2000 merc 5.7 w/ 2barrel carb detonation

[bigjim]

I need some help Iam losing my mind 2 days at my boat and still no fix.
Tried alot if not all but still not right.
Heres the deal boat idles fine and runs fine to 4500 rpm at the dock in nuetral of course. Once out from dock underway will start to ping(detonate) after 4 seconds of power.
Heres what I did changed wires, cap, rotor removed and cleaned sensor pick up and reinstalled set timing to mark on timing cover, advance is working, checked knock sensor per manual and that is working pulled fuel pick up and clean as a whistle changed seperator did pressure test fuel pump but it is pumping. I think it might have volume but no pressure, would hate to go out and drop 250.00 on a pump and have problem show its ugly head again. please any help would be great.

 

[bigjim]

Re: 2000 merc 5.7 w/ 2barrel carb detonation

I DID NOT PRESSURE TEST PUMP. Just unhooked and started motor and filled bottle of fuel not sure if pressure is there.

 

[chiefalen]

Re: 2000 merc 5.7 w/ 2barrel carb detonation

Check the spark plugs.

Are they the right spark plugs?

Are you timed right.

Bet your off a little.

 

[Don S]

Re: 2000 merc 5.7 w/ 2barrel carb detonation

2000 merc 5.7 w/ 2barrel carb

When you set the timing, did you put it in base timing mode????

If not, you are way out of time.

 

[Don S]

Re: 2000 merc 5.7 w/ 2barrel carb detonation

Here is the procedure for setting the timing on a Thunderbolt V ignition.

Timing
Thunderbolt V Models
1. Connect timing light to number 1 spark plug wire.
2. Connect a shop tachometer to the engine.
IMPORTANT: Before starting the engine, connect a jumper wire from the ignition timing lead to a good ground. This has to be done before the ignition key is turned ON to lock the Ignition Module into Base Timing Mode.
3. Before starting the engine, connect jumper wire from timing lead to a good ground.
NOTE: The PUR/WHT timing lead is located towards the front of the engine near the fuel
line or near the distributor, as equipped for your model.
4. Start engine and run at 1300 rpm until it reaches normal operating temperature.
5. Disconnect throttle cable from the carburetor.
6. With engine at idle rpm, adjust the carburetor idle rpm screw to the specified engine idle
rpm.
7. With the engine still at idle rpm, check the ignition timing. If incorrect, rotate the
distributor until timing is correct. Torque clamping screw to 18 lb-ft (25 Nm).
8. Adjust the idle mixture screw. Inward is LEAN, outward is RICH.
9. Recheck ignition timing.
10. Stop engine. Remove timing light, jumper wire and shop tachometer.
IMPORTANT: Timing jumper wire has to be removed or the Ignition Module will stay locked in the Base Timing Mode and it will not be able to advance the ignition timing correctly when the engine rpm is increased.
11. Adjust and reinstall throttle cable. Open and close remote control throttle lever to make
sure that the carburetor?s throttle lever returns against the rpm adjusting screw every
time.
12. Restart the engine, increase rpm to 1300 then return to idle position slowly and shut the
engine off. Ensure that the carburetor throttle lever came back against the idle rpm
screw.
13. Shut engine off.

 

[TilliamWe]

Re: 2000 merc 5.7 w/ 2barrel carb detonation

Is the bottom of the boat clean, bigjim?

 

[bigjim]

Re: 2000 merc 5.7 w/ 2barrel carb detonation

Thanks for the replies .

Checked spark plugs all are the same nice condition.

When timed I put it in base mode. Checked advance that works as well.

The bottom of boat clean?

Not sure what you mean.

The engine started detonating out of the blue, was coming back from ocean and slowed to let another boat pass and throttled back up and ping-ping-ping.

limped back to port at 1500 rpm.

Still going crazy over this any more IDEAS PLEASE>

 

[bruceb58]

Re: 2000 merc 5.7 w/ 2barrel carb detonation

Check and double check your spark plug wires if you happened to take them off. You may have them in the wrong firing order. I have crossed wires and gotten the same symptom.

How was the boat running before you changed all the ignition parts? Were you having a similar problem or were you just doing a tune up and this problem surfaced.

 

[chiefalen]

Re: 2000 merc 5.7 w/ 2barrel carb detonation

Ah a little more information.

You didn't think to include it in your o.p?

First>Do a compression check. Record the findings. And post them.

Or would you please pull all the spark plugs and post the findings with the compression test results.

 

[TilliamWe]

Re: 2000 merc 5.7 w/ 2barrel carb detonation

The bottom of boat clean?

Not sure what you mean.>

I mean exactly that. Is the bottom of the boat fouled with growth? If so, it can cause the engine to "lug" which makes the cylinder temps go up which leads to detonation. If you leave it that way long enough, you "tulip" valves.
Now, you describe an "all of a sudden" condition, but it still doesn't hurt to make sure the boat bottom is clean.

 

[bigjim]

Re: 2000 merc 5.7 w/ 2barrel carb detonation

Sorry I didnt get back sooner! Little life problem but now my boat problem.
I did a compression test and all cylynders were 160 but numbers 3 and 5 were 30 lbs no good I know. So that was the cause of my detonation. Now my question is when I break down the engine will I be able to just do a head gasket and be on my way or should I do a reman engine, whats your advice. I think it would be a head gasket RIGHT I hope? Please let me know, boat is coming out of water tomorrow. Thanks for all the help BIGJIM

 

[Don S]

Re: 2000 merc 5.7 w/ 2barrel carb detonation

Pull the head and look. My guess is you have tuliped valves, not a bad head gasket, and it's probably beat the valve seats in the head to death.

 

[Bondo]

Re: 2000 merc 5.7 w/ 2barrel carb detonation

Now my question is when I break down the engine will I be able to just do a head gasket and be on my way or

Ayuh,...

As long as the block's Deck is clean, flat,+ undamaged,...
And,... If the Pistons aren't beat up,...
A Head Job,+ gasket set should do it...

More importantly,... You've gotta figure out Why it happened.....

 

[TilliamWe]

Re: 2000 merc 5.7 w/ 2barrel carb detonation

Sorry I didnt get back sooner! Little life problem but now my boat problem.
I did a compression test and all cylynders were 160 but numbers 3 and 5 were 30 lbs no good I know.

Humor me Jim, okay? An easy way to identify if it's a valve problem is to remove that valve cover, and loosen up the valves on that cylinder a little. Redo your compression test. If the numbers go up, you have tulipped valves. Like I said was a possibility a month ago. Did you run the boat with a dirty (fouled) bottom? If so, I would pull both heads and have all the valves checked.

 

[bigjim]

Re: 2000 merc 5.7 w/ 2barrel carb detonation

Humor me Jim, okay? An easy way to identify if it's a valve problem is to remove that valve cover, and loosen up the valves on that cylinder a little. Redo your compression test. If the numbers go up, you have tulipped valves. Like I said was a possibility a month ago. Did you run the boat with a dirty (fouled) bottom? If so, I would pull both heads and have all the valves checked.

OK I will do that hopefully this weekend to find out if valves are tuliped or if it is something else. The bottom was clean on boat when problem happened. Now my new question is if I have tuliped valves exactly what causes that condition. Always ran the boat on 89 octane. When problem arose I was coming back from ocean came off plane and went to get back on plane then heard detonation, Then continued to putt back to dock at 1500rpms. Boat also seems to idle fine at dock and rev up as well also no signs off any water in oil not on dipstick atleast? Thanks for your profesionalism, and your input is truly appreciated. THANK YOU

 

[TilliamWe]

Re: 2000 merc 5.7 w/ 2barrel carb detonation

tulipped valves on a Vortec SBC are caused by excessive heat in the combustion chamber.

 

[Bondo]

Re: 2000 merc 5.7 w/ 2barrel carb detonation

When problem arose I was coming back from ocean came off plane and went to get back on plane then heard detonation,

Ayuh,..

Just a WAGuess off the top of my head,...
Check the Fuel Filters,....
Abit of Water could cause a Lean condition,..
Which is probably the #1 reason for Detonation in boat motors...