for a little while at this speed and then at some point suddenly start slowing down and either go very slow (like 3-4 mph) for maybe 30 seconds and then start speeding back up, or just altogether stop. If it completely quit, it would crank fine and want to start but if I let off the starter it'd stop. This happened 4 times (on the way back to the ramp). I noticed that it seemed to help it somewhat if I would take the cover off the engine. Then I could crank it and help it along and eventually let off the starter and it'd keep running. <br /><br />I took it back to the shop and asked them to look at it, and mentioned that I wondered if something they had worked on had gone out of whack. So the next week they call and another $150 they said (once again) "it runs great!" They replaced something in the wiring from the ignition switch back to the motor. They said it is something that can heat up and cause the engine to do that and to replace it meant replaicng the whole wiring harness, so they bypassed it with some sort or ballast resistor. So I took it out on the lake, it ran fine at first (questionable as to as well as the first time out of the shop though, but not complaining). So, 15 minutes later, it started doing the same stuff as the time before. So I went back to doc kand sat around awhile 15 minutes or so and then took the engine cover off and went back out. Welll, this drastically helped it. It may have missed a little but, but very little. So this seemed to help.<br /><br />Heres what else I've noticed. When shifting in and out of gear it sometimes stalls. I've read other posts on this and so i'm aware of the kill switch thing. But I'm not sure if that is the problem (especially considering the shop adjusted it) because the engine isn't starting as easily as it should. And once it starts, it idles very slowly and then works up to a more normal idle. The last thing is, the other day I took it out, and left the engine cover on. It ran fine the whole time (other than the stalling, and hard to start). Now, it was a bit cooler out that day, so I'm thinking that has soemthing to do with it. <br /><br />I can't afford to take it back to the shop again (spent over $450 there already) and really it seems like they don't fix what is broken, and aren't helping it at all. So Im asking for suggestions. I'm not sure where to go.... I'm going to run it on another coil and see if that changes anything. The other thing I'm wondering is about the fuel pump. Can heat affect it in any way and be causing this? Or maybe, is it soemthing they didn't do right with the carburetor? OH, BTW, engine temp, oil pressure, etc is all good. <br /><br />I'm sorry this is so long... just trying to get the details in for troubleshooting this thing. <br />Thank you all.

 

[craze1cars]

Re: '89 Merc 3.0 problems

Bad gas in the tank? Bad compression? Have you done a leak-down test? Bad head gasket? Cracked block or head? Weak fuel pump? Bad plug wire(s)? Vapor lock? Plugged fuel tank vent? Poor carb rebuild? Timing not properly set? Air mixture set wrong? Idle speed wrong? Improper shift cable adjustment?<br /><br />That's all that pops to mind immediately. And I fully admit they are all guesses. In my opinion, the best plan on something like this where you know nothing about the history is to get a Mercruiser Service manual and systematically follow their trouble-shooting guide starting at step one and not skipping ANY steps.<br /><br />But I'd honestly check out the first 3 items on my list above before I spent another dime. Especially since you don't know the history. You may be trying to make a bad motor run good, which is an exercise in futility.

 

[jamesr1]

Re: '89 Merc 3.0 problems

My guess would be bad gas or defective fuel pump. Does the oil smell of gas? Remove the fuel filter and dump the contents into a glass jar, let it set for a while and see if there is any seperation.

 

[Don S]

Re: '89 Merc 3.0 problems

IF it ran good for a while, I would have to eliminate bad gas, it would be bad all the time, not just after running a while. But I would think the fuel tank vent could be plugged, or the antisiphon valve or screen on the fuel tank pickup tube partially plugged. After it sits for a while, or you move the boat on the trailer, it may slosh the fuel enough to wash away the plugged pickup, and the air would have time to equalize in the tank again from a plugged up vent.<br />You could try removing the fuel fill cap when it starts missing and see if it starts running again, you could also pull the fuel pickup out of the tank and inspect it.

 

[MrBill]

Re: '89 Merc 3.0 problems

I think Don S, as usual, is heading you in the right direction. Your engine may be starving for fuel due to plugged fuel vent line. In additon to removing the cap when you encounter the problem, try another free option...run your blower whenever the engine is running to minimize any vapor lock issues that you could be encountering, and make sure your bilge is empty too, so your engine isn't breathing hot humid air.<br /><br />Another interesting note... the shop replaced a ballast wire? You don't indicate if you have points/condensor or another set-up, but with a standard (points) ignition system and difficult warm/hot starting, I usually head to the ignition system. Cracked rotors and distributor caps, tend to act up when hot, also check for any frayed/grounded wire(s) in and around the distributor. If new condenser, coil and plugs were installed during tune-up, you can probably eliminate them. But check the timing and high speed advance. <br /><br />I would rule out bad fuel...its always nice to hope the solution is that easy, but the fact is that situations like you describe...are ignition related 99 out of 100 times.

 

[Lakefisher420]

Re: '89 Merc 3.0 problems

I would have to agree with Don as well. I had sort of the same problem with my boat this summer. It was running fine for 20 minutes then it wanted to die and if I shut it off or sthaled it would give me a hard time to restart unless I had the blower on. I replaced the ignition system, filters and other stuff people thought it could have been. One day I picked up a 7 gal outboard tank and hooked it up before the water separatorand the motor runs great havnt had any problems since. There must be **** in the tank clogin up the antisiphon valve or screen on the fuel tank pickup tube. It wont hurt to try the port tank it is cheap and easy.

 

[comet traveler]

Re: '89 Merc 3.0 problems

Thanks everybody for your replies. Hopefully Friday I can go out and play with it some. The gas tested out fine but I think I may try an outboard tank on it and see what happens. Compression is 125 across the board. <br />Does anyone know if heat can affect the fuel pumps operation? It sure seems that whatever is causing it seems heat related. I know ignition parts can be affected by heat (btw yes it is points/condesor) so in some ways I want to lean towards ignition, but I'm not sure really what else (except the coil) could be affected by heat. Well Friday will be the first day I have actually devoted to trying to figure this thing out, so I should get a better idea. I'll let you all know what I find. Thanks!

 

[comet traveler]

Re: '89 Merc 3.0 problems

Is the fule pump something that can be bought from an autoparts store or does it need to be specialized. Does anyone know any way to reference it? I know when I go to an autoparts store and say anything about a boat they give me a blank stare. And I'm not really sure if this motor has ever been used in any vehicles or anything else. Thanks

 

[craze1cars]

Re: '89 Merc 3.0 problems

You're gonna want marine-specific parts on this rig, not auto parts. Especially when you're considering fuel and ignition stuff. They are especially designed to keep you from exploding on the water.

 

[Don S]

Re: '89 Merc 3.0 problems

Running it on an outboard tank will eliminate your boats fuel system completely, so don't expect it to tell you if it was bad gas or not.<br />Using the outboard tank eliminates, the vent, the fuel pickup, air leaks in the fuel lines, and a plugged antisiphon valve. The only thing it will do is tell you if it's the fuel system before the pump is the cause or not, but not which part of it.

 

[comet traveler]

Re: '89 Merc 3.0 problems

craze1 -- thanks... don't want to do that. I know NAPA carries some stuff for outboards, but I dunno with these. Just as well to go to the Mercruiser place anyway. <br />DonS -- thanks also, yea that's my idea just to try it and see. At least to give me an initial idea if it's a problem originating from that area. And, its easy for me to do. I've got a few OB tanks so im not goin and buyin anything.

 

[MrBill]

Re: '89 Merc 3.0 problems

Here...do your parts lookup using these schematics, including Mercruiser parts numbers, order here, other on-line places or at a dealer, etc. Just look up engine and go to the right area<br /><br /> http://www.mercruiserparts.com/

 

[comet traveler]

Re: '89 Merc 3.0 problems

Well it seems to have 'fixed' itself. Whether it's because it's cooler out or what I'm not sure. The engine temp is the same, so I'm thinking it must have been something going on in the fuel system... maybe still effects of old gas? Anyway, it's been doing well for the most part. It still is stalling with shifting but I've determined thats just a cable adjustment issue which I'll work on later this week. It's still hard to start after I stop and it sits for a little bit... but I've found that if I let it idle for 2 mins or so at dock and then turn it off, when I come back it starts right up liek new. So, that's something to figure out, but pretty minor.

 

[Don S]

Re: '89 Merc 3.0 problems

Well it seems to have 'fixed' itself.

Mechanical things don't heal, and they do not fix themselves. They do however, lay domant for a while and spring up on you again, at the worst possible time. <br />You still have a problem, and being intermittent means it's going to be harder to find.<br /><br />

It still is stalling with shifting but I've determined thats just a cable adjustment issue which I'll work on later this week.

They do not "Fall out of adjustment" something is defective. Probably the shift cable. Don't expect ajusting it to fix it for more than one trip or less. <br /><br />

I let it idle for 2 mins or so at dock and then turn it off, when I come back it starts right up liek new. So, that's something to figure out, but pretty minor.

ALL the modern 3.0L engines want you to idle for a couple of minutes before shutdown. This is to keep the dieseling in check. Might want to check your carb adjustment. Too lean and you will have a heck of a time starting also.