3.0 engine running rough

[capecodtodd]

Big trouble on little engine. My 1998 3.0 mercruiser will not start. Due to rough running which has been a problem the few times I have had the boat out this year, this morning I went to check the timing and it was way off. I followed the manual on how to check it and turned the distributor to were it should be and the motor stalled out. I put it back to where it was and it started fine but was still running rough. I have a suspicion that the plug wires are not on correct. I have looked at the order in the manual and here online and it seems to be a common issue. I could not find the order stamped on the block which may be different than what the cover and manual say. Where is that located on the block?
The top of my spark arrestor cover has the order typed there and it corresponds to the manual is that ok? It was running with this order but rough.
When the wires get put on the cap where am I supposed to start with #1 wire? I am assuming the distributor goes clockwise for that is the way the arrow in the manual is pointing and that is the way I put the wires on starting with #1. Is there a mark on the cap or distributor that tells me where to start on the cap with plug wire #1 ??
The boat hadn't been used in 2 seasons, so new gas and filter, new fluids, new plugs, wires, cap, rotor, thermostat, new water pump the old was leaking and rotted out a spot on front seal cover so it was dribbling oil so that is new as well. The rough running is not new this year.
Any ideas? Thanks in advance.

 

[fishrdan]

Re: 3.0 engine running rough

If it's running at all you have at least some of the plug wires on the correct way. If all the plug wires were off by 1, it wouldn't run at all. Firing order is 1, 3, 4, 2, with the cylinder at the front of the engine being #1.

To find out where #1 plug wire goes on the distributor (100% positive) you will need to turn the engine over by hand until #1 piston is coming up on it's compression stroke, continue until the timing marks are lined up at 0, then pop the dist cap off and see which cap terminal the rotor is pointing to.

Which ignition do you have? An EST ignition needs a special timing procedure or you can not time the engine correctly,,, IE; shorting certain wires at the right time puts the ignition into base timing mode.

Have you done a compression test?

Have you done anything with the carb, messed with the idle mixture screws?

 

[capecodtodd]

Re: 3.0 engine running rough

Hi
1 3 4 2 is the order I have been using but I didn't think about the piston and turning the engine by hand to find the #1 spot. When you say the timing marks should line up at 0 do you mean the line on the main pulley and the zero on the timing gauge on the front cover?
I have the EST... I think. it is electronic. There were certain wires that I needed to disconnect and loop etc... explained in the manual when I checked on the timing. I was very suprised that it was off so much.
I have not done a compression test.
I did increase the RPM just a bit since it was stalling so much at idle.
I will check those things you mentioned tomorrow. Thanks!

 

[moparmatt]

Re: 3.0 engine running rough

I would also put a compression test on it. Mine was doing the same thing when i got it and it turned out i had a head gasket leaking on the center 2 cylinders. 29.00 head gasket and 3 hours later problem solved!!

 

[capecodtodd]

Re: 3.0 engine running rough

Hello
Well I did all the things that were suggested by fishrdan except for the compression test since I don't have a tester and I did have the order correct on the wires so that is a relief. I think I screwed it up before and that is why the timing was off the chart. Now the timing is adjusted close to where it should be. It was running ok and restarting right up this morning while it was hot but now that it has sat half the day I cannot get it started now. It turns over nicely but is backfiring through the carb? I moved the lever to get the choke to close up in the starting position and the engine fired up but stalled when I backed the rpms down a bit. It sputtered and coughed.
Trouble is I don't know if this is a carb issue or ignition. New gas as of 4 days ago but could the carb need adjusting or be clogged? New plugs, wires, cap, rotor, filters, 2 months ago. Besides the compression test what else can I check that might be a common issue to help rule it out? There is nothing more frustrating than an electrical problem.
Any ideas as to a direction??

 

[Bondo]

Re: 3.0 engine running rough

but could the carb need adjusting or be clogged?

Yes...

 

[moparmatt]

Re: 3.0 engine running rough

Most any chain Auto parts stores like Autozone,Oreilleys etc. have a compression test gauge on the loan a tool program. You can rent it for free and to really get a general idea of whats going on that needs to be the first thing that you can rule out.

 

[bigdan1]

Re: 3.0 engine running rough

if it backfires in carb, it needs advance.....

turn distr ccw a bit see if it still does it ...
you might have a leaking gasket under the carb : the one that is betwwen carb & intake also ....see if carb bolts are not loose .

is intake/exhaust manifolds bolts tight?


all things to verify

 

[capecodtodd]

Re: 3.0 engine running rough

I borrowed the tool from Autozone and did the compression test. I got a reading of 60+\- 1-2 pounds in all 4 cylinders so that is a good thing. I got to thinking that it seems like a fuel issue so I had a look at the pump and inquired about a new one at the parts store. Three guys there including their mechanic said that pumps either work or they don't and their diagnosis was the carb needs to be rebuilt. Seems like they have seen alot of mercruiser carbs this summer being eaten up by new additives in gasoline. so instead of the $150 pump I got a total carb rebuild kit for $90. Once I find some time this week I wil rebuild and hopefully have it ready for the last run of the season.
Thanks for the input.

 

[moparmatt]

Re: 3.0 engine running rough

60 lbs is no where near enough cylinder pressure to run. You should have about 120-140 per cylinder. I would check it agian and if the cylinder has less than 100 lbs per cylinder It needs rebuilt.

 

[fishrdan]

Re: 3.0 engine running rough

I got a reading of 60+\- 1-2 pounds in all 4 cylinders so that is a good thing.

60PSI ... across all cylinders ???

If so that's bad, really bad. Bare minimum you should have 100PSI, and that's a tired engine, somewhere around 140 PSI is a new engine.

I'd try another autozone and get a different compression tester to see if you get different readings, higher readings. I find it kind of strange that they would all be low to the same degree, 60# +- 1-2#. I'd kind of expect, something like 65, 60, 70, 60, maybe 120, 60, 60, 110. Who knows, your readings could be accurate, if so that's bad.

Oh yeah, what was your procedure for doing the compression test?

[edit] looks like matt beat me to it....

 

[capecodtodd]

Re: 3.0 engine running rough

Oh no Now I'm getting nervous again, The gauge was a new one right out of the box from autozone. I yanked all 4 plugs screwed the gauge fitting into the 1st spark plug hole, pushed the throttle handle to fast idle spot, disconnected the coil and turned the key to crank the engine for 4 revolutions. I recorded the number on the gauge and then moved to the next cylinder and repeated process. Each cylinder was recorded at a slightly different number but very close to 60. What could have gone so bad that all 4 cylinders are so weak? I wonder now if what I thought I was hearing to count to 4 was actually 2 just an in and then an out on the stroke?
I still have the gauge so I can repeat the test if i did something wrong but I was following the manual. Did I miss something?? I bought the boat used about 6 years ago and both boat and engine were and still look to be in great condition. If there is something major wrong with the engine it doesn't show on the outside. Not that it would of course. The engine is 12 years old but has not seen alot of use and I suppose that could be an issue as well.
Now I'm worried. What could be wrong with it?

 

[moparmatt]

Re: 3.0 engine running rough

The engine is 12 years old but has not seen alot of use and I suppose that could be an issue as well.
Now I'm worried. What could be wrong with it?

Has the boat sat for a while? If it has I just wonder if your rings are froze up? If it hasnt than i would double check the valve adjustment and if thats not it than i would say the motor is just wore out.

 

[fishrdan]

Re: 3.0 engine running rough

pushed the throttle handle to fast idle spot

You should have the throttle WOT, full open, not fast idle. Also, turn it over so you have 4 compression strokes/cylinder, you can hear it bump the cylinder you are testing as it will have resistance. Stroke 1-2 and 3 will increase the reading, #4 shouldn't add much,,, but I always do 4/cylinder. You can also do a "wet test" by squirting a couple shots of oil into the cylinder, then test again (do this after the dry test). If everything is good, the dry and wet test should be close.

Try the compression test again and let us know what you come up with.

 

[bigdan1]

Re: 3.0 engine running rough

just to add to what fisherdan said ...if after dry test ,still have 60 psi ,
add oil in cyl and compression rise to 120 then rings are either shut or dirty (sticking ) .

just add some engine cleaner oil additive for 2-3 hres of running ...take test again if still low pressure ...time for a rebuild !

 

[capecodtodd]

Re: 3.0 engine running rough

Ok an UPDATE
I did another test with the throttle wide open. Looked down the carb throat to check and the pressure rose in each cylinder to 80+/- .
I also did a wet test on each cylinder and this raised the readings into the 100- 105 range. I did 4 rotations reset the gauge then did 6-7 rotations but this did not add any higher readings at the gauge. Just checking.
The engine did sit for the last 2 years without being started. I didn't have time for boating. Before then it was running well and being used once a week or so but nothing extreme. Just normal running. I think I recall it getting a little rough if I remember right towards the end of that last season.
This season I had the boat out 3 times and it was running poorly but running from 0-40 mph. The last time it was a mess stalling and sputtering and wouldn't stay running.
Now that oil is in the cylinders should I try to run the engine? Should I add in mystery oil to each cylinder? Should I try an additive to the oil.
Thanks so much for all the input.

 

[capecodtodd]

Re: 3.0 engine running rough

update.
Over the last few days I have had marel mystery oil soaking in the cylinders. Tonight i removed the plugs and did another compression test and it was about 80 across all 4 cylinders, better than the 60 it was before. For the fun of it I put it back together and started the engine. I started on the first turn and ran pretty well. The idle wasn't bad, I shut it off and it coughed once. I then pulled the plugs again did the compression test and no better. I put more oil in the cylinders turned it over once and buttoned it up. I will check again in a few days.
Todd

 

[fishrdan]

Re: 3.0 engine running rough

80PSI still doesn't sound good and the wet test only going up to 100 PSI... that's not good either. You might want to do a cylinder leakdown test and see if you can determine where the compression is being lost, rings, valves?

How fast is the engine cranking when you are doing the test, spinning really fast on a completely charged battery or dragging on a discharged battery,,, or worn out starter. If the engine is spinning slow it will affect your results. I always do a comp test with a completely charged battery, and a battery charger running to keep it topped during the test.

 

[capecodtodd]

Re: 3.0 engine running rough

Thanks for sticking with me fishrdan, you and others have given me some good advice and direction to help narrow this issue down.
I did recharge the battery on the last test 2 days ago and there was plenty of juice last night as evident when it started on the first turn.
I don't know what a cylinder leakdown test is so I will have to look into that. It would be nice to just hand this problem over to a pro but here on the Cape the good mechanics are booked up and the cost would be a real issue at this point so I have no choice but to muddle along.
I wonder why if the engine is so worn out, evidence is mounting, that it would start so easily last night and run pretty well?
Watch for future updates as more tests are done.
Thanks! Todd

 

[moparmatt]

Re: 3.0 engine running rough

I wonder why if the engine is so worn out, evidence is mounting, that it would start so easily last night and run pretty well?

I owuld say the reason that it did becuase there was still some oil left in the cylinders that tightened up the ring gap to bump the compression closer to a usable number.



I have a trick that you could "carefully" try if you dont have any success . This is what we do with muscle car motors that have been sitting for years. Pull all of plugs and fill each cylinder with kerosene. If you do this you have to make sure that you let it soak for a day or two and if the rings are stuck this will free them up. You will have to make sure you get all of the kerosene out of the cylinders by cranking the motor over by hand till it comes out the plug holes. After that let the motor sit for a day with the plugs still out of it. Then finally drain the oil and remove the filter and replace with new oil and filter before start up. If you dont get all of the kerosene by changing the oil the stuck rings will be the least of your worries!! LOL