Mercruiser 3.0 engine noise + now won't idle and must be @ 2000rpm to keep running

[Stingray190LS]

We owned the boat about approx 3mos (01 Stingray 190LS w/ a 3.0 Mercruiser) & its a whole new fun experience for the family & actually put 60hrs instantly until the recent headaches. Last Saturday, a noticeable noise is originating from the engine whether WOT or idle. The first symptom I encountered is when I noticed engine noise during WOT (top speed @ 40-45mph) so I slowed it down to check & then the engine turned off on its own. So I allowed it to rest for a few minutes (thought it was overheating) & the restarted & it fired right up w/out issues nor any noise so we continued on. A few hrs later the noise returned & our top speed is now only at 30-35mph. Turned it off & back on & it still starts right up but noise existed & now even at idle or any speed.

In light of this, we thought it was a valve adjustment so we opened it up & replaced all 8 lifters in the process because there was no play when pressure is applied on them. In addition, we replaced the V-belt & spark plugs since already working on the boat. Adjusted the valves & then sealed the push rod & valve cover after.

​After the above, we made attempts to start the engine & it cranks but won't turnover. So pumped the throttle several times & it started eventually. However, the boat struggles & cuts out when I bring the throttle back to idle. The only time the engine stays running is when the throttle is given gas at about approx 2000rpm. The engine noise remains but not as loud but it is still there.

Any suggestions what it could be? Beforehand, the boat started right up & remains on idle with no issues. Now, I have to rev it up to 2000rpm to prevent from cutting out. Also, even the lifters replaced & valve adjustment, we can still here the noise towards the front part of the engine but on the lower part. I'd like to take a video & post but I am having issues keeping the engine on unless revved up. Sorry for the long narrative but I figured to share as much background to see if someone may share their wisdom for being a Mercruiser expert. Thank you for the assist in advance.

 

[Scott Danforth]

on the running issue, my first guess is you have crud in the carburetor. you may want to also check the clear yellow hose running from the fuel pump to the carburetor. if it has fuel in it, your fuel pump diaphragm has ruptured and you are pouring fuel in the motor. if this is the case, replace fuel pump, give motor an oil change

as for the noise would be guessing here. could be anything motor related, coupler related, drive related, etc.

 

[Grub54891]

You replaced the lifters as there was no play. Them should be hydraulic lifters, what was the method you used to adjust them?

 

[alldodge]

Howdy

Is it a knock or tic noise?
How is the oil pressure and temp?

 

[Stingray190LS]

Thank you for the swift reply everyone!

It is more of a ticking noise but towards the front and lower part of the engine... the lifters were swapped from old to new and the rocker arms were tightened with the typical 3/4 turn while feeling the push rods. Does each lifter need to be adjusted (didn't know if it could...)? I thought it was a simple swap out and we did because it seemed seized and no play at all. The oil pressure was at 20psi when revved at 2000rpm and the temp was fine. Revved it up higher and did not see it go higher and in the past it was at 40psi. What I'm puzzled by as well is that the speed won't go beyond 30-35mph when full throttle while it did 40-45mph before these issues.

In reference to revving the engine to stay on... I found the yellow hose a few weeks back disconnected and melted since it sat on the valve cover so I replaced with regular same size black hose. It is dry and no fuel in it. Should I isolate first by rebuilding the carb? what's a good chemical to soak it in and how long? Lastly, what good rebuild kit is recommended?

 

[alldodge]

Start with the carb fist, if its running lean then your not getting enough fuel. Not enough fuel you will be slower, also can damage the engine due to preignition.

After the carb, get it running and try readjusting the lifters. You need them each at TDC and grab the push rod and while it should turn you need to know if the rod has any play up and down. The turn issue is just to make sure it's not sticking, zero lash is when all play in the up/down is no longer felt

Gunk makes some good carb soak/cleaner

 

[James D. Evans]

Compression test? As stated previously above, not enough fuel in...damage can be done. I know all too well, chased a miss a whole summer. Ended up being a fuel pump, but ended up costing me a cylinder head in the end. Other than the oil pressure issue, your issue sounds eerily familiar to my previous situation.

Don't rely on the gauge for oil pressure...sending unit, gauge, or wiring could be bad. Best to get a mechanical gauge and verify pressure.

 

[fishrdan]

The only time the engine stays running is when the throttle is given gas at about approx 2000rpm. The engine noise remains but not as loud but it is still there.

Sounds like either: the carb's idle circuits are all plugged up or you have a severe vacuum leak that's only overcome at 2000RPM. Did the valve cover's vent hose get connected back to the carb again?

When you replaced the lifters, did you break them in, like when breaking in a cam? (If no, they should have been broken in, 15-20 minutes at 1500-2000RPM.) To pinpoint the noise, use a mechanics sterhescope ($5+- at Harbor Freight), or a 2-3' section of heater hose held up to your ear, or a looooong screw driver held against your ear and touched around the engine. You can try removing the engine's alt belt and see if the noise goes away, to rule out the water pump or alternator making noise. The engine will be OK with the belt removed for a minute or two, for testing. Just make sure the engine is running off muffs.

 

[Stingray190LS]

Update from shop... conducted compression test and no pressure on cylinder # 1 & #4. I did advise that engine was running fine before replacing the lifters but it had a ticking noise which prompted us to replace the lifters and tighten the valves. Mechanic advised that they will now do a leak down test. Update to follow once I hear from them. Hopefully I don't have to replace with a new engine! If no pressure on #1 and #4... What comes to mind and how much will it costs?

 

[Rick Stephens]

No pressure is either holes in the pistons or the valves not able to close.

 

[alldodge]

Replaced lifters

With zero on two cylinders I think your valves need adjusting

 

[airshot]

Where did you get the info for your valve adjustment? You need a real "Mercruiser" service manual for your motor and outdrive, read thru these posts and see how many people used other publications or a friends advice and screwed up their motors. I think you are in for a good motor overhaul.

 

[fishrdan]

I'm with Rick and AllDodge, sounds like the valves were adjusted too tight, holding valve(s) on #1 & #4 open, thus no compression on those 2 cylinders...

 

[1960 Starflite]

I adjust GM hydraulic lifters (valves) with the engine running at idle. Loosen the rocker arm nuts until they tick, tighten until the tick stops and give them a slow 1/2 turn more. I agree with some other posts that you have the valves adjusted too tight, and the valves wont seat. Of course you have to get the engine idle down to 600 rpm. I think you'll have to start by loosening all the adjustment nuts a little. Repair manual is a must and will have a procedure to get the adjustments in the ballpark.

 

[Stingray190LS]

Thanks everyone! Definitely makes logical sense to me and I did take it to a Mercruiser expert to dial in all the issues I have! Appreciate the replies!

 

[Stingray190LS]

Pulled the boat out of the shop because I'm being quoted $600 for leak down + adjusting valves and oil change.

I'm going to take a shot at it and adjust the valves myself to make sure I get #1 and #4 back. My current goal is to get the engine to idle. I have read many procedures and suggestion for valve adjustments... I'd like to filter them now and ask a member who has done valve adjustments (successfully and multiple times) and please advise what steps or tips I need to properly adjust?!?

Several questions:
1. Valve cover removal... Since I have a new gasket and re-sealed with rtv...
- Can I reuse the gasket if not broken? Remove old rtv and then reapply? Or just reapply rtv?
2. Ensure at TDC - do I tighten all valves at TDC?
3. How much play on the push rod?
4. Anybody have a diagram depicting which on is cylinder #1-4? Also, a diagram for spark plug wire order?

 

[alldodge]

The no-brain or lack there of adjustment procedure is: Need a grease pencil or something to make the rocker arms

Remove all plugs, rotate the engine by hand counter clockwise, or with the starter.

The key in this procedure is there are two valves per cylinder, and you need to watch them in pairs (one intake and one exhaust). Rotate the engine until you see one of the pair of valves start to depress. you don't want it to go down that much just enough to start the valve to open. When the pair of valves has one going open, stop.

Now with the valve which was NOT moving or going open, loosen the rocker nut until you have up and down movement on the push rod. Rotate the push rod and while moving it up and down, slowly tighten the rocker stud until NO movement is felt up and down. Your rotating the rod just to make sure its fee, but this is not used to check lash, up and down is.

Once no up and down movement is felt rotate 1/2 turn further.

Mark the rocker arm and rotate until next rocker is found. Continue until all are done

4-cyl firing order is 1-3-4-2