Logo
FULL SITE MENU

engine miss

T

tater

New member
1993 mercruiser 5.0 alpha 1 gen 2 .engine will miss like someone turned the key off then back on in a matter of a second rpms drop from 4000 rpms to 2000 rpms then back up to 4000 rpms .mite do it again 10 minutes later .also diesels for bout 5 seconds when I shut it off .new distributer last year . timing is perfect .what could this be ? thanks
 
Last edited:
Pre detonation. Carbon build up on top of piston. Stays hot enough to ignite fuel when ignition is shut off. . Best way to get rid of carbon build up is to give it a drink of water. Use bottled water just the size you would normally drink out of. Disconnect the throttle cable. Take off the spark arrestor. Throttle up to about 1500 rpm and pour the water in the carb. Don't let it die. Keep the rpms up. Until all the water has been used. . You should see a lot of black coming out of the exhaust. Then let it idle for a bit.
 
DO NOT POUR WATER INTO THE CARB!!!!!!!!!!!

WHat is the temperature when running?

Maybe some history of issues or changes or anything else to form a proper opinion.
 
...........................................
tater said:
1993 mercruiser 5.0 alpha 1 gen 2 .engine will miss like someone turned the key off then back on in a matter of a second rpms drop from 4000 rpms to 2000 rpms then back up to 4000 rpms . mite do it again 10 minutes later . also diesels for bout 5 seconds when I shut it off .
Gasoline engine "Dieseling" or "run-on" is typically a result of high cylinder temperatures combined with a lean low speed fuel/air mixture.
Find out what is causing the high cylinder temperatures, and perhaps fatten up the low speed fuel/air mixture.
Some owners have found it helpful to allow the engine to cool down a bit before shutting off.

The above does not address your main issue that is occurring at high speed operation!

new distributor last year . timing is perfect .
Which ignition system, and how did you adjust the spark advance?
Did you set BASE/Initial advance ONLY, or did you take it further and look at what the progressive and total advance are doing?

Excessive ignition advance will cause Detonation (not pre-ignition), and may cause what you have described.

Typical causes of Detonation:
poor fuel quality.
excessively lean fuel/air mixture.
high cylinder temperatures.
excessive spark lead and too early.
poor cylinder combustion chamber design.

If by chance (key word "if") your issue is being caused by Detonation, it will raise cylinder temperatures and it will perpetuate itself.
If left unattended, Detonation will cause severe engine damage.




All that having been said, the above is one possibility only....... you will want to also consider other component failure.


Click to expand...
 
Last edited:
""
Which ignition system, and how did you adjust the spark advance?
Did you set BASE/Initial advance ONLY, or did you take it further and look at what the progressive and total advance are doing?

Excessive ignition advance will cause Detonation (not pre-ignition), and may cause what you have described.""


Here we go again........the old TA IA and associated BS
 
Last edited:
tater said:
1993 mercruiser 5.0 alpha 1 gen 2 .engine will miss like someone turned the key off then back on in a matter of a second rpms drop from 4000 rpms to 2000 rpms then back up to 4000 rpms .mite do it again 10 minutes later .also diesels for bout 5 seconds when I shut it off .new distributer last year . timing is perfect .what could this be ? thanks
Click to expand...

Before anyone can answer any questions OR DETERMINE ANY POSSIBLE ROOT CAUSE SUCH AS DETONATION...........

YOU NEED TO ANSWER QUESTIONS.

1. Perfect timing..................What is your perfect timing?
2. what/why distributor was replaced? OEM or aftermarket?
3. If aftermarket what if any timing control module or advance control is being used?

Temp is 160 per you.

4. What are other recent issues that have been seen with this boat?

Obviously you have had issues that required a distributor replacement for a distributor that virtually never requires to be replaced. Good to understand why!!

An intermittent loss of power from your description is difficult to diagnose.

What needs to be determined is, Is this electrical or fuel related.

So when this occurs do you loose all other power? You say rpm gauge reads.........Are you sure?
Can you think of any other symptoms to tell us about that could help indicate what the issue may be.

Short nondescript answers will only make this post go unanswered so try to answer every question with as much detail as may be needed to underdstand.
 
just bought boat last year .had boat on lake erie 5 th time I had it out It cut out a few times .had the marina take it out on lake and said they noticed a vibration right away .they said distributer had some wear on the gears so the replaced it .I never noticed a vibration .so after 800.00 dollars later I took it out and it missed again . took it back to marina and they acted like they didn't have time to mess with it so I pulled it home 3 hours away.this april had a guy from celina ohio who use to own north moore marina in st marys ohio look at it .he done some work on my lower unit and took it to st marys lake to see if it would cut out .after 45 minutes it never cut out.had boat on lake erie 5 times this year and no miss 6th time had the miss .don't no if distributer is aftermarket or oem.this guy from Celina checked timing and said it was rite where it should be .this guy really knows his stuff. he thinks I have a water issue. carb .water seperater etc . fuel filter .I don't know anything about motors just don't have the patients thanks
 
Last edited:
tater said:
..................... he thinks I have a water issue. carb .water seperater etc . fuel filter .I don't know anything about motors just don't have the patients thanks
Click to expand...

If you suspect a fuel/water issue, buy yourself a Parker/RACOR fuel filter system.
These are quite different from that of the regular water separating filters, in that they use a cyclonic affect to actually separate the water from the fuel. Whereas the run-of-the-mill filtration systems rely of filter media absorption and eventual settling of the water.

In order to be legal, you'll need the Inboard style with the metal bowl and thread-in drain plug.

RACOR fuel filters 2.jpg
 
I certainly would not be dealing with that marina and demand my old dist back., There are a number of things to cause a miss. internal motor issues or leaking elbows dumping water into the exaust ports to even a bad plug wire.
Install a fuel water sep filter , do a test run and inspect the contents in a clear container. Water will remain at the bottom quite visable. If no water found then further testing is necessary
 
RicardoMarine said:
If you suspect a fuel/water issue, buy yourself a Parker/RACOR fuel filter system.
These are quite different from that of the regular water separating filters, in that they use a cyclonic affect to actually separate the water from the fuel. Whereas the run-of-the-mill filtration systems rely of filter media absorption and eventual settling of the water.

In order to be legal, you'll need the Inboard style with the metal bowl and thread-in drain plug.

View attachment 20590
Click to expand...

BTW, If you are using E-10 fuel and you have water in your tank you have bigger problems. Because of Ethanol, water sep filter have become obsolete. When water mixes in your fuel tank, it phases the ethanol out of the gasoline along with the octane rating.
Water sep filter now only work with Non-Ethanol and diesel fuels.
 
Back
Top