Merc 5.7 loss of power and clicking

[MikDee]

Re: Merc 5.7 loss of power and clicking

I second the ignition wires as a possible source. Don S also reccomended cap and rotor, was it ever done? Sounds like something bouncing around causeing intermittent power loss.

I agree also, a spark jumping from a broken, or chafed spark plug wire would make a clicking noise, and cause a misfire dropping engine rpm quite a bit, sometimes momentarily.

 

[Bondo]

Re: Merc 5.7 loss of power and clicking

At the dock it'll idle fine and I can run it up to 3200rpm or so with no odd behavior. Could any of these possibilities occur only under load

Ayuh,.......

What it does at the Dock, in Neutral is Totally Irrelevant.......
It's All about what it does Under Load.........

 

[rodbolt]

Re: Merc 5.7 loss of power and clicking

about 5 posts ago would have been a good time to identify which induction and ign system this 5.7L GM
has.
also test the audible alarm system,if installed. if its not then install it.
that "beer can" sound can indicate issues depending on what induction/ign system is used.
the powering down can indicate stuff,again depending on the system.

 

[a70eliminator]

Re: Merc 5.7 loss of power and clicking

Mechanical fuel pump or electric, once had a mech. fuel pump that made clankity noises due to a failing pivot from the arm that rides the cam, eventually it failed to pump fuel and thats how I found what was making the clankity noise in my engine.

 

[Mkos1980]

Re: Merc 5.7 loss of power and clicking

I had the same clicking and so forth. Ended up bring a stuck exhaust flappers.

 

[MikDee]

Re: Merc 5.7 loss of power and clicking

Still having this problem. Summer?s almost over and I?ll have it looked at over the winter. Still looking for suggestions. My wife says it sounds like beer cans bouncing around down there. Idles fine, out of gear runs @ 3-3.5k rpm smooth, good oil pressure and engine temp. In gear she makes the noise and looses power around 3k. Any ideas?

If you've checked the spark plug wires, distributor cap, & coil tower, for arcing, and have found nothing, this definitely sounds like preignition, detonation, now,,, I'm assuming you have electronic spark advance, if that's the case timing doesn't usually change, so I doubt that is the problem, but be careful, you might be getting some water intrusion thru a cracked, rusted out, or faulty exhaust manifold, causing this issue. If so, it suddenly may go boom!

 

[CharlieB]

Re: Merc 5.7 loss of power and clicking

How long /what temp does the condition begin?

Does it tend to follow engine temp under load AND speed?

Not noticable at very light load, by yourself and low speed, barely on plane?

More pronounced or quicker to exhibit with the boat loaded and light to moderate speed?

Engine temp/headtemp varies with load, I've seen exhaust valve seats work when I briefly tested a craft and yet the operator and passenger pulling up a skier complain of 'noises', the seat would loosen and attempt to follow the valve, restricting airflow and reducing rpm. The operating temp of the valve and seat were greater than 'light' load operation.

Very careful observation of the fault will help us lead you to a solution

 

[John Evans]

Re: Merc 5.7 loss of power and clicking

Sorry for the delay guys but a new baby?s had us out of the water for over a year.
We had the boat in the water a bit back in the summer of 08 and after changing plugs and plug wires and a general good cleaning, including the spark arrestor, everything seemed fine, problem solved. After a month or so of good performance the problem came back on the run in to trailer it for the winter. A complicated pregnancy produced a healthy mother and son and time off the water. Fast forward, I have a 10 month old and a wife itching to be out on the lake. I?d thought about the issue a bit in the down time and when I found the same situation on the first run to the dock last week I was not surprised.
Here?s what I have now. The noise is a backfire???, there is soot and discoloration inside the spark arrestor. I thought it might be an issue with the vacuum line to the fuel regulator so I had another general cleaning, checking the vacuum lines reattaching them and remounting the spark arrestor. I went out for a short run and after a short idle out into the main channel, up to normal operating temp. I get into the throttle slowly and have a few pops on the way up to 35Krpm and on plane. I brought her back to idle, turned around and was a bit more aggressive in the throttle running back and she ran like a new one. I did this a few times settling into her sweet spot just over 3k on plane cruising everything perfect. Two days later with the wife and new kid on board feeling like a great marine problem solver we head down to a nice little floating spot, 10 minutes away, perfect run good power. The wife wants to go to another spot after a while and we take off then I?ll be damned if the problem doesn?t come back. So we turned around back to our first spot and still had a good afternoon on the lake. On the run back to the dock going through 3k rpm it happened again but I pushed it up to 4k and she held there fine. I eased it back and around 3K backfires and starts to bog down, back in the throttle up around 4k she?s fine. The bottom line is I?m still confused.

 

[CharlieB]

Re: Merc 5.7 loss of power and clicking

I suspect you have a dirty carb and the accelerator pump also needs to be replaced.

Fuel flow in the mid-range is reduced, causing a 'lean miss' or backfire, ditto for the accelerator pump not squirting quite enough fuel upon a rapid throttle opening.

You may need the model and serial # of the motor, and possibly the #'s off of the carb in order to get the correct carb rebuilt kit.

WARNING, many Merc kits from the dealer do NOT have a new accelerator pump in the kit and may be needed to order separately. ASK to find out.

It would also be a good move to replace the fuel filter.

 

[alien4fish]

Re: Merc 5.7 loss of power and clicking

I agree, carb or fuel injectors What year is the 5.7?

 

[John Evans]

Re: Merc 5.7 loss of power and clicking

5.7L EFI GM 350 V-8 1998/0L010035_0L325976

Her's a link to the Throttle Body and Fuel Filter/Cooler pdf's.

http://www.marinepartsexpress.com/Merc_Schematics/5.7L%20EFI%20GM%20350%20V-8%201998/0L010035_0L325976/FUEL%20PUMP-FUEL%20COOLER.pdf

http://www.marinepartsexpress.com/Merc_Schematics/5.7L%20EFI%20GM%20350%20V-8%201998/0L010035_0L325976/THROTTLE%20BODY.pdf

I hope this helps. I looks like the fuel pump is a hard place to get to.


Thanks in advance for you help.

 

[CharlieB]

Re: Merc 5.7 loss of power and clicking

An EFI Motor?

Forget the dirty carb senario.

You NEED the OEM Service Manual, Don has posted somewhere here on iBoats to troubleshoot this correctly.

A dirty fuel filter or failing fuel pump will fail to provide sufficient fuel flow to sustain power at RPM, yet seem to run perfectly fine at reduced speeds and 'reving' in Neutral.

Injectors normally make a 'clicking' sound, more pronounced at RPM.

The Service manual will spell out where and how to measure fuel pressure, at idle then again while underway at WOT. If pressure at WOT is reduced then it is a problem.

 

[John Evans]

Re: Merc 5.7 loss of power and clicking

I'll run the boat Sunday after I make the swim out to the mooring buoy. I'm in Tennessee and our dock's been under water all week. If she runs well at higher RPMs what should i check first? What could cause fuel flow to suffer at mid RPMs? Should i change the fuel water separator/filter first? It doesn't have many hours on it but its an easy thing to do.

 

[CharlieB]

Re: Merc 5.7 loss of power and clicking

It never hurts to change a filter, it is always the first suspect as fuel quality can always be an issue.

Water in the fuel can rear its ugly head at any speed, once present it usually doesn't not improve, it generally just worsens unless the boating conditions are smooth, runs fine, but when choppy the water under the fuel in the tank gets agitated, mixing with the fuel, then starts getting into the motor.

Go ahead and change your filter, pour it into a suitable container to let it set a couple of minutes then look to see if/how much water is in it.

The fuell pressure test at idle and again underway is very helpful in determining whether this is a fuel or ignition related problem. Fuel FLOW increases greatly with increasing loaded RPM, any weakness in a fuel pump, restriction in a hose, the fuel tank dip tube, or the check valve at the tank fitting, will limit WOT power.

Intermittent WOT problems may be a sign of a failing fuel pump, but do NOT ASSUME anything and start throwing parts at it except for the filter.

 

[John Evans]

Re: Merc 5.7 loss of power and clicking

I put some of the e10 fixing stuff in the fuel a week or so ago but didn't get a chance to run the boat. I was skeptical with the fuel filter solution because I don't have that many hours of operation on the one installed but being the cheapest next step I got a new one. i poured the old fuel into a glass jar and it looked fine, no water, no particulate matter. I also added some of the lucas fuel system cleaner and lube. Out on the lake it came up on plane fine and in the first few minutes it had maybe 2 backfires but they weren't bad enough to reduce boat speed off plane. From then on maybe 4 hours of operation she runs like a new one. I hope it holds for the rest of the summer.

Thanks guys

 

[reimelss]

Re: Merc 5.7 loss of power and clicking

I put some of the e10 fixing stuff in the fuel a week or so ago but didn't get a chance to run the boat. I was skeptical with the fuel filter solution because I don't have that many hours of operation on the one installed but being the cheapest next step I got a new one. i poured the old fuel into a glass jar and it looked fine, no water, no particulate matter. I also added some of the lucas fuel system cleaner and lube. Out on the lake it came up on plane fine and in the first few minutes it had maybe 2 backfires but they weren't bad enough to reduce boat speed off plane. From then on maybe 4 hours of operation she runs like a new one. I hope it holds for the rest of the summer.

Thanks guys

How have you been making out...
I swear i have the same problem because i have all of the same symptoms...
temp is good...OP is good...i hear a clicking, but not a knocking and i have a loss of power. I was doing fine had my rpms up to 4600 and on plane just fine...now at WOT im at 4k and cant even get out of the water.
I made a list of things to check from this thread...
so from your last post the thing that cured your boat was lucas fuel system treatment?

 

[John Evans]

Re: Merc 5.7 loss of power and clicking

We are still running good. On the last outing I feel the power may be down a bit but it could be in my mind. I've found a local gas station that sells 100% gas and will be using that from now on. Changing the filter as unlikely as it seemed to me worked. If I experience the symptoms again that'll be my first thing to try, it's cheap and easy.

 

[John Evans]

Re: Merc 5.7 loss of power and clicking

The noise and bogging down have not come back. But I still think the power's off a bit and getting worse over time. I'm going to change the fuel water separator/filter again to see if the power bounces back. If I have to change it periodically for a while I'll still be happy.